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Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic flux fields occurring in certain materials, called superconductors, when cooled below a characteristic critical temperature. It was discovered by Dutch physicist Heike Kamerlingh Onnes on April 8, 1911, in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics.
The electrical resistance of a metallic conductor decreases gradually as temperature is lowered. In ordinary conductors, such as copper or silver, this decrease is limited by impurities and other defects. Even near absolute zero, a real sample of a normal conductor shows some resistance. In a superconductor; the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing through a loop of superconducting wire can persist indefinitely with no power source.^[1][2][3][4]
In 1986, it was discovered that some cuprate-perovskite ceramic materials have a critical temperature above 90 K (−183 °C).^[5] Such a high transition temperature is theoretically impossible for a conventional superconductor, leading the materials to be termed high-temperature superconductors. The cheaply-available coolant liquid nitrogen boils at 77 K, and thus superconduction at higher temperatures than this facilitates many experiments and applications that are less practical at lower temperatures .

  A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. Persistent electric current flows on the surface of the superconductor, acting to exclude the magnetic field of the magnet (Faraday's law of induction). This current effectively forms an electromagnet that repels the magnet. 

 Video of a Meissner effect in a high-temperature superconductor (black pellet) with a NdFeB magnet (metallic) .

  A high-temperature superconductor levitating above a magnet 

There are many criteria by which superconductors are classified. The most common are:

Response to a magnetic field

A superconductor can be Type I, meaning it has a single critical field, above which all superconductivity is lost and below which the magnetic field is completely expelled from the superconductor; or Type II, meaning it has two critical fields, between which it allows partial penetration of the magnetic field through isolated points. These points are called vortices. Furthermore, in multicomponent superconductors it is possible to have combination of the two behaviours. In that case the superconductor is of Type-1.5.

By theory of operation

It is conventional if it can be explained by the BCS theory or its derivatives, or unconventional, otherwise.

By critical temperature

A superconductor is generally considered high-temperature if it reaches a superconducting state when cooled using liquid nitrogen – that is, at only T_c > 77 K) – or low-temperature if more aggressive cooling techniques are required to reach its critical temperature.

By material

Superconductor material classes include chemical elements (e.g. mercury or lead), alloys (such as niobium-titanium, germanium-niobium, and niobium nitride), ceramics (YBCO and magnesium diboride), superconducting pnictides (like fluorine-doped LaOFeAs) or organic superconductors (fullerenes and carbon nanotubes; though perhaps these examples should be included among the chemical elements, as they are composed entirely of carbon).

Elementary properties of superconductors

Most of the physical properties of superconductors vary from material to material, such as the heat capacity and the critical temperature, critical field, and critical current density at which superconductivity is destroyed.
On the other hand, there is a class of properties that are independent of the underlying material. For instance, all superconductors have exactly zero resistivity to low applied currents when there is no magnetic field present or if the applied field does not exceed a critical value. The existence of these "universal" properties implies that superconductivity is a thermodynamic phase, and thus possesses certain distinguishing properties which are largely independent of microscopic details.

Zero electrical DC resistance

Electric cables for accelerators at CERN. Both the massive and slim cables are rated for 12,500 A. Top: conventional cables for LEP; bottom: superconductor-based cables for the LHC

Cross section of a preform superconductor rod from abandoned Texas Superconducting Super Collider (SSC).

The simplest method to measure the electrical resistance of a sample of some material is to place it in an electrical circuit in series with a current source I and measure the resulting voltage V across the sample. The resistance of the sample is given by Ohm's law as R = V / I. If the voltage is zero, this means that the resistance is zero.
Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in MRI machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years. Theoretical estimates for the lifetime of a persistent current can exceed the estimated lifetime of the universe, depending on the wire geometry and the temperature.^[3]
In a normal conductor, an electric current may be visualized as a fluid of electrons moving across a heavy ionic lattice. The electrons are constantly colliding with the ions in the lattice, and during each collision some of the energy carried by the current is absorbed by the lattice and converted into heat, which is essentially the vibrational kinetic energy of the lattice ions. As a result, the energy carried by the current is constantly being dissipated. This is the phenomenon of electrical resistance and Joule heating.
The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons. Instead, it consists of bound pairs of electrons known as Cooper pairs. This pairing is caused by an attractive force between electrons from the exchange of phonons. Due to quantum mechanics, the energy spectrum of this Cooper pair fluid possesses an energy gap, meaning there is a minimum amount of energy ΔE that must be supplied in order to excite the fluid. Therefore, if ΔE is larger than the thermal energy of the lattice, given by kT, where k is Boltzmann's constant and T is the temperature, the fluid will not be scattered by the lattice. The Cooper pair fluid is thus a superfluid, meaning it can flow without energy dissipation.
In a class of superconductors known as type II superconductors, including all known high-temperature superconductors, an extremely low but nonzero resistivity appears at temperatures not too far below the nominal superconducting transition when an electric current is applied in conjunction with a strong magnetic field, which may be caused by the electric current. This is due to the motion of magnetic vortices in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is tiny compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. However, as the temperature decreases far enough below the nominal superconducting transition, these vortices can become frozen into a disordered but stationary phase known as a "vortex glass". Below this vortex glass transition temperature, the resistance of the material becomes truly zero.

Superconducting phase transition

Behavior of heat capacity (c_v, blue) and resistivity (ρ, green) at the superconducting phase transition

In superconducting materials, the characteristics of superconductivity appear when the temperature T is lowered below a critical temperature T_c. The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from around 20 K to less than 1 K. Solid mercury, for example, has a critical temperature of 4.2 K. As of 2009^[update], the highest critical temperature found for a conventional superconductor is 39 K for magnesium diboride (MgB₂),^[6][7] although this material displays enough exotic properties that there is some doubt about classifying it as a "conventional" superconductor.^[8] Cuprate superconductors can have much higher critical temperatures: YBa₂Cu₃O₇, one of the first cuprate superconductors to be discovered, has a critical temperature of 92 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. The explanation for these high critical temperatures remains unknown. Electron pairing due to phonon exchanges explains superconductivity in conventional superconductors, but it does not explain superconductivity in the newer superconductors that have a very high critical temperature.
Similarly, at a fixed temperature below the critical temperature, superconducting materials cease to superconduct when an external magnetic field is applied which is greater than the critical magnetic field. This is because the Gibbs free energy of the superconducting phase increases quadratically with the magnetic field while the free energy of the normal phase is roughly independent of the magnetic field. If the material superconducts in the absence of a field, then the superconducting phase free energy is lower than that of the normal phase and so for some finite value of the magnetic field (proportional to the square root of the difference of the free energies at zero magnetic field) the two free energies will be equal and a phase transition to the normal phase will occur. More generally, a higher temperature and a stronger magnetic field lead to a smaller fraction of the electrons in the superconducting band and consequently a longer London penetration depth of external magnetic fields and currents. The penetration depth becomes infinite at the phase transition.
The onset of superconductivity is accompanied by abrupt changes in various physical properties, which is the hallmark of a phase transition. For example, the electronic heat capacity is proportional to the temperature in the normal (non-superconducting) regime. At the superconducting transition, it suffers a discontinuous jump and thereafter ceases to be linear. At low temperatures, it varies instead as e^−α/T for some constant, α. This exponential behavior is one of the pieces of evidence for the existence of the energy gap.
The order of the superconducting phase transition was long a matter of debate. Experiments indicate that the transition is second-order, meaning there is no latent heat. However, in the presence of an external magnetic field there is latent heat, because the superconducting phase has a lower entropy below the critical temperature than the normal phase. It has been experimentally demonstrated^[9] that, as a consequence, when the magnetic field is increased beyond the critical field, the resulting phase transition leads to a decrease in the temperature of the superconducting material.
Calculations in the 1970s suggested that it may actually be weakly first-order due to the effect of long-range fluctuations in the electromagnetic field. In the 1980s it was shown theoretically with the help of a disorder field theory, in which the vortex lines of the superconductor play a major role, that the transition is of second order within the type II regime and of first order (i.e., latent heat) within the type I regime, and that the two regions are separated by a tricritical point.^[10] The results were strongly supported by Monte Carlo computer simulations.^[11]

Meissner effect

 

When a superconductor is placed in a weak external magnetic field H, and cooled below its transition temperature, the magnetic field is ejected. The Meissner effect does not cause the field to be completely ejected but instead the field penetrates the superconductor but only to a very small distance, characterized by a parameter λ, called the London penetration depth, decaying exponentially to zero within the bulk of the material. The Meissner effect is a defining characteristic of superconductivity. For most superconductors, the London penetration depth is on the order of 100 nm.
The Meissner effect is sometimes confused with the kind of diamagnetism one would expect in a perfect electrical conductor: according to Lenz's law, when a changing magnetic field is applied to a conductor, it will induce an electric current in the conductor that creates an opposing magnetic field. In a perfect conductor, an arbitrarily large current can be induced, and the resulting magnetic field exactly cancels the applied field.
The Meissner effect is distinct from this—it is the spontaneous expulsion which occurs during transition to superconductivity. Suppose we have a material in its normal state, containing a constant internal magnetic field. When the material is cooled below the critical temperature, we would observe the abrupt expulsion of the internal magnetic field, which we would not expect based on Lenz's law.
The Meissner effect was given a phenomenological explanation by the brothers Fritz and Heinz London, who showed that the electromagnetic free energy in a superconductor is minimized provided

${\displaystyle \nabla ^{2}\mathbf {H} =\lambda ^{-2}\mathbf {H} \,}$

where H is the magnetic field and λ is the London penetration depth.
This equation, which is known as the London equation, predicts that the magnetic field in a superconductor decays exponentially from whatever value it possesses at the surface.
A superconductor with little or no magnetic field within it is said to be in the Meissner state. The Meissner state breaks down when the applied magnetic field is too large. Superconductors can be divided into two classes according to how this breakdown occurs. In Type I superconductors, superconductivity is abruptly destroyed when the strength of the applied field rises above a critical value H_c. Depending on the geometry of the sample, one may obtain an intermediate state^[12] consisting of a baroque pattern^[13] of regions of normal material carrying a magnetic field mixed with regions of superconducting material containing no field. In Type II superconductors, raising the applied field past a critical value H_c1 leads to a mixed state (also known as the vortex state) in which an increasing amount of magnetic flux penetrates the material, but there remains no resistance to the flow of electric current as long as the current is not too large. At a second critical field strength H_c2, superconductivity is destroyed. The mixed state is actually caused by vortices in the electronic superfluid, sometimes called fluxons because the flux carried by these vortices is quantized. Most pure elemental superconductors, except niobium and carbon nanotubes, are Type I, while almost all impure and compound superconductors are Type II.

London moment

Conversely, a spinning superconductor generates a magnetic field, precisely aligned with the spin axis. The effect, the London moment, was put to good use in Gravity Probe B. This experiment measured the magnetic fields of four superconducting gyroscopes to determine their spin axes. This was critical to the experiment since it is one of the few ways to accurately determine the spin axis of an otherwise featureless sphere.

Back to cloud basic of superconductivity

Heike Kamerlingh Onnes (right), the discoverer of superconductivity. Paul Ehrenfest, Hendrik Lorentz, Niels Bohr stand to his left.

 

Superconductivity was discovered on April 8, 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at cryogenic temperatures using the recently produced liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistance abruptly disappeared.^[14] In the same experiment, he also observed the superfluid transition of helium at 2.2 K, without recognizing its significance. The precise date and circumstances of the discovery were only reconstructed a century later, when Onnes's notebook was found.^[15] In subsequent decades, superconductivity was observed in several other materials. In 1913, lead was found to superconduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K.
Great efforts have been devoted to finding out how and why superconductivity works; the important step occurred in 1933, when Meissner and Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect.^[16] In 1935, Fritz and Heinz London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current.^[17]

London theory

The first phenomenological theory of superconductivity was London theory. It was put forward by the brothers Fritz and Heinz London in 1935, shortly after the discovery that magnetic fields are expelled from superconductors. A major triumph of the equations of this theory is their ability to explain the Meissner effect,^[18] wherein a material exponentially expels all internal magnetic fields as it crosses the superconducting threshold. By using the London equation, one can obtain the dependence of the magnetic field inside the superconductor on the distance to the surface.^[19]
There are two London equations:

${\displaystyle {\frac {\partial \mathbf {j} _{s}}{\partial t}}={\frac {n_{s}e^{2}}{m}}\mathbf {E} ,\qquad \mathbf {\nabla } \times \mathbf {j} _{s}=-{\frac {n_{s}e^{2}}{m}}\mathbf {B} .}$

The first equation follows from Newton's second law for superconducting electrons.

Conventional theories (1950s)

During the 1950s, theoretical condensed matter physicists arrived at an understanding of "conventional" superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg-Landau theory (1950) and the microscopic BCS theory (1957).^[20][21]
In 1950, the phenomenological Ginzburg-Landau theory of superconductivity was devised by Landau and Ginzburg.^[22] This theory, which combined Landau's theory of second-order phase transitions with a Schrödinger-like wave equation, had great success in explaining the macroscopic properties of superconductors. In particular, Abrikosov showed that Ginzburg-Landau theory predicts the division of superconductors into the two categories now referred to as Type I and Type II. Abrikosov and Ginzburg were awarded the 2003 Nobel Prize for their work (Landau had received the 1962 Nobel Prize for other work, and died in 1968). The four-dimensional extension of the Ginzburg-Landau theory, the Coleman-Weinberg model, is important in quantum field theory and cosmology.
Also in 1950, Maxwell and Reynolds et al. found that the critical temperature of a superconductor depends on the isotopic mass of the constituent element.^[23][24] This important discovery pointed to the electron-phonon interaction as the microscopic mechanism responsible for superconductivity.
The complete microscopic theory of superconductivity was finally proposed in 1957 by Bardeen, Cooper and Schrieffer.^[21] This BCS theory explained the superconducting current as a superfluid of Cooper pairs, pairs of electrons interacting through the exchange of phonons. For this work, the authors were awarded the Nobel Prize in 1972.
The BCS theory was set on a firmer footing in 1958, when N. N. Bogolyubov showed that the BCS wavefunction, which had originally been derived from a variational argument, could be obtained using a canonical transformation of the electronic Hamiltonian.^[25] In 1959, Lev Gor'kov showed that the BCS theory reduced to the Ginzburg-Landau theory close to the critical temperature.
Generalizations of BCS theory for conventional superconductors form the basis for understanding of the phenomenon of superfluidity, because they fall into the lambda transition universality class. The extent to which such generalizations can be applied to unconventional superconductors is still controversial.

follower basic cloud

The first practical application of superconductivity was developed in 1954 with Dudley Allen Buck's invention of the cryotron.^[28] Two superconductors with greatly different values of critical magnetic field are combined to produce a fast, simple switch for computer elements.
Soon after discovering superconductivity in 1911, Kamerlingh Onnes attempted to make an electromagnet with superconducting windings but found that relatively low magnetic fields destroyed superconductivity in the materials he investigated. Much later, in 1955, G.B. Yntema ^[29] succeeded in constructing a small 0.7-tesla iron-core electromagnet with superconducting niobium wire windings. Then, in 1961, J.E. Kunzler, E. Buehler, F.S.L. Hsu, and J.H. Wernick ^[30] made the startling discovery that, at 4.2 kelvin, a compound consisting of three parts niobium and one part tin, was capable of supporting a current density of more than 100,000 amperes per square centimeter in a magnetic field of 8.8 tesla. Despite being brittle and difficult to fabricate, niobium-tin has since proved extremely useful in supermagnets generating magnetic fields as high as 20 tesla. In 1962 T.G. Berlincourt and R.R. Hake ^[31][32] discovered that alloys of niobium and titanium are suitable for applications up to 10 tesla. Promptly thereafter, commercial production of niobium-titanium supermagnet wire commenced at Westinghouse Electric Corporation and at Wah Chang Corporation. Although niobium-titanium boasts less-impressive superconducting properties than those of niobium-tin, niobium-titanium has, nevertheless, become the most widely used “workhorse” supermagnet material, in large measure a consequence of its very-high ductility and ease of fabrication. However, both niobium-tin and niobium-titanium find wide application in MRI medical imagers, bending and focusing magnets for enormous high-energy-particle accelerators, and a host of other applications. Conectus, a European superconductivity consortium, estimated that in 2014, global economic activity for which superconductivity was indispensable amounted to about five billion euros, with MRI systems accounting for about 80% of that total.
In 1962, Josephson made the important theoretical prediction that a supercurrent can flow between two pieces of superconductor separated by a thin layer of insulator.^[33] This phenomenon, now called the Josephson effect, is exploited by superconducting devices such as SQUIDs. It is used in the most accurate available measurements of the magnetic flux quantum Φ₀ = h/(2e), where h is the Planck constant. Coupled with the quantum Hall resistivity, this leads to a precise measurement of the Planck constant. Josephson was awarded the Nobel Prize for this work in 1973.
In 2008, it was proposed that the same mechanism that produces superconductivity could produce a superinsulator state in some materials, with almost infinite electrical resistance.^[34]

High-temperature superconductivity

Timeline of superconducting materials

 

Until 1986, physicists had believed that BCS theory forbade superconductivity at temperatures above about 30 K. In that year, Bednorz and Müller discovered superconductivity in a lanthanum-based cuprate perovskite material, which had a transition temperature of 35 K (Nobel Prize in Physics, 1987).^[5] It was soon found that replacing the lanthanum with yttrium (i.e., making YBCO) raised the critical temperature to 92 K.^[35]
This temperature jump is particularly significant, since it allows liquid nitrogen as a refrigerant, replacing liquid helium.^[35] This can be important commercially because liquid nitrogen can be produced relatively cheaply, even on-site. Also, the higher temperatures help avoid some of the problems that arise at liquid helium temperatures, such as the formation of plugs of frozen air that can block cryogenic lines and cause unanticipated and potentially hazardous pressure buildup.^[36][37]
Many other cuprate superconductors have since been discovered, and the theory of superconductivity in these materials is one of the major outstanding challenges of theoretical condensed matter physics.^[38] There are currently two main hypotheses – the resonating-valence-bond theory, and spin fluctuation which has the most support in the research community.^[39] The second hypothesis proposed that electron pairing in high-temperature superconductors is mediated by short-range spin waves known as paramagnons.^{[40][41][dubious – discuss]}
Since about 1993, the highest-temperature superconductor has been a ceramic material consisting of mercury, barium, calcium, copper and oxygen (HgBa₂Ca₂Cu₃O_8+δ) with T_c = 133–138 K.^[42][43] The latter experiment (138 K) still awaits experimental confirmation, however.
In February 2008, an iron-based family of high-temperature superconductors was discovered.^[44][45] Hideo Hosono, of the Tokyo Institute of Technology, and colleagues found lanthanum oxygen fluorine iron arsenide (LaO_1−xF_xFeAs), an oxypnictide that superconducts below 26 K. Replacing the lanthanum in LaO_1−xF_xFeAs with samarium leads to superconductors that work at 55 K.^[46]
In May 2014, hydrogen sulfide (H
2S) was predicted to be a high-temperature superconductor with a transition temperature of 80 K at 160 gigapascals of pressure.^[47] In 2015, H
2S has been observed to exhibit superconductivity at below 203 K but at extremely high pressures — around 150 gigapascals.

Applications

Play media

Video of superconducting levitation of YBCO

Superconducting magnets are some of the most powerful electromagnets known. They are used in MRI/NMR machines, mass spectrometers, the beam-steering magnets used in particle accelerators and plasma confining magnets in some tokamaks. They can also be used for magnetic separation, where weakly magnetic particles are extracted from a background of less or non-magnetic particles, as in the pigment industries.
In the 1950s and 1960s, superconductors were used to build experimental digital computers using cryotron switches. More recently, superconductors have been used to make digital circuits based on rapid single flux quantum technology and RF and microwave filters for mobile phone base stations.
Superconductors are used to build Josephson junctions which are the building blocks of SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers known. SQUIDs are used in scanning SQUID microscopes and magnetoencephalography. Series of Josephson devices are used to realize the SI volt. Depending on the particular mode of operation, a superconductor-insulator-superconductor Josephson junction can be used as a photon detector or as a mixer. The large resistance change at the transition from the normal- to the superconducting state is used to build thermometers in cryogenic micro-calorimeter photon detectors. The same effect is used in ultrasensitive bolometers made from superconducting materials.
Other early markets are arising where the relative efficiency, size and weight advantages of devices based on high-temperature superconductivity outweigh the additional costs involved. For example, in wind turbines the lower weight and volume of superconducting generators could lead to savings in construction and tower costs, offsetting the higher costs for the generator and lowering the total LCOE.^[49]
Promising future applications include high-performance smart grid, electric power transmission, transformers, power storage devices, electric motors (e.g. for vehicle propulsion, as in vactrains or maglev trains), magnetic levitation devices, fault current limiters, enhancing spintronic devices with superconducting materials,^[50] and superconducting magnetic refrigeration. However, superconductivity is sensitive to moving magnetic fields so applications that use alternating current (e.g. transformers) will be more difficult to develop than those that rely upon direct current. Compared to traditional power lines superconducting transmission lines are more efficient and require only a fraction of the space, which would not only lead to a better environmental performance but could also improve public acceptance for expansion of the electric grid.

Battery charger 

A battery charger, or recharger, is a device used to put energy into a secondary cell or rechargeable battery by forcing an electric current through it.
The charging protocol (how much voltage or current for how long, and what to do when charging is complete, for instance) depends on the size and type of the battery being charged. Some battery types have high tolerance for overcharging (i.e., continued charging after the battery has been fully charged) and can be recharged by connection to a constant voltage source or a constant current source, depending on battery type. Simple chargers of this type must be manually disconnected at the end of the charge cycle, and some battery types absolutely require, or may use a timer to cut off charging current at some fixed time, approximately when charging is complete. Other battery types cannot withstand over-charging, being damaged (reduced capacity, reduced lifetime) or overheating or even exploding. The charger may have temperature or voltage sensing circuits and a microprocessor controller to safely adjust the charging current and voltage, determine the state of charge, and cut off at the end of charge.
A trickle charger provides a relatively small amount of current, only enough to counteract self-discharge of a battery that is idle for a long time. Slow battery chargers may take several hours to complete a charge; high-rate chargers may restore most capacity much faster, but high rate chargers can be more than some battery types can tolerate. Such batteries require active monitoring of the battery to protect it from overcharge. Electric vehicles ideally need high-rate chargers; for public access, installation of such chargers and the distribution support for them is an issue in the proposed adoption of electric cars.

 

This unit charges the batteries until they reach a specific voltage and then it trickle charges the batteries until it is disconnected.

A simple charger equivalent to an AC/DC wall adapter. It applies 300mA to the battery at all times, which will damage the battery if left connected too long.

Car Battery Charger

A battery charger, or recharger, is a device used to put energy into a secondary cell or rechargeable battery by forcing an electric current through it.
  

C-rates

Charge and discharge rates are often denoted as C or C-rate, which is a measure of the rate at which a battery is charged or discharged relative to its capacity. As such the C-rate is defined as the charge or discharge current divided by the battery's capacity to store an electrical charge. While rarely stated explicitly, the unit of the C-rate is h⁻¹, equivalent to stating the battery's capacity to store an electrical charge in unit hour times current in the same unit as the charge or discharge current. The C-rate is never negative, so whether it describes a charging or discharging process depends on the context.
For example, for a battery with a capacity of 500 mAh, a discharge rate of 5000 mA (i.e. 5 A) corresponds to a C-rate of 10 (per hour), meaning that such a current can discharge 10 such batteries in one hour. Likewise, for the same battery a charge current of 250 mA corresponds to a C-rate of 1/2 (per hour), meaning that this current will increase the state of charge of this battery by 50% in one hour.^[3]
Since the unit of the C-rate is typically implied, some care is required with its notation to avoid confusing it with the battery's capacity to store a charge, which in the SI has unit coulomb with unit symbol C.
If both the (dis)charge current and the battery capacity in the C-rate ratio is multiplied by the battery voltage, the C-rate becomes a ratio of the (dis)charge power to the battery's energy capacity. For example, when the 100 kWh battery in a Tesla Model S P100D is undergoing supercharging at 120 kW the C-rate is 1.2 (per hour) and when that battery delivers its maximum power of 451 kW, its C-rate is 4.51 (per hour).
Very high C-rates, 1 per hour or higher, generally require the charger to carefully monitor battery parameters such as terminal voltage and temperature to prevent overcharging and damage to the cells. Such high charging rates are possible only with some battery types. Others will be damaged or possibly overheat or catch fire. Some may even explode.^{[citation needed]} For example, an automobile SLI (starting, lighting, ignition) lead-acid battery carries several risks of explosion.

Types of battery chargers

Simple chargers

A typical simple charger

A simple charger works by supplying a constant DC or pulsed DC power source to a battery being charged. A simple charger typically does not alter its output based on charging time or the charge on the battery. This simplicity means that a simple charger is inexpensive, but there are tradeoffs. Typically, a carefully designed simple charger takes longer to charge a battery than otherwise because it is set to use a lower charging rate to prevent damage. Even so, many batteries left on a simple charger for too long will be weakened or destroyed due to over-charging. These chargers also vary in that they can supply either a constant voltage, or a constant current, to the battery.
Simple AC-powered battery chargers usually have much higher ripple current and ripple voltage than other kinds of battery chargers because they are inexpensively designed and built. Generally, when the ripple current is within a battery's manufacturer recommended level, the ripple voltage will also be well within the recommended level. The maximum ripple current for a typical 12 V 100 Ah VRLA lead acid battery is 5 amps. As long as the ripple current is not excessive (more than 3 to 4 times the battery manufacturer recommended level), the expected life of a ripple-charged VRLA battery will be within 3% of the life of a constant DC-charged battery.^[4]

Fast chargers

Fast chargers make use of control circuitry to rapidly charge the batteries without damaging any of the cells in the battery. The control circuitry can be built into the battery (generally for each cell) or in the external charging unit, or split between both. Most such chargers have a cooling fan to help keep the temperature of the cells at safe levels. Most are also capable of acting as standard overnight chargers if used with standard NiMH cells that do not have the special control circuitry.

Inductive chargers

 

Inductive battery chargers use electromagnetic induction to charge batteries. A charging station sends electromagnetic energy through inductive coupling to an electrical device, which stores the energy in the batteries. This is achieved without the need for metal contacts between the charger and the battery. It is commonly used in electric toothbrushes and other devices used in bathrooms. Because there are no open electrical contacts, there is no risk of electrocution. At present, this charging technique is only applicable to small batteries, not to high capacity systems.

Intelligent chargers

Example of a smart charger for AA and AAA batteries

A "smart charger" should not be confused with a "smart battery". A smart battery is generally defined as one containing some sort of electronic device or "chip" that can communicate with a smart charger about battery characteristics and condition. A smart battery generally requires a smart charger it can communicate with (see Smart Battery Data). A smart charger is defined as a charger that can respond to the condition of a battery, and modify its charging actions accordingly.
Some smart chargers are designed to charge:

• "smart" batteries.
• "dumb" batteries, which lack any internal electronic circuitry.

The output current of a smart charger depends upon the battery's state. An intelligent charger may monitor the battery's voltage, temperature or time under charge to determine the optimum charge current and to terminate charging.
For Ni-Cd and NiMH batteries, the voltage across the battery increases slowly during the charging process, until the battery is fully charged. After that, the voltage decreases, which indicates to an intelligent charger that the battery is fully charged. Such chargers are often labeled as a ΔV, "delta-V," or sometimes "delta peak", charger, indicating that they monitor the voltage change.
The problem is, the magnitude of "delta-V" can become very small or even non-existent if (very) high capacity rechargeable batteries are recharged. This can cause even an intelligent battery charger to not sense that the batteries are actually already fully charged, and continue charging. Overcharging of the batteries will result in some cases. However, many so called intelligent chargers employ a combination of cut off systems, which are intended to prevent overcharging in the vast majority of cases.
A typical intelligent charger fast-charges a battery up to about 85% of its maximum capacity in less than an hour, then switches to trickle charging, which takes several hours to top off the battery to its full capacity.^[5]

Motion-powered charger

Linear induction flashlight, charged by shaking along its long axis, causing magnet (visible at right) to slide through a coil of wire (center) to generate electricity

Several companies have begun making devices that charge batteries based on human motions. One example, made by Tremont Electric, consists of a magnet held between two springs that can charge a battery as the device is moved up and down, such as when walking. Such products have not yet achieved significant commercial success.^[6]
A pedal powered charger for mobile phones, fitted into desks has been created by a Belgian company WeWatt, for installation in public spaces, such as at airports, railway stations and universities have been installed in a number of countries on several continents.^[7]

Pulse chargers

Some chargers use pulse technology in which a series of voltage or current pulses is fed to the battery. The DC pulses have a strictly controlled rise time, pulse width, pulse repetition rate (frequency) and amplitude. This technology is said to work with any size, voltage, capacity or chemistry of batteries, including automotive and valve-regulated batteries.^[8] With pulse charging, high instantaneous voltages can be applied without overheating the battery. In a Lead–acid battery, this breaks down lead-sulfate crystals, thus greatly extending the battery service life.^[9]
Several kinds of pulse charging are patented.^[10][11][12] Others are open source hardware.
Some chargers use pulses to check the current battery state when the charger is first connected, then use constant current charging during fast charging, then use pulse charging as a kind of trickle charging to maintain the charge.^[13]
Some chargers use "negative pulse charging", also called "reflex charging" or "burp charging". Such chargers use both positive and brief negative current pulses. There is no significant evidence, however, that negative pulse charging is more effective than ordinary pulse charging.

Solar chargers

Solar chargers convert light energy into DC current. They are generally portable, but can also be fixed mount. Fixed mount solar chargers are also known as solar panels. Solar panels are often connected to the electrical grid, whereas portable solar chargers are used off-the-grid (i.e. cars, boats, or RVs).

Timer-based(HI) chargers

The output of a timer charger is terminated after a pre-determined time. Timer chargers were the most common type for high-capacity Ni-Cd cells in the late 1990s for example (low-capacity consumer Ni-Cd cells were typically charged with a simple charger).
Often a timer charger and set of batteries could be bought as a bundle and the charger time was set to suit those batteries. If batteries of lower capacity were charged then they would be overcharged, and if batteries of higher capacity were charged they would be only partly charged. With the trend for battery technology to increase capacity year on year, an old timer charger would only partly charge the newer batteries.
Timer based chargers also had the drawback that charging batteries that were not fully discharged, even if those batteries were of the correct capacity for the particular timed charger, would result in over-charging.

Trickle chargers

A trickle charger is typically a low-current (5–1,500 mA) battery charger. A trickle charger is generally used to charge small capacity batteries (2–30 Ah). These types of battery chargers are also used to maintain larger capacity batteries (> 30 Ah) that are typically found on cars, boats, RVs and other related vehicles. In larger applications, the current of the battery charger is sufficient only to provide a maintenance or trickle current (trickle is commonly the last charging stage of most battery chargers). Depending on the technology of the trickle charger, it can be left connected to the battery indefinitely. Some battery chargers that can be left connected to the battery without causing the battery damage are also referred to as smart or intelligent chargers. Note that not all battery types can tolerate trickle charging after being fully charged; most Li-ion batteries are damaged by trickle charging.

Universal battery charger–analyzers

The most sophisticated types are used in critical applications (e.g. military or aviation batteries). These heavy-duty automatic “intelligent charging” systems can be programmed with complex charging cycles specified by the battery maker. The best are universal (i.e. can charge all battery types), and include automatic capacity testing and analyzing functions too.

USB-based chargers

Australian and New Zealand power socket with USB charger socket

See also: USB § Power

Since the Universal Serial Bus specification provides for a five-volt power supply, it is possible to use a USB cable to connect a device to a power supply. Products based on this approach include chargers for cellular phones, portable digital audio players, and tablet computers. They may be fully compliant USB peripheral devices adhering to USB power discipline, or uncontrolled in the manner of USB decorations.
Although portable solar chargers obtain energy from the sun only, they still can (depending on the technology) be used in low light (i.e. cloudy) applications. Portable solar chargers are typically used for trickle charging, although some solar chargers (depending on the wattage), can completely recharge batteries. Other devices may exist, which combine this with other sources of energy for added recharging efficacy.

Powerbank

Powerbank charging a smartphone.

Powerbanks are popular for charging smartphones and mobile tablet devices. A powerbank is a portable device that can supply power from its built-in batteries through a USB port. They usually recharge with USB power supply. Technically, a powerbank consists of rechargeable Lithium-ion or Lithium-Polymer batteries installed in a protective casing, guided by a printed circuit board (PCB) which provides various protective and safety measures. Due to its general purpose, powerbanks are also gaining popularity as a branding and promotional tool. Different brands and promotional companies use it as a promotional tool and provide a customized product.

Many powerbanks use the common 18650 size lithium-ion battery which may or may not be user-replaceable.

