Hall effect
Encyclopedia
The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor
, transverse to an electric current
in the conductor and a magnetic field
perpendicular to the current. It was discovered by Edwin Hall
in 1879.
The Hall coefficient is defined as the ratio of the induced electric field to the product of the current density and the applied magnetic field. It is a characteristic of the material from which the conductor is made, since its value depends on the type, number, and properties of the charge
carriers that constitute the current.
in Baltimore, Maryland. His measurements of the tiny effect produced in the apparatus he used was an experimental tour de force, accomplished 18 years before the electron
was discovered.
s, typically electron
s, holes
, ions (see Electromigration
) or all three. When a magnetic field is present that is perpendicular to the direction of motion of moving charges, these charges experience a force, called the Lorentz force
. When such a magnetic field is absent, the charges follow approximately straight, 'line of sight' paths between collisions with impurities, phonons, etc. However, when a perpendicular magnetic field is applied, their paths between collisions are curved so that moving charges accumulate on one face of the material. This leaves equal and opposite charges exposed on the other face, where there is a scarcity of mobile charges. The result is an asymmetric
distribution of charge density across the Hall element that is perpendicular to both the 'line of sight' path and the applied magnetic field. The separation of charge establishes an electric field
that opposes the migration of further charge, so a steady electrical potential builds up for as long as the charge is flowing.
It shall be noted that in the classical
view, there are only electrons moving in the same average direction both in the case of electron or hole conductivity. This cannot explain the opposite sign of the Hall effect observed. The difference is that electrons in the upper bound of the valence band
have opposite group velocity
and wave vector
direction when moving, which can be effectively treated as if positively charged particles (holes) moved in the opposite direction to that of the electrons.
For a simple metal where there is only one type of charge carrier
(electrons) the Hall voltage VH is given by
where I is the current across the plate length, B is the magnetic field, d is the depth (thickness) of the plate, e is the electron charge, and n is the charge carrier density
of the carrier electrons.
The Hall coefficient is defined as
where j is the current density
of the carrier electrons, and
is the induced electric field. In SI units, this becomes
As a result, the Hall effect is very useful as a means to measure either the carrier density or the magnetic field.
One very important feature of the Hall effect is that it differentiates between positive charges moving in one direction and negative charges moving in the opposite. The Hall effect offered the first real proof that electric currents in metals are carried by moving electrons, not by protons. The Hall effect also showed that in some substances (especially p-type semiconductor
s), it is more appropriate to think of the current as positive "holes
" moving rather than negative electrons. A common source of confusion with the Hall Effect is that holes moving to the left are really electrons moving to the right, so one expects the same sign of the Hall coefficient for both electrons and holes. This confusion, however, can only be resolved by modern quantum mechanical theory of transport in solids.
It must be noted though that the sample inhomogeneity might result in spurious sign of the Hall effect, even in ideal van der Pauw
configuration of electrodes. For example, positive Hall effect was observed in evidently n-type semiconductors.
is kept in a magnetic field, the charge carriers of the semiconductor experience a force in a direction perpendicular to both the magnetic field and the current. At equilibrium, a voltage appears at the semiconductor edges.
The simple formula for the Hall coefficient given above becomes more complex in semiconductors where the carriers are generally both electrons and holes
which may be present in different concentrations and have different mobilities
. For moderate magnetic fields the Hall coefficient is
where
is the electron concentration, 
the hole concentration, 
the electron mobility, 
the hole mobility and 
the absolute value
of the electronic charge.
For large applied fields the simpler expression analogous to that for a single carrier type holds.
with
. In the presence of large magnetic field
strength and low temperature
, one can observe the quantum Hall effect, which is the quantization
of the Hall voltage.
), the Hall resistivity includes an additional contribution, known as the anomalous Hall effect (or the extraordinary Hall effect), which depends directly on the magnetization
of the material, and is often much larger than the ordinary Hall effect. (Note that this effect is not due to the contribution of the magnetization
to the total magnetic field
.) Although a well-recognized phenomenon, there is still debate about its origins in the various materials. The anomalous Hall effect can be either an extrinsic (disorder-related) effect due to spin
-dependent scattering
of the charge carrier
s, or an intrinsic effect which can be described in terms of the Berry phase effect in the crystal momentum space (k-space).
