Alternating current-excited magnetoresistive sensor

Abstract

Thin-film anisotropic magnetoresistors are superior to semiconductor magnetic field sensors. ac excitation of the sensor bridge reduced the noise level to 10 nT p-p. The offset reduction and sensor characteristic stabilization was achieved by periodical flipping by means of 100 mA/100 μs current pulses into a 400 turns coil wound across the sensor perpendicular to the sensitive axis. The use of the flipping mechanism can significantly improve the performance of the permalloy anisotropic magnetoresistors: long-term offset stability of 10 nT, hysteresis below 100 ppm FS and 5 nT p-p noise can be achieved with low-power sensor electronic circuits. The array of eight magnetoresistors was used in a contactless dc current meter. A sensitivity of 0.1 mA and high geometrical selectivity was obtained.