Specifications:

• Capacity in Wh: Total power capacity measured by multiplying mAh by voltage.^[14]
• Capacity in mAh:^[15] mAh stands for milli Ampere-hour and measures the amount of power flow that can be supplied by a certain powerbank at a specific voltage. Many manufacturers rate their products at 3.7 V, the voltage of cell(s) inside. Since USB outputs at 5 V, calculations at this voltage will yield a lower mAh number. For example, a battery pack advertised with a 3000 mAh capacity (at 3.7 V) will produce 2220 mAh at 5 V. Power losses due to efficiency of the charging circuitry also occur.^[16]
• Simultaneous charging and discharging: need to specify if the powerbank can be used while it is charging.
• Number of output USB ports: This specifies the number of devices that can be charged simultaneously.
• Output current rating: This specifies the current rating that it can charge maximum. The higher the number, the better the powerbank. This can vary from output port to output port.
• Input Current Rating: Input current rating is the amount of current the powerbank is able to draw at its maximum level while getting charged.
• Safety Protections: Over Voltage Protection, Over Charge Protections, Over Current Protections, Over Heat Protections, Short-Circuit Protections and Over Discharge Protections are the common safety measures observed with standard powerbanks.
• LED Indications: The Led glows as per indicating the amount of charging ability left with the powerbank.

Compatibility

Mini, micro and J10 USB charging connectors

Lightning connector

Australian 240V USB charger with three different types of charging ports

Although a standard exists for USB chargers,^[17] there are two areas of common incompatibility.

• The connector on the device to be charged. There are several current and many obsolete connectors, including:
  • The Micro USB connector
  • The Mini USB connector
  • The lightning connector
  • The J10 connector
  • Various sizes of coaxial power connector, particularly the smaller sizes
  • The 3.5 mm jack and 2.5 mm jack

and others. It is essential that the connectors on the device and charger match exactly.

• The charging port. This may be smart or dumb, and each in various current ratings. Compatibility varies. A mismatched charger will charge more slowly, and sometimes not at all.

Applications

Since a battery charger is intended to be connected to a battery, it may not have voltage regulation or filtering of the DC voltage output. Battery chargers equipped with both voltage regulation and filtering are sometimes termed battery eliminators.

Battery charger for vehicles

There are two main types of chargers used for vehicles:

• To recharge a fuel vehicle's starter battery, where a modular charger is used; typically an 3-stage charger.
• To recharge an electric vehicle (EV) battery pack; see Charging station.

Chargers for car batteries come in varying ratings. Chargers that are rated up to two amperes may be used to maintain charge on parked vehicle batteries or for small batteries on garden tractors or similar equipment. A motorist may keep a charger rated a few amperes to ten or fifteen amperes for maintenance of automobile batteries or to recharge a vehicle battery that has accidentally discharged. Service stations and commercial garages will have a large charger to fully charge a battery in an hour or two; often these chargers can briefly source the hundreds of amperes required to crank an internal combustion engine starter.

Electric vehicle batteries

Electric vehicle battery chargers come in a variety of brands and characteristics. Zivan, Manzanita Micro, Elcon, Quick Charge, Rossco, Brusa, Delta-Q, Kelly, Lester and Soneil are the top 10 EV chargers in 2011 according to EVAlbum.com. These chargers vary from 1 kW to 7.5 kW maximum charge rate. Some use algorithm charge curves, others use constant voltage, constant current. Some are programmable by the end user through a CAN port, some have dials for maximum voltage and amperage, some are preset to specified battery pack voltage, amp-hour and chemistry. Prices range from $400 to $4500.
A 10 amp-hour battery could take 15 hours to reach a fully charged state from a fully discharged condition with a 1 amp charger as it would require roughly 1.5 times the battery's capacity.
Public EV charging stations provide 6 kW (host power of 208 to 240 VAC off a 40 amp circuit). 6 kW will recharge an EV roughly 6 times faster than 1 kW overnight charging.
Rapid charging results in even faster recharge times and is limited only by available AC power, battery type, and the type of charging system.^[18]
Onboard EV chargers (change AC power to DC power to recharge the EV's pack) can be:

• Isolated: they make no physical connection between the A/C electrical mains and the batteries being charged. These typically employ some form of Inductive charging. Some isolated chargers may be used in parallel. This allows for an increased charge current and reduced charging times. The battery has a maximum current rating that cannot be exceeded
• Non-isolated: the battery charger has a direct electrical connection to the A/C outlet's wiring. Non-isolated chargers cannot be used in parallel.

Power Factor Correction (PFC) chargers can more closely approach the maximum current the plug can deliver, shortening charging time.

Charge stations

 

Project Better Place was deploying a network of charging stations and subsidizing vehicle battery costs through leases and credits until filing for bankruptcy in May 2013.

Auxiliary charger designed to fit a variety of proprietary devices

Non-contact magnetic charging

Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed an electric transport system (called Online Electric Vehicle, OLEV) where the vehicles get their power needs from cables underneath the surface of the road via non-contact magnetic charging, (where a power source is placed underneath the road surface and power is wirelessly picked up on the vehicle itself.^[19]

Mobile phone charger

 

 

Micro USB mobile phone charger

Pay-per-charge kiosk, illustrating the variety of mobile phone charger connectors

Most mobile phone chargers are not really chargers, only power adapters that provide a power source for the charging circuitry which is almost always contained within the mobile phone. Older ones are notoriously diverse, having a wide variety of DC connector-styles and voltages, most of which are not compatible with other manufacturers' phones or even different models of phones from a single manufacturer.
Users of publicly accessible charging kiosks must be able to cross-reference connectors with device brands/models and individual charge parameters and thus ensure delivery of the correct charge for their mobile device. A database-driven system is one solution, and is being incorporated into some designs of charging kiosks.
Mobile phones can usually accept a relatively wide range of voltages^{[citation needed]}, as long as it is sufficiently above the phone battery's voltage. However, if the voltage is too high, it can damage the phone. Mostly, the voltage is 5 volts or slightly higher, but it can sometimes vary up to 12 volts when the power source is not loaded.^{[citation needed]}.
There are also human-powered chargers sold on the market, which typically consists of a dynamo powered by a hand crank and extension cords. A French startup offers a kind of dynamo charger inspired by the ratchet that can be used with only one hand.^[20] There are also solar chargers, including one that is a fully mobile personal charger and panel, which you can easily transport.
China, the European Commission and other countries are making a national standard on mobile phone chargers using the USB standard.^[21] In June 2009, 10 of the world's largest mobile phone manufacturers signed a Memorandum of Understanding to develop specifications for and support a microUSB-equipped common External Power Supply (EPS) for all data-enabled mobile phones sold in the EU.^[22] On October 22, 2009, the International Telecommunication Union announced a standard for a universal charger for mobile handsets (Micro-USB).^[23]

Stationary battery plants

Telecommunications, electric power, and computer uninterruptible power supply facilities may have very large standby battery banks (installed in battery rooms) to maintain critical loads for several hours during interruptions of primary grid power. Such chargers are permanently installed and equipped with temperature compensation, supervisory alarms for various system faults, and often redundant independent power supplies and redundant rectifier systems. Chargers for stationary battery plants may have adequate voltage regulation and filtration and sufficient current capacity to allow the battery to be disconnected for maintenance, while the charger supplies the DC system load. Capacity of the charger is specified to maintain the system load and recharge a completely discharged battery within, say, 8 hours or other interval.

Use in experiments

A battery charger can work as a DC power adapter for experimentation. It may, however, require an external capacitor to be connected across its output terminals in order to "smooth" the voltage sufficiently, which may be thought of as a DC voltage plus a "ripple" voltage added to it. There may be an internal resistance connected to limit the short circuit current, and the value of that internal resistance may have to be taken into consideration in experiments.

Prolonging battery life

What practices are best depend on the type of battery. NiCd cells must be fully discharged occasionally, or else the battery loses capacity over time due to a phenomenon known as "memory effect." Once a month (once every 30 charges) is sometimes recommended. This extends the life of the battery since memory effect is prevented while avoiding full charge cycles which are known to be hard on all types of dry-cell batteries, eventually resulting in a permanent decrease in battery capacity.
Most modern cell phones, laptops, and most electric vehicles use Lithium-ion batteries. These batteries last longest if the battery is frequently charged; fully discharging them will degrade their capacity relatively quickly. When storing however, lithium batteries degrade more while fully charged than if they are only 40% charged. As with all battery types, degradation also occurs faster at higher temperatures. Degradation in lithium-ion batteries is caused by an increased internal battery resistance due to cell oxidation. This decreases the efficiency of the battery, resulting in less net current available to be drawn from the battery. However, if Li-ION cells are discharged below a certain voltage a chemical reaction occurs that make them dangerous if recharged, which is why probably all such batteries in consumer goods now have an "electronic fuse" that permanently disables them if the voltage falls below a set level. The electronic fuse draws a small amount of current from the battery, which means that if a laptop battery is left for a long time without charging it, and with a very low initial state of charge, the battery may be permanently destroyed.
Motor vehicles, such as boats, RVs, ATVs, motorcycles, cars, trucks, and more use lead–acid batteries. These batteries employ a sulfuric acid electrolyte and can generally be charged and discharged without exhibiting memory effect, though sulfation (a chemical reaction in the battery which deposits a layer of sulfates on the lead) will occur over time. Typically sulfated batteries are simply replaced with new batteries, and the old ones recycled. Lead–acid batteries will experience substantially longer life when a maintenance charger is used to "float charge" the battery. This prevents the battery from ever being below 100% charge, preventing sulfate from forming. Proper temperature compensated float voltage should be used to achieve the best results.


Battery management system 

A battery management system (BMS) is any electronic system that manages a rechargeable battery (cell or battery pack), such as by protecting the battery from operating outside its Safe Operating Area, monitoring its state, calculating secondary data, reporting that data, controlling its environment, authenticating it and / or balancing it.^[1]
A battery pack built together with a battery management system with an external communication data bus is a smart battery pack. A smart battery pack must be charged by a smart battery charger

Functions

Monitor

A BMS may monitor the state of the battery as represented by various items, such as:

• Voltage: total voltage, voltages of individual cells, minimum and maximum cell voltage or voltage of periodic taps
• Temperature: average temperature, coolant intake temperature, coolant output temperature, or temperatures of individual cells
• State of charge (SOC) or depth of discharge (DOD), to indicate the charge level of the battery
• State of health (SOH), a variously-defined measurement of the overall condition of the battery
• Coolant flow: for air or fluid cooled batteries
• Current: current in or out of the battery

Electric Vehicle Systems: Energy Recovery

• The BMS will also control the recharging of the battery by redirecting the recovered energy (i.e.- from regenerative braking) back into the battery pack (typically composed of a few batteries, each composed of a few cells).

Computation

Additionally, a BMS may calculate values based on the above items, such as:

• Maximum charge current as a charge current limit (CCL)
• Maximum discharge current as a discharge current limit (DCL)
• Energy [kWh] delivered since last charge or charge cycle
• Internal impedance of a cell (to determine open circuit voltage)
• Charge [Ah] delivered or stored (sometimes this feature is called Coulomb counter)
• Total energy delivered since first use
• Total operating time since first use
• Total number of cycles

Communication

The central controller of a BMS communicates internally with its cell level hardware, or externally with high level hardware such as laptops or HMI.
High level external communication are simple and use several methods:

• Different types of Serial communications.
• CAN bus communications, commonly used in automotive environments.
• DC-BUS - Serial communication over power-line
• Different types of Wireless communications.^[2]

Low voltage centralized BMSs mostly do not have any internal communications. They measure cell voltage by resistance divide.
Distributed or modular BMSs must use some low level internal cell-controller (Modular architecture) or controller-controller (Distributed architecture) communication. These types of communications are difficult, especially for high voltage systems. The problem is voltage shift between cells. The first cell ground signal may be hundreds of volts higher than the other cell ground signal. Apart from software protocols, there are two known ways of hardware communication for voltage shifting systems, Optical-isolator and wireless communication. Another restriction for internal communications is the maximum number of cells. For modular architecture most hardware is limited to maximum 255 nodes. For high voltage systems the seeking time of all cells is another restriction, limiting minimum bus speeds and losing some hardware options. Cost of modular systems is important, because it may be comparable to the cell price.^[3] Combination of hardware and software restrictions results to be a few options for internal communication:

• Isolated serial communications
• wireless serial communications

Protection

A BMS may protect its battery by preventing it from operating outside its safe operating area, such as:

• Over-current (may be different in charging and discharging modes)
• Over-voltage (during charging)
• Under-voltage (during discharging), especially important for lead–acid and Li-ion cells
• Over-temperature
• Under-temperature
• Over-pressure (NiMH batteries)
• Ground fault or leakage current detection (system monitoring that the high voltage battery is electrically disconnected from any conductive object touchable to use like vehicle body)

The BMS may prevent operation outside the battery's safe operating area by:

• Including an internal switch (such as a relay or solid state device) which is opened if the battery is operated outside its safe operating area
• Requesting the devices to which the battery is connected to reduce or even terminate using the battery.
• Actively controlling the environment, such as through heaters, fans, air conditioning or liquid cooling
  

  BMS Main Controller

Battery connection to load circuit

A BMS may also feature a precharge system allowing a safe way to connect the battery to different loads and eliminating the excessive inrush currents to load capacitors.
The connection to loads is normally controlled through electromagnetic relays called contactors. The precharge circuit can be either power resistors connected in series with the loads until the capacitors are charged. Alternatively, a switched mode power supply connected in parallel to loads can be used to charge the voltage of the load circuit up to a level close enough to battery voltage in order to allow closing the contactors between battery and load circuit. A BMS may have a circuit that can check whether a relay is already closed before precharging (due to welding for example) to prevent inrush currents to occur.

Optimization[edit]

Distributed Battery Management system

In order to maximize the battery's capacity, and to prevent localized under-charging or over-charging, the BMS may actively ensure that all the cells that compose the battery are kept at the same voltage or State of Charge, through balancing. The BMS can balance the cells by:

• Wasting energy from the most charged cells by connecting them to a load (such as through passive regulators)
• Shuffling energy from the most charged cells to the least charged cells (balancers)
• Reducing the charging current to a sufficiently low level that will not damage fully charged cells, while less charged cells may continue to charge (does not apply to Lithium chemistry cells)
• Modular charging ^[4]

Topologies

Cable Data transfer module

BMS Wireless Communication

BMS technology varies in complexity and performance:

• Simple passive regulators achieve balancing across batteries or cells by bypassing charging current when the cell's voltage reaches a certain level. The cell voltage is a poor indicator of the cell's SOC (and for certain Lithium chemistries such as LiFePO4 it is no indicator at all), thus, making cell voltages equal using passive regulators does not balance SOC, which is the goal of a BMS. Therefore, such devices, while certainly beneficial, have severe limitations in their effectiveness.
• Active regulators intelligently turning on and off a load when appropriate, again to achieve balancing. If only the cell voltage is used as a parameter to enable the active regulators, the same constraints noted above for passive regulators apply.
• A complete BMS also reports the state of the battery to a display, and protects the battery.

BMS topologies fall in 3 categories:

• Centralized: a single controller is connected to the battery cells through a multitude of wires
• Distributed: a BMS board is installed at each cell, with just a single communication cable between the battery and a controller
• Modular: a few controllers, each handing a certain number of cells, with communication between the controllers

Centralized BMSs are most economical, least expandable, and are plagued by a multitude of wires. Distributed BMSs are the most expensive, simplest to install, and offer the cleanest assembly. Modular BMSs offer a compromise of the features and problems of the other two topologies.
The requirements for a BMS in mobile applications (such as electric vehicles) and stationary applications (like stand-by UPSs in a server room) are quite different, especially from the space and weight constraint requirements, so the hardware and software implementations must be tailored to the specific use. In the case of electric or hybrid vehicles, the BMS is only a subsystem and cannot work as a standalone device. It must communicate with at least a charger (or charging infrastructure), a load, thermal management and emergency shutdown subsystems. Therefore, in a good vehicle design the BMS is tightly integrated with those subsystems. Some small mobile applications (such as medical equipment carts, motorized wheelchairs, scooters, and fork lifts) often have external charging hardware, however the on-board BMS must still have tight design integration with the external charger.
Various Battery balancing methods are in use, some of them based on state of charge theory.

Battery Management System

Advanced battery technologies such as lithium ion, Lipo & Lifepo4 require Battery Management Systems to ensure safety and long life performance of the battery packs. Lian Innovative lithium Battery management system is the most configurable and modular one available in the market. We started to develop custom lithium ion battery packs a long time ago. It results in in-depth knowledge of Lithium Battery Management System. The other competitor doesn’t build battery packs, so how could they know what really works? Lian Innovative has introduced a range of scalable and highly configurable battery management systems which could be used as Electric Vehicle,  Solar energy, Marine vessels, Large lithium ion battery packs, Uninterruptable Power System and Hybrid Vehicles battery management system.
Our product is designed at its core to operate in the environments with harsh electrical noise. Its performances are excellent as battery management system for electric vehicles. The advanced design allows our product to withstand very significant EMI that other BMS cannot.
Lian Innovative lithium Battery Management Systems are the outcome of eight years of experience delivering custom lithium battery management systems. It has evolved to the point where we can claim it to be one of the most reliable and effective lithium ion, Lipo, Lifepo4 battery management systems available on the market. Various models are designed for applications ranging from Large lithium battery packs grid energy storage systems, telecom power backup, Marine vessels, UAVs & UUVs and Electric Vehicle battery management system. Lian Innovative battery management systems could be used as off the shelf plug and play product, Semi-custom versions or full custom design version.
In our custom projects, we work very closely with our customer in order to deliver a custom turnkey Battery Management System solution within tight timescales and budgets. We have more than eight years of experience in designing Battery Management System for large lithium battery packs and many lessons learned from more than 12 projects worldwide.

Lithium Battery Management Systems Structure

Our BMS has three fully modular sections. Each one can be selected to be most suited to the user needs.

1. The Central Controller Unit (CCU).
2. The Power Controller Unit (PCU).
3. The Cell Boards (CB).

The CCU control the functionality of the whole system and is the same in all battery management systems. It is just one model and there is no need to be changed if the battery voltage, configuration, type and other parameter changes. 
The main function of the PCU is to connect/disconnect battery from load or charger. It also measures current and voltage of the battery pack and limits the inrush current of capacitors. PCU model depends on battery pack specs. For different pack voltage and current, different PCU must be selected. Please consult us for further info. 
The CB function is to monitor the cell’s voltage and temperature and to balance it if needed. There are three different types of CB offered by Lian innovative. Selection is based on the layout of the cells and can be selected by the user to mostly suited for the application.

 Central Controller Unit

The CCU main function is to control the whole system. The user interfacing, storing data, monitoring cells, activation of the contactors and all other standard tasks are done by CCU. Lian Innovative Battery Management Systems CCU is equipped with an SD card which can log all details of battery packs. It is ideal for unmanned mobile robots. After missions, the operator can be informed about each cell performance. It can also be used by Battery Management System manufacturer companies as a witness during guaranty period. We have developed algorithms that will allow the Lithium Battery Management System to identify normal aging and performance trends of cells versus those that are non-typical. Maximum life cycle and reliability will be achieved by monitoring cell performance and compared with the expected ranges from cycle to cycle. In the case where an abnormal trend is identified, the CCU will take appropriate action to inform users of the situation to increase reliability and safety.
Various isolated and protected Analog and Digital IO have been provided on the system which can be setup easily by the user. Full protection is provided on central controller boards to cover user mistakes such as reverse polarity, over voltage, etc.

Central Controller Unit Specs:

• Full battery protections
• Balancing Lithium ion batteries (different kinds)
• In site Auto/Manual configurable
• Cell performances log and analyzes
• Logs and reports up to thousands hour of full details of cells and pack
• State of Charge (SOC), State of Health (SOH),
• Automatic %SOC calibration
• Operational status and full alarm status indicators
• Auto sleep function to put battery modules to sleep when not in use
• Built in self Balancing Lithium batteries algorithms to maintain battery pack balance and optimize the charging function
• Configurable Opto-isolated digital and analog I/O
• Low power consumption
• Internal alarm buzzer for audible warning
• Communication flexibility with a variety of communication ports
• Various ignition configurable
• Firmware revision updates capability
• Self-healing – abnormal conditions “clear” without intervention when condition subsides

 Power Control Unit

Old battery management systems do not include power control unit. Supplier advises the user to find some contactors, relays, fuses, shunts and other parts, connect them with some copper connectors assembling them together and run the battery. Lian Innovative discovered that most of the customers have lots of problem in power units that leads to some critical safety problem or system failure.
Lian Innovative is the first company to offer Power Control Units that integrated all parts and circuits needed to connect/disconnect the battery pack from load/charger. It fully compatible with CCU and no engineering is needed to use it in the system.
In some applications, users need an Auxiliary 12/24/48 volts supply to run the PcBs and circuits. Some battery experts advise them to use another low voltage battery, that results to increase weight, costs and reduces the reliability and etc. Lian Innovative is the first company that integrated an advanced, reliable, DC-DC converter to PCU that not only supply the power of its internal circuits but also can supply users external circuits power. This advanced option makes the system designs as simple and reliable as possible.The PCU provides the ability to differentiate in-rush currents (such as engine start) from short-circuiting currents. Direct hardware monitoring ensures a quick response to short-circuit or overcurrent conditions as witnessed by the main battery shunt. Special contactors can connect and disconnect heavy loads from battery pack safely and reliably. A current limiter is provided to be used on systems with high capacitors in parallel to the load.
Lots of options and sizes available to helps users to select the best-suited choice for their applications. It is totally cost effective, safe, time effective and fault proof solution that helps the users to integrate the battery management system easily and with less engineering.

  Power Control Unit Specs:

• Aux power supply can be up to 750w, 48 volt
• Handle up to 1000A 900Vdc 
• Precise pack current measurement by Shunt sensor
• Precise pack voltage measurement 
• Safely and reliably connects/disconnects battery pack to load/charger
• Inrush current limiter
• DC fuse included
• Reverse voltage protected
• protection against inductive load disconnection

 

	Switching Current	Switching Voltage	Aux Power supply voltage	Aux Power supply power	Inductive loading switch	Dc Line Fuse	Dual line Relay	Capactive load switching	Dimension mmxmmxmm
PCU500	500A+	900Vdc	5/12/24/48	250/500/750	yes	750A	yes	yes	270x220x103
PCU200	200A	350VDC	5/12/24/48	250/500/750	yes	300A	yes	yes	260x190x103
PCU100	100A	350Vdc	5/12/24/48	250/500/750	yes	150A	yes	yes	240x190x103
PCU60	60A	350Vdc	5/12/24/48	250/500/750	yes	90A	yes	yes	220x170x103

 Cell Boards

Three different cell boards introduced by Lian Innovative for various applications, distributed wired, distributed wireless and integrated board. They cover all needs of different battery packs including Hybrid Vehicle, Marine vessels, Autonomous Underwater Vehicles, Large lithium battery packs, Uninterruptable Power System, EV Battery Management system, and etc. Full protection is provided on the cell monitoring boards to cover user mistakes such as reverse polarity, over voltage, etc.

• InnoCab: distributed wired CB       
• InnoLess: distributed wireless CB     
• InnoTeg:  integrated CB    

. . .

InnoCab, Distributed Wired cell monitoring

Innocab is a distributed cell monitoring board which suited for large lithium battery packs with considerable distance between cells or battery packs of which the configuration or voltage may vary during the design and development.

InnoCab Battery Management System unique specs:

• Fully configurable from 1 to 252 cells
• large lithium battery packs for lithium ion/Lipo/Lifepo4 battery packs from 3.7Vdc to 1000Vdc
• No engineering needs to setup and use
• Auto sleep function to put battery modules to sleep when not in use
• Temperature compensated voltage measurements resolution down to 1 mV with 10 mV accuracy in full temperature range
• temperature measurement resolution down to 0.1 C and 1 C accuracy.
• Cell balancing current up to 2A
• Voltage and temperature of each cell to ensure the safety and long life
• Highly redundancy for data cable disconnection, or one cell monitor board crash
• Fail safe network guarantees that if one cell monitor board crashes the others can continue their job
• Epoxy-encased cell modules resist dust and moisture
• LED indicators on each cell

. . .

InnoLess, Distributed Wireless cell monitoring

Innocab is wireless distributed Battery Management system which suited for battery packs with a very large distance between cells, or for whom which not happy with bird nested wiring or very high voltage battery packs which electrical shock hazard concerns for the user, repairmen, and maintenance service men.

InnoLess BMS specs are as below:

• Fully configurable from 1 to 252 cells
• Battery Management System for lithium ion, Lifepo4 battery packs from 3.7Vdc to 1000Vdc
• No engineering needs to setup and use
• Voltage and temperature of each cell to ensure the safety and long life
• Auto sleep function to put battery modules to sleep when not in use
• Temperature compensated voltage measurements resolution down to 1 mV with 10 mV accuracy in full temperature range
• temperature measurement resolution down to 0.1 C and 1 C accuracy.
• Cell balancing current up to 2A
• Highly redundancy for wireless connection, or one cell monitor board crash
• Fail safe network guaranties that if one cell monitor board crashes the others can continue their job
• Epoxy-encased cell modules resist dust and moisture
• LED indicators on each cell

. . .

InnoTeg, Integrated cell monitoring

Innoteg is advanced integrated Battery Management System which suited for economical mass productions battery packs that price is the main parameter.

 

InnoTeg unique specs:

• Fully configurable from 5 to 252 cells
• Battery Management System for lithium ion, Lifepo4 battery packs from 20Vdc to 1000Vdc
• Voltage of each cell and temperature of each 14 cells to ensure the safety and long life
• Auto sleep function to put battery modules to sleep when not in use
• Temperature compensated voltage measurements resolution down to 1 mV with 10 mV accuracy in full temperature range
• Temperature measurement resolution down to 0.1 C and 1 C accuracy.
• Cell balancing current up to 0.5A

Underwater Robot Engineering, Consulting, and Optimization

Problem definition:
Our client reports that his old underwater robots range which expected to be more than 55 miles are about 35 miles. And its velocity is 6 Knots which is supposed to be 8.5 Knots. These two parameters were nominal and no one can be witnessed that the underwater robot was qualified for when they were new. then the problem was totally vague. The problem was some kind of blind engineering consulting.
Winning the contract
The user had no view about the source of the problem. It was impossible to tests the underwater robot in the field before the contract. He just looks someone to analyses and solves the problem in shortest time and lowest price. Here Lian Innovative entered to the problem by offering shortest time and lowest price just by analyzing the problem not by doing field tests.
Startup
Lian Innovative analyzed the system and draw a complete energy transfer line from batteries of the underwater robot to the Hull of the underwater robot.
Each subsystem performance and efficiency tested in the system, and separately to understand assembly problems if there were any. Surprisingly results showed that overall efficiency from battery pack to Hull was less than 23% !!! That was too low for an underwater robot which its energy comes from expensive batteries.

Field tests

After it, Lian Innovative focused on energy consumption of the hull. At first, the towing test (drag test) in the sea was done. Total drag force was measured in different speeds precisely and carefully.

Lab test

In the next step, Lian Innovative designed and developed a scaled model of the underwater robot, and did the  towing test in the tank.

Field test reports confirmed the underwater robot model test results. It revealed that the drag force is beyond what was expected from theory and analyses. Froud No. and Reynolds No. carefully computed and discovered that the main factor which increases the drag force is Up-welling Fluid. 

In synchronous with our client, we decided to change the underwater robot nose shape. Six different standard nose performances were investigated. All of them designed and manufactured to be used on downscaled model.

The drag force of all models in different speeds precisely measured by towing test. Two of them with lowest drag force was selected, and other factors such as manufacturability and maneuverability were carefully investigated and tested.

Results show that proposed underwater robot nose reduces the drag force to 53% of the main nose. That was great!!!

By huge investigation and having experienced consultant engineers, it revealed that the rudder and elevator airfoils and their bases were not optimum in water streamline and have a considerable effect on underwater robot performance. Engineering consultation and training, let the client understand the side effects of the problem. He accepted the problem analyses deeper.

With client acceptance, Lian Innovative developed a newly designed control surfaces and repeat the drag tests by the towing test. Results show that finalized model drag forces were about 32% of the main model. Wonderful!!!

Field Verification Test

To prove our model test results, we need to make two full-scale underwater robot nose prototype and control surfaces, assembled them on the real underwater robot, and repeated the field test with the new configuration. The client didn’t accept to had any modifications on his underwater robot body and structure. Any kind of welding, drilling, and permanent modifications were prohibited. Lots of innovative engineering solutions by Lian Innovative mechanical engineers consultant helped us to find a way to do the test due to client restrictions. Finally filed tests were ran and the results validated model test by error less than 4%. Client accepted to change the nose and hydrodynamic surfaces.

In the next step Lian innovative propose  to change old fashion underwater robot thruster, to a new modern high efficiency, low noise PMSM Underwater Thruster. A custom designed enhanced underwater thruster was designed and developed and a prototype was manufactured.

 

Prototype underwater thruster along with new nose and control surfaces started to be tested in the field for more than 250 hours. Client accepted the whole story. The speed of underwater robot set to be 8.5 Knots as the client ordered. But its range goes up to 75 miles with same batteries !!! that’s because not only the underwater thruster system efficiency raised up to 58% from 23%, But also the hull consumption reduced to 32% of initial value. This wonderful results convinced the client to ordered Lian Innovative to renew 12 of his underwater robots.

Limited production:

Client accepted to apply newly design system to all 12 robots. And we did it proudly!!! 

Electric Motorcycle Engineering, Consulting, and Optimization

The client was a famous Electric Motorcycle manufacturer, whose product price were not competitive to the other brands and he loses the market share steadily. He decided to reduce his products cost without any reduction in quality. It was some kind of mechanical/Electrical Engineering, Consulting, and Optimization problem. Lian Innovative analysed the electric motorcycle carefully, and noticed that he can help the client to stands in the market,  proposed his solution, wins the contract and enters to the project.

Startup
Lian Innovative analyzed the Electric Motorcycle and draw a complete energy transfer line from batteries to the wheel of Electric Motorcycle. Each subsystem performance and efficiency tested in the system, and separately to understand assembly problems if there were any. Surprisingly results showed that overall efficiency from battery pack to wheel was in the range of 32% to 45% !!! That was too low for an Electric Motorcycle which its energy comes from expensive Lithium ion batteries.

Analyses & Solution
Initial idea was to use a high-efficiency electric motor to reduce the capacity of the battery pack. But there was a problem. Not only the high-efficiency electric motor price are higher than low efficiency one, but also initial cost including design and development of new motor would impose lots of cost to the manufacture.
Detailed cost estimation and the market search revealed that the reduction in the battery cost is considerable and can compensate electric motor initial and production cost.
In the next step, Lian Innovative carefully proposed a business plan to replace old fashion BLDC motor, by a new modern high efficiency, Light, PMSM hub wheel motor and reduce the capacity of the expensive Lithium ion battery pack to about one half. By this shift, the initial cost of the new design could be refunded by saving in the battery price in first 5324 Electric Motorcycle and after that the total production cost reduced by 36%. Which keep the product competitive in the market.
A custom designed enhanced PMSM hub wheel motor was designed and developed and a prototype were manufactured. Also, new low capacity lithium ion battery pack was design and developed and a prototype was manufactured.

Results

Electric Motorcycle with new configuration tested by client and Lian Innovative experts. All efficiency tests repeated and results were wonderful. The range was unchanged, weight reduced by 14Kg and overall efficiency increased to more than 82%.

 

Smart Battery

   

Almost all laptops use smart batteries.

Smart battery components

A smart battery or a smart battery pack is a rechargeable battery pack with a built-in battery management system (BMS), usually designed for use in a portable computer such as a laptop. Besides the usual plus and minus terminals, it also has two or more terminals to connect to the BMS; typically minus is also used as BMS "ground". BMS interface examples are: SMBus, PMBus, EIA-232, EIA-485, MIPI BIF and Local Interconnect Network.
The smarter battery can internally measure voltage and current, and deduce charge level and SoH (State of Health) parameters, indicating the state of the cells. Externally the smart battery can communicate with a smart battery charger and a "smart energy user" via the bus interface. The smart battery can demand that the charging stops, ask for charging, or demand that the smart energy user stop using power from this battery. There are standard specifications for smart batteries: Smart Battery System^[1] and many ad-hoc specifications.


Rechargeable battery

A rechargeable battery, storage battery, secondary cell, or accumulator is a type of electrical battery which can be charged, discharged into a load, and recharged many times, while a non-rechargeable or primary battery is supplied fully charged, and discarded once discharged. It is composed of one or more electrochemical cells. The term "accumulator" is used as it accumulates and stores energy through a reversible electrochemical reaction. Rechargeable batteries are produced in many different shapes and sizes, ranging from button cells to megawatt systems connected to stabilize an electrical distribution network. Several different combinations of electrode materials and electrolytes are used, including lead–acid, nickel cadmium (NiCd), nickel metal hydride (NiMH), lithium ion (Li-ion), and lithium ion polymer (Li-ion polymer).
Rechargeable batteries typically initially cost more than disposable batteries, but have a much lower total cost of ownership and environmental impact, as they can be recharged inexpensively many times before they need replacing. Some rechargeable battery types are available in the same sizes and voltages as disposable types, and can be used interchangeably with them.

  A battery bank used for an uninterruptible power supply in a data center

 A rechargeable lithium polymer mobile phone battery

 A common consumer battery charger for rechargeable AA and AAA batteries 

Usage and applications

Cylindrical cell (18650) prior to assembly. Several thousand of them (lithium ion) form the Tesla Model S battery (see Gigafactory).