The Hall effect in an ionized gas (plasma
) is significantly different from the Hall effect in solids (where the Hall parameter is always very inferior to unity). In a plasma, the Hall parameter can take any value. The Hall parameter, β, in a plasma is the ratio between the electron gyrofrequency, Ωe, and the electron-heavy particle collision frequency, ν:
where
The Hall parameter value increases with the magnetic field strength.
Physically, the trajectories of electrons are curved by the Lorentz force
. Nevertheless when the Hall parameter is low, their motion between two encounters with heavy particles (neutral
or ion
) is almost linear. But if the Hall parameter is high, the electron movements are highly curved. The current density
vector, J, is no longer colinear with the electric field
vector, E. The two vectors J and E make the Hall angle, θ, which also gives the Hall parameter:
s, i.e. to measure magnetic fields, or inspect materials (such as tubing or pipelines) using the principles of magnetic flux leakage
.
Hall effect devices produce a very low signal level and thus require amplification. While suitable for laboratory instruments, the vacuum tube
amplifier
s available in the first half of the 20th century were too expensive, power consuming, and unreliable for everyday applications. It was only with the development of the low cost integrated circuit
that the Hall effect sensor became suitable for mass application. Many devices now sold as Hall effect sensor
s in fact contain both the sensor as described above plus a high gain integrated circuit
(IC) amplifier in a single package. Recent advances have further added into one package an analog-to-digital converter
and I²C
(Inter-integrated circuit communication protocol) IC for direct connection to a microcontroller
's I/O port.
When electrons flow through a conductor, a magnetic field is produced. Thus, it is possible to create a non-contacting current sensor. The device has three terminals.
A sensor voltage is applied across two terminals and the third provides a voltage proportional to the current being sensed. This has several advantages; no additional resistance (a shunt
, required for the most common current sensing method) need be inserted in the primary circuit. Also, the voltage present on the line to be sensed is not transmitted to the sensor, which enhances the safety of measuring equipment.
-based circuit.
s are readily available from a number of different manufacturers, and may be used in various sensors such as rotating speed sensors (bicycle wheels, gear-teeth, automotive speedometers, electronic ignition systems), fluid flow sensor
s, current sensor
s, and pressure sensor
s. Common applications are often found where a robust and contactless switch or potentiometer is required. These include: electric airsoft
guns, triggers of electropneumatic paintball guns, go-cart speed controls, smart phones, and some global positioning systems.
). This configuration also provides an improvement in signal-to-noise ratio and drift effects of over 20 times that of a bare Hall device.
The range of a given feedthrough sensor may be extended upward and downward by appropriate wiring. To extend the range to lower currents, multiple turns of the current-carrying wire may be made through the opening. To extend the range to higher currents, a current divider may be used. The divider splits the current across two wires of differing widths and the thinner wire, carrying a smaller proportion of the total current, passes through the sensor.
The principle of increasing the number of windings a conductor takes around the ferrite core is well understood, each turn having the effect of multiplying the current under measurement. Often these additional turns are carried out by a staple on the PCB.
and grounded emitter, meaning that rather than a voltage being produced at the Hall sensor signal output wire, the transistor is turned on providing a circuit to ground through the signal output wire.
enhancements.
s use Hall effect sensors to detect the position of the rotor and feed that information to the motor controller. This allows for more precise motor control
(HET) is a relatively low power device that is used to propel some spacecraft
, once they get into orbit
or farther out into space. In the HET, atoms are ionized and accelerated by an electric field
. A radial magnetic field established by magnets on the thruster is used to trap electrons which then orbit and create an electric field
due to the Hall effect. A large potential is established between the end of the thruster where neutral propellant is fed and the part where electrons are produced, so electrons trapped in the magnetic field cannot fall down the potential, and thus are extremely energetic allowing them to ionize neutral atoms. Neutral propellant is pumped into the chamber and is ionized by the trapped electrons. Then positive ions and electrons are ejected from the thruster as a quasineutral plasma, creating thrust.
effect is a phenomenon involving the Hall effect, but a disc-shaped metal sample is used in place of a rectangular one. Because of its shape the Corbino disc allows the observation of Hall-effect–based magnetoresistance
without the associated Hall voltage.
