An alternative capacitive transducer design for sensitivity enhancement in MEMS Lorentz force magnetometers

The magnetometer is an essential component in a number of scientific and technical disciplines, including instrumentation and space navigation. To detect magnetic fields, a traditional Lorentz force capacitive magnetometer utilizes transverse, parallel-plate combs. Due to the substantial squeeze-film damping effects, increasing the number of comb fingers reduces the quality factor, and hence does not increase the device's sensitivity, thus restricting applications. To address this shortcoming, we propose a longitudinal comb transducer design for space navigation. Its structure consists of a proof mass and beams, acting as driving elements, and two pairs of longitudinal combs, acting as electrostatic sensing elements. The magnetic field is measured by using the displacement that the Lorentz force induces on the current-carrying beams. Differential capacitance is utilized to transduce the displacement into the electrical domain. The resulting MEMS magnetometer has been fabricated using a low-cost MEMS process. A test bed was set under near-vacuum conditions to measure the static capacitance and resonant frequency of the sensing element. The static capacitance was found to be 1.27 pF, while measurements at the resonance frequency of 35.4 kHz show a high quality factor of 200 and consequently a high sensitivity. The resolution is estimated to be 295 nT/ root Hzp. With the exception of slight differences, these results were in accordance with the simulation.