Lithium ion battery monitoring electronics (over- and discharge protection)

Devices which use rechargeable batteries include automobile starters, portable consumer devices, light vehicles (such as motorized wheelchairs, golf carts, electric bicycles, and electric forklifts), tools, uninterruptible power supplies, and battery storage power stations. Emerging applications in hybrid internal combustion-battery and electric vehicles drive the technology to reduce cost, weight, and size, and increase lifetime.^[1]
Older rechargeable batteries self-discharge relatively rapidly, and require charging before first use; some newer low self-discharge NiMH batteries hold their charge for many months, and are typically sold factory-charged to about 70% of their rated capacity.
Battery storage power stations use rechargeable batteries for load-leveling (storing electric energy at times of low demand for use during peak periods) and for renewable energy uses (such as storing power generated from photovoltaic arrays during the day to be used at night). Load-leveling reduces the maximum power which a plant must be able to generate, reducing capital cost and the need for peaking power plants.
The US National Electrical Manufacturers Association estimated in 2006 that US demand for rechargeable batteries was growing twice as fast as demand for disposables.^[2]
Small rechargeable batteries can power portable electronic devices, power tools, appliances, and so on. Heavy-duty batteries power electric vehicles, ranging from scooters to locomotives and ships. They are used in distributed electricity generation and in stand-alone power systems.

Charging and discharging

A solar-powered charger for rechargeable AA batteries

 

During charging, the positive active material is oxidized, producing electrons, and the negative material is reduced, consuming electrons. These electrons constitute the current flow in the external circuit. The electrolyte may serve as a simple buffer for internal ion flow between the electrodes, as in lithium-ion and nickel-cadmium cells, or it may be an active participant in the electrochemical reaction, as in lead–acid cells.
The energy used to charge rechargeable batteries usually comes from a battery charger using AC mains electricity, although some are equipped to use a vehicle's 12-volt DC power outlet. Regardless, to store energy in a secondary cell, it has to be connected to a DC voltage source. The negative terminal of the cell has to be connected to the negative terminal of the voltage source and the positive terminal of the voltage source with the positive terminal of the battery. Further, the voltage output of the source must be higher than that of the battery, but not too much higher: the greater the difference between the power source and the battery's voltage capacity, the faster the charging process, but also the greater the risk of overcharging and damaging the battery.
Chargers take from a few minutes to several hours to charge a battery. Slow "dumb" chargers without voltage or temperature-sensing capabilities will charge at a low rate, typically taking 14 hours or more to reach a full charge. Rapid chargers can typically charge cells in two to five hours, depending on the model, with the fastest taking as little as fifteen minutes. Fast chargers must have multiple ways of detecting when a cell reaches full charge (change in terminal voltage, temperature, etc.) to stop charging before harmful overcharging or overheating occurs. The fastest chargers often incorporate cooling fans to keep the cells from overheating. Different battery chemistries require different charging schemes, or alternatively, not every charger will work with every battery. Charging a battery incorrectly can, depending on the difference between what the battery requires and the charger supplies, cause a battery to fail, damage a battery so that its life is reduced, overheat a battery or damage the chemicals it includes so much that the battery explodes or catches fire. Matching a charger to the battery it is to charge is important, but not always obvious to an end user. Some charger manufacturers claim they are compatible with batteries that they are not; caution is required.

Diagram of the charging of a secondary cell or battery.

Battery charging and discharging rates are often discussed by referencing a "C" rate of current. The C rate is that which would theoretically fully charge or discharge the battery in one hour. For example, trickle charging might be performed at C/20 (or a "20 hour" rate), while typical charging and discharging may occur at C/2 (two hours for full capacity). The available capacity of electrochemical cells varies depending on the discharge rate. Some energy is lost in the internal resistance of cell components (plates, electrolyte, interconnections), and the rate of discharge is limited by the speed at which chemicals in the cell can move about. For lead-acid cells, the relationship between time and discharge rate is described by Peukert's law; a lead-acid cell that can no longer sustain a usable terminal voltage at a high current may still have usable capacity, if discharged at a much lower rate. Data sheets for rechargeable cells often list the discharge capacity on 8-hour or 20-hour or other stated time; cells for uninterruptible power supply systems may be rated at 15 minute discharge.
Battery manufacturers' technical notes often refer to voltage per cell (VPC) for the individual cells that make up the battery. For example, to charge a 12 V lead-acid battery (containing 6 cells of 2 V each) at 2.3 VPC requires a voltage of 13.8 V across the battery's terminals.
Non-rechargeable alkaline and zinc–carbon cells output 1.5V when new, but this voltage drops with use. Most NiMH AA and AAA cells are rated at 1.2 V, but have a flatter discharge curve than alkalines and can usually be used in equipment designed to use alkaline batteries.

Damage from cell reversal

Subjecting a discharged cell to a current in the direction which tends to discharge it further to the point the positive and negative terminals switch polarity causes a condition called cell reversal. Generally, pushing current through a discharged cell in this way causes undesirable and irreversible chemical reactions to occur, resulting in permanent damage to the cell. Cell reversal can occur under a number of circumstances, the two most common being:

• When a battery or cell is connected to a charging circuit the wrong way around.
• When a battery made of several cells connected in series is deeply discharged.

In the latter case, the problem occurs due to the different cells in a battery having slightly different capacities. When one cell reaches discharge level ahead of the rest, the remaining cells will force the current through the discharged cell.
Many battery-operated devices have a low-voltage cutoff that prevents deep discharges from occurring that might cause cell reversal.
Cell reversal can occur to a weakly charged cell even before it is fully discharged. If the battery drain current is high enough, the cell's internal resistance can create a resistive voltage drop that is greater than the cell's forward emf. This results in the reversal of the cell's polarity while the current is flowing.^[3][4] The higher the required discharge rate of a battery, the better matched the cells should be, both in the type of cell and state of charge, in order to reduce the chances of cell reversal.
In some situations, such as when correcting Ni-Cad batteries that have been previously overcharged,^[5] it may be desirable to fully discharge a battery. To avoid damage from the cell reversal effect, it is necessary to access each cell separately: each cell is individually discharged by connecting a load clip across the terminals of each cell, thereby avoiding cell reversal.

Damage during storage in fully discharged state

If a multi-cell battery is fully discharged, it will often be damaged due to the cell reversal effect mentioned above. It is possible however to fully discharge a battery without causing cell reversal—either by discharging each cell separately, or by allowing each cell's internal leakage to dissipate its charge over time.
Even if a cell is brought to a fully discharged state without reversal, however, damage may occur over time simply due to remaining in the discharged state. An example of this is the sulfation that occurs in lead-acid batteries that are left sitting on a shelf for long periods. For this reason it is often recommended to charge a battery that is intended to remain in storage, and to maintain its charge level by periodically recharging it. Since damage may also occur if the battery is overcharged, the optimal level of charge during storage is typically around 30% to 70%.

Depth of discharge

Depth of discharge (DOD) is normally stated as a percentage of the nominal ampere-hour capacity; 0% DOD means no discharge. As the usable capacity of a battery system depends on the rate of discharge and the allowable voltage at the end of discharge, the depth of discharge must be qualified to show the way it is to be measured. Due to variations during manufacture and aging, the DOD for complete discharge can change over time or number of charge cycles. Generally a rechargeable battery system will tolerate more charge/discharge cycles if the DOD is lower on each cycle.^[6]

Lifespan and cycle stability

If batteries are used repeatedly even without mistreatment, they lose capacity as the number of charge cycles increases, until they are eventually considered to have reached the end of their useful life.
Lithium iron phosphate batteries reach according to the manufacturer more than 5000 cycles at respective depth of discharge of 70%.^[7] After 7500 cycles with discharge of 85% this still have a spare capacity of at least 80% at a rate of 1 C; which corresponds with a full cycle per day to a lifetime of min. 20.5 years.
The lithium iron phosphate battery Sony Fortelion has after 10,000 cycles at 100% discharge level still a residual capacity of 71%. This battery has been on the market since 2009.^[8]
Lithium-ion batteries have partly a very high cycle resistance of more than 10,000 charge and discharge cycles and a long service life of up to 20 years.^[9][10]
Plug in America has carried out a survey among drivers of the Tesla Roadster, with respect to the service life of the installed battery. It was found that after 100,000 miles = 160,000 km, the battery still had a remaining capacity of 80 to 85 percent. This was regardless of in which climate zone the car is moved.^[11][12] The Tesla Roadster was built and sold between 2008 and 2012. For its 85-kWh batteries in the Tesla Model S Tesla are 8-year warranty with unlimited mileage.^[13]
Varta Storage guarantees its engion battery systems for 14,000 full cycles and a service life of 10 years.
As of 2017, the best-selling electric car is the Nissan Leaf, which is produced since of 2010. Nissan stated in 2015 that until then only 0.01 percent of batteries had to be replaced because of failures or problems and then only because of externally inflicted damage. There are few vehicles that have already covered more than 200,000 km away. These have no problems with the battery.^[16]

Recharging time

BYD e6 taxi. Recharging in 15 Minutes to 80 percent

Electric cars like Tesla Model S, Renault Zoe, BMW i3, etc. can recharge their batteries at quick charging stations within 30 minutes to 80 percent.^{[17][18][19][20]} The Porsche Mission E will be able to charge to 80 percent within 15 minutes.^[21]
In laboratories the company StoreDot from Israel reportedly demonstrated the first lab samples of unspecified batteries that can, as of April 2014, be charged in 30 seconds in mobile phones.^[22][23]
Researchers from Singapore in 2014 developed a battery that can be recharged in 2 minutes to 70 percent. The batteries rely on lithium-ion technology. However, the anode and the negative pole in the battery is no longer made of graphite, but a titanium dioxide gel. The gel accelerates the chemical reaction significantly, thus ensuring a faster charging. In particular, these batteries are to be used in electric cars.^[24][25][26] Already in 2012 researchers at the Ludwig-Maximilian-University in Munich have discovered the basic principle.^[27]
Scientists at Stanford University in California have developed a battery that can be charged within one minute. The anode is made of aluminium and the cathode made of graphite (see Aluminium-ion battery).^[28][29]
The electric car Volar-e of the company Applus + IDIADA, based on the Rimac Concept One, contains lithium iron phosphate batteries that can be recharged in 15 minutes.^[30]
According to the manufacturer BYD the lithium iron phosphate battery of the electric car e6 is charged at a fast charging station within 15 minutes to 80%, after 40 minutes at 100%.^[31]
In 2005, handheld device battery designs by Toshiba were claimed to be able to accept an 80% charge in as little as 60 seconds.^[32]
Scientists of university of Oslo from Norway have developed a battery which can be recharged less than one second. According to the scientists this battery would be interesting for example for city buses, which could be loaded at each bus stop, and thus would require only a relatively small battery. A disadvantage is, according to the researchers that the bigger the battery, the greater must be the charging current. Thus, the battery can not be very big. According to the researchers of the new battery could also be used as a buffer in sports car to provide power in the short term. For now, however, the researchers think of applications in small and micro devices.
According to the manufacturer battery of the smartphone OnePlus 3 can be charged from 0 to 60 percent within 30 minutes.^[35]

Price history

Lead-acid batteries typically cost €100 / kWh. Li-Ion batteries cost in January 2014, however, typically around €110 / kWh (150 USD / kWh). The prices for Li-Ion batteries have, since 2011, dropped significantly (2011: €500 / kWh, 2012: €350 / kWh, 2013: €200 / kWh)  At a conference for electric mobility October 2013 mentioned the trend researcher Lars Thomsen, that Tesla has built its battery at the time 200 USD / kWh (equivalent to €148 / kWh).^[41] for the planned for autumn 2016 e-mobile Bolt expects General Motors 145 USD / kWh, and a reduction to 100 USD / kWh by 2022.^[42] Eric Feunteun, head of the Elektromobile division at Renault, said in July 2017 that Renault costs a kWh battery 80 dollars.^[43][44] Reasons for the price decline is the increasing mass production, which has reduced costs through better technologies and economies of scale.
In Germany LiFePO4 battery cells retail for about 420 €/kWh (1.35 €/Ah) as of January 2015.^[45]
Tesla's Powerpack sold for 250 USD per kWh^[46] (see Tesla Powerwall) in spring 2016.
According to a study conducted by McKinsey & Co. the price of rechargeable batteries dropped by 80 percent between 2010 and 2016.

Active components

The active components in a secondary cell are the chemicals that make up the positive and negative active materials, and the electrolyte. The positive and negative are made up of different materials, with the positive exhibiting a reduction potential and the negative having an oxidation potential. The sum of these potentials is the standard cell potential or voltage.
In primary cells the positive and negative electrodes are known as the cathode and anode, respectively. Although this convention is sometimes carried through to rechargeable systems—especially with lithium-ion cells, because of their origins in primary lithium cells—this practice can lead to confusion. In rechargeable cells the positive electrode is the cathode on discharge and the anode on charge, and vice versa for the negative electrode.

Types

 

The lead–acid battery, invented in 1859 by French physicist Gaston Planté, is the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, its ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. These features, along with the low cost, makes it attractive for use in motor vehicles to provide the high current required by automobile starter motors.
The nickel–cadmium battery (NiCd) was invented by Waldemar Jungner of Sweden in 1899. It uses nickel oxide hydroxide and metallic cadmium as electrodes. Cadmium is a toxic element, and was banned for most uses by the European Union in 2004. Nickel–cadmium batteries have been almost completely superseded by nickel–metal hydride (NiMH) batteries.
The nickel–metal hydride battery (NiMH) became available in 1989.^[48] These are now a common consumer and industrial type. The battery has a hydrogen-absorbing alloy for the negative electrode instead of cadmium.
The lithium-ion battery was introduced in the market in 1991, and it is the choice in most consumer electronics and has the best energy density and a very slow loss of charge when not in use. It does have drawbacks too, particularly the risk of unexpected ignition from the heat generated by the battery.^[49] Such incidents are rare and according to experts, they can be minimized "via appropriate design, installation, procedures and layers of safeguards" so the risk is acceptable.^[50]
Lithium-ion polymer batteries (LiPo) are light in weight, offer slightly higher energy density than Li-ion at slightly higher cost, and can be made in any shape. They are available^[51] but have not displaced Li-ion in the market.^[52] A primary use is for LiPo batteries is in powering remote-controlled cars, boats and airplanes. LiPo packs are readily available on the consumer market, in various configurations, up to 44.4v, for powering certain certain R/C vehicles and helicopters or drones.^{[53] [54]} Some test reports warn of the risk of fire when the batteries are not used in accordance with the instructions.^[55] Independent reviews of the technology discuss the risk of fire and explosion from Lithium-ion batteries under certain conditions because they use liquid electrolytes. ^[56]

Solid state

On 28 February 2017, The University of Texas at Austin issued a press release about a new type of solid-state battery, developed by a team of engineers led by Lithium-ion (Li-Ion) inventor John Goodenough, "that could lead to safer, faster-charging, longer-lasting rechargeable batteries for handheld mobile devices, electric cars and stationary energy storage".^[57] More specifics about the new technology were published by Goodenough and his team of engineers on 9 December 2016 in the peer-reviewed scientific journal Energy & Environmental Science.^[58]
Independent reviews of the technology discuss the risk of fire and explosion from Lithium-ion batteries under certain conditions because they use liquid electrolytes. The newly developed battery should be safer since it uses glass electrolytes, that should eliminate short circuits. (More specifically, the battery uses glass electrolytes that enable the use of an alkali-metal anode without the formation of dendrites. ^[59])
The solid-state battery is also said to have "three times the energy density" increasing its useful life in electric vehicles, for example. It should also be more ecologically sound since the technology uses less expensive, earth-friendly materials such as sodium extracted from seawater. Another claimed benefit is longer useable life; ("the cells have demonstrated more than 1,200 cycles with low cell resistance"). The research and prototypes are not expected to lead to a commercially viable product in the near future, if ever, according to Chris Robinson of LUX Research. "This will have no tangible effect on electric vehicle adoption in the next 15 years, if it does at all. A key hurdle that many solid-state electrolytes face is lack of a scalable and cost-effective manufacturing process," he told The American Energy News in an e-mail.^[60]

Other experimental types

Type	Voltagea	Energy densityb			Powerc	E/$e	Self-disch.f	Charge Efficiency	Cyclesg	Lifeh
	(V)	(MJ/kg)	(Wh/kg)	(Wh/L)	(W/kg)	(Wh/$)	(%/month)	(%)	(#)	(years)
Lithium sulfur[61]	2.0	0.94-1.44[62]	400[63]	350					~1400[64]
Sodium-ion[65]	3.6			30		3.3			5000+	Testing
Thin film lithium	?		300[66]	959[66]	6000[66]	?p[66]			40000[66]
Zinc-bromide		0.27-0.31	75-85
Zinc-cerium	2.5[67]									Under testing
Vanadium redox	1.15-1.55	0.09-0.13	25-35[68]				20%[69]		14,000[70]	10 (stationary)[69]
Sodium-sulfur		0.54	150					89–92%	2500—4500
Molten salt	2.58	0.25-1.04	70-290[71]	160[72]	150-220	4.54[73]			3000+	<=20
Silver-zinc	1.86	0.47	130	240
Quantum Battery (oxide semiconductor)[74][75]	1.5-3			500	8000(W/L)				100,000

‡ citations are needed for these parameters

Notes

• ^a Nominal cell voltage in V.
• ^b Energy density = energy/weight or energy/size, given in three different units
• ^c Specific power = power/weight in W/kg
• ^e Energy/consumer price in W·h/US$ (approximately)
• ^f Self-discharge rate in %/month
• ^g Cycle durability in number of cycles
• ^h Time durability in years
• ⁱ VRLA or recombinant includes gel batteries and absorbed glass mats
• ^p Pilot production

The lithium–sulfur battery was developed by Sion Power in 1994.^[76] The company claims superior energy density to other lithium technologies.^[77]
The thin film battery (TFB) is a refinement of lithium ion technology by Excellatron.^[78] The developers claim a large increase in recharge cycles to around 40,000 and higher charge and discharge rates, at least 5 C charge rate. Sustained 60 C discharge and 1000C peak discharge rate and a significant increase in specific energy, and energy density.^[79]
A smart battery has voltage monitoring circuit built inside. Carbon foam-based lead acid battery: Firefly Energy developed a carbon foam-based lead acid battery with a reported energy density of 30-40% more than their original 38 Wh/kg,^[80] with long life and very high power density.
UltraBattery, a hybrid lead-acid battery and ultracapacitor invented by Australia’s national science organisation CSIRO, exhibits tens of thousands of partial state of charge cycles and has outperformed traditional lead-acid, lithium and NiMH-based cells when compared in testing in this mode against variability management power profiles.^[81] UltraBattery has kW and MW-scale installations in place in Australia, Japan and the U.S.A. It has also been subjected to extensive testing in hybrid electric vehicles and has been shown to last more than 100,000 vehicle miles in on-road commercial testing in a courier vehicle. The technology is claimed to have a lifetime of 7 to 10 times that of conventional lead-acid batteries in high rate partial state-of-charge use, with safety and environmental benefits claimed over competitors like lithium-ion. Its manufacturer suggests an almost 100% recycling rate is already in place for the product.
The potassium-ion battery delivers around a million cycles, due to the extraordinary electrochemical stability of potassium insertion/extraction materials such as Prussian blue.^[82]
The sodium-ion battery is meant for stationary storage and competes with lead–acid batteries. It aims at a low total cost of ownership per kWh of storage. This is achieved by a long and stable lifetime. The effective number of cycles is above 5000 and the battery is not damaged by deep discharge. The energy density is rather low, somewhat lower than lead–acid.^{[citation needed]}
The quantum battery (oxide semiconductor) was developed by MJC. It is a small, lightweight cell with a multi-layer film structure and high energy and high power density. It is incombustible, has no electrolyte and generates a low amount of heat during charge. Its unique feature is its ability to capture electrons physically rather than chemically.^[83]
In 2007, Yi Cui and colleagues at Stanford University's Department of Materials Science and Engineering discovered that using silicon nanowires as the anode of a lithium-ion battery increases the anode's volumetric charge density by up to a factor of 10, leading to the development of the nanowire battery.^[84]
Another development is the paper-thin flexible self-rechargeable battery combining a thin-film organic solar cell with an extremely thin and highly flexible lithium-polymer battery, which recharges itself when exposed to light.^[85]
Ceramatec, a research and development unit of CoorsTek, as of 2009^[update] was testing a battery comprising a chunk of solid sodium metal mated to a sulfur compound by a paper-thin ceramic membrane which conducts ions back and forth to generate a current. The company claimed that it could fit about 40 kilowatt hours of energy into a package about the size of a refrigerator, and operate below 90 °C; and that their battery would allow about 3,650 discharge/recharge cycles (or roughly 1 per day for one decade).^[86]
Battery electrodes can be microscopically viewed while bathed in wet electrolytes, resembling conditions inside operating batteries.^[87]
In 2014, an Israeli company, StoreDot, claimed to be able to charge batteries in 30 seconds.
Secondary magnesium battery types are an active (2015) topic of research, as a replacement for lithium ion cells.
Aluminium-ion battery types had big success in 2015 in research.

Alternatives

A rechargeable battery is only one of several types of rechargeable energy storage systems. Several alternatives to rechargeable batteries exist or are under development. For uses such as portable radios, rechargeable batteries may be replaced by clockwork mechanisms which are wound up by hand, driving dynamos, although this system may be used to charge a battery rather than to operate the radio directly. Flashlights may be driven by a dynamo directly. For transportation, uninterruptible power supply systems and laboratories, flywheel energy storage systems store energy in a spinning rotor for conversion to electric power when needed; such systems may be used to provide large pulses of power that would otherwise be objectionable on a common electrical grid.
Ultracapacitors—capacitors of extremely high value— are also used; an electric screwdriver which charges in 90 seconds and will drive about half as many screws as a device using a rechargeable battery was introduced in 2007,^[92] and similar flashlights have been produced. In keeping with the concept of ultracapacitors, betavoltaic batteries may be utilized as a method of providing a trickle-charge to a secondary battery, greatly extending the life and energy capacity of the battery system being employed; this type of arrangement is often referred to as a "hybrid betavoltaic power source" by those in the industry.^[93]
Ultracapacitors are being developed for transportation, using a large capacitor to store energy instead of the rechargeable battery banks used in hybrid vehicles. One drawback of capacitors compared to batteries is that the terminal voltage drops rapidly; a capacitor that has 25% of its initial energy left in it will have one-half of its initial voltage. By contrast, battery systems tend to have a terminal voltage that does not decline rapidly until nearly exhausted. The undesirable characteristic complicates the design of power electronics for use with ultracapacitors. However, there are potential benefits in cycle efficiency, lifetime, and weight compared with rechargeable systems. China started using ultracapacitors on two commercial bus routes in 2006; one of them is route 11 in Shanghai.^[94]
Flow batteries, used for specialized applications, are recharged by replacing the electrolyte liquid. A flow battery can be considered to be a type of rechargeable fuel cell.

Research

Lithium Ion batteries normally have an anode made of graphite. Using an anode made of silicon (Si) can increase the capacity up to 6 times, because the Si-anode can accept much more Lithium-ion than a graphite-anode. A problem was, that the Si-anode expands 300–400% when charged. The Si-anode had only a small lifespan. Researchers of the university of Stuttgart (institute of photovoltaic (IPV), Prof. Dr. Jürgen H. Werner and his team) found a way making the Si-anode porous, so that accepting so many Lithium-ion will not longer increase the volume of the Si-anode, so that the lifespan of the battery with Si-anode is now four times higher than batteries with graphite-anode. The battery is ready for production.^[95][96]
John B. Goodenough, one of the inventor of lithium-ion battery, recently (2017) helped develop the glass battery, a developmental battery with a glass electrolyte that is reported to exceed current lithium-ion batteries in energy density, operating temperature range, and safety.

 

Metal–air electrochemical cell

   

Energy density (Wh/kg) for different types of metal–air batteries

A metal–air electrochemical cell is an electrochemical cell that uses an anode made from pure metal and an external cathode of ambient air, typically with an aqueous electrolyte.

 

Types

The Li–air battery discharge reaction between Li and oxygen Li₂O, according to 4Li + O₂ → 2Li₂O, has an open-circuit voltage of 2.91 V and a theoretical specific energy of 5,210 watt-hours per kilogram (Wh/kg). Since oxygen is not stored in the battery, the theoretical specific energy excluding oxygen is 11,140 Wh/kg (40.1 MJ/kg). Compare this to the figure of 12,200 Wh/kg (44 MJ/kg) for gasoline (see Petrol energy content).

Metal–air battery	Theoretical specific energy, Wh/kg (including oxygen)	Theoretical specific energy, Wh/kg (excluding oxygen)	Calculated open-circuit voltage, V
Aluminium–air	4300[3]	8140[4]	1.2
Germanium–air	1480	7850	1
Calcium-air	2990	4180	3.12
Iron–air	1431	2044	1.3
Lithium–air	5210	11140	2.91
Magnesium air	2789	6462	2.93
Potassium-air	935	1700	2.48
Sodium–air	1677	2260	2.3
Silicon–air	4217	9036	1.6
Tin–air at 1000 K [9]	860	6250	0.95
Zinc-air	1090	1350	1.65

Iron-air

Iron-air rechargeable batteries are an attractive technology with the potential of grid-scale energy storage. The main raw-material of this technology is iron oxide (rust) which is abundant, non-toxic, inexpensive and environmentally friendly.^[10] Most of the batteries being developed right now utilize iron oxide (mostly powders) to generate/store hydrogen via the Fe/FeO reduction/oxidation (redox) reaction (Fe + H₂O = FeO + H₂).^[11] In conjunction with a fuel cell this enables the system to behave as a rechargeable battery creating H₂O/H₂ via production/consumption of electricity.^[12] Furthermore, this technology has minimal environmental impact as it could be used to store energy from intermittent solar and wind power sources, developing an energy system with low carbon dioxide emissions.

The way the system works can start by using the Fe/FeO redox reaction, then the hydrogen created during the oxidation of iron can be consumed by a fuel cell in conjunction with oxygen from the air to create electricity. When electricity must be stored, hydrogen generated from water by operating the fuel cell in reverse is consumed during the reduction of the iron oxide to metallic iron. The combination of both of this cycles is what makes the system operate as an iron-air rechargeable battery.

Limitations of this technology come from the materials used. Generally, iron oxide powder beds are selected, however, rapid sintering and pulverization of the powders limit the ability to achieve a high number of cycles resulting in a lower capacity. Other methods, such as 3D-Printing  and freeze casting, currently under investigation seek to enable the creation of architecture materials to allow for high surface area and volume changes during the redox reaction.

 

                               

 

Rechargeable fuel batteries are a new type of rechargeable battery that researchers have developed which uses electrodes in liquid form. This type of battery can either be recharged or the liquid electrodes can be replaced.

These batteries could allow electric cars to travel 500 miles before recharging. Replacing the liquid electrodes could only take a few minutes while recharging batteries takes much longer. These batteries don't have the problems of short circuits and overheating. The downsides are that nanoparticles degrade quickly, the technology is new and needs more development, they need to focus on cheaper production, and refilling stations would cost a lot to build .

 

 

               

 

                                                  KREDIT ON LINIER MOTOR

 

Linear motor

 

A linear motor is an electric motor that has had its stator and rotor "unrolled" so that instead of producing a torque (rotation) it produces a linear force along its length. However, linear motors are not necessarily straight. Characteristically, a linear motor's active section has ends, whereas more conventional motors are arranged as a continuous loop.

The most common mode of operation is as a Lorentz-type actuator, in which the applied force is linearly proportional to the current and the magnetic field ${\displaystyle ({\vec {F}}=I{\vec {L}}\times {\vec {B}})}$.

Many designs have been put forward for linear motors, falling into two major categories, low-acceleration and high-acceleration linear motors. Low-acceleration linear motors are suitable for maglev trains and other ground-based transportation applications. High-acceleration linear motors are normally rather short, and are designed to accelerate an object to a very high speed, for example see the coilgun.

High-acceleration linear motors are typically used in studies of hypervelocity collisions, as weapons, or as mass drivers for spacecraft propulsion.^{[citation needed]} They are usually of the AC linear induction motor (LIM) design with an active three-phase winding on one side of the air-gap and a passive conductor plate on the other side. However, the direct current homopolar linear motor railgun is another high acceleration linear motor design. The low-acceleration, high speed and high power motors are usually of the linear synchronous motor (LSM) design, with an active winding on one side of the air-gap and an array of alternate-pole magnets on the other side. These magnets can be permanent magnets or electromagnets. The Shanghai Transrapid motor is an LSM.

 

  Free-body diagram of a U-channel synchronous linear motor. The view is perpendicular to the channel axis. The two coils at centre are mechanically connected, and are energized in "quadrature" (with a phase difference of 90° (π/2 radians)). If the bottom coil (as shown) leads in phase (reaching its maximum in one direction a quarter of a period before the upper coil reaches it maximum in the other direction), then the motor will move upward (in the drawing), and vice versa. (Not to scale)

 

 Synchronous linear motors are straightened versions of permanent magnet rotor motors 

 

Types

Synchronous

In this design the rate of movement of the magnetic field is controlled, usually electronically, to track the motion of the rotor. For cost reasons synchronous linear motors rarely use commutators, so the rotor often contains permanent magnets, or soft iron. Examples include coilguns and the motors used on some maglev systems, as well as many other linear motors.

Induction

A typical 3 phase linear induction motor. An aluminium plate on top often forms the secondary "rotor".

Main article: Linear induction motor

In this design, the force is produced by a moving linear magnetic field acting on conductors in the field. Any conductor, be it a loop, a coil or simply a piece of plate metal, that is placed in this field will have eddy currents induced in it thus creating an opposing magnetic field, in accordance with Lenz's law. The two opposing fields will repel each other, thus creating motion as the magnetic field sweeps through the metal.

Homopolar

Railgun schematic

 

In this design a large current is passed through a metal sabot across sliding contacts that are fed from two rails. The magnetic field this generates causes the metal to be projected along the rails.

Piezo electric

Piezoelectric motor action

 

Piezoelectric drive is often used to drive small linear motors.

basic cloud to back

ART trains propel themselves using an aluminium induction strip placed between the rails.

Low acceleration

The history of linear electric motors can be traced back at least as far as the 1840s, to the work of Charles Wheatstone at King's College in London,^[1] but Wheatstone's model was too inefficient to be practical. A feasible linear induction motor is described in the U.S. Patent 782,312 (1905 - inventor Alfred Zehden of Frankfurt-am-Main), for driving trains or lifts. The German engineer Hermann Kemper built a working model in 1935.^[2] In the late 1940s, Dr. Eric Laithwaite of Manchester University, later Professor of Heavy Electrical Engineering at Imperial College in London developed the first full-size working model. In a single sided version the magnetic repulsion forces the conductor away from the stator, levitating it, and carrying it along in the direction of the moving magnetic field. He called the later versions of it magnetic river.

A linear motor for trains running Toei Oedo line

Because of these properties, linear motors are often used in maglev propulsion, as in the Japanese Linimo magnetic levitation train line near Nagoya. However, linear motors have been used independently of magnetic levitation, as in Bombardier's Advanced Rapid Transit systems worldwide and a number of modern Japanese subways, including Tokyo's Toei Oedo Line.

Similar technology is also used in some roller coasters with modifications but, at present, is still impractical on street running trams, although this, in theory, could be done by burying it in a slotted conduit.

Outside of public transportation, vertical linear motors have been proposed as lifting mechanisms in deep mines, and the use of linear motors is growing in motion control applications. They are also often used on sliding doors, such as those of low floor trams such as the Citadis and the Eurotram. Dual axis linear motors also exist. These specialized devices have been used to provide direct X-Y motion for precision laser cutting of cloth and sheet metal, automated drafting, and cable forming. Most linear motors in use are LIM (linear induction motor), or LSM (linear synchronous motor). Linear DC motors are not used due to higher cost and linear SRM suffers from poor thrust. So for long run in traction LIM is mostly preferred and for short run LSM is mostly preferred.

Close-up of the flat passive conductor surface of a motion control linear motor

High acceleration

High-acceleration linear motors have been suggested for a number of uses. They have been considered for use as weapons, since current armour-piercing ammunition tends to consist of small rounds with very high kinetic energy, for which just such motors are suitable. Many amusement park launched roller coasters now use linear induction motors to propel the train at a high speed, as an alternative to using a lift hill. The United States Navy is also using linear induction motors in the Electromagnetic Aircraft Launch System that will replace traditional steam catapults on future aircraft carriers. They have also been suggested for use in spacecraft propulsion. In this context they are usually called mass drivers. The simplest way to use mass drivers for spacecraft propulsion would be to build a large mass driver that can accelerate cargo up to escape velocity, though RLV launch assist like StarTram to low earth orbit has also been investigated.

High-acceleration linear motors are difficult to design for a number of reasons. They require large amounts of energy in very short periods of time. One rocket launcher design^[3] calls for 300 GJ for each launch in the space of less than a second. Normal electrical generators are not designed for this kind of load, but short-term electrical energy storage methods can be used. Capacitors are bulky and expensive but can supply large amounts of energy quickly. Homopolar generators can be used to convert the kinetic energy of a flywheel into electric energy very rapidly. High-acceleration linear motors also require very strong magnetic fields; in fact, the magnetic fields are often too strong to permit the use of superconductors. However, with careful design, this need not be a major problem.

Two different basic designs have been invented for high-acceleration linear motors: railguns and coilguns.

Usage

Linear motors are widely used. One of the major uses of linear motors is for propelling the shuttle in looms.

Linear motors have been used for sliding doors and various similar actuators. Also, they have been used for baggage handing and can even drive large-scale bulk materials transport solutions.