A radial current through a circular disc, subjected to a magnetic field perpendicular to the plane of the disc, produces a "circular" current through the disc.
The absence of the free transverse boundaries renders the interpretation of the Corbino effect simpler than that of the Hall effect.
General
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
, transverse to an electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
in the conductor and a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
perpendicular to the current. It was discovered by Edwin Hall
Edwin Hall
Edwin Herbert Hall was an American physicist who discovered the "Hall effect". Hall conducted thermoelectric research at Harvard and also wrote numerous physics textbooks and laboratory manuals.- Biography :...
in 1879.
The Hall coefficient is defined as the ratio of the induced electric field to the product of the current density and the applied magnetic field. It is a characteristic of the material from which the conductor is made, since its value depends on the type, number, and properties of the charge
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
carriers that constitute the current.
Discovery
The Hall effect was discovered in 1879 by Edwin Herbert Hall while he was working on his doctoral degree at Johns Hopkins UniversityJohns Hopkins University
The Johns Hopkins University, commonly referred to as Johns Hopkins, JHU, or simply Hopkins, is a private research university based in Baltimore, Maryland, United States...
in Baltimore, Maryland. His measurements of the tiny effect produced in the apparatus he used was an experimental tour de force, accomplished 18 years before the electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
was discovered.
Theory
The Hall effect comes about due to the nature of the current in a conductor. Current consists of the movement of many small charge carrierCharge carrier
In physics, a charge carrier is a free particle carrying an electric charge, especially the particles that carry electric currents in electrical conductors. Examples are electrons and ions...
s, typically electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s, holes
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
, ions (see Electromigration
Electromigration
Electromigration is the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. The effect is important in applications where high direct current densities are used, such as in...
) or all three. When a magnetic field is present that is perpendicular to the direction of motion of moving charges, these charges experience a force, called the Lorentz force
Lorentz force
In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:...
. When such a magnetic field is absent, the charges follow approximately straight, 'line of sight' paths between collisions with impurities, phonons, etc. However, when a perpendicular magnetic field is applied, their paths between collisions are curved so that moving charges accumulate on one face of the material. This leaves equal and opposite charges exposed on the other face, where there is a scarcity of mobile charges. The result is an asymmetric
Asymmetric
Something which is asymmetric displays asymmetry. Specific uses of the term may include:*Asymmetric relation for information on such relations in mathematics and set theory*Asymmetric warfare for information and theories of modern war...
distribution of charge density across the Hall element that is perpendicular to both the 'line of sight' path and the applied magnetic field. The separation of charge establishes an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
that opposes the migration of further charge, so a steady electrical potential builds up for as long as the charge is flowing.
It shall be noted that in the classical
Classical physics
What "classical physics" refers to depends on the context. When discussing special relativity, it refers to the Newtonian physics which preceded relativity, i.e. the branches of physics based on principles developed before the rise of relativity and quantum mechanics...
view, there are only electrons moving in the same average direction both in the case of electron or hole conductivity. This cannot explain the opposite sign of the Hall effect observed. The difference is that electrons in the upper bound of the valence band
Valence band
In solids, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature....
have opposite group velocity
Group velocity
The group velocity of a wave is the velocity with which the overall shape of the wave's amplitudes — known as the modulation or envelope of the wave — propagates through space....
and wave vector
Wave vector
In physics, a wave vector is a vector which helps describe a wave. Like any vector, it has a magnitude and direction, both of which are important: Its magnitude is either the wavenumber or angular wavenumber of the wave , and its direction is ordinarily the direction of wave propagation In...
direction when moving, which can be effectively treated as if positively charged particles (holes) moved in the opposite direction to that of the electrons.
