Improved magnetic sensor using laminated magnetic multilayer with coupled exciting and sensing micro planar coils

Abstract

To improve the magnetic field sensitivity of giant magnetoimpedance (GMI) sensor at the low frequency, the authors reported a laminated magnetic multilayer with coupled exciting and sensing planar coils (i.e., FCseCexCseFCseCexCseF), which consists of two serially connected sandwich structures (i.e., FeNiCoSiB/sensing planar coil + exciting planar coil + sensing planar coil/FeNiCoSiB). Different from the previous FCexFCexF (i.e., FeNiCoSiB/exciting planar coil/FeNiCoSiB/exciting planar coil/FeNiCoSiB) multilayer and FCexF (i.e., FeNiCoSiB/exciting planar coil/FeNiCoSiB) sandwich laminates with only exciting coils, the investigated magnetic sensor uses the strong electromagnetic coupling between sensing coil and exciting coil, and the mutual inductance induced output voltage gets rid of the small resistance variation effect (caused by weak skin effect) at low frequency and also increases the ratio of additional inductance contributed by the magnetic ribbons to that by naked coils. The investigated magnetic sensor provides the magnetic field sensitivity of 188.6 mV/Oe at 1 MHz frequency, which is about 2.97 and 4.50 times as high as that for FCexFCexF and FCexF laminates, respectively. The investigated prototype also shows magnetic noise of 82.2 pT/Hz, which is 15% and 19% of noises for the FCexFCexF and conventional FCexF laminates at 1 MHz, respectively.