Glossary: ​​Magnetic sensor

A sensor that detects the approach, movement, or rotation of an object by placing a small magnet on the moving object and capturing the magnetic field strength and changes. Currently, it is mainly used in portable products. In particular, in foldable mobile phones, it is often used to detect the opening and closing of the mobile phone when it is closed to automatically cut off the power supply of the LCD panel backlight . Recently, the sensor is expanding to notebook computer panels, refrigerator door opening and closing detection, air conditioner fan blade control, automobile tire pressure detection, pedal and gearbox position detection, etc. Magnetic sensors use the principle that the output voltage changes with the change of magnetic flux density. The magnetic sensors currently in production can be roughly divided into two types. One is to use Hall elements to generate electromotive force through the Hall effect of the interaction between magnetic field and current. The other is to use various magnetoresistive (MR: magnetoresistive) elements whose resistance changes with the magnetic field strength to form a Wheatstone bridge.

The output voltage characteristics of the two sensor elements in response to changes in the magnetic field are different. Magnetic sensors using Hall elements use the interaction between current and magnetic field to apply Lorentz force to the current, turning it into an electromotive force V (Figure (a)). In MR sensors, the resistance of the magnetoresistive element changes with the presence of a magnetic field, causing the output voltage V of the bridge to change (Figure (b)). For sensors using Hall elements, when the polarity of the magnetic flux density B is reversed, the output voltage V will also reverse. In addition, the sensitivity range of B is large. The output of the MR sensor does not change when the polarity of B is reversed, and the sensitivity range is small.

In addition, the "magnetoresistive (MI) method" using amorphous wire and the "flux gate method" that detects induced current by introducing magnetic flux into the coil are also used, but there are few precedents for mass production in the field of magnetic sensors.