For a simple metal where there is only one type of charge carrier
Charge carrier
In physics, a charge carrier is a free particle carrying an electric charge, especially the particles that carry electric currents in electrical conductors. Examples are electrons and ions...
(electrons) the Hall voltage VH is given by
where I is the current across the plate length, B is the magnetic field, d is the depth (thickness) of the plate, e is the electron charge, and n is the charge carrier density
Charge carrier density
The charge carrier density denotes the number of charge carriers per volume. It is measured in m−3. As any density it can depend on position.It should not be confused with the charge density, which is the number of charges per volume at a given energy....
of the carrier electrons.
The Hall coefficient is defined as
where j is the current density
Current density
Current density is a measure of the density of flow of a conserved charge. Usually the charge is the electric charge, in which case the associated current density is the electric current per unit area of cross section, but the term current density can also be applied to other conserved...
of the carrier electrons, and
is the induced electric field. In SI units, this becomesAs a result, the Hall effect is very useful as a means to measure either the carrier density or the magnetic field.
One very important feature of the Hall effect is that it differentiates between positive charges moving in one direction and negative charges moving in the opposite. The Hall effect offered the first real proof that electric currents in metals are carried by moving electrons, not by protons. The Hall effect also showed that in some substances (especially p-type semiconductor
P-type semiconductor
A P-type semiconductor is obtained by carrying out a process of doping: that is, adding a certain type of atoms to the semiconductor in order to increase the number of free charge carriers ....
s), it is more appropriate to think of the current as positive "holes
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
" moving rather than negative electrons. A common source of confusion with the Hall Effect is that holes moving to the left are really electrons moving to the right, so one expects the same sign of the Hall coefficient for both electrons and holes. This confusion, however, can only be resolved by modern quantum mechanical theory of transport in solids.
It must be noted though that the sample inhomogeneity might result in spurious sign of the Hall effect, even in ideal van der Pauw
Van der Pauw method
The van der Pauw Method is a technique commonly used to measure the Resistivity and the Hall Coefficient of a sample. Its power lies in its ability to accurately measure the properties of a sample of any arbitrary shape, so long as the sample is approximately two-dimensional The van der Pauw...
configuration of electrodes. For example, positive Hall effect was observed in evidently n-type semiconductors.
Hall effect in semiconductors
When a current-carrying semiconductorSemiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
is kept in a magnetic field, the charge carriers of the semiconductor experience a force in a direction perpendicular to both the magnetic field and the current. At equilibrium, a voltage appears at the semiconductor edges.
The simple formula for the Hall coefficient given above becomes more complex in semiconductors where the carriers are generally both electrons and holes
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
which may be present in different concentrations and have different mobilities
Electron mobility
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field. In semiconductors, there is an analogous quantity for holes, called hole mobility...
. For moderate magnetic fields the Hall coefficient is
where
is the electron concentration, the hole concentration, the electron mobility, the hole mobility and the absolute valueAbsolute value
In mathematics, the absolute value |a| of a real number a is the numerical value of a without regard to its sign. So, for example, the absolute value of 3 is 3, and the absolute value of -3 is also 3...
of the electronic charge.
For large applied fields the simpler expression analogous to that for a single carrier type holds.
with
Quantum Hall effect
For a two dimensional electron system which can be produced in a MOSFETMOSFET
The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
. In the presence of large magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
strength and low temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, one can observe the quantum Hall effect, which is the quantization
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
of the Hall voltage.
