What is the Hall Effect? Where are Hall Effect Sensors Used?
American physicist Edwin Herbert Hall first described an unusual physical phenomenon in 1879 during an experiment passing a magnetic flux through a thin gold plate. This phenomenon was later named after him.
The Hall Effect is the occurrence of a potential difference across the edges of a conductor placed in a transverse magnetic field when a current is passed perpendicular to the field.
Physical Explanation
When a plate—conductor or semiconductor—is placed in a magnetic field at 90° to the direction of the magnetic flux lines, electrons will move across the plate under the influence of the Lorentz force*.
The direction of the electrons depends on the direction of the current and the magnetic flux lines. In other words, the Hall effect (HE) is a particular case of the Lorentz force, meaning the action of a magnetic field on a charged particle.
In this case, electrons deviate perpendicularly to their movement, causing an excess of electrons on one side of the deviation and a corresponding deficiency on the opposite side.
This charge separation can be compared to the charge separation in a capacitor. Since the positively and negatively charged sides are now opposite each other, an electric field is created. This electric field exerts a force on the electrons opposite to the Lorentz force. If these two forces compensate each other to the same degree, the charge separation intensification stops.
As with a capacitor, the voltage can be tapped off here. This electric voltage is called Hall voltage, which increases linearly with the magnetic field and is inversely proportional to the charge carrier density. This is explained by the fact that a constant current force with fewer charge carriers can only be achieved by increasing the velocity of individual carriers. A stronger Lorentz force acts on faster charge carriers, increasing the Hall voltage.
This effect is called the ordinary Hall effect since there are other phenomena based on the interaction of a conductor, current, and magnetic field.
*Hendrik Lorentz proved that electromagnetic induction interacts with charged particles. These interactions lead to the occurrence of the Lorentz force. This force occurs under the influence of magnetic induction. It is perpendicular to the velocity vector of the moving particle. A necessary condition for the occurrence of this force is the movement of the electric charge.
Applications of the Hall Effect
The most important application of HE is determining the concentration of charge carriers in materials that conduct electricity, particularly semiconductors, whose carrier concentration can be arbitrarily changed, for example, by introducing impurities.
Devices based on HE can have valuable and even unique properties and play an important role in measuring equipment, automation, and radio technology.
With a constant current magnitude, the Hall EMF is directly proportional to the magnetic induction. The linear dependence of these values for Hall sensors (HS) is an advantage over induction-based magnetoresistive meters. HS also allows measuring the electrical and magnetic characteristics of metals and semiconductors.
In semiconductor material production, HE is used to measure the mobility and concentration of carriers. For this purpose, the Hall EMF is measured on a specially prepared sample, and its magnitude is used to assess the mobility and concentration of charge carriers in the material.
Today, due to their high accuracy and data consistency, HS are widely used in various branches of science and technology. They can be used to measure force, pressure, angles, displacements, and other non-electrical quantities.
Advantages of Hall Sensors
Hall sensors measure the magnitude of the magnetic field – this is one of the most widely used types of magnetic transducers.
Hall Effect Method is a method of magnetic non-destructive testing based on recording the magnetic fields of the test object by Hall transducers.
The main advantages of HS are contactlessness, the absence of mechanical stress and contamination, low cost, reliability, and the ability to withstand harsh environmental conditions.
HS safety is achieved through electrical insulation. Sensors are made from materials like germanium and silicon. They are doped with arsenic or phosphorus antimony.
The material must have high carrier mobility. To achieve the greatest effect, the substance should not have high electrical conductivity. These devices' advantage is their low dependence on temperature changes.
Practical Application
Hall sensors are ideal for creating systems that control the rotation frequency of anything, from fans to motors in machinery.
They are used in servo motors (measuring the rotation angle of the motor shaft); in creating contactless unipolar and bipolar switches; they are installed in car starters, PC cooling systems, drives, and computer equipment ventilation systems.
