Frequency Modulated MEMS Lorentz Force Magnetometer Using CW/CCW Modes

This paper reports a fully differential frequency modulated (FM) Lorentz force MEMS magnetometer using superposed clockwise (CW) and counter clockwise (CCW) modes of a 2-axis degenerated resonator. The Lorentz force generated by sensing currents synchronous to the oscillation modulate the resonant frequencies. Sensing currents correspond to CW mode and CCW mode have the same amplitudes but opposite directions, thus the frequency difference could be generated by the applied magnetic field. The common-mode shift of frequency caused by temperature could be removed by this method. The principle of operation was demonstrated by the numerical simulation. The sensitivity of the frequency to the applied magnetic field estimated by the simulation was 55.2 Hz/T. The MEMS device was fabricated and the sensitivity of the magnetometer was experimentally evaluated by using frequency modulation mode. The experimental sensitivity of magnetometer was 63.46 Hz/T, which was close to the result of simulation.