Spin Hall effect
The spin Hall effect consists in the spin accumulation on the lateral boundaries of a current-carrying sample. No magnetic field is needed. It was predicted by M.I. Dyakonov and V.I. Perel in 1971 and observed experimentally more than 30 years later, both in semiconductors and in metals, at cryogenic as well as at room temperatures.Quantum spin Hall effect
For HgTe two dimensional quantum wells with strong spin-orbit coupling, in zero magnetic field, at low temperature, the Quantum Spin Hall effect has been recently observed.Anomalous Hall effect
In ferromagnetic materials (and paramagnetic materials in a magnetic fieldMagnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
), the Hall resistivity includes an additional contribution, known as the anomalous Hall effect (or the extraordinary Hall effect), which depends directly on the magnetization
Magnetization
In classical electromagnetism, magnetization or magnetic polarization is the vector field that expresses the density of permanent or induced magnetic dipole moments in a magnetic material...
of the material, and is often much larger than the ordinary Hall effect. (Note that this effect is not due to the contribution of the magnetization
Magnetization
In classical electromagnetism, magnetization or magnetic polarization is the vector field that expresses the density of permanent or induced magnetic dipole moments in a magnetic material...
to the total magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
.) Although a well-recognized phenomenon, there is still debate about its origins in the various materials. The anomalous Hall effect can be either an extrinsic (disorder-related) effect due to spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
-dependent scattering
Scattering
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of...
of the charge carrier
Charge carrier
In physics, a charge carrier is a free particle carrying an electric charge, especially the particles that carry electric currents in electrical conductors. Examples are electrons and ions...
s, or an intrinsic effect which can be described in terms of the Berry phase effect in the crystal momentum space (k-space).
Hall effect in ionized gases
(See electrochemical instability)The Hall effect in an ionized gas (plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
) is significantly different from the Hall effect in solids (where the Hall parameter is always very inferior to unity). In a plasma, the Hall parameter can take any value. The Hall parameter, β, in a plasma is the ratio between the electron gyrofrequency, Ωe, and the electron-heavy particle collision frequency, ν:
where
- e is the elementary chargeElementary chargeThe elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...
(approx. 1.6 × 10-19 C) - B is the magnetic field (in teslasTesla (unit)The tesla is the SI derived unit of magnetic field B . One tesla is equal to one weber per square meter, and it was defined in 1960 in honour of the inventor, physicist, and electrical engineer Nikola Tesla...
) - me is the electron mass (approx. 9.1×10-31 kg).
The Hall parameter value increases with the magnetic field strength.
Physically, the trajectories of electrons are curved by the Lorentz force
Lorentz force
In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:...
. Nevertheless when the Hall parameter is low, their motion between two encounters with heavy particles (neutral
Neutral particle
In physics, a neutral particle is a particle with no electric charge. This is not to be confused with a real neutral particle, a neutral particle that is also identical to its own antiparticle.-Stable or long-lived neutral particles:...
or ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
) is almost linear. But if the Hall parameter is high, the electron movements are highly curved. The current density
Current density
Current density is a measure of the density of flow of a conserved charge. Usually the charge is the electric charge, in which case the associated current density is the electric current per unit area of cross section, but the term current density can also be applied to other conserved...
vector, J, is no longer colinear with the electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
vector, E. The two vectors J and E make the Hall angle, θ, which also gives the Hall parameter:
Applications
Hall probes are often used as magnetometerMagnetometer
A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...
s, i.e. to measure magnetic fields, or inspect materials (such as tubing or pipelines) using the principles of magnetic flux leakage
Magnetic flux leakage
Magnetic flux leakage is a magnetic method of nondestructive testing that is used to detect corrosion and pitting in steel structures, most commonly pipelines and storage tanks. The basic principle is that a powerful magnet is used to magnetize the steel. At areas where there is corrosion or...
.
Hall effect devices produce a very low signal level and thus require amplification. While suitable for laboratory instruments, the vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
s available in the first half of the 20th century were too expensive, power consuming, and unreliable for everyday applications. It was only with the development of the low cost integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
that the Hall effect sensor became suitable for mass application. Many devices now sold as Hall effect sensor
Hall effect sensor
A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications....
s in fact contain both the sensor as described above plus a high gain integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
(IC) amplifier in a single package. Recent advances have further added into one package an analog-to-digital converter
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
and I²C
I²C
I²C is a multi-master serial single-ended computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, cellphone, or other electronic device. Since the mid 1990s, several competitors I²C ("i-squared cee" or "i-two cee"; Inter-Integrated Circuit;...