Linear motors are sometimes used to create rotary motion, for example, they have been used at observatories to deal with the large radius of curvature.

A linear motor has been used for accelerating cars for crash tests.

Guangzhou Metro L5 vehicle made by CSR Sifang Locomotive and Rolling Stock and Kawasaki Heavy Industries

Train propulsion

Conventional rails

All applications are in rapid transit.

Guangzhou Metro L4 vehicle made by CSR Sifang Locomotive and Rolling Stock & Kawasaki Heavy Industries

• Bombardier ART:
  • Airport Express in Beijing (opened 2008)
  • AirTrain JFK in New York (opened 2003)
  • Detroit People Mover in Detroit (using ICTS) opened 1987
  • EverLine Rapid Transit System in Yongin (opened 2013)
  • Kelana Jaya Line in Kuala Lumpur (opened 1998)
  • Scarborough RT in Toronto (using UTDC's (predecessor) ICTS technology - opened 1985)
  • UTDC ICTS test track in Millhaven, Ontario
  • SkyTrain in Vancouver (Expo Line (using ITCS) opened 1985 and Millennium Line opened in 2002)
• Several subways in Japan and China, built by Kawasaki Heavy Industries:
  • Limtrain in Saitama (short-lived demonstration track, 1988)
  • Nagahori Tsurumi-ryokuchi Line in Osaka (opened 1990)
  • Toei Ōedo Line in Tokyo (opened 2000)
  • Kaigan Line in Kobe (opened 2001)
  • Nanakuma Line in Fukuoka (opened 2005)
  • Imazatosuji Line in Osaka (opened 2006)
  • Green Line in Yokohama (opened 2008)
  • Sendai Subway Tōzai Line in Sendai, Japan (opened 2015)
  • Line 4 of Guangzhou Metro in Guangzhou, China (opened 2005).^[6]
  • Line 5 of Guangzhou Metro in Guangzhou, China (open in December 2009).
  • Line 6 of Guangzhou Metro in Guangzhou, China (open in December 2013).

Both the Kawasaki trains and Bombardier's ART have the active part of the motor in the cars and use overhead wires (Japanese subways^[7][8]) or a third rail (ART^[9]) to transfer power to the train.

Monorail

• There is at least one known monorail system which is not magnetically levitated, but nonetheless uses linear motors. This is the Moscow Monorail. Originally, traditional motors and wheels were to be used. However, it was discovered during test runs that the proposed motors and wheels would fail to provide adequate traction under some conditions, for example, when ice appeared on the rail. Hence, wheels are still used, but the trains use linear motors to accelerate and slow down. This is possibly the only use of such a combination, due to the lack of such requirements for other train systems.
• The TELMAGV is a prototype of a monorail system that is also not magnetically levitated but uses linear motors.

Magnetic levitation

 

The Birmingham International Maglev shuttle

• High-speed trains:
  • Transrapid: first commercial use in Shanghai (opened in 2004)
  • SCMaglev, under test in Japan
• Rapid transit:
  • Birmingham Airport, UK (opened 1984, closed 1995)
  • M-Bahn in Berlin, Germany (opened in 1989, closed in 1991)
  • Daejeon EXPO, Korea (ran only 1993)^[10]
  • HSST: Linimo line in Aichi Prefecture, Japan (opened 2005)
  • Incheon Airport Maglev (opened July 2014)

Amusement rides

There are many roller coasters throughout the world that use LIMs to accelerate the ride vehicles. The first being Flight of Fear at Kings Island and Kings Dominion. Both opened in 1996.
e.g.:

• Blue Fire - Where the LSM accelerates the train from 0 to 100 km/h in 2.5 s.
• California Screamin' - Roller coaster LIM application
• Maverick - A roller coaster LSM application
• Tomorrowland Transit Authority - Slow ride LIM application
• Dreamworld, Australia - LSM reverse freefall roller coaster
• Rock 'n' Roller Coaster Starring Aerosmith - LSM accelerated rollercoaster
• Battlestar Galactica: Human vs. Cylon - LSM accelerated inverted & seated rollercoaster
• Red Force - Fastest LSM accelerated rollercoaster in world (180 km/h in 5 s)

Aircraft Launching

• Electromagnetic Aircraft Launch System

Proposed & research

• Launch loop - A proposed system for launching vehicles into space using a linear motor powered loop
• StarTram - Concept for a linear motor on extreme scale
• Tether cable catapult system
• Research Test Vehicle 31 - A hovercraft-type vehicle guided by a track
• Hyperloop - a conceptual high-speed transportation system put forward by entrepreneur Elon Musk
• Elevator "ThyssenKrupp Elevator: ThyssenKrupp develops the world’s first rope-free elevator system to enable the building industry face the challenges of global urbanization:". Archived from the original on 2016-03-03. Retrieved 2015-06-02. 
• Lift "Technology: Linear Synchronous Motor Elevators Become a Reality". Retrieved 2015-06-02. 

Railgun 

A railgun is a device that uses electromagnetic force to launch high velocity projectiles, by means of a sliding armature that is accelerated along a pair of conductive rails.^[2] It is typically constructed as a weapon and the projectile normally does not contain explosives, relying on the projectile's high speed to inflict damage. The railgun uses a pair of parallel conductors, or rails, along which a sliding armature is accelerated by the electromagnetic effects of a current that flows down one rail, into the armature and then back along the other rail. It is based on principles similar to those of the homopolar motor.^[3]
Railguns are being researched as weapons that would use neither explosives nor propellant, but rather rely on electromagnetic forces to impart a very high kinetic energy to a projectile (e.g. APFSDS). While explosive-powered military guns cannot readily achieve a muzzle velocity of more than about 2 km/s, railguns can readily exceed 3 km/s, and perhaps exceed conventionally delivered munitions in range and destructive force. The absence of explosive propellants or warheads to store and handle, as well as the low cost of projectiles compared to conventional weaponry come as additional advantages.^[4]
Notwithstanding the above advantages, railguns are still very much at the research stage and it remains to be seen whether or not railguns will ever be deployed as practical military weapons. Any trade-off analysis between electromagnetic (EM) propulsion systems and chemical propellants for weapons applications must also factor in the novelty and complexity of the pulsed power supplies that are needed in electromagnetic launcher systems.
In addition to military applications, NASA has proposed to use a railgun to launch "wedge-shaped aircraft with scramjets" to high-altitude at Mach 10, where they will then fire a small payload into orbit using conventional rocket propulsion.^[5] Alternatively, the extreme g-forces involved with direct railgun ground-launch to space may necessarily restrict the usage to only the sturdiest of payloads or very long rail systems to further reduce launch acceleration.^[6]
   Naval Surface Warfare Center test firing in January 2008

Basics

In its simplest (and most commonly used) form, the railgun differs from a traditional electric motor^[7] in that no use is made of additional field windings (or permanent magnets). This basic configuration is formed by a single loop of current and thus requires high currents (e.g., of order one million amperes) to produce sufficient accelerations (and muzzle velocities). A relatively common variant of this configuration is the augmented railgun in which the driving current is channelled through additional pairs of parallel conductors, arranged to increase ("augment") the magnetic field experienced by the moving armature.^[8] These arrangements reduce the current required for a given acceleration. In electric motor terminology, augmented railguns are usually series-wound configurations.
The armature may be an integral part of the projectile, but it may also be configured to accelerate a separate, electrically isolated or non-conducting projectile. Solid, metallic sliding conductors are often the preferred form of railgun armature but "plasma" or "hybrid" armatures can also be used.^[9] A plasma armature is formed by an arc of ionised gas that is used to push a solid, non-conducting payload in a similar manner to the propellant gas pressure in a conventional gun. A hybrid armature uses a pair of "plasma" contacts to interface a metallic armature to the gun rails. Solid armatures may also "transition" into hybrid armatures, typically after a particular velocity threshold is exceeded.
A railgun requires a pulsed DC power supply.^[10] For potential military applications, railguns are usually of interest because they can achieve much greater muzzle velocities than guns powered by conventional chemical propellants. Increased muzzle velocities with better aerodynamically streamlined projectiles can convey the benefits of increased firing ranges while, in terms of target effects, increased terminal velocities can allow the use of kinetic energy rounds incorporating hit-to-kill guidance, as replacements for explosive shells. Therefore, typical military railgun designs aim for muzzle velocities in the range of 2000–3500 m/s with muzzle energies of 5–50 MJ. For comparison, 50MJ is equivalent to the kinetic energy of a school bus weighing 5 metric tons, travelling at 509 km/h (316 mph).^[11] For single loop railguns, these mission requirements require launch currents of a few million amperes, so a typical railgun power supply might be designed to deliver a launch current of 5 MA for a few milliseconds. As the magnetic field strengths required for such launches will typically be approximately 10 tesla (100 kilogauss), most contemporary railgun designs are effectively "air-cored", i.e., they do not use ferromagnetic materials such as iron to enhance the magnetic flux. However, if the barrel is magnetic, i.e., produces a magnetic field perpendicular to the current flow, the force is augmented.
It may be noted that railgun velocities generally fall within the range of those achievable by two-stage light-gas guns; however, the latter are generally only considered to be suitable for laboratory use while railguns are judged to offer some potential prospects for development as military weapons. Another light gas gun, the Combustion Light Gas Gun in a 155 mm prototype form was projected to achieve 2500 m/s with a .70 caliber barrel. In some hypervelocity research projects, projectiles are "pre-injected" into railguns, to avoid the need for a standing start, and both two-stage light-gas guns and conventional powder guns have been used for this role. In principle, if railgun power supply technology can be developed to provide safe, compact, reliable, combat survivable, and lightweight units, then the total system volume and mass needed to accommodate such a power supply and its primary fuel can become less than the required total volume and mass for a mission equivalent quantity of conventional propellants and explosive ammunition. Arguably such technology has been matured with the introduction of the EMALS aircraft launch system (albeit that railguns require much higher system powers, because roughly similar energies must be delivered in a few milliseconds, as opposed to a few seconds) . Such a development would then convey a further military advantage in that the elimination of explosives from any military weapons platform will decrease its vulnerability to enemy fire.

cloud basic to back

German railgun diagrams

In 1918, French inventor Louis Octave Fauchon-Villeplee invented an electric cannon which is an early form of railgun. He filed for a US patent on 1 April 1919, which was issued in July 1922 as patent no. 1,421,435 "Electric Apparatus for Propelling Projectiles".^[12] In his device, two parallel busbars are connected by the wings of a projectile, and the whole apparatus surrounded by a magnetic field. By passing current through busbars and projectile, a force is induced which propels the projectile along the bus-bars and into flight.^[13]
In 1944, during World War II, Joachim Hänsler of Germany's Ordnance Office proposed the first theoretically viable railgun.^[14] By late 1944, the theory behind his electric anti-aircraft gun had been worked out sufficiently to allow the Luftwaffe's Flak Command to issue a specification, which demanded a muzzle velocity of 2,000 m/s (6,600 ft/s) and a projectile containing 0.5 kg (1.1 lb) of explosive. The guns were to be mounted in batteries of six firing twelve rounds per minute, and it was to fit existing 12.8 cm FlaK 40 mounts. It was never built. When details were discovered after the war it aroused much interest and a more detailed study was done, culminating with a 1947 report which concluded that it was theoretically feasible, but that each gun would need enough power to illuminate half of Chicago.^[13]
During 1950, Sir Mark Oliphant, an Australian physicist and first director of the Research School of Physical Sciences at the new Australian National University, initiated the design and construction of the world's largest (500 megajoule) homopolar generator.^[15] This machine was operational from 1962 and was later used to power a large-scale railgun that was used as a scientific experiment.^[16]
Late into the first decade of the 2000s, the U.S. Navy tested a railgun that accelerates a 3.2 kg (7 pound) projectile to hypersonic velocities of approximately 2.4 kilometres per second (8,600 km/h), about Mach 7.^[17] They gave the project the motto "Velocitas Eradico", Latin for "I, [who am] speed, eradicate"—or in the vernacular, "Speed Kills".

Design

Theory

A railgun consists of two parallel metal rails (hence the name) connected to an electrical power supply. When a conductive projectile is inserted between the rails (at the end connected to the power supply), it completes the circuit. Electrons flow from the negative terminal of the power supply up the negative rail, across the projectile, and down the positive rail, back to the power supply.^[18]
This current makes the railgun behave as an electromagnet, creating a magnetic field inside the loop formed by the length of the rails up to the position of the armature. In accordance with the right-hand rule, the magnetic field circulates around each conductor. Since the current is in the opposite direction along each rail, the net magnetic field between the rails (B) is directed at right angles to the plane formed by the central axes of the rails and the armature. In combination with the current (I) in the armature, this produces a Lorentz force which accelerates the projectile along the rails, away from the power supply. There are also Lorentz forces acting on the rails and attempting to push them apart, but since the rails are mounted firmly, they cannot move.
By definition, if a current of one ampere flows in a pair of ideal infinitely long parallel conductors that are separated by a distance of one meter, then the magnitude of the force on each meter of those conductors will be exactly 0.2 micro-newtons. Furthermore, in general, the force will be proportional to the square of the magnitude of the current and inversely proportional to the distance between the conductors. It also follows that, for railguns with projectile masses of a few kg and barrel lengths of a few m, very large currents will be required to accelerate projectiles to velocities of the order of 1000 m/s.
A very large power supply, providing on the order of one million amperes of current, will create a tremendous force on the projectile, accelerating it to a speed of many kilometres per second (km/s). Although these speeds are possible, the heat generated from the propulsion of the object is enough to erode the rails rapidly. Under high-use conditions, current railguns would require frequent replacement of the rails, or to use a heat-resistant material that would be conductive enough to produce the same effect. At this time it is generally acknowledged that it will take major breakthroughs in materials science and related disciplines to produce high-powered railguns capable of firing more than a few shots from a single set of rails. The barrel must withstand these conditions for up to several rounds per minute for thousands of shots without failure or significant degradation. These parameters are well beyond the state of the art in materials science.^[19]

Mathematical formula

If a railgun could be designed to provide a uniform magnetic field of strength ${\displaystyle B}$, oriented at right angles to both the armature and the bore axis, then, with an armature current ${\displaystyle I}$ and an armature length ${\displaystyle {\boldsymbol {\ell }}}$, the force ${\displaystyle F}$ accelerating the projectile would be given by the well known formula:

${\displaystyle {\boldsymbol {F}}=I{\boldsymbol {\ell }}\times {\boldsymbol {B}}}$

In practice, the force must be calculated after making due allowances for the spatial variation of the magnetic field over the volume of the armature. For example, the magnitude of the force vector can be determined from a form of the Biot–Savart law and a result of the Lorentz force. It can be derived mathematically in terms of the permeability constant (${\displaystyle \mu _{0}}$), the radius of the rails (which are assumed to be circular in cross section) (${\displaystyle r}$), the distance between the central axes of the rails (${\displaystyle d}$) and the current (${\displaystyle I}$) as follows:
It can be shown from the Biot-Savart law that at one end of a semi-infinite current-carrying wire, the magnetic field at a given perpendicular distance (${\displaystyle s}$) from the end of the wire is given by:^[20]

${\displaystyle \mathbf {B} (s)={\frac {\mu _{0}I}{4\pi s}}{\hat {\phi }}}$

Note this is if the wire runs from the location of the armature e.g. from x = 0 back to ${\displaystyle x=-\infty }$ and ${\displaystyle s}$ is measured relative to the axis of the wire.
So, if the armature connects the ends of two such semi-infinite wires separated by a distance, ${\displaystyle d}$, a fairly good approximation assuming the length of the wires is much larger than ${\displaystyle d}$, the total field from both wires at any point on the armature, or any point in the plane between the two wires is:

${\displaystyle \mathbf {B} (s)={\frac {\mu _{0}I}{4\pi }}\left({\frac {1}{s}}+{\frac {1}{d-s}}\right){\hat {z}}}$

Where ${\displaystyle s}$ is the perpendicular distance from the point on the armature to the axis of one of the wires.
Note that ${\displaystyle {\hat {\phi }}}$ between the rails is ${\displaystyle {\hat {z}}}$ assuming the rails are lying in the xy plane and run from x = 0 back to ${\displaystyle x=-\infty }$ as suggested above.
To obtain an approximate expression for the force on the railgun armature, we start by again assuming that the railgun rails can be modeled as a pair of semi-infinite conductors. This allows us to use the above expression for the magnetic field on the armature in the Lorentz Force Law,

${\displaystyle \mathbf {F} =I\int \mathrm {d} {\boldsymbol {\ell }}\times \mathbf {B} }$

Inserting the expression for the magnetic field into the Lorentz force law and setting the bounds of integration to ${\displaystyle r}$ and ${\displaystyle d-r}$, assuming the armature is a bar between and perpendicular to the rails making ${\displaystyle \mathrm {d} {\boldsymbol {\ell }}}$ point in the ${\displaystyle {\hat {y}}}$, we find the force on the armature is

${\displaystyle \mathbf {F} =I\int _{r}^{d-r}\mathrm {d} {\boldsymbol {\ell }}\times {\frac {\mu _{0}I}{4\pi }}\left({\frac {1}{s}}+{\frac {1}{d-s}}\right){\hat {z}}={\frac {\mu _{0}I^{2}}{2\pi }}\ln {\left({\frac {d-r}{r}}\right)}{\hat {x}}}$

The formula is based on the assumption that the distance (${\displaystyle l}$) between the point where the force (${\displaystyle F}$) is measured and the beginning of the rails is greater than the separation of the rails (${\displaystyle d}$) by a factor of about 3 or 4 (${\displaystyle l>3d}$). Some other simplifying assumptions have also been made; to describe the force more accurately, the geometry of the rails and the projectile must be considered.
With most practical railgun geometries, it is not easy to produce an electromagnetic expression for the railgun force that is both simple and reasonably accurate. Instead, most practical railgun analyses actually used a lumped circuit model to describe the relationship between the driving current and the railgun force. In these models the voltage across the railgun breech is given by:

${\displaystyle V=IR+{\frac {{\text{d}}(LI)}{{\text{d}}t}}}$

Then the barrel resistance and inductance are assumed to vary linearly with the projectile position, so that

${\displaystyle R=R'x}$

${\displaystyle L=L'x}$

from which

${\displaystyle V=I(R'x+L'v)+L'x{\frac {{\text{d}}I}{{\text{d}}t}}}$

If the driving current is held constant, there is a power flow equal to ${\displaystyle I^{2}L'v}$ which represents the electromagnetic work done. In this simple model, exactly half of this is assumed to be needed to establish the magnetic field along the barrel, i.e., as the length of the current loop increases. The other half represents the power flow into the kinetic energy of the projectile. Since power can be expressed as force times speed, this gives the standard result that the force on the railgun armature is given by:
${\displaystyle F={\frac {L'I^{2}}{2}}}$
This simple equation shows that high accelerations will require very high currents. For an ideal square bore railgun, the value of ${\displaystyle L'}$ would be about 0.6 microHenries per metre (${\displaystyle \mu }$.H/m) but most practical railgun barrels exhibit lower values of ${\displaystyle L'}$ than this.
Since the lumped circuit model describes the railgun force in terms of fairly normal circuit equations, it becomes possible to specify a simple time domain model of a railgun.
Ignoring friction and air drag, the projectile acceleration is given by:

${\displaystyle {\frac {{\text{d}}v}{{\text{d}}t}}={\frac {L'I^{2}}{2m}}}$

where m is the projectile mass. The motion along the barrel is given by:

${\displaystyle {\frac {{\text{d}}x}{{\text{d}}t}}=v}$

and the above voltage and current terms can be placed into appropriate circuit equations to determine the time variation of current and voltage.
It can also be noted that the textbook formula for the high frequency inductance per unit length of a pair of parallel round wires, of radius r and axial separation d is:

${\displaystyle L'={\frac {\mu _{0}}{\pi }}\ln {\left({\frac {d-r}{r}}\right)}}$

so the lumped parameter model also predicts the force for this case as:
${\displaystyle F={\frac {L'I^{2}}{2}}={\frac {\mu _{0}I^{2}}{2\pi }}\ln {\left({\frac {d-r}{r}}\right)}}$.
With practical railgun geometries, much more accurate two or three dimensional models of the rail and armature current distributions (and the associated forces) can be computed, e.g., by using finite element methods to solve formulations based on either the scalar magnetic potential or the magnetic vector potential.

Design considerations

The power supply must be able to deliver large currents, sustained and controlled over a useful amount of time. The most important gauge of power supply effectiveness is the energy it can deliver. As of December 2010, the greatest known energy used to propel a projectile from a railgun was 33 megajoules.^[21] The most common forms of power supplies used in railguns are capacitors and compulsators which are slowly charged from other continuous energy sources.
The rails need to withstand enormous repulsive forces during shooting, and these forces will tend to push them apart and away from the projectile. As rail/projectile clearances increase, arcing develops, which causes rapid vaporization and extensive damage to the rail surfaces and the insulator surfaces. This limited some early research railguns to one shot per service interval.
The inductance and resistance of the rails and power supply limit the efficiency of a railgun design. Currently different rail shapes and railgun configurations are being tested, most notably by the United States Navy (Naval Research Laboratory), the Institute for Advanced Technology at the University of Texas at Austin, and BAE Systems.

Materials used

The rails and projectiles must be built from strong conductive materials; the rails need to survive the violence of an accelerating projectile, and heating due to the large currents and friction involved. Some erroneous work has suggested that the recoil force in railguns can be redirected or eliminated; careful theoretical and experimental analysis reveals that the recoil force acts on the breech closure just as in a chemical firearm.^{[22][23][24][25]} The rails also repel themselves via a sideways force caused by the rails being pushed by the magnetic field, just as the projectile is. The rails need to survive this without bending and must be very securely mounted. Currently published material suggests that major advances in material science must be made before rails can be developed that allow railguns to fire more than a few full-power shots before replacement of the rails is required.

Heat dissipation

In current designs massive amounts of heat are created by the electricity flowing through the rails, as well as by the friction of the projectile leaving the device. This causes three main problems: melting of equipment, decreased safety of personnel, and detection by enemy forces due to increased infrared signature. As briefly discussed above, the stresses involved in firing this sort of device require an extremely heat-resistant material. Otherwise the rails, barrel, and all equipment attached would melt or be irreparably damaged.
In practice, the rails used with most railgun designs are subject to erosion from each launch. Additionally, projectiles can be subject to some degree of ablation, and this can limit railgun life, in some cases severely.^[26]

Applications

Railguns have a number of potential practical applications, primarily for the military. However, there are other theoretical applications currently being researched.

Launch or launch assist of spacecraft

 

Electrodynamic assistance to launch rockets has been studied.^[27] Space applications of this technology would likely involve specially formed electromagnetic coils and superconducting magnets.^[28] Composite materials would likely be used for this application.^[29]
For space launches from Earth, relatively short acceleration distances (less than a few km) would require very strong acceleration forces, higher than humans can tolerate. Other designs include a longer helical (spiral) track, or a large ring design whereby a space vehicle would circle the ring numerous times, gradually gaining speed, before being released into a launch corridor leading skyward. Nevertheless, if technically feasible and cost effective to build, imparting hyper-velocity escape velocity to a projectile launching at sea level, where the atmosphere is the most dense, may result in much of the launch velocity being lost to aerodynamic drag. In addition, the projectile might still require some form of on-board guidance and control to realize a useful orbital insertion angle that may not be achievable based simply on the launcher's upward elevation angle relative to the surface of the earth, (see practical considerations of escape velocity).
In 2003, Ian McNab outlined a plan to turn this idea into a realized technology.^[6] Because of strong acceleration, this system would launch only sturdy materials, such as food, water, and – most importantly – fuel. Under ideal circumstances (equator, mountain, heading east) the system would cost $528/kg,^[6] compared with $5,000/kg on the conventional rocket.^[30] The McNab's railgun could make approximately 2000 launches per year, for a total of maximum 500 tons launched per year. Because the launch track would be 1.6 km long, power will be supplied by a distributed network of 100 rotating machines (compulsator) spread along the track. Each machine would have a 3.3-ton carbon fibre rotor spinning at high speeds. A machine can recharge in a matter of hours using 10 MW power. This machine could be supplied by a dedicated generator. The total launch package would weigh almost 1.4 tons. Payload per launch in these conditions is over 400 kg.^[6] There would be a peak operating magnetic field of 5 T—half of this coming from the rails, and the other half from augmenting magnets. This halves the required current through the rails, which reduces the power fourfold.

Weaponry

Drawings of electric gun projectiles

Electromagnetic Railgun located at the Naval Surface Warfare Center

Railguns are being researched as weapons with projectiles that do not contain explosives or propellants, but are given extremely high velocities: 2,500 m/s (8,200 ft/s) (approximately Mach 7 at sea level) or more. For comparison, the M16 rifle has a muzzle speed of 930 m/s (3,050 ft/s), and the 16"/50 caliber Mark 7 gun that armed World War II American battleships has a muzzle speed of 760 m/s (2,490 ft/s)), which because of its much greater projectile mass (up to 2,700 pounds) generated a muzzle energy of 360 MJ and a downrange kinetic impact of energy of over 160 MJ (see also Project HARP). By firing smaller projectiles at extremely high velocities, railguns may yield kinetic energy impacts equal or superior to the destructive energy of 5"/54 caliber Mark 45 gun Naval guns, (which achieve up to 10MJ at the muzzle), but with much greater range. This decreases ammunition size and weight, allowing more ammunition to be carried and eliminating the hazards of carrying explosives or propellants in a tank or naval weapons platform. Also, by firing more aerodynamically streamlined projectiles at greater velocities, railguns may achieve greater range, less time to target, and at shorter ranges less wind drift, bypassing the physical limitations of conventional firearms: "the limits of gas expansion prohibit launching an unassisted projectile to velocities greater than about 1.5 km/s and ranges of more than 50 miles [80 km] from a practical conventional gun system."^[31]
Current railgun technologies necessitate a long and heavy barrel, but a railgun's ballistics far outperform conventional cannons of equal barrel lengths. Railguns can also deliver area of effect damage by detonating a bursting charge in the projectile which unleashes a swarm of smaller projectiles over a large area.^[32][33]
Assuming that the many technical challenges facing fieldable railguns are overcome, including issues like railgun projectile guidance, rail endurance, and combat survivability and reliability of the electrical power supply, the increased launch velocities of railguns may provide advantages over more conventional guns for a variety of offensive and defensive scenarios. Railguns have the potential to be used against both surface and airborne targets.
Although many arguments in favor of EM guns revolve around the assumption that greater muzzle velocity is always better, this is open to challenge.^[34] Parametric relationships between range, payload weight, and launch velocity show that this is not a strong argument for many suggested EM gun applications.^[35] For example, due to lower aerodynamic drag at launch, a slower but heavier projectile may actually fly farther than a lighter faster one, making the velocity limitations of chemical propulsion perfectly acceptable. In addition, explosive fragmentary warhead lethality is largely unaffected by velocity and does not require more demanding hit-to-kill guidance electronics that may not survive extremely high gun launch accelerations. Significantly, explosively formed penetrator and shaped charge warheads already drive what is technically a kinetic energy penetrator to velocities well in excess of EM gun launch capabilities, up to 8 km/s for a shaped charge, upon detonation with the target; and it has been demonstrated that with respect to armor penetration, increased impact velocity much above 2 km/s does not necessarily result in a deeper hole; (although the crater may be wider as more energy is deposited with increased impact velocity).^[36]
The first weaponized railgun planned for production, the General Atomics Blitzer system, began full system testing in September 2010. The weapon launches a streamlined discarding sabot round designed by Boeing's Phantom Works at 1,600 m/s (5,200 ft/s) (approximately Mach 5) with accelerations exceeding 60,000 g_n.^[37] During one of the tests, the projectile was able to travel an additional 7 kilometres (4.3 mi) downrange after penetrating a ¹⁄₈ inch (3.2 mm) thick steel plate. The company hopes to have an integrated demo of the system by 2016 followed by production by 2019, pending funding. Thus far, the project is self-funded.^[38]
In October 2013, General Atomics unveiled a land based version of the Blitzer railgun. A company official claimed the gun could be ready for production in "two to three years".^[39]
Railguns are being examined for use as anti-aircraft weapons to intercept air threats, particularly anti-ship cruise missiles, in addition to land bombardment. A supersonic sea-skimming anti-ship missile can appear over the horizon 20 miles from a warship, leaving a very short reaction time for a ship to intercept it. Even if conventional defense systems react fast enough, they are expensive and only a limited number of large interceptors can be carried. A railgun projectile can reach several times the speed of sound faster than a missile; because of this, it can hit a target, such as a cruise missile, much faster and farther away from the ship. Projectiles are also typically much cheaper and smaller, allowing for many more to be carried (they have no guidance systems, and rely on the railgun to supply their kinetic energy, rather than providing it themselves). The speed, cost, and numerical advantages of railgun systems may allow them to replace several different systems in the current layered defense approach.^[40] A railgun projectile without the ability to change course can hit fast-moving missiles at a maximum range of 30 nmi (35 mi; 56 km).^[41] As is the case with the Phalanx CIWS, unguided railgun rounds will require multiple/many shots to bring down maneuvering supersonic anti-ship missiles, with the odds of hitting the missile improving dramatically the closer it gets. The Navy plans for railguns to be able to intercept endoatmospheric ballistic missiles, stealthy air threats, supersonic missiles, and swarming surface threats; a prototype system for supporting interception tasks is to be ready by 2018, and operational by 2025. This timeframe suggests the weapons are planned to be installed on the Navy's next-generation surface combatants, expected to start construction by 2028.^[42]
BAE Systems^[43][44] is interested in installing railguns on Future Combat Vehicles (FVC)^[45][46][47] - US Army's third attempt to replace the aging M2 Bradley.
The Russian Federation, China,^[48] and Turkey's defence company ASELSAN ^[49] are also developing railguns.^[50][51]

Helical railgun

Helical railguns^[52] are multi-turn railguns that reduce rail and brush current by a factor equal to the number of turns. Two rails are surrounded by a helical barrel and the projectile or re-usable carrier is also helical. The projectile is energized continuously by two brushes sliding along the rails, and two or more additional brushes on the projectile serve to energize and commute several windings of the helical barrel direction in front of and/or behind the projectile. The helical railgun is a cross between a railgun and a coilgun. They do not currently exist in a practical, usable form.
A helical railgun was built at MIT in 1980 and was powered by several banks of, for the time, large capacitors (approximately 4 farads). It was about 3 meters long, consisting of 2 meters of accelerating coil and 1 meter of decelerating coil. It was able to launch a glider or projectile about 500 meters.

Plasma railgun

A plasma railgun is a linear accelerator and a plasma energy weapon which, like a projectile railgun, uses two long parallel electrodes to accelerate a "sliding short" armature. However, in a plasma railgun, the armature and ejected projectile consists of plasma, or hot, ionized, gas-like particles, instead of a solid slug of material. MARAUDER (Magnetically Accelerated Ring to Achieve Ultra-high Directed Energy and Radiation) is, or was, a United States Air Force Research Laboratory project concerning the development of a coaxial plasma railgun. It is one of several United States Government efforts to develop plasma-based projectiles.^[53] The first computer simulations occurred in 1990, and its first published experiment appeared on August 1, 1993.^[54][55] As of 1993 the project appeared to be in the early experimental stages. The weapon was able to produce doughnut-shaped rings of plasma and balls of lightning that exploded with devastating effects when hitting their target.^[56] The project's initial success led to it becoming classified, and only a few references to MARAUDER appeared after 1993. The project may or may not have been scrapped some time after 1995.

Tests

Diagram showing the cross-section of a linear motor cannon

Full-scale models have been built and fired, including a 90 mm (3.5 in) bore, 9 MJ kinetic energy gun developed by the US DARPA. Rail and insulator wear problems still need to be solved before railguns can start to replace conventional weapons. Probably the oldest consistently successful system was built by the UK's Defence Research Agency at Dundrennan Range in Kirkcudbright, Scotland. This system was established in 1993 and has been operated for over 10 years.
The Yugoslavian Military Technology Institute developed, within a project named EDO-0, a railgun with 7 kJ kinetic energy, in 1985. In 1987 a successor was created, project EDO-1, that used projectile with a mass of 0.7 kg (1.5 lb) and achieved speeds of 3,000 m/s (9,800 ft/s), and with a mass of 1.1 kg (2.4 lb) reached speeds of 2,400 m/s (7,900 ft/s). It used a track length of 0.7 m (2.3 ft). According to those working on it, with other modifications it was able to achieve a speed of 4,500 m/s (14,800 ft/s). The aim was to achieve projectile speed of 7,000 m/s (23,000 ft/s).
China is now one of the major players in electromagnetic launchers; in 2012 it hosted the 16th International Symposium on Electromagnetic Launch Technology (EML 2012) at Beijing.^[57] Satellite imagery in late 2010 suggested that tests were being conducted at an armor and artillery range near Baotou, in the Inner Mongolia Autonomous Region.^[58]

U.S. military tests

The United States military is funding railgun experiments. At the University of Texas at Austin Center for Electromechanics, military railguns capable of delivering tungsten armor-piercing bullets with kinetic energies of nine megajoules have been developed.^[59] 9 MJ is enough energy to deliver 2 kg (4.4 lb) of projectile at 3 km/s (1.9 mi/s)—at that velocity, a sufficiently long rod of tungsten or another dense metal could easily penetrate a tank, and potentially pass through it, (see APFSDS).

