The angle and position sensors based on Giant Magnetoresistance (GMR) Effect are widely served to CNC machines, vehicle speed measurement, non-contacting switch and rotary encoder. GMR sensor has low power and volume, meanwhile, reliability and output signal is relatively high.
What is Giant Magnetoresistance (GMR) Effect?
Magnetoresistance Effect refer to the resistance change of conductor and semi-conductor under the magnetic field, therefore, the magnetoresitance value over 10 times higher than magnetic metal’s, and this phenomenon is called Giant Magnetoresistance (GMR) Effect. The Giant Magnetoresistance (GMR) Effect was discovered by both Peter Grünberg and Albert Fert in 1988, and thus they won the Nobel Prize for their discovery on 2007.
One of the magnetic layers is regarded as the reference layer which has fixed magnetization direction, and another one is called free layer that magnetization direction changes with the direction of the external parallel magnetic field. The spacer between free layer and the reference layer is made from non-magnetic thin film. The giant magnetoresistance value is determined by the included angle of two layer’s magnetization direction. The lowest value will be got when magnetization direction of the free layer and the reference layer are same, and opposite direction will obtain the highest giant magnetoresistance value.
About GMR Sensor Magnet
It should be noted that the GMR sensor and Hall Effect sensor detect horizontal magnetic field and vertical magnetic field against magnet location respectively. The operation of GMR sensor has certain requirements regard to the magnetic field strength, therefore, GMR sensor magnet should provide strong enough magnetic field strength in designated air gap. Either too large or too weak field strength will enhance additionally angle deviation. Low field strength cannot drive magnetization direction of free layer align with external magnetic fields, and too powerful field strength will influence the magnetization direction of the reference layer. SDM has also collected much experience in GMR sensor magnet, and SDM will provide detailed technical solution according to air gap, temperature range and stability requirements.
