Lorentz Force Frequency Modulated MEMS Magnetometer Using CW/CCW Mode Separator on Quad Mass Resonator

Abstract

This paper reports a Lorentz force frequency modulated (FM) MEMS magnetometer using superposed clockwise (CW) and counter clockwise (CCW) modes on a degenerated quad mass resonator. Sensing currents synchronous to the oscillation generate Lorentz forces which modify the modal stiffnesses, eventually resonant frequencies. Sensing currents correspond to both modes have the same amplitudes but opposite directions, thus the frequencies of CW and CCW modes could be shifted in the opposite direction by the applied magnetic field. In this paper, the principle of magnetometer was introduced using theoretical model. The whole system including the MEMS resonator, CW/CCW mode separators, feedback controllers were modelled and numerically simulated. The degenerated CW and CCW modes could be successfully separated and independently controlled. The frequencies of these modes were modulated by the magnetic field as predicted by the theory. The estimated sensitivity was 4.91Hz/mT. The MEMS resonator for the proposed system was designed, fabricated and the basic functions of transducers in the device were evaluated. Both the electrostatic and electromagnetic transducers worked as designed. The resonant frequency was 8.1kHz and the Q factor was 26,000.