U.S. Navy tests

The United States Naval Surface Warfare Center Dahlgren Division demonstrated an 8 MJ railgun firing 3.2 kg (7.1 lb) projectiles in October 2006 as a prototype of a 64 MJ weapon to be deployed aboard Navy warships. The main problem the U.S. Navy has had with implementing a railgun cannon system is that the guns wear out due to the immense pressures, stresses and heat that are generated by the millions of amperes of current necessary to fire projectiles with megajoules of energy. While not nearly as powerful as a cruise missile like a BGM-109 Tomahawk, that will deliver 3,000 MJ of destructive energy to a target, such weapons would, in theory, allow the Navy to deliver more granular firepower at a fraction of the cost of a missile, and will be much harder to shoot down versus future defensive systems. For context, another relevant comparison is the Rheinmetall 120mm gun used on main battle tanks generates 9 MJ of muzzle energy. A Mark 8 round fired from the 16-inch guns of an Iowa-class battleship at 2,500 ft/s (762 m/s) has 356 MJ of kinetic energy at the muzzle.
Since then, BAE Systems has delivered a 32 MJ prototype (muzzle energy) to the U.S. Navy.^[60] The same amount of energy is released by the detonation of 4.8 kg (11 lb) of C4.
On January 31, 2008, the U.S. Navy tested a railgun that fired a projectile at 10.64 MJ with a muzzle velocity of 2,520 m/s (8,270 ft/s).^[61] The power was provided by a new 9-megajoule prototype capacitor bank using solid-state switches and high-energy-density capacitors delivered in 2007 and an older 32-MJ pulse power system from the US Army’s Green Farm Electric Gun Research and Development Facility developed in the late 1980s that was previously refurbished by General Atomics Electromagnetic Systems (EMS) Division.^[62] It is expected to be ready between 2020 and 2025.^[63]
A test of a railgun took place on December 10, 2010, by the US Navy at the Naval Surface Warfare Center Dahlgren Division.^[64] During the test, the Office of Naval Research set a world record by conducting a 33 MJ shot from the railgun, which was built by BAE Systems.^[21][65]
A test took place in February, 2012, at the Naval Surface Warfare Center Dahlgren Division. While similar in energy to the aforementioned test, the railgun used is considerably more compact, with a more conventional looking barrel. A General Atomics-built prototype was delivered for testing in October 2012.^[66]
The U.S. Navy plans to integrate a railgun that has a range of over 160 km (100 mi) onto a ship by 2016.^[67] This weapon, while having a form factor more typical of a naval gun, will utilize components largely in common with those developed and demonstrated at Dahlgren.^[68] The hyper-velocity rounds weigh 10 kg (23 lb), are 18 in (460 mm), and are fired at Mach 7.^[69]
A future goal is to develop projectiles that are self-guided - a necessary requirement to hit distant targets or intercepting missiles.^[70] When the guided rounds are developed, the Navy is projecting each round to cost about $25,000,^[71] though it must be noted that developing guided projectiles for guns has a history of doubling or tripling initial cost estimates. Some high velocity projectiles developed by the Navy have command guidance, but the accuracy of the command guidance is not known, nor even if it can survive a full power shot.
Currently, the only US Navy ships that can produce enough electrical power to get desired performance are the Zumwalt-class destroyers; they can generate 78 megawatts of power, more than is necessary to power a railgun. Engineers are working to derive technologies developed for the DDG-1000 series ships into a battery system so other warships can operate a railgun.^[72] Most current destroyers can spare only nine megawatts of additional electricity, while it would require 25 megawatts to propel a projectile to the desired maximum range ^[73] (i.e., to launch 32MJ projectiles at a rate of 10 shots per minute). Even if current ships, such as the Arleigh Burke-class destroyer, can be upgraded with enough electrical power to operate a railgun, the space taken up on the ships by the integration of an additional weapon system may force the removal of existing weapon systems to make room available.^[74] The first shipboard tests will be from a railgun installed on an Spearhead-class Expeditionary Fast Transport (EFT). Though ships of that class are non-combatants, they were chosen for their available cargo and topside space and schedule flexibility. They will not be permanently installed on the EFT, and the Navy has yet to decide which ship classes will receive a fully operational railgun.^[75] Single shot tests will be held in 2016, followed by an autoloader in 2018.^[76] According to the Navy, "current research is focused on a rep-rate capability of multiple rounds per minute which entails development of a tactical prototype gun barrel and pulsed power systems incorporating advanced cooling techniques. Components are designed to transition directly into prototype systems now being conceptualized."^[68] So as of March 2014 multiple rep railgun were in the conceptual stage and have a ways to go before reaching the prototype stage.
Though the 23 lb projectiles have no explosives, their Mach 7 velocity gives them 32 megajoules of energy, but impact kinetic energy downrange will typically be 50 percent or less of the muzzle energy. The Navy is looking into other uses for railguns, besides land bombardment, such as air defense; with the right targeting systems, projectiles could intercept aircraft, cruise missiles, and even ballistic missiles. The Navy is also developing directed energy weapons for air defense use, but it will be years before they will be effective.
The railgun will be part of a Navy fleet that envisions future offensive and defensive capabilities being provided in layers: lasers to provide close range defense, railguns to provide medium range attack and defense, and cruise missiles to provide long-range attack; though railguns will cover targets up to 100 miles away that previously needed a missile.^[77] The Navy may eventually enhance railgun technology to enable it to fire at a range of 200 nmi (230 mi; 370 km) and impact with 64 megajoules of energy. One shot would require 6 million amps of current, so it will take a long time to develop capacitors that can generate enough energy and strong enough gun materials.^[58]
The most promising near-term application for weapons-rated railguns and electromagnetic guns, in general, is probably aboard naval ships with sufficient spare electrical generating capacity and battery storage space. In exchange, ship survivability may be enhanced through a comparable reduction in the quantities of potentially dangerous chemical propellants and explosives currently employed. Ground combat forces, however, may find that co-locating an additional electrical power supply on the battlefield for every gun system may not be as weight and space efficient, survivable, or convenient a source of immediate projectile-launching energy as conventional propellants, which are currently manufactured safely behind the lines and delivered to the weapon, pre-packaged, through a robust and dispersed logistics system.

Outstanding issues in fielding railgun weapons

Major technological and operational hurdles must be overcome before railguns can be deployed:

1. Railgun durability: To date railgun demonstrations, while impressive, have not demonstrated an ability to fire multiple full power shots from the same set of rails. The Navy has claimed hundreds of shots from the same set of rails. In a March 2014 statement to the Intelligence, Emerging Threats and Capabilities Subcommittee of the House Armed Services Committee, Chief of Naval Research Admiral Matthew Klunder stated, "Barrel life has increased from tens of shots to over 400, with a program path to achieve 1000 shots."^[68] However, the Office of Naval Research (ONR) will not confirm that the 400 shots are full-power shots. Further there is nothing published to indicate there are any high megajoule class railguns with the capability of firing hundreds of full-power shots while staying within the strict operational parameters necessary to fire railgun shots accurately and safely. According to an article by Globalsecurity.org:^[78] railguns should be able to fire 6 rounds per minute with a rail life of about 3000 rounds. Tolerating launch accelerations of tens of thousands of g's, extreme pressures and megaampere currents over this sort of duty cycle is currently beyond the state of the art.
2. Projectile guidance: A future capability critical to fielding a real railgun weapon is developing a robust guidance package that will allow the railgun to fire at distant targets or to hit incoming missiles. Developing such a package is a real challenge. The Navy's RFP Navy SBIR 2012.1 - Topic N121-102^[79] for developing such a package gives a good overview of just how challenging railgun projectile guidance is:

The package must fit within the mass (< 2 kg), diameter (< 40 mm outer diameter), and volume (200 cm³) constraints of the projectile and do so without altering the center of gravity. It should also be able to survive accelerations of at least 20,000 g (threshold) / 40,000 g (objective) in all axes, high electromagnetic fields (E > 5,000 V/m, B > 2 T), and surface temperatures of > 800 deg C. The package should be able to operate in the presence of any plasma that may form in the bore or at the muzzle exit and must also be radiation hardened due to exo-atmospheric flight. Total power consumption must be less than 8 watts (threshold)/5 watts (objective) and the battery life must be at least 5 minutes (from initial launch) to enable operation during the entire engagement. In order to be affordable, the production cost per projectile must be as low as possible, with a goal of less than $1,000 per unit.

On June 22, 2015, General Atomics’ Electromagnetic Systems announced that projectiles with on-board electronics survived the whole railgun launch environment and performed their intended functions in four consecutive tests on June 9 and 10 June at the U.S. Army’s Dugway Proving Ground in Utah. The on-board electronics successfully measured in-bore accelerations and projectile dynamics, for several kilometers downrange, with the integral data link continuing to operate after the projectiles impacted the desert floor, which is essential for precision guidance.

Trigger for inertial confinement fusion

Railguns may also be miniaturized for inertial confinement nuclear fusion.

• Fusion is triggered by very high temperature and pressure at the core.
  • Current technology calls for multiple lasers, usually over 100, to concurrently strike a fuel pellet, creating a symmetrical compressive pressure.
  • Railguns may be able to trigger fusion by firing energetic plasma from multiple directions. The process developed involves four key steps.^[81]
    • Plasma is pumped into a chamber.
    • When the pressure is great enough, a diaphragm will rupture, sending gas down the rail.
    • Shortly afterwards, a sufficient voltage is applied to the rails, creating a conduction path of ionized gas.
    • This plasma is accelerated down the rail, eventually being ejected at a large velocity.
• The rails and dimensions are on the order of centimetres. 

Piezoelectric motor

    

Insides of a slip-stick piezoelectric motor. Two piezoelectric crystals are visible that provide the mechanical torque. ^[1]

A piezoelectric motor or piezo motor is a type of electric motor based on the change in shape of a piezoelectric material when an electric field is applied. Piezoelectric motors use the converse piezoelectric effect of piezoelectric sensors, in which deformation or vibration of the piezoelectric material produces an electric charge. An electrical circuit makes acoustic or ultrasonic vibrations in the piezoelectric material, which produce linear or rotary motion. In one mechanism, the elongation in a single plane makes a series of stretches and position holds, similar to the way a caterpillar moves

 

Current designs

A slip-stick actuator.

One drive technique uses piezoelectric ceramics to push a stator. These piezoelectric motors use three groups of crystals—two locking, and one motive that permanently connects to either the motor's casing or stator (not both). The motive group, sandwiched between the other two, provides the motion. These piezoelectric motors are fundamentally stepping motors, with each step comprising either two or three actions, based on the locking type. These motors are also known as inchworm motors Another mechanism uses surface acoustic waves (SAW) to generate linear or rotational motion.

A second drive type, the squiggle motor, uses piezoelectric elements bonded orthogonally to a nut. Their ultrasonic vibrations rotate a central lead screw. This is a direct drive mechanism.

Locking mechanisms

The non-powered behaviour of the first type of piezoelectric motor is one of two options: normally locked or normally free. When no power is applied to a normally locked motor, the spindle or carriage (for rotary or linear types, respectively) does not move under external force. A normally free motor's spindle or carriage does move freely under external force. However, if both locking groups are powered at rest, a normally free motor resists external force without providing any motive force.

A combination of mechanical latches and crystals can do the same thing, but would restrict the maximum stepping rate of the motor. The non-power behaviour of the second type of motor is locked, as the drive screw is locked by the threads on the nut. Thus it holds its position with the power off.

Stepping actions

Piezoelectric "inchworm" motor

Fig. 1: Stepping stages of Normally Free motor

Regardless of locking type, stepping type piezoelectric motors—linear and rotary—use the same mechanism to create movement:

1. First, one group of locking crystals is activated to lock one side and unlock other side of the 'sandwich' of piezo crystals.
2. Next, the motive crystal group is triggered and held. The expansion of this group moves the unlocked locking group along the motor path. This is the only stage where the motor moves.
3. Then the locking group triggered in stage one releases (in normally locking motors, in the other it triggers).
4. Then the motive group releases, retracting the 'trailing' locking group.
5. Finally, both locking groups return to their default states.

Direct drive actions

The direct drive piezoelectric motor creates movement through continuous ultrasonic vibration. It's control circuit applies a two-channel sinusoidal or square wave to the piezoelectric elements that matches the bending resonant frequency of the threaded tube—typically an ultrasonic frequency of 40 kHz to 200 kHz. This creates orbital motion that drives the screw.

Speed and precision

The growth and forming of piezoelectric crystals is a well-developed industry, yielding very uniform and consistent distortion for a given applied potential difference. This, combined with the minute scale of the distortions, gives the piezoelectric motor the ability to make very fine steps. Manufacturers claim precision to the nanometer scale. High response rate and fast distortion of the crystals also let the steps happen at very high frequencies—upwards of 5 MHz. This provides a maximum linear speed of approximately 800 mm per second, or nearly 2.9 km/h.
A unique capability of piezoelectric motors is their ability to operate in strong magnetic fields. This extends their usefulness to applications that cannot use traditional electromagnetic motors—such as inside nuclear magnetic resonance antennas. The maximum operating temperature is limited by the Curie temperature of the used piezoelectric ceramic and can exceed +250C.

Other designs

Single action

Fig. 2: Piezo ratchet stepping motor.

Very simple single-action stepping motors can be made with piezoelectric crystals. For example, with a hard and rigid rotor-spindle coated with a thin layer of a softer material (like a polyurethane rubber), a series of angled piezoelectric transducers can be arranged. (see Fig. 2). When the control circuit triggers one group of transducers, they push the rotor one step. This design cannot make steps as small or precise as more complex designs, but can reach higher speeds and is cheaper to manufacture.

Patents

The first U.S. patent to disclose a vibrationally-driven motor may be "Method and Apparatus for Delivering Vibratory Energy" (U.S. Pat. No. 3,184,842, Maropis, 1965). The Maropis patent describes a "vibratory apparatus wherein longitudinal vibrations in a resonant coupling element are converted to torsional vibrations in a toroid type resonant terminal element." The first practical piezomotors were designed and produced by V. Lavrinenko in Piezoelectronic Laboratory, starting 1964, Kiev Polytechnic Institute, USSR. Other important patents in the early development of this technology include:

• "Electrical motor", V. Lavrinenko, M. Nekrasov, Patent USSR # 217509, priority May 10, 1965.
• "Piezoelectric motor structures" (U.S. Pat. No. 4,019,073, Vishnevsky, et al., 1977)
• "Piezoelectrically driven torsional vibration motor" (U.S. Pat. No. 4,210,837, Vasiliev, et al., 1980)

Canon EF lens mount 

Introduced in 1987, the EF lens mount is the standard lens mount on the Canon EOS family of SLR film and digital cameras. EF stands for "Electro-Focus": automatic focusing on EF lenses is handled by a dedicated electric motor built into the lens. Mechanically, it is a bayonet-style mount, and all communication between camera and lens takes place through electrical contacts; there are no mechanical levers or plungers.
In 2003, Canon introduced the EF-S lens mount, a derivative of the EF mount that is strictly for digital EOS cameras with APS-C sensors released after 2003. EF lenses can be mounted on EF-S bodies but EF-S lenses cannot be mounted on EF bodies. In October 2012, Canon introduced the EF-M lens mount, a derivative designed exclusively for mirrorless interchangeable-lens cameras (MILCs) with APS-C sensors. EF and EF-S lenses can be mounted on EF-M bodies via the optional Mount Adapter EF-EOS M.^[1]
Canon claims to have produced its 100-millionth EF-series interchangeable lens (including those for their cameras from other companies), for EOS cameras, on 22 April 2014. Sources including EF-S and Cinema lenses

  The electronic contacts (gold-plated) of an EF mount lens

cloud basic to back

Number of Canon EF lenses sold over time (red), compared with Nikon F mount lenses (blue)

The EF mount replaces its predecessor, the FD mount. The standard autofocus lens mounting technology of the time used a motor in the camera body to drive the mechanics of the focus helicoid in the lens by using a transfer lever. The key innovation of the EF series was to use a motor inside the lens itself for focusing. This allowed for autofocusing lenses which did not require mechanical levers in the mount mechanism, only electrical contacts to supply power and instructions to the lens motor. The motors were designed for the particular lens they were installed in.
When the EF mount was introduced in 1987, it had the largest mount diameter (54 mm internal) among all 35 mm SLR cameras.^[3]
The EF series includes over eighty lenses. The EF series has encompassed focal lengths from 8 to 1200 mm. The EF-M mount was introduced with two lenses, a 22mm prime and an 18–55mm zoom.^[1] Many EF lenses include such features as Canon's ultrasonic motor (USM) drive, an image stabilization system (IS), diffractive optics (DO) and, particularly for L-series lenses, fluorite and aspherical lens elements.

Versatility

The EF mount of a Canon EOS 50

Electronics of an EF-S lens

Its large diameter and relatively short flange focal distance of 44.0 mm allows mechanical adaptation of EF camera bodies to many types of non-EF lenses.^[4] It is possible to mount lenses using the Nikon F mount, Olympus OM, Leica R and universal M42 lens mounts (among others) by the use of a mechanical adapter without electronic control of the aperture or autofocus. Conversely, parfocal adaptation of EF lenses to non-EF camera bodies is not generally possible with only a mechanical adapter that does not contain optical elements.
Lenses for the earlier Canon FD lens mount are not usable for general photography on an EF or EF-S mount camera, unless adapters with optical elements are used because they are made for a flange focal distance of only 42.0 mm. Most of these lenses require autofocus and aperture motors inside the body which isn't available in EOS bodies. Infinity focus would be lost with an adapter which lacks optical elements. The Canon FD-EOS adapter is rare and is only usable with certain FD telephoto lenses. With a manual connection, the aperture and focus controls of the lens cannot be controlled or read from the camera; the lens must be focused manually. Since the only possible metering is through-the-lens, the lens must be manually stopped down to accurately meter at anything less than full aperture. (This is called stop-down metering.) With the introduction of the Canon EOS-M mirror-less digital camera, an inexpensive adapter allows the full use, including infinity focusing, of nearly all FD and FL lenses.
For other lens types, an adapter would act as an extension tube, causing the lens to lose the ability to focus to infinity. Alternatively, the lens adapters would include optical elements and act as weak teleconverters, as well as possibly losing optical quality.

Third-party lenses

Compatible third-party lenses with the EF lens mount are manufactured by Samyang, Schneider, Sigma, Tamron, Tokina, and Carl Zeiss. The manufacturers of these lenses have reverse engineered the EOS electronics—except Zeiss which doesn't have the rights to use the autofocus or the electronic aperture control of EOS cameras. The use of these third-party lenses is not supported by Canon. Sometimes compatibility problems arise, as no third party has access to Canon's specifications for camera to body communication.^[5] These compatibility issues mostly occur when using a newer body with an older third-party lens. Over time, most of these issues have been resolved by the major third-party brands.

Third-party cameras

Due to the high market penetration of EF-mount lenses, other camera manufacturers began to offer EF-mount cameras. Since the EF-mount was created for SLR cameras with their long focal flange distance, mirrorless interchangeable lens cameras can use EF lenses with a mechanical adaptor that bridges the distance.
Red Digital Cinema Company offers various camera models that can be equipped with an electronic EF-mount. Many Blackmagic Design cameras are sold in EF-mount variants. For Sony E-mount various adaptors enable using EF-mount lenses with full electronic control.

Controls and features

An EF lens showing its different controls and features

Canon EF lenses typically have a number of controls, switches and physical features, used by the photographer to control the lens. The types and number of the controls can vary from lens to lens. With the most basic lenses having only a few, to the most complex having over a dozen different controls and switches.
This is a list of the different controls and switches found on most Canon EF lenses, along with a detailed description on what they are used for.
Lens mount index: This marking is found on all EF lenses. It is used for matching the EF lens mount to the mount on an EOS body, so one can connect the lens to the body quickly. On EF lenses, this is a raised, round red mark, while on EF-S lenses it is a square white mark.
Focusing ring: This control, found on most EF lenses, is used for focusing the lens. It is usually a ring on the lens body, that can be turned. On some lenses, such as the Canon EF-S 18-55mm lens, this is simply the inner lens barrel.
Zoom ring: This control is found on most EF zoom lenses. It is used for changing the focal length of the lens. The zoom ring usually has certain, common, focal lengths marked on it. To set the zoom ring to any given focal length, one must turn the ring so that the marked focal length matches the zoom index. The zoom index is typically a white, or black, line found next to the zoom ring.

Distance scale of an EF lens

Distance scale window: This feature is found on many EF lenses. This feature, while not a control or switch, is useful to the photographer for determining, or setting, the lens's focus distance. It is used in conjunction with the Focusing ring. When rotated, the distance scale will also rotate to show the changing focus distance. On some lenses the distance scale also has an infrared index. These are shown as red markings below the distance scale. This is used for making focus adjustments when the photographer is doing infrared photography, as lenses typically focus infrared light at a different point than visible light, and therefore achieving correct focus using visible light will result in an out-of-focus infrared image. To make an adjustment, first focus the subject, then turn the Focusing ring so it matches the corresponding infrared index mark.

Focus mode, and focusing range switches

Focus mode switch: This switch is found on most EF lenses that have an autofocus feature. It is used for setting the lens to either autofocus mode, or manual focus. When set to autofocus mode (AF), the lens will autofocus when directed to by the camera. When set to manual focus (MF), the lens is focused using the Focusing ring. Some lenses support full-time manual focusing (FT-M), which allows the photographer to focus the lens manually even with the mode switch set to AF, without damaging the lens (as could happen if a lens without FT-M is manually focused while in AF mode).
Focusing distance range limiter switch: This switch is found on most longer focal length lenses, and macro lenses. It is used for limiting the focusing distance range of the lens when using it in autofocus mode. Most lenses have two settings; these are usually full focus range (from minimum focus distance to infinity), and distant focus range (from halfway point of focus range to infinity). Other lenses have three settings, with the additional setting usually being near focus range (from minimum focus distance to halfway point of focus range). Longer focal length lenses and macro lenses have a relatively long travel distance for the focusing mechanism inside the lens; this feature shortens the autofocus time. When the photographer knows they will not need a certain part of the focus distance range, limiting it will help shorten the autofocus time, and possibly prevent "focus hunting".
Soft Focus Ring: This ring is found only on the 135 mm 'Soft Focus' prime lens, and enables a variable soft focus effect from completely sharp (0) to very soft (2), although it has little effect when used with apertures over f/5.6. Although the ring can be set to any position, two 'stops' are implemented at positions 1 and 2.

Both types of image stabilizer switches

Image stabilizer switch: This switch is found on all EF lenses that feature an image stabilizer. It is used for turning the image stabilizer "on"( | ), or "off"( o ).
Image stabilizer mode switch: This switch is found on many EF lenses that feature an image stabilizer, particularly those of longer focal lengths. The switch has two settings on most lenses: Mode 1 and Mode 2. The newest IS Mark II versions of certain EF super telephoto lenses (the 300mm f/2.8L,^[6] 400mm f/2.8L,^[7] 500mm f/4L,^[8] and 600mm f/4L^[9]), plus the 200–400mm f/4L IS^[10] and 100–400mm f/4–5.6L IS II,^[11] have a third setting, Mode 3. Mode 1 is normal mode, used for typical photography, where the subject does not move. Mode 2 is used for panning; this is useful for sports or wildlife photography, where the subject moves constantly and one will need to pan. Mode 3, intended to track action, is similar to Mode 2 in that it ignores panning; however, it only applies stabilization when the shutter is released—the viewfinder image is not stabilized.^[9] One should not use Mode 1 for panning as this will typically cause blurred photographs; the image stabilizer will attempt to correct for all motion, including the panning motion, but cannot do so due to the limited range of motion of the IS mechanism. Older lenses that have an image stabilizer, but do not feature this switch, are permanently in Mode 1. Some newer lenses, such as the Canon EF-S 18-200mm lens, are able to detect if they are being panned in either axis and will automatically disable the stabilization for the axis parallel to movement and therefore do not require this switch.
Autofocus stop buttons: These buttons are found on some super telephoto EF lenses, evenly spaced around the front collar of the lens. They are used for temporarily stopping the autofocus feature of the lens. Only one button needs to be pressed to activate the feature. To use this button, one must first have the autofocus active, then when one wishes to halt autofocus, one presses and holds the button. To resume autofocus, one releases the button. Some newer bodies allow these buttons to be assigned to perform other functions; for instance, the Canon EOS 7D allows the photographer to set these buttons to perform any of six functions.
Focus preset: The focus preset feature is found on most super telephoto EF lenses. The focus preset feature uses one switch, one button, and one ring. It is used for presetting a given focus distance into memory, so that the photographer can quickly recall the focus distance, without the need for autofocus. The switch has three settings "off"( o ), "on"( | ), or "on with sound"( ((- ), and is used for turning on the feature, and deciding if sound is desired. The "set" button is used for saving the focus distance into memory. The focus preset ring is used for recalling the memory save point. It is a thin knurled ring, usually located in front of the Focusing ring. To use this feature, one must set the switch to either "on" or "on with sound", focus the lens to the desired distance, then press the "set" button. After this, when the feature is turned on, the photographer can turn the focus preset ring, and the lens will recall and focus quickly to the distance that was saved. This feature is useful for sports and birding photography (for instance, to allow rapid focusing on the goal or on a spot where the birds may perch).

Rear gel filter holder on an EF lens

Filter mounting: This mount is used for attaching filters to EF lenses. There are three types: front threaded mount, inner drop-in mount, and rear gelatin holders. Front threaded filters are used on most lenses, and are attached by threading and tightening the filter. Inner, drop-in filter mounts are used on super telephoto EF lenses. They are attached by first pressing the two buttons on the filter mount, and pulling it out. Then either a round threaded filter is attached, or one can use a gelatin filter. Rear gelatin filter holders are used by cutting out a sheet of gelatin, to the size shown on the back of the lens and then sliding it into the holder. Filter mounts are useful for all types of photography, and every EF lens has either one or two of the three types used.
Lens hood mount: This feature is found on most EF lenses. This mount is used for attaching the lens hood. The hood mount is of a bayonet style on most EF lenses, though a clip-on style hood mount is used for a small selection of current lenses.
Tripod collar: This feature is found on most longer focal length lenses, and macro lenses. The tripod collar is used for attaching the tripod ring. There are two main styles of tripod rings. One type is opened up, placed on the lens' tripod collar, then closed and tightened. The other type does not open, but instead is slid up the lens from the mount end (which can only be done when the lens is not mounted on a camera body) and tightened. To set the tripod ring so that it is level with the lens, rotate the ring until the index mark on the tripod ring matches the index mark on the distance scale. The tripod ring is used for attaching a tripod/monopod near to the point of balance of the lens-body combination, more conveniently than the camera body. In the case of larger and heavier lenses, there is also less strain on the lens mount if the body is supported by the tripod-mounted lens than if the lens were to be supported by a tripod-mounted body.

Related technologies

With the release of the EOS 300D Canon introduced a variation on the standard EF lens mount called EF-S. The "S" stands for "Small image circle". EF-S uses the standard EF bayonet mount, but with minor physical alterations which prevent EF-S lenses from being mounted on bodies which do not support them.
There are a couple of benefits to EF-S lenses, both related to the smaller (1.6× or APS-C) sensor size. One is that since a lens designed for a smaller sensor need only project an image circle large enough to cover the small sensor, the lens itself can be smaller; it can therefore also be lighter and have lower materials costs, since the lens elements, made of relatively heavy and expensive optical glass, will be smaller than in a comparable full-frame lens. Such a lens, if used on a body with a larger sensor, would leave the outer portions of the sensor outside its image circle, and therefore they would be black, but since EF-S lenses will not physically mount on incompatible bodies, this problem is avoided.
The second benefit is that, since a body with a smaller sensor can use a smaller mirror, the rear element of the lens can extend somewhat into the body without danger of being struck by the mirror. Particularly for a wide-angle lens, this gives the lens designers more freedom in designing the lens' optical formula.
Note that even though the first four models of the 1D line of Canon EOS cameras have a 1.3× crop sensor, they are not compatible with EF-S lenses. The most recent entries in the 1D line, the 1D X and 1D X Mark II, are full-frame.
The release of the Canon EOS M, the company's first mirrorless interchangeable-lens camera, saw the introduction of another variation on the standard EF mount, called EF-M (with the "M" presumably standing for "mirrorless"). Because Canon reduced the flange focal distance from that of its EOS DSLR line, the mount was altered so that EF and EF-S lenses cannot mount directly on EF-M bodies. Canon supplies an optional adapter that allows both EF and EF-S lenses to be mounted on EF-M bodies.^[1]

Ultrasonic motor drive

Ultrasonic logo

Ultrasonic motor (USM) lenses appeared with the introduction of the EF 300 mm f/2.8L USM lens in 1987. Canon was the first camera maker to successfully commercialise the USM technology. EF lenses equipped with USM drives have fast, silent and precise autofocus operations, and consume less power compared to other AF drive motors.
There are three types of USMs: ring-type USM, micromotor USM, and Nano USM. Ring-type USM allows for full-time manual focus (FT-M) operations without switching out of AF mode. Micromotor USM is used to bring down the cost of the lens. It is possible to implement FT-M even with micromotor USM; however, it requires additional mechanical components, and the vast majority of micro-USM lenses do not offer such capability. Nano USM was introduced in 2016 with the release of Canon's latest iteration of the EF-S 18–135mm lens. It is intended to offer the AF speed of ring-type USM with the quietness of STM mechanisms (see below).
Some older USM lenses are identified with a gold ring and the word "Ultrasonic" printed in gold on the lens barrel. L lenses with USM don't have the gold ring, but they still have the word "Ultrasonic" printed on the lens barrel.

Stepping motor

Canon EF 40mm f/2.8 STM pancake lens

Canon announced Stepping motor (STM) lenses first in June 2012, alongside the EOS 650D/Rebel T4i/Kiss X6i.
Canon stated that this technology allows smooth and silent autofocus, and with compatible bodies (the first of which is the 650D) will provide continuous autofocus in live view and video.^[12] Unlike USM, STM lenses use focus-by-wire to enable full-time manual mode. Two main disadvantages are linked to focus-by-wire: First, the need to computationally process the input before the intended action is executed leads to a sometimes perceptible lag. Second, using the motor requires power, so when an STM lens is not connected to a camera or the camera is switched off, changing the focus is impossible.
All EF-M lenses introduced to date—the EF-M 22mm pancake prime and EF-M 18–55mm zoom introduced with the EOS-M,^[1] plus the later 11–22mm, 15–45mm, 18–150mm, and 55–200mm zooms, and the 28mm macro lens—feature STM technology.
All stepping-motor lenses are marked with the letters "STM" on the front of the lens as part of the model designation.

Image stabilizer

The image-stabilized Canon EF 300mm f/4L IS USM lens

The image stabilization (IS) technology detects handheld motion and optically corrects it. It only corrects handheld motion; if the subject of the photograph is moving, IS will not stop it. It also can only stabilize so much motion, ranging from two to five stops, depending on the specific IS in the lens. Canon has released several versions of the IS system, including the following:

• The first version, first used in the 75-300mm lens (1995), takes approximately one second to stabilize, provides approximately two stops of stability, is not suitable for use on a tripod, or for panning.
• The 300mm f/4L IS USM lens, released in 1997, adds IS Mode 2, which detects whether panning is taking place horizontally or vertically, and only compensates for vibration in the plane perpendicular to the plane of panning.
• In 1999, with the release of the IS super-telephoto lenses (300mm f/2.8L through 600mm f/4L), tripod detection was added, so that the lens could be used on a tripod with IS turned on.
• In 2001, a new version of the Image Stabilizer was created for the 70–200mm f/2.8L. This version takes approximately 0.5s and can be stabilized up to three stops.
• In 2006, the 70–200 mm f/4L IS USM was released with an Image Stabilizer which allows up to four stops of stabilization.^[13]
• In 2008, the 200mm f/2L IS USM was released with a new version of IS which allows up to five stops of stabilization.^[14]
• In 2009, the 100 mm f/2.8L Macro IS USM became the first Canon lens with a Hybrid Image Stabilizer.^[15] In addition to correcting angular movement, Hybrid IS also corrects for shift movement.^[16]
• In 2011, with the release of the 300mm f/2.8L IS II and 400mm f/2.8L IS II, IS Mode 3 was added. This mode is similar to Mode 2, except that stabilization is applied only when the shutter is released.
• Some newer lenses include an Image Stabilizer which can automatically detect whether the user is panning and respond accordingly, and therefore these lenses do not have an IS mode switch.

All EF lenses that support IS have the words "Image Stabilizer" written on the lens. On some of Canon's larger telephoto lenses, the words "Image Stabilizer" are etched onto a metal plate affixed to the lens.

Diffractive optics

The green-ringed EF 70–300 mm f/4.5–5.6 DO IS USM

Diffractive optics (DO) are special lens elements that are used in some lenses. DO lenses are usually smaller and lighter and are better at handling chromatic aberration, compared to conventional lenses of similar focal length and aperture value. They are more expensive to make. Only the EF 400 mm f/4 DO IS USM, its updated Mark II version, and the EF 70–300 mm f/4.5–5.6 DO IS USM contain DO elements. DO lenses have a green ring on the barrel.