(Inter-integrated circuit communication protocol) IC for direct connection to a microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
's I/O port.
Advantages over other methods
Hall effect devices when appropriately packaged are immune to dust, dirt, mud, and water. These characteristics make Hall effect devices better for position sensing than alternative means such as optical and electromechanical sensing.A sensor voltage is applied across two terminals and the third provides a voltage proportional to the current being sensed. This has several advantages; no additional resistance (a shunt
Shunt (electrical)
In electronics, a shunt is a device which allows electric current to pass around another point in the circuit. The term is also widely used in photovoltaics to describe an unwanted short circuit between the front and back surface contacts of a solar cell, usually caused by wafer damage.-Defective...
, required for the most common current sensing method) need be inserted in the primary circuit. Also, the voltage present on the line to be sensed is not transmitted to the sensor, which enhances the safety of measuring equipment.
Disadvantages compared with other methods
Magnetic flux from the surroundings (such as other wires) may diminish or enhance the field the Hall probe intends to detect, rendering the results inaccurate. Also, as Hall voltage is often on the order of millivolts, the output from this type of sensor cannot be used to directly drive actuators but instead must be amplified by a transistorTransistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
-based circuit.
Contemporary applications
Hall effect sensorHall effect sensor
A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications....
s are readily available from a number of different manufacturers, and may be used in various sensors such as rotating speed sensors (bicycle wheels, gear-teeth, automotive speedometers, electronic ignition systems), fluid flow sensor
Flow sensor
A flow sensor is a device for sensing the rate of fluid flow. Typically a flow sensor is the sensing element used in a flow meter, or flow logger, to record the flow of fluids....
s, current sensor
Current sensor
A current sensor is a device that detects electrical current in a wire, and generates a signal proportional to it.The generated signal could be analog voltage or current or even digital output.It can be then utilized to display the measured current in an ammeter or can be stored for further...
s, and pressure sensor
Pressure sensor
A pressure sensor measures pressure, typically of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the...
s. Common applications are often found where a robust and contactless switch or potentiometer is required. These include: electric airsoft
Airsoft
Airsoft is a sport in which participants shoot round non-metallic pellets launched via replica firearms.Gameplay varies in style and composition but often range from short-term skirmishes, organized scenarios, military simulations, historical reenactments, to competition target shooting events...
guns, triggers of electropneumatic paintball guns, go-cart speed controls, smart phones, and some global positioning systems.
Ferrite toroid Hall effect current transducer
Hall sensors can detect stray magnetic fields easily, including that of Earth, so they work well as electronic compasses: but this also means that such stray fields can hinder accurate measurements of small magnetic fields. To solve this problem, Hall sensors are often integrated with magnetic shielding of some kind. For example, a Hall sensor integrated into a ferrite ring (as shown) can reduce the detection of stray fields by a factor of 100 or better (as the external magnetic fields cancel across the ring, giving no residual magnetic fluxMagnetic flux
Magnetic flux , is a measure of the amount of magnetic B field passing through a given surface . The SI unit of magnetic flux is the weber...
). This configuration also provides an improvement in signal-to-noise ratio and drift effects of over 20 times that of a bare Hall device.
The range of a given feedthrough sensor may be extended upward and downward by appropriate wiring. To extend the range to lower currents, multiple turns of the current-carrying wire may be made through the opening. To extend the range to higher currents, a current divider may be used. The divider splits the current across two wires of differing widths and the thinner wire, carrying a smaller proportion of the total current, passes through the sensor.
The principle of increasing the number of windings a conductor takes around the ferrite core is well understood, each turn having the effect of multiplying the current under measurement. Often these additional turns are carried out by a staple on the PCB.
