Sensors based on bulk soft magnetic materials: Advances and challenges

Sensors with cores, yokes or field concentrators made of bulk magnetic material are more sensitive and stable than thin-film sensors. Non-linearity and temperature dependence of sensitivity is often suppressed by a feedback. The common problem of these sensors is remanence, cross-field sensitivity and temperature stability of offset. The long-time effort to miniaturize the fluxgates led only to a few practical designs. For flat sensors (either pcb or CMOS) the core etched from amorphous tape gives better properties then electrodeposited or sputtered core. We compare traditional miniature fluxgates using wire cores based on longitudinal fluxgate effect with sensors using transverse fluxgate effect and GMI effect. Well-designed field concentrators or yokes can improve the parameters of any magnetic sensor. The achievable stable amplification factor is 10–100. Having a means to demagnetize the field concentrator is desirable. Overview of magnetic sensors for mechanical quantities is also given with special focus on torque sensors.