Contactless potentiometer based on giant magnetoresistance sensors

We present a magnetic sensor based on the giant magnetoresistance (GMR) effect, which can be used as a contactless potentiometer. The sensor consists of a novel GMR sensor scheme with an artificial antiferromagnetic subsystem. The sensor gives a sinusoidal signal in dependence on the direction of a rotating external magnetic field H-rot. With two sensors in a planar setup, the whole 360 degrees angle range can easily be covered. The amplitude Delta R/R of the signal is about 5%. The signal amplitude runs through a very flat maximum and changes only by 5% within a field range of about 4.4-27.2 kA/m. This large field range, the magnetic window (H-w), is the main advantage of this sensor compared to other magnetic sensor physical principles for contactless potentiometers. Therefore, large mounting tolerances and variations in the field strength of the rotating permanent magnet can be accepted. The temperature dependence of the sensor is linear both for the ground resistance (R-0) and the signal amplitude (Delta R), allowing simple and effective electronic temperature compensation. The sensor can be operated up to 150 degrees C. (C) 1997 American Institute of Physics.