Split ring clamp-on sensor
A variation on the ring sensor uses a split sensor which is clamped onto the line enabling the device to be used in temporary test equipment. If used in a permanent installation, a split sensor allows the electric current to be tested without dismantling the existing circuit.Analog multiplication
The output is proportional to both the applied magnetic field and the applied sensor voltage. If the magnetic field is applied by a solenoid, the sensor output is proportional to the product of the current through the solenoid and the sensor voltage. As most applications requiring computation are now performed by small (even tiny) digital computers, the remaining useful application is in power sensing, which combines current sensing with voltage sensing in a single Hall effect device.Current sensing
By sensing the current provided to a load and using the device's applied voltage as a sensor voltage it is possible to determine the power dissipated by a device.Position and motion sensing
Hall effect devices used in motion sensing and motion limit switches can offer enhanced reliability in extreme environments. As there are no moving parts involved within the sensor or magnet, typical life expectancy is improved compared to traditional electromechanical switches. Additionally, the sensor and magnet may be encapsulated in an appropriate protective material. This application is used in brushless DC motors.Automotive ignition and fuel injection
Commonly used in distributors for ignition timing (and in some types of crank and camshaft position sensors for injection pulse timing, speed sensing, etc.) the Hall effect sensor is used as a direct replacement for the mechanical breaker points used in earlier automotive applications. Its use as an ignition timing device in various distributor types is as follows. A stationary permanent magnet and semiconductor Hall effect chip are mounted next to each other separated by an air gap, forming the Hall effect sensor. A metal rotor consisting of windows and tabs is mounted to a shaft and arranged so that during shaft rotation, the windows and tabs pass through the air gap between the permanent magnet and semiconductor Hall chip. This effectively shields and exposes the Hall chip to the permanent magnet's field respective to whether a tab or window is passing though the Hall sensor. For ignition timing purposes, the metal rotor will have a number of equal-sized tabs and windows matching the number of engine cylinders. This produces a uniform square wave output since the on/off (shielding and exposure) time is equal. This signal is used by the engine computer or ECU to control ignition timing. Many automotive Hall effect sensors have a built-in internal NPN transistor with an open collectorOpen collector
An open collector is a common type of output found on many integrated circuits . Instead of outputting a signal of a specific voltage or current, the output signal is applied to the base of an internal NPN transistor whose collector is externalized on a pin of the IC. The emitter of the...
and grounded emitter, meaning that rather than a voltage being produced at the Hall sensor signal output wire, the transistor is turned on providing a circuit to ground through the signal output wire.
Wheel rotation sensing
The sensing of wheel rotation is especially useful in anti-lock brake systems. The principles of such systems have been extended and refined to offer more than anti-skid functions, now providing extended vehicle handlingCar handling
Automobile handling and vehicle handling are descriptions of the way wheeled vehicles perform transverse to their direction of motion, particularly during cornering and swerving. It also includes their stability when moving at rest. Handling and braking are the major components of a vehicle's...
enhancements.
Electric motor control
Some types of brushless DC electric motorBrushless DC electric motor
Brushless DC motors also known as electronically commutated motors are electric motors powered by direct-current electricity and having electronic commutation systems, rather than mechanical commutators and brushes...
s use Hall effect sensors to detect the position of the rotor and feed that information to the motor controller. This allows for more precise motor control
Industrial applications
Applications for Hall Effect sensing have also expanded to industrial applications, which now use Hall Effect joysticks to control hydraulic valves, replacing the traditional mechanical levers with contactless sensing. Such applications include; Mining Trucks, Backhoe Loaders, Cranes, Diggers, Scissor Lifts, etc.Spacecraft propulsion
A Hall effect thrusterHall effect thruster
In spacecraft propulsion, a Hall thruster is a type of ion thruster in which the propellant is accelerated by an electric field. Hall thrusters trap electrons in a magnetic field and then use the electrons to ionize propellant, efficiently accelerate the ions to produce thrust, and neutralize the...