L-series lenses

Main article: Canon L lens

Top range Canon EF lenses are designated "L-series", or "Luxury" lenses.^[17] L series lenses are compatible with the full range of EF or EF-S mounts and as they are aimed at the high-end user, most also include environmental or weather sealing and a constant maximum aperture. All L lenses are supplied complete with a hood and pouch, which are not included with non-L lenses. Distinctive visual cues include a red ring around the lens and an off-white colour on longer-focal-length models. The latter also helps to reflect light and reduce heat absorption.
All L lenses include at least one fluorite or ultra-low-dispersion glass element, and/or certain types of aspherical elements. Other mechanical characteristics of L lenses (but not exclusive to them or present in all L lenses) are the use of an ultrasonic motor (USM) for focusing (particularly in recent years) and image stabilization (IS).

Timeline of innovations

In 1987 Canon was the first to use USM (Ultra Sonic Motor) with the Canon EF 300mm f/2.8L USM.
In 1989 Canon was the first to create an f/1.0 AF (AutoFocus) lens with the Canon EF 50mm f/1.0L USM.
In 1993 Canon was the first to create an interchangeable 10× superzoom lens for SLR cameras. That lens was Canon EF 35-350mm f/3.5-5.6L USM.
In 1993 Canon created the first Super UD (Ultra low Dispertion) lens with the Canon EF 400mm f/5.6L USM.
In 1995 Canon created the first lens with IS (Image Stabilization). That lens was the Canon EF 75-300mm f/4-5.6 IS USM.
Canon in 2001 was the first to create a lens with DO (multi layered Diffractive Optical element) element. That lens was the Canon EF 400mm f/4 DO IS USM.
Canon in 2008 created the first lens with SWC technology (Subwavelentgh Structure Coating). That lens was the Canon EF 24mm f/1.4L II USM.
Canon in 2009 created the first lens with Hybrid IS (Image Stabilization) which compensates both angle camera shake and shift camera shake with the Canon EF 100mm f/2.8L Macro IS USM.
Canon in 2010 was the first to create a lens with Fluorine coating. That lens was the Canon EF 70-300mm f/4-5.6L IS USM.
Canon in 2011 made the first fisheye zoom lens, both circular and rectangular. That lens was the Canon EF 8-15mm f/4L Fisheye USM.
Canon in 2012 made the first wide angle lens with Image Stabilization. That lens was the Canon EF 24mm f/2.8 IS USM.
Canon in 2013 created the first telephoto with built-in 1.4× extender. That lens was Canon EF 200-400mm f/4L IS USM Extender 1.4x.^[18]

Communication protocol

The communication protocol between the camera is 8-data-bit, 1-stop-bit SPI (mode 3). The pins, from right to left on the lens, are:

Canon EF mount pins

Name	Function	Notes
VBat	+6 V to power internal lens focus motors	Present on all EOS bodies and lenses
P-Gnd	Power ground
P-Gnd
VDD	+5.5 V Digital logic power
DCL	Data from camera to the lens (MOSI)
DLC	Data from the lens to the camera (MISO)
LCLK	Camera body generated clock signal (SCLK, CPOL=1)
D-GND	Digital logic ground
COM1	Teleconverter common[20][21][22]	Only on most L-series and some macro lenses
EXT0	Short to COM1 for 'Life Size Converter' and 1.4× teleconverter
EXT1	Short to COM1 for 2× and 1.4× teleconverter

The information from the lens is used by the camera body for focusing and metering, and with digital camera bodies it is used to record the lens parameters in the Exif data in the images.
All L series primes 135mm or longer, the 400mm DO, the 70–200mm zooms, the 100–400mm zooms, the 200–400mm zoom and the 50mm Compact Macro have three additional communication pins. These additional pins are used by the Canon Extender EF adapters and the Life-Size Converter EF to indicate to the lens the change in focal length so that it is able to report the correct focal length and aperture to the camera body when mounted on a teleconverter. The lens also reduces autofocus speed when a teleconverter is attached to improve autofocus accuracy.

List of EF lenses

 

The following is a list of EF lenses made by Canon. The "I", "II", "III" Roman numeral suffix after the focal length(s) indicates the generation number. While I is used in the table below, it is never used in official Canon model numbers; the original model lacks a Roman numeral and only the second and subsequent generations have them. Roman numerals are used only when the entire model designation—focal length(s), aperture, IS, DO, L status, and motor mechanism—is identical from one version to the next. This means, for example, that when Canon introduced IS to lenses whose prior versions lacked that feature (24mm, 28mm, 35mm IS primes in 2012, 16–35mm IS zoom in 2014), the first IS versions lacked Roman numerals.
The EF lenses are grouped below by their focal lengths:

• Zoom: for zoom lenses that have a range of focal lengths
• Prime: for prime lenses that have a single focal length

Zoom

Canon EF 35–70 mm f/3.5–4.5 lens

Canon EF - 1.4x and 2.0x

Focal length	Aperture	Introduction	USM	IS	L-series	DO	Filter size
8–15 mm (fisheye)	f/4	2010	Yes	No	Yes	No	none
11–24 mm	f/4	2015	Yes	No	Yes	No	rear
16–35 mm I	f/2.8	2001	Yes	No	Yes	No	77 mm
16–35 mm II	f/2.8	2007	Yes	No	Yes	No	82 mm
16–35 mm III	f/2.8	2016	Yes	No	Yes	No	82 mm
16–35 mm IS	f/4	2014	Yes	Yes	Yes	No	77 mm
17–35 mm	f/2.8	1996	Yes	No	Yes	No	77 mm
17–40 mm	f/4	2003	Yes	No	Yes	No	77 mm
20–35 mm	f/2.8	1989	No	No	Yes	No	72 mm
20–35 mm	f/3.5–4.5	1993	Yes	No	No	No	77 mm
22–55 mm	f/4-5.6	1998	Yes	No	No	No	58 mm
24–70 mm	f/2.8	2002	Yes	No	Yes	No	77 mm
24–70 mm II	f/2.8	2012	Yes	No	Yes	No	82 mm
24–70 mm	f/4	2012	Yes	Yes	Yes	No	77 mm
24–85 mm	f/3.5-4.5	1996	Yes	No	No	No	67 mm
24–105 mm	f/4	2005	Yes	Yes	Yes	No	77 mm
24–105 mm II	f/4	2016	Yes	Yes	Yes	No	77 mm
24–105 mm STM	f/3.5-5.6	2014	No	Yes	No	No	77 mm
28–70 mm	f/2.8	1993	Yes	No	Yes	No	77 mm
28–70 mm II	f/3.5-4.5	1988	No	No	No	No	52 mm
28–80 mm	f/2.8-4	1989	Yes	No	Yes	No	72 mm
28–80 mm	f/3.5-5.6	1996	No	No	No	No	58mm
28–80 mm II	f/3.5-5.6	1999	No	No	No	No	58 mm
28–80 mm I	f/3.5-5.6	1991	Yes	No	No	No	58mm
28–80 mm II	f/3.5-5.6	1993	Yes	No	No	No	58 mm
28–80 mm III	f/3.5-5.6	1995	Yes	No	No	No	58mm
28–80 mm IV	f/3.5-5.6	1996	Yes	No	No	No	58 mm
28–80 mm V	f/3.5-5.6	1999	Yes	No	No	No	58 mm
28–90 mm II	f/4-5.6	2003	Yes	No	No	No	58 mm
28–90 mm III	f/4-5.6	2004	No	No	No	No	58 mm
28–105 mm	f/3.5-4.5	1992	Yes	No	No	No	58 mm
28–105 mm II	f/3.5-4.5	2000	Yes	No	No	No	58 mm
28–105 mm	f/4-5.6	2002	Yes	No	No	No	58 mm
28–135 mm	f/3.5-5.6	1998	Yes	Yes	No	No	72 mm
28–200 mm	f/3.5-5.6	2000	Yes	No	No	No	72 mm
28–200 mm	f/3.5-5.6	2000	No	No	No	No	72 mm
28–300 mm	f/3.5-5.6	2004	Yes	Yes	Yes	No	77 mm
35–70 mm	f/3.5-4.5	1987	No	No	No	No	52 mm
35–70 mm	f/3.5-4.5A	1988	No	No	No	No	52 mm
35–80 mm III	f/4-5.6	1995	No	No	No	No	52 mm
35–80 mm	f/4-5.6	1992	Yes	No	No	No	52 mm
35–80 mm PZ	f/4-5.6	1990	Yes	No	No	No	52 mm
35–105 mm	f/3.5-4.5	1987	No	No	No	No	58 mm
35–105 mm	f/4.5-5.6	1992	Yes	No	No	No	58 mm
35–135 mm	f/3.5-4.5	1988	No	No	No	No	58 mm
35–135 mm	f/4-5.6	1990	Yes	No	No	No	58 mm
35–350 mm	f/3.5-5.6	1993	Yes	No	Yes	No	72 mm
38–76 mm	f/4.5-5.6	1995	No	No	No	No	52 mm
50–200 mm	f/3.5-4.5	1987	No	No	No	No	58 mm
50–200 mm	f/3.5-4.5	1988	No	No	Yes	No	58 mm
55–200 mm II	f/4.5-5.6	2003	Yes	No	No	No	52 mm
70–200 mm	f/2.8	2001	Yes	Yes	Yes	No	77 mm
70–200 mm II	f/2.8	2010	Yes	Yes	Yes	No	77 mm
70–200 mm	f/2.8	1995	Yes	No	Yes	No	77 mm
70–200 mm	f/4	2006	Yes	Yes	Yes	No	67 mm
70–200 mm	f/4	1999	Yes	No	Yes	No	67 mm
70–210 mm	f/3.5-4.5	1990	Yes	No	No	No	58 mm
70–210 mm	f/4	1987	No	No	No	No	58 mm
70–300 mm	f/4.5-5.6	2004	Yes	Yes	No	Yes	58 mm
70–300 mm	f/4-5.6	2005	Yes	Yes	No	No	58 mm
70–300 mm	f/4-5.6	2010	Yes	Yes	Yes	No	67 mm[23]
70–300  mm II	f/4-5.6	2016	Yes	Yes	No	No	67 mm[24]
75–300 mm	f/4-5.6	1995	Yes	Yes	No	No	58 mm
75–300 mm II	f/4-5.6	1991	No	No	No	No	58 mm
75–300 mm III	f/4-5.6	1999	Yes	No	No	No	58 mm
80–200 mm	f/2.8	1989	No	No	Yes	No	72 mm
80–200 mm	f/4.5-5.6	1992	Yes	No	No	No	52 mm
80–200 mm II	f/4.5-5.6	1990	No	No	No	No	52 mm
90–300 mm	f/4.5-5.6	2003	No	No	No	No	58 mm
90–300 mm	f/4.5-5.6	2002	Yes	No	No	No	58 mm
100–200 mm	f/4.5A	1988	No	No	No	No	58 mm
100–300 mm	f/4.5-5.6	1990	Yes	No	No	No	58 mm
100–300 mm	f/5.6	1987	No	No	No	No	58 mm
100–300 mm	f/5.6	1987	No	No	Yes	No	58 mm
100–400 mm	f/4.5-5.6	1998	Yes	Yes	Yes	No	77 mm
100–400 mm II	f/4.5-5.6	2014	Yes	Yes	Yes	No	77 mm
200–400 mm	f/4	2013	Yes	Yes	Yes	No	52 mm rear

Two EF lenses and an EF-S lens (center).

Prime

Focal length	Aperture	Introduction	Macro	USM	IS	L-series	DO	Filter size
14 mm	f/2.8	1991	No	Yes	No	Yes	No	gel
14 mm II	f/2.8	2007	No	Yes	No	Yes	No	gel
15 mm (fisheye)	f/2.8	1987	No	No	No	No	No	gel
20 mm	f/2.8	1992	No	Yes	No	No	No	72mm
24 mm	f/1.4	1997	No	Yes	No	Yes	No	77mm
24 mm II	f/1.4	2008	No	Yes	No	Yes	No	77mm
24 mm	f/2.8	1988	No	No	No	No	No	58mm
24 mm IS	f/2.8	2012	No	Yes	Yes	No	No	58mm
28 mm	f/1.8	1995	No	Yes	No	No	No	58mm
28 mm	f/2.8	1987	No	No	No	No	No	52mm
28 mm IS	f/2.8	2012	No	Yes	Yes	No	No	58mm
35 mm	f/1.4	1998	No	Yes	No	Yes	No	72mm
35 mm II	f/1.4	2015	No	Yes	No	Yes	No	72mm
35 mm	f/2	1990	No	No	No	No	No	52mm
35 mm IS	f/2	2012	No	Yes	Yes	No	No	67mm
40 mm	f/2.8	2012	No	No	No	No	No	52mm
50 mm	f/1	1989	No	Yes	No	Yes	No	72mm
50 mm	f/1.2	2006	No	Yes	No	Yes	No	72mm
50 mm	f/1.4	1993	No	Yes	No	No	No	58mm
50 mm	f/1.8	1987	No	No	No	No	No	52mm
50 mm II	f/1.8	1990	No	No	No	No	No	52mm
50 mm STM	f/1.8	2015	No	No	No	No	No	49mm
50 mm	f/2.5	1987	Yes[a]	No	No	No	No	52mm
65 mm	f/2.8	1999	Yes	No	No	No	No	58mm
85 mm	f/1.2	1989	No	Yes	No	Yes	No	72mm
85 mm II	f/1.2	2006	No	Yes	No	Yes	No	72mm
85 mm	f/1.8	1992	No	Yes	No	No	No	58mm
100 mm	f/2	1991	No	Yes	No	No	No	58mm
100 mm	f/2.8	1990	Yes	No	No	No	No	58mm
100 mm	f/2.8	2000	Yes	Yes	No	No	No	58mm
100 mm	f/2.8	2009	Yes	Yes	Yes	Yes	No	67mm
135 mm	f/2	1996	No	Yes	No	Yes	No	72mm
135 mm (SoftFocus)	f/2.8	1987	No	No	No	No	No	52mm
180 mm	f/3.5	1996	Yes	No	No	Yes	No	72mm
200 mm	f/1.8	1988	No	Yes	No	Yes	No	48mm rear
200 mm	f/2	2008	No	Yes	Yes	Yes	No	52mm rear
200 mm	f/2.8	1991	No	Yes	No	Yes	No	72mm
200 mm II	f/2.8	1996	No	Yes	No	Yes	No	72mm
300 mm	f/2.8	1987	No	Yes	No	Yes	No	48mm rear
300 mm IS	f/2.8	1999	No	Yes	Yes	Yes	No	52mm rear
300 mm IS II	f/2.8	2010	No	Yes	Yes	Yes	No	52mm rear
300 mm	f/4	1991	No	Yes	No	Yes	No	77mm
300 mm IS	f/4	1997	No	Yes	Yes	Yes	No	77mm
400 mm	f/2.8	1991	No	Yes	No	Yes	No	48mm rear
400 mm II	f/2.8	1996	No	Yes	No	Yes	No	48mm rear
400 mm IS	f/2.8	1999	No	Yes	Yes	Yes	No	52mm rear
400 mm IS II	f/2.8	2011	No	Yes	Yes	Yes	No	52mm rear
400 mm	f/4	2001	No	Yes	Yes	No	Yes	52mm rear
400 mm II	f/4	2014	No	Yes	Yes	No	Yes	52mm rear
400 mm	f/5.6	1993	No	Yes	No	Yes	No	77mm
500 mm	f/4.5	1992	No	Yes	No	Yes	No	48mm rear
500 mm IS	f/4	1999	No	Yes	Yes	Yes	No	52mm rear
500 mm IS II	f/4	2011	No	Yes	Yes	Yes	No	52mm rear
600 mm	f/4	1988	No	Yes	No	Yes	No	48mm rear
600 mm IS	f/4	1999	No	Yes	Yes	Yes	No	52mm rear
600 mm IS II	f/4	2011	No	Yes	Yes	Yes	No	52mm rear
800 mm	f/5.6	2008	No	Yes	Yes	Yes	No	52mm rear
1200 mm	f/5.6	1993	No	Yes	No	Yes	No	48mm rear

1. Jump up ^ 0.5× magnification only. When paired with the "Life-Size Converter EF", a separate accessory, the lens provides up to 1.0× magnification but at the loss of infinity focus.

Exceptions

Canon has two further types of lenses compatible with the EF mount: Tilt-shift and the 1-5x Macro lens, which are not designated EF, but TS-E and MP-E respectively. TS stands for Tilt-shift while MP stands for macro-photo. These types of lenses are not designated EF as they are manual-focus only lenses. They do, however, retain electronic aperture control as well as focus confirmation 


Sonication 

Sonication is the act of applying sound energy to agitate particles in a sample, for various purposes. Ultrasonic frequencies (>20 kHz) are usually used, leading to the process also being known as ultrasonication or ultra-sonication.^[1]
In the laboratory, it is usually applied using an ultrasonic bath or an ultrasonic probe, colloquially known as a sonicator. In a paper machine, an ultrasonic foil can distribute cellulose fibres more uniformly and strengthen the paper 

  A sonicator at the Weizmann Institute of Science during sonication 

Effects

Sonication has numerous effects, both chemical and physical. The chemical effects of ultrasound are concerned with understanding the effect of sonic waves on chemical systems, this is called sonochemistry.^[2] The chemical effects of ultrasound do not come from a direct interaction with molecular species. Studies have shown that no direct coupling of the acoustic field with chemical species on a molecular level can account for sonochemistry^[3] or sonoluminescence.^[4] Instead, sonochemistry arises from acoustic cavitation: the formation, growth, and implosive collapse of bubbles in a liquid.

Applications

Sonication can be used for the production of nanoparticles, such as nanoemulsions,^[6] nanocrystals, liposomes and wax emulsions, as well as for wastewater purification, degassing, extraction of plant oil, extraction of anthocyanins and antioxidants,^[7] production of biofuels, crude oil desulphurization, cell disruption, polymer and epoxy processing, adhesive thinning, and many other processes. It is applied in pharmaceutical, cosmetic, water, food, ink, paint, coating, wood treatment, metalworking, nanocomposite, pesticide, fuel, wood product and many other industries.
Sonication can be used to speed dissolution, by breaking intermolecular interactions. It is especially useful when it is not possible to stir the sample, as with NMR tubes. It may also be used to provide the energy for certain chemical reactions to proceed. Sonication can be used to remove dissolved gases from liquids (degassing) by sonicating the liquid while it is under a vacuum. This is an alternative to the freeze-pump-thaw and sparging methods.
In biological applications, sonication may be sufficient to disrupt or deactivate a biological material. For example, sonication is often used to disrupt cell membranes and release cellular contents. This process is called sonoporation. Small unilamellar vesicles (SUVs) can be made by sonication of a dispersion of large multilamellar vesicles (LMVs). Sonication is also used to fragment molecules of DNA, in which the DNA subjected to brief periods of sonication is sheared into smaller fragments.
Sonication is commonly used in nanotechnology for evenly dispersing nanoparticles in liquids. Additionally, it is used to break up aggregates of micron-sized colloidal particles.
Sonication can also be used to initiate crystallisation processes and even control polymorphic crystallisations.^[8] It is used to intervene in anti-solvent precipitations (crystallisation) to aid mixing and isolate small crystals.
Sonication is the mechanism used in ultrasonic cleaning—loosening particles adhering to surfaces. In addition to laboratory science applications, sonicating baths have applications including cleaning objects such as spectacles and jewelry.
Sonication is used in food industry as well. Main applications are for dispersion to save expensive emulgators (mayonnaise) or to speed up filtration processes (vegetable oil etc.). Experiments with sonification for artificial ageing of liquers and other alcoholic beverages were conducted.
Soil samples are often subjected to ultrasound in order to break up soil aggregates; this allows the study of the different constituents of soil aggregates (especially soil organic matter) without subjecting them to harsh chemical treatment.^[9]
Sonication is also used to extract microfossils from rock.^[10]
Sonication can also refer to buzz pollination – the process that bees use to shake pollen from flowers by vibrating their wing muscles.

Equipment

Schematic of bench and industrial-scale ultrasonic liquid processors

Substantial intensity of ultrasound and high ultrasonic vibration amplitudes are required for many processing applications, such as nano-crystallization, nano-emulsification,^[6] deagglomeration, extraction, cell disruption, as well as many others. Commonly, a process is first tested on a laboratory scale to prove feasibility and establish some of the required ultrasonic exposure parameters. After this phase is complete, the process is transferred to a pilot (bench) scale for flow-through pre-production optimization and then to an industrial scale for continuous production. During these scale-up steps, it is essential to make sure that all local exposure conditions (ultrasonic amplitude, cavitation intensity, time spent in the active cavitation zone, etc.) stay the same. If this condition is met, the quality of the final product remains at the optimized level, while the productivity is increased by a predictable "scale-up factor". The productivity increase results from the fact that laboratory, bench and industrial-scale ultrasonic processor systems incorporate progressively larger ultrasonic horns, able to generate progressively larger high-intensity cavitation zones and, therefore, to process more material per unit of time. This is called "direct scalability". It is important to point out that increasing the power capacity of the ultrasonic processor alone does not result in direct scalability, since it may be (and frequently is) accompanied by a reduction in the ultrasonic amplitude and cavitation intensity. During direct scale-up, all processing conditions must be maintained, while the power rating of the equipment is increased in order to enable the operation of a larger ultrasonic horn. Finding the optimum operation condition for this equipment is a challenge for process engineers and needs deep knowledge about side effects of ultrasonic processors. 



ultrasonic in basic at naturally flower 

Flower 

the process that bees use to shake pollen from flowers by vibrating their wing muscles

 

A poster with flowers or clusters of flowers produced by twelve species of flowering plants from different families

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in plants that are floral (plants of the division Magnoliophyta, also called angiosperms). The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs. Flowers may facilitate outcrossing (fusion of sperm and eggs from different individuals in a population) or allow selfing (fusion of sperm and egg from the same flower). Some flowers produce diaspores without fertilization (parthenocarpy). Flowers contain sporangia and are the site where gametophytes develop. Many flowers have evolved to be attractive to animals, so as to cause them to be vectors for the transfer of pollen. After fertilization, the ovary of the flower develops into fruit containing seeds.

In addition to facilitating the reproduction of flowering plants, flowers have long been admired and used by humans to bring beauty to their environment, and also as objects of romance, ritual, religion, medicine and as a source of food.

 

Morphology

Main parts of a mature flower (Ranunculus glaberrimus)

Diagram of flower parts

Floral parts

The essential parts of a flower can be considered in two parts: the vegetative part, consisting of petals and associated structures in the perianth, and the reproductive or sexual parts. A stereotypical flower consists of four kinds of structures attached to the tip of a short stalk. Each of these kinds of parts is arranged in a whorl on the receptacle. The four main whorls (starting from the base of the flower or lowest node and working upwards) are as follows:

Perianth

Main articles: Perianth, Sepal, and Corolla (flower)

Collectively the calyx and corolla form the perianth (see diagram).

• Calyx: the outermost whorl consisting of units called sepals; these are typically green and enclose the rest of the flower in the bud stage, however, they can be absent or prominent and petal-like in some species.
• Corolla: the next whorl toward the apex, composed of units called petals, which are typically thin, soft and colored to attract animals that help the process of pollination.

Reproductive

Main articles: Plant reproductive morphology, Androecium, and Gynoecium

Reproductive parts of Easter Lily (Lilium longiflorum). 1. Stigma, 2. Style, 3. Stamens, 4. Filament, 5. Petal

• Androecium (from Greek andros oikia: man's house): the next whorl (sometimes multiplied into several whorls), consisting of units called stamens. Stamens consist of two parts: a stalk called a filament, topped by an anther where pollen is produced by meiosis and eventually dispersed.
• Gynoecium (from Greek gynaikos oikia: woman's house): the innermost whorl of a flower, consisting of one or more units called carpels. The carpel or multiple fused carpels form a hollow structure called an ovary, which produces ovules internally. Ovules are megasporangia and they in turn produce megaspores by meiosis which develop into female gametophytes. These give rise to egg cells. The gynoecium of a flower is also described using an alternative terminology wherein the structure one sees in the innermost whorl (consisting of an ovary, style and stigma) is called a pistil. A pistil may consist of a single carpel or a number of carpels fused together. The sticky tip of the pistil, the stigma, is the receptor of pollen. The supportive stalk, the style, becomes the pathway for pollen tubes to grow from pollen grains adhering to the stigma. The relationship to the gynoecium on the receptacle is described as hypogynous (beneath a superior ovary), perigynous (surrounding a superior ovary), or epigynous (above inferior ovary).

Structure

Although the arrangement described above is considered "typical", plant species show a wide variation in floral structure.^[1] These modifications have significance in the evolution of flowering plants and are used extensively by botanists to establish relationships among plant species.
The four main parts of a flower are generally defined by their positions on the receptacle and not by their function. Many flowers lack some parts or parts may be modified into other functions and/or look like what is typically another part. In some families, like Ranunculaceae, the petals are greatly reduced and in many species the sepals are colorful and petal-like. Other flowers have modified stamens that are petal-like; the double flowers of Peonies and Roses are mostly petaloid stamens.^[2] Flowers show great variation and plant scientists describe this variation in a systematic way to identify and distinguish species.
Specific terminology is used to describe flowers and their parts. Many flower parts are fused together; fused parts originating from the same whorl are connate, while fused parts originating from different whorls are adnate; parts that are not fused are free. When petals are fused into a tube or ring that falls away as a single unit, they are sympetalous (also called gamopetalous). Connate petals may have distinctive regions: the cylindrical base is the tube, the expanding region is the throat and the flaring outer region is the limb. A sympetalous flower, with bilateral symmetry with an upper and lower lip, is bilabiate. Flowers with connate petals or sepals may have various shaped corolla or calyx, including campanulate, funnelform, tubular, urceolate, salverform or rotate.
Referring to "fusion," as it is commonly done, appears questionable because at least some of the processes involved may be non-fusion processes. For example, the addition of intercalary growth at or below the base of the primordia of floral appendages such as sepals, petals, stamens and carpels may lead to a common base that is not the result of fusion.^[3][4][5]

Left: A normal zygomorphic Streptocarpus flower. Right: An aberrant peloric Streptocarpus flower. Both of these flowers appeared on the Streptocarpus hybrid 'Anderson's Crows' Wings'.

Many flowers have a symmetry. When the perianth is bisected through the central axis from any point, symmetrical halves are produced, forming a radial symmetry. These flowers are also known to be actinomorphic or regular, e.g. rose or trillium. When flowers are bisected and produce only one line that produces symmetrical halves the flower is said to be irregular or zygomorphic, e.g. snapdragon or most orchids.
Flowers may be directly attached to the plant at their base (sessile—the supporting stalk or stem is highly reduced or absent). The stem or stalk subtending a flower is called a peduncle. If a peduncle supports more than one flower, the stems connecting each flower to the main axis are called pedicels. The apex of a flowering stem forms a terminal swelling which is called the torus or receptacle.

Inflorescence

The familiar calla lily is not a single flower. It is actually an inflorescence of tiny flowers pressed together on a central stalk that is surrounded by a large petal-like bract.

Main article: Inflorescence

In those species that have more than one flower on an axis, the collective cluster of flowers is termed an inflorescence. Some inflorescences are composed of many small flowers arranged in a formation that resembles a single flower. The common example of this is most members of the very large composite (Asteraceae) group. A single daisy or sunflower, for example, is not a flower but a flower head—an inflorescence composed of numerous flowers (or florets). An inflorescence may include specialized stems and modified leaves known as bracts.

Floral diagrams and floral formulae

 

A floral formula is a way to represent the structure of a flower using specific letters, numbers and symbols, presenting substantial information about the flower in a compact form. It can represent a taxon, usually giving ranges of the numbers of different organs, or particular species. Floral formulae have been developed in the early 19th century and their use has declined since. Prenner et al. (2010) devised an extension of the existing model to broaden the descriptive capability of the formula.^[6] The format of floral formulae differs in different parts of the world, yet they convey the same information.^{[7][8][9][10]}
The structure of a flower can also be expressed by the means of floral diagrams. The use of schematic diagrams can replace long descriptions or complicated drawings as a tool for understanding both floral structure and evolution. Such diagrams may show important features of flowers, including the relative positions of the various organs, including the presence of fusion and symmetry, as well as structural details.^[7]

Development

A flower develops on a modified shoot or axis from a determinate apical meristem (determinate meaning the axis grows to a set size). It has compressed internodes, bearing structures that in classical plant morphology are interpreted as highly modified leaves.^[11] Detailed developmental studies, however, have shown that stamens are often initiated more or less like modified stems (caulomes) that in some cases may even resemble branchlets.^[5][12] Taking into account the whole diversity in the development of the androecium of flowering plants, we find a continuum between modified leaves (phyllomes), modified stems (caulomes), and modified branchlets (shoots).^[13][14]

Flowering transition

The transition to flowering is one of the major phase changes that a plant makes during its life cycle. The transition must take place at a time that is favorable for fertilization and the formation of seeds, hence ensuring maximal reproductive success. To meet these needs a plant is able to interpret important endogenous and environmental cues such as changes in levels of plant hormones and seasonable temperature and photoperiod changes.^[15] Many perennial and most biennial plants require vernalization to flower. The molecular interpretation of these signals is through the transmission of a complex signal known as florigen, which involves a variety of genes, including CONSTANS, FLOWERING LOCUS C and FLOWERING LOCUS T. Florigen is produced in the leaves in reproductively favorable conditions and acts in buds and growing tips to induce a number of different physiological and morphological changes.^[16]
The first step of the transition is the transformation of the vegetative stem primordia into floral primordia. This occurs as biochemical changes take place to change cellular differentiation of leaf, bud and stem tissues into tissue that will grow into the reproductive organs. Growth of the central part of the stem tip stops or flattens out and the sides develop protuberances in a whorled or spiral fashion around the outside of the stem end. These protuberances develop into the sepals, petals, stamens, and carpels. Once this process begins, in most plants, it cannot be reversed and the stems develop flowers, even if the initial start of the flower formation event was dependent of some environmental cue.^[17] Once the process begins, even if that cue is removed the stem will continue to develop a flower.
Yvonne Aitken has shown that flowering transition depends on a number of factors, and that plants flowering earliest under given conditions had the least dependence on climate whereas later-flowering varieties reacted strongly to the climate setup.

Organ development

 

The ABC model of flower development

The molecular control of floral organ identity determination appears to be fairly well understood in some species. In a simple model, three gene activities interact in a combinatorial manner to determine the developmental identities of the organ primordia within the floral meristem. These gene functions are called A, B and C-gene functions. In the first floral whorl only A-genes are expressed, leading to the formation of sepals. In the second whorl both A- and B-genes are expressed, leading to the formation of petals. In the third whorl, B and C genes interact to form stamens and in the center of the flower C-genes alone give rise to carpels. The model is based upon studies of mutants in Arabidopsis thaliana and snapdragon, Antirrhinum majus. For example, when there is a loss of B-gene function, mutant flowers are produced with sepals in the first whorl as usual, but also in the second whorl instead of the normal petal formation. In the third whorl the lack of B function but presence of C-function mimics the fourth whorl, leading to the formation of carpels also in the third whorl.
Most genes central in this model belong to the MADS-box genes and are transcription factors that regulate the expression of the genes specific for each floral organ.

Floral function

 

An example of a "perfect flower", this Crateva religiosa flower has both stamens (outer ring) and a pistil (center).

The principal purpose of a flower is the reproduction of the individual and the species. All flowering plants are heterosporous, producing two types of spores. Microspores are produced by meiosis inside anthers while megaspores are produced inside ovules, inside an ovary. In fact, anthers typically consist of four microsporangia and an ovule is an integumented megasporangium. Both types of spores develop into gametophytes inside sporangia. As with all heterosporous plants, the gametophytes also develop inside the spores (are endosporic).
In the majority of species, individual flowers have both functional carpels and stamens. Botanists describe these flowers as being perfect or bisexual and the species as hermaphroditic. Some flowers lack one or the other reproductive organ and called imperfect or unisexual. If unisex flowers are found on the same individual plant but in different locations, the species is said to be monoecious. If each type of unisex flower is found only on separate individuals, the plant is dioecious.

Flower specialization and pollination

 

Flowering plants usually face selective pressure to optimize the transfer of their pollen, and this is typically reflected in the morphology of the flowers and the behaviour of the plants. Pollen may be transferred between plants via a number of 'vectors'. Some plants make use of abiotic vectors — namely wind (anemophily) or, much less commonly, water (hydrophily). Others use biotic vectors including insects (entomophily), birds (ornithophily), bats (chiropterophily) or other animals. Some plants make use of multiple vectors, but many are highly specialised.
Cleistogamous flowers are self-pollinated, after which they may or may not open. Many Viola and some Salvia species are known to have these types of flowers.
The flowers of plants that make use of biotic pollen vectors commonly have glands called nectaries that act as an incentive for animals to visit the flower. Some flowers have patterns, called nectar guides, that show pollinators where to look for nectar. Flowers also attract pollinators by scent and color. Still other flowers use mimicry to attract pollinators. Some species of orchids, for example, produce flowers resembling female bees in color, shape, and scent. Flowers are also specialized in shape and have an arrangement of the stamens that ensures that pollen grains are transferred to the bodies of the pollinator when it lands in search of its attractant (such as nectar, pollen, or a mate). In pursuing this attractant from many flowers of the same species, the pollinator transfers pollen to the stigmas—arranged with equally pointed precision—of all of the flowers it visits.
Anemophilous flowers use the wind to move pollen from one flower to the next. Examples include grasses, birch trees, ragweed and maples. They have no need to attract pollinators and therefore tend not to be "showy" flowers. Male and female reproductive organs are generally found in separate flowers, the male flowers having a number of long filaments terminating in exposed stamens, and the female flowers having long, feather-like stigmas. Whereas the pollen of animal-pollinated flowers tends to be large-grained, sticky, and rich in protein (another "reward" for pollinators), anemophilous flower pollen is usually small-grained, very light, and of little nutritional value to animals.

