Orthogonal micro-fluxgate with S-shape excitation wire and 3D solenoid detection coil

A novel orthogonal micro-fluxgate fabricated by a simple and inexpensive process is described in this paper. The sensor consists of an S-shape excitation wire surrounded by an electroplated Permalloy layer and a 3D micro-solenoid. The problem of low sensitivity, low input resistance and high noise of orthogonal micro-fluxgate were solved with the proposed structure. Standard Micro-Electro-Mechanic System (MEMS) technology is adopted for the micro-fabrication procedure. In particular, we fabricated the sensors with electroplating and wet etching, which contributes to the low-cost fabrication process. A simple testing system was established to characterize the orthogonal micro-fluxgate and second harmonic operation principle was utilized in this process. The sensitivity of the developed sensor was 660.8 V/T in the linear range of ±150 μT with operational frequency of 750 kHz and excitation current of 80 mA-rms. The measured magnetic noise spectrum density was 4.1 nT/√Hz at 1 Hz and the noise rms level was 7.28 nT in the frequency range of 250 mHz to 10 Hz.