Oscillatory Airflow Sensing Employing MEMS Weakly Coupled Resonators

This paper, for the first time, investigates the oscillatory airflow sensing application of weakly coupled resonators (WCRs) based on a mode-localized flow sensor. The kinetics of WCRs with input harmonic stiffness perturbation is analyzed. The amplitude ratios of WCRs at resonance are theoretically proven to be sinusoidal, and the amplitude magnitude is proportional to the amplitude of input harmonic stiffness perturbation. A closed-loop drive circuit based on the phase-locked loop (PLL) is utilized to track the natural frequency of WCRs rapidly, and an open-loop sense circuit based on coherent demodulation is proposed to extract the magnitude of amplitude ratios accurately. The system-level circuit simulation is implemented to optimize the control parameters. The experiment results demonstrate that the fabricated mode-localized flow sensor prototype has a mechanical sensitivity of 1.497 x 10(-2)/(mm/s) and a detection threshold of 1.868 mm/s. The evaluated resolution is 0.5096 (mm/s)/Hz(1/2,) and the measured bias instability is 52.458 mm/s, which represent the background noises in a short time span and long time span, respectively. This work validates that the mode localization phenomenon can be utilized to measure the oscillatory airflow with an effective signal demodulation method.