Pollination

 

Grains of pollen sticking to this bee will be transferred to the next flower it visits

The primary purpose of a flower is reproduction. Since the flowers are the reproductive organs of plant, they mediate the joining of the sperm, contained within pollen, to the ovules — contained in the ovary. Pollination is the movement of pollen from the anthers to the stigma. The joining of the sperm to the ovules is called fertilization. Normally pollen is moved from one plant to another, but many plants are able to self pollinate. The fertilized ovules produce seeds that are the next generation. Sexual reproduction produces genetically unique offspring, allowing for adaptation. Flowers have specific designs which encourages the transfer of pollen from one plant to another of the same species. Many plants are dependent upon external factors for pollination, including: wind and animals, and especially insects. Even large animals such as birds, bats, and pygmy possums can be employed. The period of time during which this process can take place (the flower is fully expanded and functional) is called anthesis. The study of pollination by insects is called anthecology.

Pollen

The types of pollen that most commonly cause allergic reactions are produced by the plain-looking plants (trees, grasses, and weeds) that do not have showy flowers. These plants make small, light, dry pollen grains that are custom-made for wind transport.
The type of allergens in the pollen is the main factor that determines whether the pollen is likely to cause hay fever. For example, pine tree pollen is produced in large amounts by a common tree, which would make it a good candidate for causing allergy. It is, however, a relatively rare cause of allergy because the types of allergens in pine pollen appear to make it less allergenic.^[18]
Among North American plants, weeds are the most prolific producers of allergenic pollen.^[19] Ragweed is the major culprit, but other important sources are sagebrush, redroot pigweed, lamb's quarters, Russian thistle (tumbleweed), and English plantain.
There is much confusion about the role of flowers in allergies. For example, the showy and entomophilous goldenrod (Solidago) is frequently blamed for respiratory allergies, of which it is innocent, since its pollen cannot be airborne. Instead the allergen is usually the pollen of the contemporary bloom of anemophilous ragweed (Ambrosia), which can drift for many kilometers.
Scientists have collected samples of ragweed pollen 400 miles out at sea and 2 miles high in the air.^[18] A single ragweed plant can generate a million grains of pollen per day.^[20]
It is common to hear people say they are allergic to colorful or scented flowers like roses. In fact, only florists, gardeners, and others who have prolonged, close contact with flowers are likely to be sensitive to pollen from these plants. Most people have little contact with the large, heavy, waxy pollen grains of such flowering plants because this type of pollen is not carried by wind but by insects such as butterflies and bees.

Attraction methods

A Bee orchid has evolved over many generations to better mimic a female bee to attract male bees as pollinators.

Plants cannot move from one location to another, thus many flowers have evolved to attract animals to transfer pollen between individuals in dispersed populations. Flowers that are insect-pollinated are called entomophilous; literally "insect-loving" in Greek. They can be highly modified along with the pollinating insects by co-evolution. Flowers commonly have glands called nectaries on various parts that attract animals looking for nutritious nectar. Birds and bees have color vision, enabling them to seek out "colorful" flowers.
Some flowers have patterns, called nectar guides, that show pollinators where to look for nectar; they may be visible only under ultraviolet light, which is visible to bees and some other insects. Flowers also attract pollinators by scent and some of those scents are pleasant to our sense of smell. Not all flower scents are appealing to humans; a number of flowers are pollinated by insects that are attracted to rotten flesh and have flowers that smell like dead animals, often called Carrion flowers, including Rafflesia, the titan arum, and the North American pawpaw (Asimina triloba). Flowers pollinated by night visitors, including bats and moths, are likely to concentrate on scent to attract pollinators and most such flowers are white.
Other flowers use mimicry to attract pollinators. Some species of orchids, for example, produce flowers resembling female bees in color, shape, and scent. Male bees move from one such flower to another in search of a mate.

Pollination mechanism

The pollination mechanism employed by a plant depends on what method of pollination is utilized.
Most flowers can be divided between two broad groups of pollination methods:
Entomophilous: flowers attract and use insects, bats, birds or other animals to transfer pollen from one flower to the next. Often they are specialized in shape and have an arrangement of the stamens that ensures that pollen grains are transferred to the bodies of the pollinator when it lands in search of its attractant (such as nectar, pollen, or a mate). In pursuing this attractant from many flowers of the same species, the pollinator transfers pollen to the stigmas—arranged with equally pointed precision—of all of the flowers it visits. Many flowers rely on simple proximity between flower parts to ensure pollination. Others, such as the Sarracenia or lady-slipper orchids, have elaborate designs to ensure pollination while preventing self-pollination.

Grass flower with vestigial perianth or lodicules

Anemophilous: flowers use the wind to move pollen from one flower to the next, examples include the grasses, Birch trees, Ragweed and Maples. They have no need to attract pollinators and therefore tend not to grow large blossoms. Whereas the pollen of entomophilous flowers tends to be large-grained, sticky, and rich in protein (another "reward" for pollinators), anemophilous flower pollen is usually small-grained, very light, and of little nutritional value to insects, though it may still be gathered in times of dearth. Honeybees and bumblebees actively gather anemophilous corn (maize) pollen, though it is of little value to them.
Some flowers are self-pollinated and use flowers that never open or are self-pollinated before the flowers open, these flowers are called cleistogamous. Many Viola species and some Salvia have these types of flowers.

Flower-pollinator relationships

Many flowers have close relationships with one or a few specific pollinating organisms. Many flowers, for example, attract only one specific species of insect, and therefore rely on that insect for successful reproduction. This close relationship is often given as an example of coevolution, as the flower and pollinator are thought to have developed together over a long period of time to match each other's needs.
This close relationship compounds the negative effects of extinction. The extinction of either member in such a relationship would mean almost certain extinction of the other member as well. Some endangered plant species are so because of shrinking pollinator populations.

Fertilization and dispersal

Main articles: Biological dispersal and Plant reproductive morphology

Some flowers with both stamens and a pistil are capable of self-fertilization, which does increase the chance of producing seeds but limits genetic variation. The extreme case of self-fertilization occurs in flowers that always self-fertilize, such as many dandelions. Conversely, many species of plants have ways of preventing self-fertilization. Unisexual male and female flowers on the same plant may not appear or mature at the same time, or pollen from the same plant may be incapable of fertilizing its ovules. The latter flower types, which have chemical barriers to their own pollen, are referred to as self-sterile or self-incompatible.

Evolution

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Orange labels: known ice ages.
Also see: Human timeline and Nature timeline

Further information: Evolution of flowers and Floral biology

While land plants have existed for about 425 million years, the first ones reproduced by a simple adaptation of their aquatic counterparts: spores. In the sea, plants—and some animals—can simply scatter out genetic clones of themselves to float away and grow elsewhere. This is how early plants reproduced. But plants soon evolved methods of protecting these copies to deal with drying out and other damage which is even more likely on land than in the sea. The protection became the seed, though it had not yet evolved the flower. Early seed-bearing plants include the ginkgo and conifers. An early fossil of a flowering plant, Archaefructus liaoningensis from China, is dated about 125 million years old.^[21] Even earlier from China is the 125–130 million years old Archaefructus sinensis. Now, another plant (130 million-year-old Montsechia vidalii, discovered in Spain) takes the title of world's oldest flower from Archaefructus sinensis.^[22]

Archaefructus liaoningensis, one of the earliest known flowering plants

Several groups of extinct gymnosperms, particularly seed ferns, have been proposed as the ancestors of flowering plants but there is no continuous fossil evidence showing exactly how flowers evolved. The apparently sudden appearance of relatively modern flowers in the fossil record posed such a problem for the theory of evolution that it was called an "abominable mystery" by Charles Darwin. Recently discovered angiosperm fossils such as Archaefructus, along with further discoveries of fossil gymnosperms, suggest how angiosperm characteristics may have been acquired in a series of steps.
Recent DNA analysis (molecular systematics)^[23][24] shows that Amborella trichopoda, found on the Pacific island of New Caledonia, is the sister group to the rest of the flowering plants, and morphological studies^[25] suggest that it has features which may have been characteristic of the earliest flowering plants.
The general assumption is that the function of flowers, from the start, was to involve animals in the reproduction process. Pollen can be scattered without bright colors and obvious shapes, which would therefore be a liability, using the plant's resources, unless they provide some other benefit. One proposed reason for the sudden, fully developed appearance of flowers is that they evolved in an isolated setting like an island, or chain of islands, where the plants bearing them were able to develop a highly specialized relationship with some specific animal (a wasp, for example), the way many island species develop today. This symbiotic relationship, with a hypothetical wasp bearing pollen from one plant to another much the way fig wasps do today, could have eventually resulted in both the plant(s) and their partners developing a high degree of specialization. Island genetics is believed to be a common source of speciation, especially when it comes to radical adaptations which seem to have required inferior transitional forms. Note that the wasp example is not incidental; bees, apparently evolved specifically for symbiotic plant relationships, are descended from wasps.
Likewise, most fruit used in plant reproduction comes from the enlargement of parts of the flower. This fruit is frequently a tool which depends upon animals wishing to eat it, and thus scattering the seeds it contains.
While many such symbiotic relationships remain too fragile to survive competition with mainland organisms, flowers proved to be an unusually effective means of production, spreading (whatever their actual origin) to become the dominant form of land plant life.

Amborella trichopoda, the sister group to the rest of the flowering plants

While there is only hard proof of such flowers existing about 130 million years ago, there is some circumstantial evidence that they did exist up to 250 million years ago. A chemical used by plants to defend their flowers, oleanane, has been detected in fossil plants that old, including gigantopterids,^[26] which evolved at that time and bear many of the traits of modern, flowering plants, though they are not known to be flowering plants themselves, because only their stems and prickles have been found preserved in detail; one of the earliest examples of petrification.
The similarity in leaf and stem structure can be very important, because flowers are genetically just an adaptation of normal leaf and stem components on plants, a combination of genes normally responsible for forming new shoots.^[27] The most primitive flowers are thought to have had a variable number of flower parts, often separate from (but in contact with) each other. The flowers would have tended to grow in a spiral pattern, to be bisexual (in plants, this means both male and female parts on the same flower), and to be dominated by the ovary (female part). As flowers grew more advanced, some variations developed parts fused together, with a much more specific number and design, and with either specific sexes per flower or plant, or at least "ovary inferior".
Flower evolution continues to the present day; modern flowers have been so profoundly influenced by humans that many of them cannot be pollinated in nature. Many modern, domesticated flowers used to be simple weeds, which only sprouted when the ground was disturbed. Some of them tended to grow with human crops, and the prettiest did not get plucked because of their beauty, developing a dependence upon and special adaptation to human affection.^[28]
In August 2017, scientists presented a detailed description and 3D model image of possibly the first flower that lived about 140 million years ago.^[29][30]

Color

Spectrum of the flowers of rose species. A red rose absorbs about 99.7% of light across a broad area below the red wavelengths of the spectrum, leading to an exceptionally pure red. A yellow rose will reflect about 5% of blue light, producing an unsaturated yellow (a yellow with a degree of white in it).

Many flowering plants reflect as much light as possible within the range of visible wavelengths of the pollinator the plant intends to attract. Flowers that reflect the full range of visible light are generally perceived as white by a human observer. An important feature of white flowers is that they reflect equally across the visible spectrum. While many flowering plants use white to attract pollinators, the use of color is also widespread (even within the same species). Color allows a flowering plant to be more specific about the pollinator it seeks to attract. The color model used by human color reproduction technology (CMYK) relies on the modulation of pigments that divide the spectrum into broad areas of absorption. Flowering plants by contrast are able to shift the transition point wavelength between absorption and reflection. If it is assumed that the visual systems of most pollinators view the visible spectrum as circular then it may be said that flowering plants produce color by absorbing the light in one region of the spectrum and reflecting the light in the other region. With CMYK, color is produced as a function of the amplitude of the broad regions of absorption. Flowering plants by contrast produce color by modifying the frequency (or rather wavelength) of the light reflected. Most flowers absorb light in the blue to yellow region of the spectrum and reflect light from the green to red region of the spectrum. For many species of flowering plant, it is the transition point that characterizes the color that they produce. Color may be modulated by shifting the transition point between absorption and reflection and in this way a flowering plant may specify which pollinator it seeks to attract. Some flowering plants also have a limited ability to modulate areas of absorption. This is typically not as precise as control over wavelength. Humans observers will perceive this as degrees of saturation (the amount of white in the color).

Symbolism

Lilies are often used to denote life or resurrection

Flowers are common subjects of still life paintings, such as this one by Ambrosius Bosschaert the Elder

Main article: Language of flowers

Many flowers have important symbolic meanings in Western culture.^[31] The practice of assigning meanings to flowers is known as floriography. Some of the more common examples include:

• Red roses are given as a symbol of love, beauty, and passion.^[32]
• Poppies are a symbol of consolation in time of death. In the United Kingdom, New Zealand, Australia and Canada, red poppies are worn to commemorate soldiers who have died in times of war.
• Irises/Lily are used in burials as a symbol referring to "resurrection/life". It is also associated with stars (sun) and its petals blooming/shining.
• Daisies are a symbol of innocence.

Flowers within art are also representative of the female genitalia,^[33] as seen in the works of artists such as Georgia O'Keeffe, Imogen Cunningham, Veronica Ruiz de Velasco, and Judy Chicago, and in fact in Asian and western classical art. Many cultures around the world have a marked tendency to associate flowers with femininity.
The great variety of delicate and beautiful flowers has inspired the works of numerous poets, especially from the 18th–19th century Romantic era. Famous examples include William Wordsworth's I Wandered Lonely as a Cloud and William Blake's Ah! Sun-Flower.
Because of their varied and colorful appearance, flowers have long been a favorite subject of visual artists as well. Some of the most celebrated paintings from well-known painters are of flowers, such as Van Gogh's sunflowers series or Monet's water lilies. Flowers are also dried, freeze dried and pressed in order to create permanent, three-dimensional pieces of flower art.
Their symbolism in dreams has also been discussed, with possible interpretations including "blossoming potential".^[34]
The Roman goddess of flowers, gardens, and the season of Spring is Flora. The Greek goddess of spring, flowers and nature is Chloris.
In Hindu mythology, flowers have a significant status. Vishnu, one of the three major gods in the Hindu system, is often depicted standing straight on a lotus flower.^[35] Apart from the association with Vishnu, the Hindu tradition also considers the lotus to have spiritual significance.^[36] For example, it figures in the Hindu stories of creation.^[37]

Usage

Flower market – Detroit's Eastern Market

A woman spreading flowers over a lingam in a temple in Varanasi

In modern times people have sought ways to cultivate, buy, wear, or otherwise be around flowers and blooming plants, partly because of their agreeable appearance and smell.^{[citation needed]} Around the world, people use flowers for a wide range of events and functions that, cumulatively, encompass one's lifetime:

• For new births or christenings
• As a corsage or boutonniere worn at social functions or for holidays
• As tokens of love or esteem
• For wedding flowers for the bridal party, and for decorations for the hall
• As brightening decorations within the home
• As a gift of remembrance for bon voyage parties, welcome-home parties, and "thinking of you" gifts
• For funeral flowers and expressions of sympathy for the grieving
• For worshiping goddesses. In Hindu culture adherents commonly bring flowers as a gift to temples

People therefore grow flowers around their homes, dedicate entire parts of their living space to flower gardens, pick wildflowers, or buy flowers from florists who depend on an entire network of commercial growers and shippers to support their trade.
Flowers provide less food than other major plants parts (seeds, fruits, roots, stems and leaves) but they provide several important foods and spices. Flower vegetables include broccoli, cauliflower and artichoke. The most expensive spice, saffron, consists of dried stigmas of a crocus. Other flower spices are cloves and capers. Hops flowers are used to flavor beer. Marigold flowers are fed to chickens to give their egg yolks a golden yellow color, which consumers find more desirable; dried and ground marigold flowers are also used as a spice and colouring agent in Georgian cuisine. Flowers of the dandelion and elder are often made into wine. Bee pollen, pollen collected from bees, is considered a health food by some people. Honey consists of bee-processed flower nectar and is often named for the type of flower, e.g. orange blossom honey, clover honey and tupelo honey.
Hundreds of fresh flowers are edible but few are widely marketed as food. They are often used to add color and flavor to salads. Squash flowers are dipped in breadcrumbs and fried. Edible flowers include nasturtium, chrysanthemum, carnation, cattail, honeysuckle, chicory, cornflower, canna, and sunflower. Some edible flowers are sometimes candied such as daisy, rose, and violet (one may also come across a candied pansy).
Flowers can also be made into herbal teas. Dried flowers such as chrysanthemum, rose, jasmine, camomile are infused into tea both for their fragrance and medical properties. Sometimes, they are also mixed with tea leaves for the added fragrance.
Flowers have been used since as far back as 50,000 years in funeral rituals. Many cultures do draw a connection between flowers and life and death, and because of their seasonal return flowers also suggest rebirth, which may explain why many people place flowers upon graves. In ancient times the Greeks would place a crown of flowers on the head of the deceased as well as cover tombs with wreaths and flower petals. Rich and powerful women in ancient Egypt would wear floral headdresses and necklaces upon their death as representations of renewal and a joyful afterlife, and the Mexicans to this day use flowers prominently in their Day of the Dead celebrations in the same way that their Aztec ancestors did.


Sound character in world at basic the earth 

In physics, sound is a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as air, water or other materials.
In human physiology and psychology, sound is the reception of such waves and their perception by the brain.^[1] Humans can hear sound waves with frequencies between about 20 Hz and 20 kHz. Sound above 20 kHz is ultrasound and below 20 Hz is infrasound. Other animals have different hearing ranges

 

A drum produces sound via a vibrating membrane 

Acoustics

Acoustics is the interdisciplinary science that deals with the study of mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound, and infrasound. A scientist who works in the field of acoustics is an acoustician, while someone working in the field of acoustical engineering may be called an acoustical engineer.^[2] An audio engineer, on the other hand, is concerned with the recording, manipulation, mixing, and reproduction of sound.
Applications of acoustics are found in almost all aspects of modern society, subdisciplines include aeroacoustics, audio signal processing, architectural acoustics, bioacoustics, electro-acoustics, environmental noise, musical acoustics, noise control, psychoacoustics, speech, ultrasound, underwater acoustics, and vibration.^[3]

Definition

Sound is defined as "(a) Oscillation in pressure, stress, particle displacement, particle velocity, etc., propagated in a medium with internal forces (e.g., elastic or viscous), or the superposition of such propagated oscillation. (b) Auditory sensation evoked by the oscillation described in (a)."^[4]

Physics of sound

Play media

Experiment using two tuning forks oscillating usually at the same frequency. One of the forks is being hit with a rubberized mallet. Although the first tuning fork hasn't been hit, while the other fork is visibly excited due to the oscillation caused by the periodic change in the pressure and density of the air by hitting the other fork, creating an acoustic resonance between the forks. However, if we place a piece of metal on a prong, we see that the effect dampens, and the excitations become less and less pronounced as resonance isn't achieved as effectively.

Sound can propagate through a medium such as air, water and solids as longitudinal waves and also as a transverse wave in solids (see Longitudinal and transverse waves, below). The sound waves are generated by a sound source, such as the vibrating diaphragm of a stereo speaker. The sound source creates vibrations in the surrounding medium. As the source continues to vibrate the medium, the vibrations propagate away from the source at the speed of sound, thus forming the sound wave. At a fixed distance from the source, the pressure, velocity, and displacement of the medium vary in time. At an instant in time, the pressure, velocity, and displacement vary in space. Note that the particles of the medium do not travel with the sound wave. This is intuitively obvious for a solid, and the same is true for liquids and gases (that is, the vibrations of particles in the gas or liquid transport the vibrations, while the average position of the particles over time does not change). During propagation, waves can be reflected, refracted, or attenuated by the medium.^[5]
The behavior of sound propagation is generally affected by three things:

• A complex relationship between the density and pressure of the medium. This relationship, affected by temperature, determines the speed of sound within the medium.
• Motion of the medium itself. If the medium is moving, this movement may increase or decrease the absolute speed of the sound wave depending on the direction of the movement. For example, sound moving through wind will have its speed of propagation increased by the speed of the wind if the sound and wind are moving in the same direction. If the sound and wind are moving in opposite directions, the speed of the sound wave will be decreased by the speed of the wind.
• The viscosity of the medium. Medium viscosity determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.

When sound is moving through a medium that does not have constant physical properties, it may be refracted (either dispersed or focused).^[5]

Spherical compression (longitudinal) waves

The mechanical vibrations that can be interpreted as sound can travel through all forms of matter: gases, liquids, solids, and plasmas. The matter that supports the sound is called the medium. Sound cannot travel through a vacuum.

Longitudinal and transverse waves

Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called compression waves. It requires a medium to propagate. Through solids, however, it can be transmitted as both longitudinal waves and transverse waves. Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction, while transverse waves (in solids) are waves of alternating shear stress at right angle to the direction of propagation.
Sound waves may be "viewed" using parabolic mirrors and objects that produce sound.^[6]
The energy carried by an oscillating sound wave converts back and forth between the potential energy of the extra compression (in case of longitudinal waves) or lateral displacement strain (in case of transverse waves) of the matter, and the kinetic energy of the displacement velocity of particles of the medium.

Sound wave properties and characteristics

A 'pressure over time' graph of a 20 ms recording of a clarinet tone demonstrates the two fundamental elements of sound: Pressure and Time.

Sounds can be represented as a mixture of their component Sinusoidal waves of different frequencies. The bottom waves have higher frequencies than those above. The horizontal axis represents time.

Although there are many complexities relating to the transmission of sounds, at the point of reception (i.e. the ears), sound is readily dividable into two simple elements: pressure and time. These fundamental elements form the basis of all sound waves. They can be used to describe, in absolute terms, every sound we hear.
However, in order to understand the sound more fully, a complex wave such as this is usually separated into its component parts, which are a combination of various sound wave frequencies (and noise).^[7][8][9]
Sound waves are often simplified to a description in terms of sinusoidal plane waves, which are characterized by these generic properties:

• Frequency, or its inverse, wavelength
• Amplitude, sound pressure or Intensity
• Speed of sound
• Direction

Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm. Sometimes speed and direction are combined as a velocity vector; wave number and direction are combined as a wave vector.
Transverse waves, also known as shear waves, have the additional property, polarization, and are not a characteristic of sound waves.

Speed of sound

U.S. Navy F/A-18 approaching the sound barrier. The white halo is formed by condensed water droplets thought to result from a drop in air pressure around the aircraft (see Prandtl-Glauert Singularity).^[10]

The speed of sound depends on the medium that the waves pass through, and is a fundamental property of the material. The first significant effort towards the measure of the speed of sound was made by Newton. He believed that the speed of sound in a particular substance was equal to the square root of the pressure acting on it divided by its density:
${\displaystyle c={\sqrt {p \over \rho }}\,}$
This was later proven wrong when found to incorrectly derive the speed. The French mathematician Laplace corrected the formula by deducing that the phenomenon of sound travelling is not isothermal, as believed by Newton, but adiabatic. He added another factor to the equation—gamma—and multiplied ${\displaystyle {\sqrt {\gamma }}\,}$ by ${\displaystyle {\sqrt {p \over \rho }}\,}$, thus coming up with the equation ${\displaystyle c={\sqrt {\gamma \cdot {p \over \rho }}}\,}$. Since ${\displaystyle K=\gamma \cdot p\,}$, the final equation came up to be ${\displaystyle c={\sqrt {\frac {K}{\rho }}}\,}$, which is also known as the Newton-Laplace equation. In this equation, K = elastic bulk modulus, c = velocity of sound, and ${\displaystyle {\rho }}$ = density. Thus, the speed of sound is proportional to the square root of the ratio of the bulk modulus of the medium to its density.
Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In 20 °C (68 °F) air at sea level, the speed of sound is approximately 343 m/s (1,230 km/h; 767 mph) using the formula "v = (331 + 0.6 T) m/s". In fresh water, also at 20 °C, the speed of sound is approximately 1,482 m/s (5,335 km/h; 3,315 mph). In steel, the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph). The speed of sound is also slightly sensitive, being subject to a second-order anharmonic effect, to the sound amplitude, which means that there are non-linear propagation effects, such as the production of harmonics and mixed tones not present in the original sound (see parametric array).

Perception of sound

A distinct use of the term sound from its use in physics is that in physiology and psychology, where the term refers to the subject of perception by the brain. The field of psychoacoustics is dedicated to such studies. Historically the word "sound" referred exclusively to an effect in the mind. Webster's 1947 dictionary defined sound as: "that which is heard; the effect which is produced by the vibration of a body affecting the ear."^[11] This meant (at least in 1947) the correct response to the question: "if a tree falls in the forest with no one to hear it fall, does it make a sound?" was "no". However, owing to contemporary usage, definitions of sound as a physical effect are prevalent in most dictionaries. Consequently, the answer to the same question (see above) is now "yes, a tree falling in the forest with no one to hear it fall does make a sound".
The physical reception of sound in any hearing organism is limited to a range of frequencies. Humans normally hear sound frequencies between approximately 20 Hz and 20,000 Hz (20 kHz),^[12]:382 The upper limit decreases with age.^[12]:249 Sometimes sound refers to only those vibrations with frequencies that are within the hearing range for humans^[13] or sometimes it relates to a particular animal. Other species have different ranges of hearing. For example, dogs can perceive vibrations higher than 20 kHz, but are deaf below 40 Hz.
As a signal perceived by one of the major senses, sound is used by many species for detecting danger, navigation, predation, and communication. Earth's atmosphere, water, and virtually any physical phenomenon, such as fire, rain, wind, surf, or earthquake, produces (and is characterized by) its unique sounds. Many species, such as frogs, birds, marine and terrestrial mammals, have also developed special organs to produce sound. In some species, these produce song and speech. Furthermore, humans have developed culture and technology (such as music, telephone and radio) that allows them to generate, record, transmit, and broadcast sound.

Elements of sound perception

Figure 1. Pitch perception

Figure 2. Duration perception

There are six experimentally separable ways in which sound waves are analysed. They are: pitch, duration, loudness, timbre, sonic texture and spatial location.^[14]

Pitch

Pitch is perceived as how "low" or "high" a sound is and represents the cyclic, repetitive nature of the vibrations that make up sound. For simple sounds, pitch relates to the frequency of the slowest vibration in the sound (called the fundamental harmonic). In the case of complex sounds, pitch perception can vary. Sometimes individuals identify different pitches for the same sound, based on their personal experience of particular sound patterns. Selection of a particular pitch is determined by pre-conscious examination of vibrations, including their frequencies and the balance between them. Specific attention is given to recognising potential harmonics.^[15][16] Every sound is placed on a pitch continuum from low to high. For example: white noise (random noise spread evenly across all frequencies) sounds higher in pitch than pink noise (random noise spread evenly across octaves) as white noise has more high frequency content. Figure 1 shows an example of pitch recognition. During the listening process, each sound is analysed for a repeating pattern (See Figure 1: orange arrows) and the results forwarded to the auditory cortex as a single pitch of a certain height (octave) and chroma (note name).

Duration

Duration is perceived as how "long" or "short" a sound is and relates to onset and offset signals created by nerve responses to sounds. The duration of a sound usually lasts from the time the sound is first noticed until the sound is identified as having changed or ceased.^[17] Sometimes this is not directly related to the physical duration of a sound. For example; in a noisy environment, gapped sounds (sounds that stop and start) can sound as if they are continuous because the offset messages are missed owing to disruptions from noises in the same general bandwidth.^[18] This can be of great benefit in understanding distorted messages such as radio signals that suffer from interference, as (owing to this effect) the message is heard as if it was continuous. Figure 2 gives an example of duration identification. When a new sound is noticed (see Figure 2, Green arrows), a sound onset message is sent to the auditory cortex. When the repeating pattern is missed, a sound offset messages is sent.

Loudness

Loudness is perceived as how "loud" or "soft" a sound is and relates to the totalled number of auditory nerve stimulations over short cyclic time periods, most likely over the duration of theta wave cycles.^[19][20][21] This means that at short durations, a very short sound can sound softer than a longer sound even though they are presented at the same intensity level. Past around 200 ms this is no longer the case and the duration of the sound no longer affects the apparent loudness of the sound. Figure 3 gives an impression of how loudness information is summed over a period of about 200 ms before being sent to the auditory cortex. Louder signals create a greater 'push' on the Basilar membrane and thus stimulate more nerves, creating a stronger loudness signal. A more complex signal also creates more nerve firings and so sounds louder (for the same wave amplitude) than a simpler sound, such as a sine wave.

Timbre

Timbre is perceived as the quality of different sounds (e.g. the thud of a fallen rock, the whir of a drill, the tone of a musical instrument or the quality of a voice) and represents the pre-conscious allocation of a sonic identity to a sound (e.g. “it’s an oboe!"). This identity is based on information gained from frequency transients, noisiness, unsteadiness, perceived pitch and the spread and intensity of overtones in the sound over an extended time frame.^[7][8][9] The way a sound changes over time (see figure 4) provides most of the information for timbre identification. Even though a small section of the wave form from each instrument looks very similar (see the expanded sections indicated by the orange arrows in figure 4), differences in changes over time between the clarinet and the piano are evident in both loudness and harmonic content. Less noticeable are the different noises heard, such as air hisses for the clarinet and hammer strikes for the piano.

Figure 3. Loudness perception

Figure 4. Timbre perception

Sonic texture

Sonic texture relates to the number of sound sources and the interaction between them. The word 'texture', in this context, relates to the cognitive separation of auditory objects.^[24] In music, texture is often referred to as the difference between unison, polyphony and homophony, but it can also relate (for example) to a busy cafe; a sound which might be referred to as 'cacophony'. However texture refers to more than this. The texture of an orchestral piece is very different to the texture of a brass quartet because of the different numbers of players. The texture of a market place is very different to a school hall because of the differences in the various sound sources.

Spatial location

Spatial location  represents the cognitive placement of a sound in an environmental context; including the placement of a sound on both the horizontal and vertical plane, the distance from the sound source and the characteristics of the sonic environment. In a thick texture, it is possible to identify multiple sound sources using a combination of spatial location and timbre identification. It is the main reason why we can pick the sound of an oboe in an orchestra and the words of a single person at a cocktail party.

Sound measurements
Characteristic	Symbols
Sound pressure	p, SPL
Particle velocity	v, SVL
Particle displacement	δ
Sound intensity	I, SIL
Sound power	P, SWL
Sound energy	W
Sound energy density	w
Sound exposure	E, SEL
Acoustic impedance	Z
Speed of sound	c
Audio frequency	AF
Transmission loss	TL

Noise

Noise is a term often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal. However, in sound perception it can often be used to identify the source of a sound and is an important component of timbre perception (see above).

Soundscape

Soundscape is the component of the acoustic environment that can be perceived by humans. The acoustic environment is the combination of all sounds (whether audible to humans or not) within a given area as modified by the environment and understood by people, in context of the surrounding environment.

Sound pressure level

Sound pressure is the difference, in a given medium, between average local pressure and the pressure in the sound wave. A square of this difference (i.e., a square of the deviation from the equilibrium pressure) is usually averaged over time and/or space, and a square root of this average provides a root mean square (RMS) value. For example, 1 Pa RMS sound pressure (94 dBSPL) in atmospheric air implies that the actual pressure in the sound wave oscillates between (1 atm ${\displaystyle -{\sqrt {2}}}$ Pa) and (1 atm ${\displaystyle +{\sqrt {2}}}$ Pa), that is between 101323.6 and 101326.4 Pa. As the human ear can detect sounds with a wide range of amplitudes, sound pressure is often measured as a level on a logarithmic decibel scale. The sound pressure level (SPL) or L_p is defined as

${\displaystyle L_{\mathrm {p} }=10\,\log _{10}\left({\frac {{p}^{2}}{{p_{\mathrm {ref} }}^{2}}}\right)=20\,\log _{10}\left({\frac {p}{p_{\mathrm {ref} }}}\right){\mbox{ dB}}\,}$

where p is the root-mean-square sound pressure and ${\displaystyle p_{\mathrm {ref} }}$ is a reference sound pressure. Commonly used reference sound pressures, defined in the standard ANSI S1.1-1994, are 20 µPa in air and 1 µPa in water. Without a specified reference sound pressure, a value expressed in decibels cannot represent a sound pressure level.

Since the human ear does not have a flat spectral response, sound pressures are often frequency weighted so that the measured level matches perceived levels more closely. The International Electrotechnical Commission (IEC) has defined several weighting schemes. A-weighting attempts to match the response of the human ear to noise and A-weighted sound pressure levels are labeled dBA. C-weighting is used to measure peak levels.

