High-resolution micro-fluxgate sensing elements using closely coupled coil structures

This paper describes high-resolution micro-fluxgate magnetic sensing elements using magnetic thin films and closely coupled excitation and pick-up coils based on a solenoid-shaped coil structure. In order to improve the sensitivity of the sensing element, the optimal coupling structure between excitation and pick-up coils, and the formation method of permalloy magnetic films are investigated. The closely coupled coil structure allows the magnetic core to be excited in an optimal condition with reduced excitation current. The addition of indium to the permalloy plating bath greatly reduces the degradation of the magnetic core due to the thermal treatment process. The sensitivity of the fabricated sensing element is measured to be 2700 V T-1 at an excitation frequency of 3 Ml-Iz. The noise level, or resolution, in d.c. to 10 Hz bandwidth is measured to br about 40 nT(p-p).