Crossfield response of industrial magnetic sensors

Abstract

Magnetic sensors used for non-destructive testing, metal detection and other applications are subjected to large perpendicular field. In this paper we show that the existing models describing the response of anisotropic magnetoresistors (AMR) cannot be used for fields larger than the critical value, which is 350 μT for the Honeywell HMC1001. This critical value is one order of magnitude lower than the anisotropy field and it is decreasing with increased value of the measured field. From our findings it is clear that AMR sensors cannot be safely used in applications in which fields above 250 μT can appear. Neither flipping, nor feedback compensation can compensate for this error. We show that this behaviour is caused by the fact that the single-domain state of the AMR is broken at the mentioned critical field. Compared to that, fluxgate sensors including microfluxgates are by principle immune against the crossfield. Unlike in AMR, crossfield sensitivity in fluxgate sensors is second-order effect, which can be kept under control by proper design. We show that even crossfield of 10 mT does not cause significant degradation of the sensor precision.