Characterization of Vibration Sensitivity of One-Port and Two-Port MEMS Microphones

Micro-electromechanical system (MEMS) microphones (mics) with two ports are receiving considerable interest in both industry and academia, with the prospect of achieving higher directional sensitivity than their one port counterpart. However, two-port mics measures the pressure differences that exists inside the soundwave itself to record sound, which is fundamentally smaller than the absolute pressure measured in typical one-port mics. This typically commands the use of softer sensing element that are potentially more prone to interference from external vibrations. This work derives a universal expression for microphone sensitivity to vibration and validates it experimentally for two emerging two-port mics. We find that the acoustically-referred vibration sensitivity of two-port MEMS mics, in unit of measured acoustic pressure per external acceleration (i.e., Pascals per g), does not depend on the sensing element stiffness nor on its natural frequency. The vibration sensitivity of two-port MEMS mics is also shown to be inversely proportional to frequency as opposed to the frequency independent behavior observed in one-port MEMS mics.