Ultrasound 

Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is no different from 'normal' (audible) sound in its physical properties, except in that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz (20,000 hertz) in healthy, young adults. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz.
Ultrasound is used in many different fields. Ultrasonic devices are used to detect objects and measure distances. Ultrasound imaging or sonography is often used in medicine. In the nondestructive testing of products and structures, ultrasound is used to detect invisible flaws. Industrially, ultrasound is used for cleaning, mixing, and to accelerate chemical processes. Animals such as bats and porpoises use ultrasound for locating prey and obstacles.^[1] Scientist are also studying ultrasound using graphene diaphragms as a method of communication

 Ultrasound image of a fetus in the womb, viewed at 12 weeks of pregnancy (bidimensional-scan)

  An ultrasonic examination 

 Fetal ultrasound 

cloud basic to back

Galton whistle, one of the first devices to produce ultrasound

Acoustics, the science of sound, starts as far back as Pythagoras in the 6th century BC, who wrote on the mathematical properties of stringed instruments. Echolocation in bats was discovered by Lazzaro Spallanzani in 1794, when he demonstrated that bats hunted and navigated by inaudible sound and not vision. Francis Galton in 1893 invented the Galton whistle, an adjustable whistle which produced ultrasound, which he used to measure the hearing range of humans and other animals, demonstrating that many animals could hear sounds above the hearing range of humans. The first technological application of ultrasound was an attempt to detect submarines by Paul Langevin in 1917. The piezoelectric effect, discovered by Jacques and Pierre Curie in 1880, was useful in transducers to generate and detect ultrasonic waves in air and water.^[3]

Definition

Approximate frequency ranges corresponding to ultrasound, with rough guide of some applications

Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 kHz." In air at atmospheric pressure ultrasonic waves have wavelengths of 1.9 cm or less.

Perception

Humans

The upper frequency limit in humans (approximately 20 kHz) is due to limitations of the middle ear. Auditory sensation can occur if high‐intensity ultrasound is fed directly into the human skull and reaches the cochlea through bone conduction, without passing through the middle ear.^[4]
Children can hear some high-pitched sounds that older adults cannot hear, because in humans the upper limit pitch of hearing tends to decrease with age.^[5] An American cell phone company has used this to create ring signals supposedly only able to be heard by younger humans;^[6] but many older people can hear the signals, which may be because of the considerable variation of age-related deterioration in the upper hearing threshold. The Mosquito is an electronic device that uses a high pitched frequency to deter loitering by young people.

Animals

Bats use ultrasounds to navigate in the darkness.

A dog whistle, a whistle which emits sound in the ultrasonic range, used to train dogs and other animals

Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey. They can detect frequencies beyond 100 kHz, possibly up to 200 kHz.^[7]
Many insects have good ultrasonic hearing and most of these are nocturnal insects listening for echolocating bats. This includes many groups of moths, beetles, praying mantids and lacewings. Upon hearing a bat, some insects will make evasive manoeuvres to escape being caught.^[8] Ultrasonic frequencies trigger a reflex action in the noctuid moth that cause it to drop slightly in its flight to evade attack.^[9] Tiger moths also emit clicks which may disturb bats' echolocation, but may also in other cases evade being eaten by advertising the fact that they are poisonous by emitting sound.
Dogs and cats' hearing range extends into the ultrasound; the top end of a dog's hearing range is about 45 kHz, while a cat's is 64 kHz. The wild ancestors of cats and dogs evolved this higher hearing range to hear high-frequency sounds made by their preferred prey, small rodents.^[14] A dog whistle is a whistle that emits ultrasound, used for training and calling dogs. The frequency of most dog whistles is within the range of 23 to 54 kHz,^[16]
Toothed whales, including dolphins, can hear ultrasound and use such sounds in their navigational system (biosonar) to orient and capture prey.^[17] Porpoises have the highest known upper hearing limit, at around 160 kHz.^[18] Several types of fish can detect ultrasound. In the order Clupeiformes, members of the subfamily Alosinae (shad), have been shown to be able to detect sounds up to 180 kHz, while the other subfamilies (e.g. herrings) can hear only up to 4 kHz.^[19]
Ultrasound generator/speaker systems are sold as electronic pest control devices, which are claimed to frighten away rodents and insects, but there is no scientific evidence that the devices work.^[20][21][22]

Detection and ranging

Non-contact sensor

An ultrasonic level or sensing system requires no contact with the target. For many processes in the medical, pharmaceutical, military and general industries this is an advantage over inline sensors that may contaminate the liquids inside a vessel or tube or that may be clogged by the product.
Both continuous wave and pulsed systems are used. The principle behind a pulsed-ultrasonic technology is that the transmit signal consists of short bursts of ultrasonic energy. After each burst, the electronics looks for a return signal within a small window of time corresponding to the time it takes for the energy to pass through the vessel. Only a signal received during this window will qualify for additional signal processing.
A popular consumer application of ultrasonic ranging was the Polaroid SX-70 camera which included a light-weight transducer system to focus the camera automatically. Polaroid later licensed this ultrasound technology and it became the basis of a variety of ultrasonic products.

Motion sensors and flow measurement

A common ultrasound application is an automatic door opener, where an ultrasonic sensor detects a person's approach and opens the door. Ultrasonic sensors are also used to detect intruders; the ultrasound can cover a wide area from a single point. The flow in pipes or open channels can be measured by ultrasonic flowmeters, which measure the average velocity of flowing liquid. In rheology, an acoustic rheometer relies on the principle of ultrasound. In fluid mechanics, fluid flow can be measured using an ultrasonic flow meter.

Non-destructive testing

 Macrosonic and Ultrasonic testing

Principle of flaw detection with ultrasound. A void in the solid material reflects some energy back to the transducer, which is detected and displayed.

Ultrasonic testing is a type of nondestructive testing commonly used to find flaws in materials and to measure the thickness of objects. Frequencies of 2 to 10 MHz are common but for special purposes other frequencies are used. Inspection may be manual or automated and is an essential part of modern manufacturing processes. Most metals can be inspected as well as plastics and aerospace composites. Lower frequency ultrasound (50–500 kHz) can also be used to inspect less dense materials such as wood, concrete and cement.
Ultrasound inspection of welded joints has been an alternative to radiography for non-destructive testing since the 1960s. Ultrasonic inspection eliminates the use of ionizing radiation, with safety and cost benefits. Ultrasound can also provide additional information such as the depth of flaws in a welded joint. Ultrasonic inspection has progressed from manual methods to computerized systems that automate much of the process. An ultrasonic test of a joint can identify the existence of flaws, measure their size, and identify their location. Not all welded materials are equally amenable to ultrasonic inspection; some materials have a large grain size that produces a high level of background noise in measurements.^[23]

Non-destructive testing of a swing shaft showing spline cracking

Ultrasonic thickness measurement is one technique used to monitor quality of welds.

Ultrasonic range finding

Principle of an active sonar

 

A common use of ultrasound is in underwater range finding; this use is also called Sonar. An ultrasonic pulse is generated in a particular direction. If there is an object in the path of this pulse, part or all of the pulse will be reflected back to the transmitter as an echo and can be detected through the receiver path. By measuring the difference in time between the pulse being transmitted and the echo being received, it is possible to determine the distance.
The measured travel time of Sonar pulses in water is strongly dependent on the temperature and the salinity of the water. Ultrasonic ranging is also applied for measurement in air and for short distances. For example, hand-held ultrasonic measuring tools can rapidly measure the layout of rooms.
Although range finding underwater is performed at both sub-audible and audible frequencies for great distances (1 to several kilometers), ultrasonic range finding is used when distances are shorter and the accuracy of the distance measurement is desired to be finer. Ultrasonic measurements may be limited through barrier layers with large salinity, temperature or vortex differentials. Ranging in water varies from about hundreds to thousands of meters, but can be performed with centimeters to meters accuracy

Ultrasound Identification (USID)

Ultrasound Identification (USID) is a Real Time Locating System (RTLS) or Indoor Positioning System (IPS) technology used to automatically track and identify the location of objects in real time using simple, inexpensive nodes (badges/tags) attached to or embedded in objects and devices, which then transmit an ultrasound signal to communicate their location to microphone sensors.

Imaging

Sonogram of a fetus at 14 weeks (profile)

Head of a fetus, aged 29 weeks, in a "3D ultrasound"

The potential for ultrasonic imaging of objects, with a 3 GHZ sound wave producing resolution comparable to an optical image, was recognized by Sokolov in 1939 but techniques of the time produced relatively low-contrast images with poor sensitivity.^[24] Ultrasonic imaging uses frequencies of 2 megahertz and higher; the shorter wavelength allows resolution of small internal details in structures and tissues. The power density is generally less than 1 watt per square centimetre, to avoid heating and cavitation effects in the object under examination.^[25] High and ultra high ultrasound waves are used in acoustic microscopy, with frequencies up to 4 gigahertz. Ultrasonic imaging applications include industrial non-destructive testing, quality control and medical uses.^[24]

Acoustic microscopy

Acoustic microscopy is the technique of using sound waves to visualize structures too small to be resolved by the human eye. Frequencies up to several gigahertz are used in acoustic microscopes. The reflection and diffraction of sound waves from microscopic structures can yield information not available with light.

Human medicine

Medical sonography (ultrasonography) is an ultrasound-based diagnostic medical imaging technique used to visualize muscles, tendons, and many internal organs, to capture their size, structure and any pathological lesions with real time tomographic images. Ultrasound has been used by radiologists and sonographers to image the human body for at least 50 years and has become a widely used diagnostic tool. The technology is relatively inexpensive and portable, especially when compared with other techniques, such as magnetic resonance imaging (MRI) and computed tomography (CT). Ultrasound is also used to visualize fetuses during routine and emergency prenatal care. Such diagnostic applications used during pregnancy are referred to as obstetric sonography. As currently applied in the medical field, properly performed ultrasound poses no known risks to the patient.^[26] Sonography does not use ionizing radiation, and the power levels used for imaging are too low to cause adverse heating or pressure effects in tissue.^{[citation needed]} Although the long-term effects due to ultrasound exposure at diagnostic intensity are still unknown,^[27] currently most doctors feel that the benefits to patients outweigh the risks.^[28] The ALARA (As Low As Reasonably Achievable) principle has been advocated for an ultrasound examination – that is, keeping the scanning time and power settings as low as possible but consistent with diagnostic imaging – and that by that principle non-medical uses, which by definition are not necessary, are actively discouraged.^[29]
Ultrasound is also increasingly being used in trauma and first aid cases, with emergency ultrasound becoming a staple of most EMT response teams. Furthermore, ultrasound is used in remote diagnosis cases where teleconsultation is required, such as scientific experiments in space or mobile sports team diagnosis.^{[30][dead link]}
According to RadiologyInfo,^[31] ultrasounds are useful in the detection of pelvic abnormalities and can involve techniques known as abdominal (transabdominal) ultrasound, vaginal (transvaginal or endovaginal) ultrasound in women, and also rectal (transrectal) ultrasound in men.

Veterinary medicine

 

Diagnostic ultrasound is used externally in horses for evaluation of soft tissue and tendon injuries, and internally in particular for reproductive work – evaluation of the reproductive tract of the mare and pregnancy detection.^[32] It may also be used in an external manner in stallions for evaluation of testicular condition and diameter as well as internally for reproductive evaluation (deferent duct etc.).^[33]
Starting at the turn of the century, ultrasound technology began to be used by the beef cattle industry to improve animal health and the yield of cattle operations.^[34] Ultrasound is used to evaluate fat thickness, rib eye area, and intramuscular fat in living animals.^[35] It is also used to evaluate the health and characteristics of unborn calves.
Ultrasound technology provides a means for cattle producers to obtain information that can be used to improve the breeding and husbandry of cattle. The technology can be expensive, and it requires a substantial time commitment for continuous data collection and operator training.^[35] Nevertheless, this technology has proven useful in managing and running a cattle breeding operation.^[34]

Processing and power

High-power applications of ultrasound often use frequencies between 20 kHz and a few hundred kHz. Intensities can be very high; above 10 watts per square centimeter, cavitation can be inducted in liquid media, and some applications use up to 1000 watts per square centimeter. Such high intensities can induce chemical changes or produce significant effects by direct mechanical action, and can inactivate harmful microorganisms.

Physical therapy

 

Ultrasound has been used since the 1940s by physical and occupational therapists for treating connective tissue: ligaments, tendons, and fascia (and also scar tissue).^[36] Conditions for which ultrasound may be used for treatment include the follow examples: ligament sprains, muscle strains, tendonitis, joint inflammation, plantar fasciitis, metatarsalgia, facet irritation, impingement syndrome, bursitis, rheumatoid arthritis, osteoarthritis, and scar tissue adhesion.

Biomedical applications

Ultrasound also has therapeutic applications, which can be highly beneficial when used with dosage precautions^[37] Relatively high power ultrasound can break up stony deposits or tissue, accelerate the effect of drugs in a targeted area, assist in the measurement of the elastic properties of tissue, and can be used to sort cells or small particles for research.

Ultrasonic impact treatment

Ultrasonic impact treatment (UIT) uses ultrasound to enhance the mechanical and physical properties of metals. It is a metallurgical processing technique in which ultrasonic energy is applied to a metal object. Ultrasonic treatment can result in controlled residual compressive stress, grain refinement and grain size reduction. Low and high cycle fatigue are enhanced and have been documented to provide increases up to ten times greater than non-UIT specimens. Additionally, UIT has proven effective in addressing stress corrosion cracking, corrosion fatigue and related issues.
When the UIT tool, made up of the ultrasonic transducer, pins and other components, comes into contact with the work piece it acoustically couples with the work piece, creating harmonic resonance.^[38] This harmonic resonance is performed at a carefully calibrated frequency, to which metals respond very favorably.
Depending on the desired effects of treatment a combination of different frequencies and displacement amplitude is applied. These frequencies range between 25 and 55 kHz,^[39] with the displacement amplitude of the resonant body of between 22 and 50 µm (0.00087 and 0.0020 in).
UIT devices rely on magnetostrictive transducers.

Processing

 

Ultrasonication offers great potential in the processing of liquids and slurries, by improving the mixing and chemical reactions in various applications and industries. Ultrasonication generates alternating low-pressure and high-pressure waves in liquids, leading to the formation and violent collapse of small vacuum bubbles. This phenomenon is termed cavitation and causes high speed impinging liquid jets and strong hydrodynamic shear-forces. These effects are used for the deagglomeration and milling of micrometre and nanometre-size materials as well as for the disintegration of cells or the mixing of reactants. In this aspect, ultrasonication is an alternative to high-speed mixers and agitator bead mills. Ultrasonic foils under the moving wire in a paper machine will use the shock waves from the imploding bubbles to distribute the cellulose fibres more uniformly in the produced paper web, which will make a stronger paper with more even surfaces. Furthermore, chemical reactions benefit from the free radicals created by the cavitation as well as from the energy input and the material transfer through boundary layers. For many processes, this sonochemical (see sonochemistry) effect leads to a substantial reduction in the reaction time, like in the transesterification of oil into biodiesel.

Schematic of bench and industrial-scale ultrasonic liquid processors

Substantial ultrasonic intensity and high ultrasonic vibration amplitudes are required for many processing applications, such as nano-crystallization, nano-emulsification,^[40] deagglomeration, extraction, cell disruption, as well as many others. Commonly, a process is first tested on a laboratory scale to prove feasibility and establish some of the required ultrasonic exposure parameters. After this phase is complete, the process is transferred to a pilot (bench) scale for flow-through pre-production optimization and then to an industrial scale for continuous production. During these scale-up steps, it is essential to make sure that all local exposure conditions (ultrasonic amplitude, cavitation intensity, time spent in the active cavitation zone, etc.) stay the same. If this condition is met, the quality of the final product remains at the optimized level, while the productivity is increased by a predictable "scale-up factor". The productivity increase results from the fact that laboratory, bench and industrial-scale ultrasonic processor systems incorporate progressively larger ultrasonic horns, able to generate progressively larger high-intensity cavitation zones and, therefore, to process more material per unit of time. This is called "direct scalability". It is important to point out that increasing the power of the ultrasonic processor alone does not result in direct scalability, since it may be (and frequently is) accompanied by a reduction in the ultrasonic amplitude and cavitation intensity. During direct scale-up, all processing conditions must be maintained, while the power rating of the equipment is increased in order to enable the operation of a larger ultrasonic horn.

Ultrasonic manipulation and characterization of particles

A researcher at the Industrial Materials Research Institute, Alessandro Malutta, devised an experiment that demonstrated the trapping action of ultrasonic standing waves on wood pulp fibers diluted in water and their parallel orienting into the equidistant pressure planes.^[44] The time to orient the fibers in equidistant planes is measured with a laser and an electro-optical sensor. This could provide the paper industry a quick on-line fiber size measurement system. A somewhat different implementation was demonstrated at Pennsylvania State University using a microchip which generated a pair of perpendicular standing surface acoustic waves allowing to position particles equidistant to each other on a grid. This experiment, called acoustic tweezers, can be used for applications in material sciences, biology, physics, chemistry and nanotechnology.

Ultrasonic cleaning

 

Ultrasonic cleaners, sometimes mistakenly called supersonic cleaners, are used at frequencies from 20 to 40 kHz for jewellery, lenses and other optical parts, watches, dental instruments, surgical instruments, diving regulators and industrial parts. An ultrasonic cleaner works mostly by energy released from the collapse of millions of microscopic cavitations near the dirty surface. The bubbles made by cavitation collapse forming tiny jets directed at the surface.

Ultrasonic disintegration

Similar to ultrasonic cleaning, biological cells including bacteria can be disintegrated. High power ultrasound produces cavitation that facilitates particle disintegration or reactions. This has uses in biological science for analytical or chemical purposes (sonication and sonoporation) and in killing bacteria in sewage. High power ultrasound can disintegrate corn slurry and enhance liquefaction and saccharification for higher ethanol yield in dry corn milling plants.^{[45][dead link][46][dead link]}

Ultrasonic humidifier

The ultrasonic humidifier, one type of nebulizer (a device that creates a very fine spray), is a popular type of humidifier. It works by vibrating a metal plate at ultrasonic frequencies to nebulize (sometimes incorrectly called "atomize") the water. Because the water is not heated for evaporation, it produces a cool mist. The ultrasonic pressure waves nebulize not only the water but also materials in the water including calcium, other minerals, viruses, fungi, bacteria,^[47] and other impurities. Illness caused by impurities that reside in a humidifier's reservoir fall under the heading of "Humidifier Fever".
Ultrasonic humidifiers are frequently used in aeroponics, where they are generally referred to as foggers.

Ultrasonic welding

In ultrasonic welding of plastics, high frequency (15 kHz to 40 kHz ) low amplitude vibration is used to create heat by way of friction between the materials to be joined. The interface of the two parts is specially designed to concentrate the energy for maximum weld strength.

Sonochemistry

Main article: Sonochemistry

Power ultrasound in the 20–100 kHz range is used in chemistry. The ultrasound does not interact directly with molecules to induce the chemical change, as its typical wavelength (in the millimeter range) is too long compared to the molecules. Instead, the energy causes cavitation which generates extremes of temperature and pressure in the liquid where the reaction happens. Ultrasound also breaks up solids and removes passivating layers of inert material to give a larger surface area for the reaction to occur over. Both of these effects make the reaction faster. In 2008, Atul Kumar reported synthesis of Hantzsch esters and polyhydroquinoline derivatives via multi-component reaction protocol in aqueous micelles using ultrasound.^[48]
Ultrasound is used in extraction, using different frequencies.

Weapons

Ultrasound has been studied as a basis for sonic weapons, for applications such as riot control, disorientation of attackers, up to lethal levels of sound.

Wireless communication

In July 2015, The Economist reported that researchers at the University of California, Berkeley have conducted ultrasound studies using graphene diaphragms. The thinness and low weight of graphene combined with its strength make it an effective material to use in ultrasound communications. One suggested application of the technology would be underwater communications, where radio waves typically do not travel well.^[2]

Other uses

Ultrasound when applied in specific configurations can produce short bursts of light in an exotic phenomenon known as sonoluminescence. This phenomenon is being investigated partly because of the possibility of bubble fusion (a nuclear fusion reaction hypothesized to occur during sonoluminescence).
Ultrasound is used when characterizing particulates through the technique of ultrasound attenuation spectroscopy or by observing electroacoustic phenomena or by transcranial pulsed ultrasound.
Audio can be propagated by modulated ultrasound.
A formerly popular consumer application of ultrasound was in television remote controls for adjusting volume and changing channels. Introduced by Zenith in the late 1950s, the system used a hand-held remote control containing short rod resonators struck by small hammers, and a microphone on the set. Filters and detectors discriminated between the various operations. The principal advantages were that no battery was needed in the hand-held control box, and unlike radio waves, the ultrasound was unlikely to affect neighboring sets. Ultrasound remained in use until displaced by infrared systems starting in the late 1980s.

Safety

Occupational exposure to ultrasound in excess of 120 dB may lead to hearing loss. Exposure in excess of 155 dB may produce heating effects that are harmful to the human body, and it has been calculated that exposures above 180 dB may lead to death. The UK's independent Advisory Group on Non-ionising Radiation (AGNIR) produced a report in 2010, which was published by the UK Health Protection Agency (HPA). This report recommended an exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above). 


Infrasound 

Infrasound, sometimes referred to as low-frequency sound, is sound that is lower in frequency than 20 Hz or cycles per second, the "normal" limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. The ear is the primary organ for sensing infrasound, but at higher intensities it is possible to feel infrasound vibrations in various parts of the body.
The study of such sound waves is sometimes referred to as infrasonics, covering sounds beneath 20 Hz down to 0.1 Hz and rarely to 0.001 Hz. People use this frequency range for monitoring earthquakes, charting rock and petroleum formations below the earth, and also in ballistocardiography and seismocardiography to study the mechanics of the heart.
Infrasound is characterized by an ability to cover long distances and get around obstacles with little dissipation. In music, acoustic waveguide methods, such as a large pipe organ or, for reproduction, exotic loudspeaker designs such as transmission line, rotary woofer, or traditional subwoofer designs can produce low-frequency sounds, including near-infrasound. Subwoofers designed to produce infrasound are capable of sound reproduction an octave or more below that of most commercially available subwoofers, and are often about 10 times the size.

 Infrasound arrays at infrasound monitoring station in Qaanaaq, Greenland 

Definition

Infrasound is defined by the American National Standards Institute as "sound at frequencies less than 20 Hz 

The Allies of World War I first used infrasound to locate artillery.^[1] One of the pioneers in infrasonic research was French scientist Vladimir Gavreau.^[2] His interest in infrasonic waves first came about in his laboratory during the 1960s, when he and his laboratory assistants experienced shaking laboratory equipment and pain in the eardrums, but his microphones did not detect audible sound. He concluded it was infrasound caused by a large fan and duct system, and soon got to work preparing tests in the laboratories. One of his experiments was an infrasonic whistle, an oversized organ pipe.

Sources

Patent for a double bass reflex loudspeaker enclosure design intended to produce infrasonic frequencies ranging from 5 to 25 hertz, of which traditional subwoofer designs are not readily capable.

Infrasound can result from both natural and man-made sources:

• Natural events: infrasonic sound sometimes results naturally from severe weather, surf,^[6] lee waves, avalanches, earthquakes, volcanoes, bolides,^[7] waterfalls, calving of icebergs, aurorae, meteors, lightning and upper-atmospheric lightning.^[8] Nonlinear ocean wave interactions in ocean storms produce pervasive infrasound vibrations around 0.2 Hz, known as microbaroms.^[9] According to the Infrasonics Program at NOAA, infrasonic arrays can be used to locate avalanches in the Rocky Mountains, and to detect tornadoes on the high plains several minutes before they touch down.^[10]

• Animal communication: whales, elephants,^[11] hippopotamuses,^[12] rhinoceros,^[13][14] giraffes,^[15] okapi,^[16] and alligators are known to use infrasound to communicate over distances—up to hundreds of miles in the case of whales. In particular, the Sumatran Rhinoceros has been shown to produce sounds with frequencies as low as 3 Hz which have similarities with the song of the humpback whale.^[14] The roar of the tiger contains infrasound of 18 Hz and lower,^[17] and the purr of felines is reported to cover a range of 20 to 50 Hz.^[18][19][20] It has also been suggested that migrating birds use naturally generated infrasound, from sources such as turbulent airflow over mountain ranges, as a navigational aid.^[21] Infrasound also may be used for long-distance communication, especially well documented in baleen whales (see Whale vocalization), and African elephants.^[22] The frequency of baleen whale sounds can range from 10 Hz to 31 kHz,^[23] and that of elephant calls from 15 Hz to 35 Hz. Both can be extremely loud (around 117 dB), allowing communication for many kilometres, with a possible maximum range of around 10 km (6 mi) for elephants,^[24] and potentially hundreds or thousands of kilometers for some whales.^{[citation needed]} Elephants also produce infrasound waves that travel through solid ground and are sensed by other herds using their feet, although they may be separated by hundreds of kilometres. These calls may be used to coordinate the movement of herds and allow mating elephants to find each other.^{[citation needed]}

• Human singers: some vocalists, including Tim Storms, can produce notes in the infrasound range.^[25]

• Human created sources: infrasound can be generated by human processes such as sonic booms and explosions (both chemical and nuclear), or by machinery such as diesel engines, wind turbines and specially designed mechanical transducers (industrial vibration tables). Certain specialized loudspeaker designs are also able to reproduce extremely low frequencies; these include large-scale rotary woofer models of subwoofer loudspeaker,^[26] as well as large horn loaded, bass reflex, sealed and transmission line loudspeakers.

Animal reactions

 

Animals have been known to perceive the infrasonic waves going through the earth by natural disasters and can use these as an early warning. A recent example of this is the 2004 Indian Ocean earthquake and tsunami. Animals were reported to flee the area hours before the actual tsunami hit the shores of Asia.^[29][30] It is not known for sure that this is the cause; some have suggested that it may have been the influence of electromagnetic waves, and not of infrasonic waves, that prompted these animals to flee.^[31]
Research in 2013 by Jon Hagstrum of the US Geological Survey suggests that homing pigeons use low-frequency infrasound to navigate.^[32]

Human reactions

20 Hz is considered the normal low-frequency limit of human hearing. When pure sine waves are reproduced under ideal conditions and at very high volume, a human listener will be able to identify tones as low as 12 Hz.^[33] Below 10 Hz it is possible to perceive the single cycles of the sound, along with a sensation of pressure at the eardrums.
From about 1000 Hz, the dynamic range of the auditory system decreases with decreasing frequency. This compression is observable in the equal-loudness-level contours, and it implies that even a slight increase in level can change the perceived loudness from barely audible to loud. Combined with the natural spread in thresholds within a population, its effect may be that a very low-frequency sound which is inaudible to some people may be loud to others.
One study has suggested that infrasound may cause feelings of awe or fear in humans. It has also been suggested that since it is not consciously perceived, it may make people feel vaguely that odd or supernatural events are taking place.^[34]
A scientist working at Sydney University's Auditory Neuroscience Laboratory reports growing evidence that infrasound may affect some people's nervous system by stimulating the vestibular system, and this has shown in animal models an effect similar to sea sickness.^[35] In a study of 45 people, Tehran University researchers stated: “Despite all the good benefits of wind turbines ... this technology has health risks for all those exposed to its sound” — in particular, sleep disorder.
In a study at Ibaraki University in Japan, researchers said EEG tests showed that the infrasound produced by wind turbines was “considered to be an annoyance to the technicians who work close to a modern large-scale wind turbine.”

Infrasonic 17 Hz tone experiment

On 31 May 2003 a group of UK researchers held a mass experiment, where they exposed some 700 people to music laced with soft 17 Hz sine waves played at a level described as "near the edge of hearing", produced by an extra-long-stroke subwoofer mounted two-thirds of the way from the end of a seven-meter-long plastic sewer pipe. The experimental concert (entitled Infrasonic) took place in the Purcell Room over the course of two performances, each consisting of four musical pieces. Two of the pieces in each concert had 17 Hz tones played underneath.^[39][40]
In the second concert, the pieces that were to carry a 17 Hz undertone were swapped so that test results would not focus on any specific musical piece. The participants were not told which pieces included the low-level 17 Hz near-infrasonic tone. The presence of the tone resulted in a significant number (22%) of respondents reporting feeling uneasy or sorrowful, getting chills down the spine or nervous feelings of revulsion or fear.^[39][40]
In presenting the evidence to the British Association for the Advancement of Science, Professor Richard Wiseman said "These results suggest that low frequency sound can cause people to have unusual experiences even though they cannot consciously detect infrasound. Some scientists have suggested that this level of sound may be present at some allegedly haunted sites and so cause people to have odd sensations that they attribute to a ghost—our findings support these ideas."^[34]

Suggested relationship to ghost sightings

Psychologist Richard Wiseman of the University of Hertfordshire suggests that the odd sensations that people attribute to ghosts may be caused by infrasonic vibrations. Vic Tandy, experimental officer and part-time lecturer in the school of international studies and law at Coventry University, along with Dr. Tony Lawrence of the University's psychology department, wrote in 1998 a paper called "Ghosts in the Machine" for the Journal of the Society for Psychical Research. Their research suggested that an infrasonic signal of 19 Hz might be responsible for some ghost sightings. Tandy was working late one night alone in a supposedly haunted laboratory at Warwick, when he felt very anxious and could detect a grey blob out of the corner of his eye. When Tandy turned to face the grey blob, there was nothing.
The following day, Tandy was working on his fencing foil, with the handle held in a vice. Although there was nothing touching it, the blade started to vibrate wildly. Further investigation led Tandy to discover that the extractor fan in the lab was emitting a frequency of 18.98 Hz, very close to the resonant frequency of the eye given as 18 Hz by NASA.^[41] This, Tandy conjectured, was why he had seen a ghostly figure—it was, he believed, an optical illusion caused by his eyeballs resonating. The room was exactly half a wavelength in length, and the desk was in the centre, thus causing a standing wave which caused the vibration of the foil.^[42]
Tandy investigated this phenomenon further and wrote a paper entitled The Ghost in the Machine.^[43] He carried out a number of investigations at various sites believed to be haunted, including the basement of the Tourist Information Bureau next to Coventry Cathedral^[44][45] and Edinburgh Castle.^[46][47]

Infrasound for nuclear detonation detection

Infrasound is one of several techniques used to identify if a nuclear detonation has occurred. A network of 60 infrasound stations, in addition to seismic and hydroacoustic stations, comprise the International Monitoring System (IMS) that is tasked with monitoring compliance with the Comprehensive Nuclear Test-Ban Treaty (CTBT).^[48] IMS Infrasound stations consist of eight microbarometer sensors and space filters arranged in an array covering an area of approximately 1 to 9 km^2.^[48][49] The space filters used are radiating pipes with inlet ports along their length, designed to average out pressure variations like wind turbulence for more precise measurements.^[49] The microbarometers used are designed to monitor frequencies below approximately 20 hertz.^[48] Sound waves below 20 hertz have longer wavelengths and are not easily absorbed, allowing for detection across large distances.^[48]
Infrasound wavelengths can be generated artificially through detonations and other human activity, or naturally from earthquakes, severe weather, lighting, and other sources.^[48] Like forensic seismology, algorithms and other filter techniques are required to analyze gathered data and characterize events to determine if a nuclear detonation has actually occurred. Data is transmitted from each station via secure communication links for further analysis. A digital signature is also embedded in the data sent from each station to verify if the data is authentic.^[50]

Detection and measurement

NASA Langley has designed and developed an infrasonic detection system that can be used to make useful infrasound measurements at a location where it was not possible previously. The system comprises an electret condenser microphone PCB Model 377M06, having a 3-inch membrane diameter, and a small, compact windscreen.^[51] Electret-based technology offers the lowest possible background noise, because Johnson noise generated in the supporting electronics (preamplifier) is minimized.^[51]
The microphone features a high membrane compliance with a large backchamber volume, a prepolarized backplane and a high impedance preamplifier located inside the backchamber. The windscreen, based on the high transmission coefficient of infrasound through matter, is made of a material having a low acoustic impedance and has a sufficiently thick wall to ensure structural stability.^[52] Close-cell polyurethane foam has been found to serve the purpose well. In the proposed test, test parameters will be sensitivity, background noise, signal fidelity (harmonic distortion), and temporal stability.
The microphone design differs from that of a conventional audio system in that the peculiar features of infrasound are taken into account. First, infrasound propagates over vast distances through the Earth's atmosphere as a result of very low atmospheric absorption and of refractive ducting that enables propagation by way of multiple bounces between the Earth's surface and the stratosphere. A second property that has received little attention is the great penetration capability of infrasound through solid matter – a property utilized in the design and fabrication of the system windscreens.^[52]
Thus the system fulfills several instrumentation requirements advantageous to the application of acoustics: (1) a low-frequency microphone with especially low background noise, which enables detection of low-level signals within a low-frequency passband; (2) a small, compact windscreen that permits (3) rapid deployment of a microphone array in the field. The system also features a data acquisition system that permits real time detection, bearing, and signature of a low-frequency source.^[52]
The Comprehensive Nuclear-Test-Ban Treaty Organization Preparatory Commission uses infrasound as one of its monitoring technologies, along with seismic, hydroacoustic, and atmospheric radionuclide monitoring. The loudest infrasound recorded to date by the monitoring system was generated by the 2013 Chelyabinsk meteor   








                                            

    This picture from a NASA study on wingtip vortices qualitatively illustrates wake turbulence

A pipe tee. The net flow of water into a piping tee (filled with water) must equal the net flow out.

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  Capacitor:  a flexible diaphragm sealed inside a pipe.
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  Inductor:  a heavy paddle wheel or turbine placed in the current.
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  Voltage or current source:  A dynamic pump with feedback control.