(HET) is a relatively low power device that is used to propel some spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
, once they get into orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
or farther out into space. In the HET, atoms are ionized and accelerated by an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
. A radial magnetic field established by magnets on the thruster is used to trap electrons which then orbit and create an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
due to the Hall effect. A large potential is established between the end of the thruster where neutral propellant is fed and the part where electrons are produced, so electrons trapped in the magnetic field cannot fall down the potential, and thus are extremely energetic allowing them to ionize neutral atoms. Neutral propellant is pumped into the chamber and is ionized by the trapped electrons. Then positive ions and electrons are ejected from the thruster as a quasineutral plasma, creating thrust.
The Corbino effect
The CorbinoOrso Mario Corbino
Orso Mario Corbino was an Italian physicist and politician. He served as the minister for education in 1921 and as the minister for economy in 1921. He also served as professor in Messina and in Rome...
effect is a phenomenon involving the Hall effect, but a disc-shaped metal sample is used in place of a rectangular one. Because of its shape the Corbino disc allows the observation of Hall-effect–based magnetoresistance
Magnetoresistance
Magnetoresistance is the property of a material to change the value of its electrical resistance when an external magnetic field is applied to it. The effect was first discovered by William Thomson in 1856, but he was unable to lower the electrical resistance of anything by more than 5%. This...
without the associated Hall voltage.
A radial current through a circular disc, subjected to a magnetic field perpendicular to the plane of the disc, produces a "circular" current through the disc.
The absence of the free transverse boundaries renders the interpretation of the Corbino effect simpler than that of the Hall effect.
See also
- CapacitorCapacitorA capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
- Eddy currents
- Elementary chargeElementary chargeThe elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...
- Eric FawcettEric FawcettEric Fawcett , was a professor of physics at the University of Toronto for 23 years. He also co-founded Science for Peace.- Academic and Professional Life :...
- Hall effect sensorHall effect sensorA Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications....
- Hall effect thrusterHall effect thrusterIn spacecraft propulsion, a Hall thruster is a type of ion thruster in which the propellant is accelerated by an electric field. Hall thrusters trap electrons in a magnetic field and then use the electrons to ionize propellant, efficiently accelerate the ions to produce thrust, and neutralize the...
- Hall probe
- Nernst effectNernst effectIn physics and chemistry, the Nernst Effect is a thermoelectric phenomenon observed when a sample allowing electrical conduction is subjected to a magnetic field and a temperature gradient normal...
- Nernst-Ettinghausen effect
- Quantum Hall effect
- Spin Hall effect
- Thermal Hall effectThermal Hall effectThe thermal Hall effect is the thermal analog of the Hall effect. Here, a thermal gradient is produced across a solid instead of an electric field. When a magnetic field is applied, an orthogonal temperature gradient develops....
- Senftleben-Beenakker effectSenftleben-Beenakker effectThe Senftleben-Beenakker effect is the dependence on a magnetic or electric field of transport properties of polyatomic gases. The effect is caused by the precession of the dipole of the gas molecules between collisions...
- TransducerTransducerA transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...
- Van der Pauw methodVan der Pauw methodThe van der Pauw Method is a technique commonly used to measure the Resistivity and the Hall Coefficient of a sample. Its power lies in its ability to accurately measure the properties of a sample of any arbitrary shape, so long as the sample is approximately two-dimensional The van der Pauw...
- Coulomb potential between two current loops embedded in a magnetic field
Further reading
- Classical Hall effect in scanning gate experiments: A. Baumgartner et al., Phys. Rev. B 74, 165426 (2006),
External links
Patents, P. H. Craig, System and apparatus employing the Hall effectGeneral
- Interactive Java tutorial on the Hall Effect National High Magnetic Field Laboratory
- Science World (wolfram.com) article.
- "The Hall Effect". nist.gov.
- Hall, Edwin, "On a New Action of the Magnet on Electric Currents". American Journal of Mathematics vol 2 1879.
- Spin Hall Effect Detected at Room Temperature
- Hall Effect Sensing and Application. Honeywell documentation on hall effect sensing, interfacing and applications.
- Table with Hall coefficients of different elements at room temparature.