What Is a Magnetic Field Sensor?
A magnetic field sensor is a sensor that detects the earth’s magnetism (geomagnetism).
There are two types: a 2-axis type that can detect the XY axis and a 3-axis type that can detect the XYZ axis. The 2-axis type can be used on flat terrain, but the 3-axis type cannot accurately detect the geomagnetic field unless it is used on a slope.
Uses of Magnetic Field Sensors
Magnetic field sensors are used to detect direction. They are used as electronic compasses in GPS devices for mountain climbing and are also used in smartphones and car navigation systems to measure the orientation of the device on a map.
The 2-axis type is used in automobiles to detect the XY axis, while the 3-axis type, which can detect the XYZ axis, should be used in aircraft and other vehicles capable of three-dimensional motion such as pitch and yaw.
Principle of Magnetic Field Sensors
A magnetic field sensor measures the magnetic force in the X-axis, Y-axis, and in the case of a 3-axis sensor, in the direction of the Z-axis, and calculates the azimuth.
There are three types of magnetic field sensors: Hall sensors, MR (Magneto Resistance) sensors, and MI (Magneto Impedance) sensors are the most common types of magnetic field sensors. The principle of each type of sensor is explained below.
1. Hall Sensor
The magnetic flux, which is the perpendicular component of the magnetic field, gives an electromotive force to the Hall element, which is then sensed as geomagnetism. The Hall effect is used to measure the magnetic flux density, and after passing through an amplification circuit, the sensor outputs a voltage proportional to the magnetic flux density. It is characterized by its ease of use.
2. MR Sensor
In MR sensors, the magnetic flux, which is the horizontal component of the magnetic field, ohms the MR element, which is then sensed as the geomagnetic field. It differs from a Hall sensor in that it measures the magnitude of the geomagnetic field by utilizing the change in the electrical resistance of the MR element caused by the magnetic field.
Because of its higher sensitivity and lower power consumption compared to Hall sensors, it is used more frequently and is often used for geomagnetic sensing applications such as electronic compasses, motor rotation, and position sensing applications.
3. MI Sensor
MI sensors use wires made of a special material called amorphous wire, which does not have a crystalline state. When a pulse current is applied to the amorphous wire in the presence of geomagnetic field, the MI effect is generated and the geomagnetic field is detected using the change in magnetic impedance. The MI effect is more than 10,000 times more sensitive than a Hall sensor, so even minute changes in the geomagnetic field can be measured with high accuracy.
The MI effect is a phenomenon in which the impedance of a magnetic material changes with high sensitivity in an external magnetic field when a high-frequency current that causes a skin effect is applied to the magnetic material.
The skin effect refers to the effect that when a high-frequency current flows through a conductor, the current density increases near the surface of the conductor and decreases as it moves toward the interior.
Other Information on Magnetic Field Sensors
1. Hall Element
A Hall element is a magnetic sensor that uses the Hall effect. The Hall effect is a phenomenon in which an electromotive force is generated in a direction perpendicular to the current and the magnetic field when a magnetic field is applied perpendicular to the electrons flowing through a material.
The charged particles that carry the current are subjected to the Lorentz force under the influence of the magnetic field, which causes a bias in the charge within the material. At this time, a potential difference is generated within the material, resulting in an electromotive force.
2. MR Sensor Element
MR sensor elements are magnetic sensor elements that utilize the magnetoresistive effect (MR effect), a phenomenon in which the resistance value changes when the magnetic field is changed.
Electrons have two spin states called up-spin and down-spin. As electrons move through a ferromagnetic material, the scattering probability within the magnetized material fluctuates when the spin state of the electrons changes up or down. This is what causes the MR effect.