The deflection of the carriers of charge in a conductor, caused by an externally applied magnetic field; described in 1879 by US physicist Edwin Hall (18551938). A potential difference forms at right angles to both current and field. It may be used to demonstrate the difference in the nature of the charge carriers in metals and semiconductors.
The Hall effect refers to the potential difference (Hall voltage) on opposite sides of a thin sheet of conducting or semiconducting material in the form of a 'Hall bar' (or a van der Pauw element) through which an electric current is flowing, created by a magnetic field applied perpendicular to the Hall element.
Explanation
The Hall effect comes about due to the nature of the current flow in the conductor. The result is an asymmetric distribution of charge density across the hall element perpendicular to the 'line of sight' path the electrons would take in the absence of 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 semiconductors), it is more appropriate to think of the current as positive "holes" moving rather than negative electrons.
By measuring the Hall voltage across the element, one can determine the strength of the magnetic field applied. This can be expressed as
where VH is the voltage across the width of the plate, I is the current across the plate length, B is the magnetic flux density, d is the depth of the plate, e is the electron charge, and n is the bulk density of the carrier electrons.
So-called "Hall effect sensors" are readily available from a number of different manufacturers, and may be used in various sensors such as fluid flow sensors, power sensors, and pressure sensors.
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 resistance.
In ferromagnetic materials (and paramagnetic materials in a magnetic field), 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. The anomalous Hall effect can be either an extrinsic (disorder-related) effect due to spin-dependent scattering of the charge carriers, or an intrinsic effect which can be described in terms of the Berry phase effect in the crystal momentum space (k-space).
Applications
Hall effect devices produce a very low signal level and thus require amplification. 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 sensors" are in fact a device containing both the sensor described above and a high gain integrated circuit (IC) amplifier in a single package. Recent advances have resulted in the addition of ADC (Analog to Digital) converters and I2C (Inter-integrated circuit communication protocol) IC for direct connection to a microcontroller's I/O port being integrated into a single package, see Advanced Hall Effect Current Transducer. Reed switch electrical motors using the hall effect IC is another application.
Hall probes are used to measure magnetic fields, and make use of the Hall effect.
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.
Ferrite toroid Hall effect current transducer
Hall sensors can easily detect stray magnetic fields, including that of Earth, so they work well as electronic compasses. 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 stray fields by a factor of 100 or better. 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 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.
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.
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 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.
Power 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.
Automotive ignition and fuel injection
If the magnetic field is provided by a rotating magnet resembling a toothed gear, an output pulse will be generated each time a tooth passes the sensor.
Solar Car energy management
Accurate and efficient management of all aspects of energy is a critical aspect of any successful solar car - Hall effect current transducers are an ideal solution due to their high accuracy, environmental hardiness and low power consumption.
The Corbino effect
The Corbino effect is a phenomenon similar to the Hall effect, but a disk-shaped metal sample is used in place of a rectangular one.
User Comments Add a comment…