Mechanical design of a novel MEMS resonant sensor for monitoring in-plane magnetic fields

We present the mechanical design of a novel MEMS-based magnetic field sensor with optical sensing for monitoring in-plane magnetic fields. It has a diamond-shaped resonator composed by four polysilicon beams (198 × 12 × 2.25 µm), an aluminum loop (957 × 8 × 0.7 µm) and two mirrors (31 × 32 × 0.7 µm), which are designed considering the Sandia Ultra-planar Multi-level MEMS Technology process. The sensor exploits Lorentz force to detect different components of in-plane magnetic fields, which are related with the mirrors displacements. Analytical models are developed to predict the damping, resonant frequency, and mirrors displacements caused by temperature shifts. In addition, Castigliano’s second theorem is used to obtain an analytical model of the mirrors displacements at resonance as a function of in-plane magnetic fields with inclination angles from 0 to 360° and electrical currents. The results of the analytical models agree well with those determined by finite element method models. The sensor operates at resonant frequency of 33.6 kHz, a quality factor of 98, a power consumption of 259 mW and a sensitivity of 259 nm·mT⁻¹. This sensor design could have potential applications in non-destructive testing of ferromagnetic materials.