Effects of flux concentrators on the low frequency noise in magnetoresistive sensing devices

摘要

Flux concentrators (FCs) are used to increase the response of a magnetoresistive sensing element to small magnetic fields [1]. Another application of FCs is to modulate the incoming signal and thus shift the operating frequency of the sensor [2]. This can be accomplished by placing FCs on MEMS structures that oscillate at kHz frequencies. The oscillation frequency is set high enough in order to mitigate certain types of 1/f noise that are ubiquitous among magnetic sensors. Depending upon the sensor, shifting the frequency reduces the sensor's 1/f noise by one to three orders of magnitude at 1Hz. An important consideration is whether the FCs introduce magnetic noise. To address this, we compare results for the cases of bare (without FCs) sensors and those with FCs. We show that FCs can be a source of broad-band low frequency noise when the signal modulation amplitudes are sufficiently high.