Microphone vibration sensitivity

Conventional MEMS microphones are typically designed to respond to acoustic pressure fields; however, they can also produce unintentional output when subjected to external mechanical vibrations. The design of conventional MEMS microphones relies on a small, lightweight diaphragm that readily moves in response to airborne sound waves. But the mechanical vibrations conducted through structural contacts will also cause changes in capacitance between the diaphragm and the fixed backplate. In fact, the primary source of intrinsic vibration sensitivity in a MEMS microphone is the mass of its diaphragm.

Over the years, there have been efforts to enhance the Signal-to-Noise Ratio (SNR) and Acoustic Overload Point (AOP) of conventional MEMS microphones. The design has evolved from single diaphragm/single backplate architecture to single diaphragm/dual backplate architecture and/or dual diaphragm/single backplate architecture. This evolution has led to improvements in SNR, from 65 dB for single diaphragm/single backplate architecture to 70 dB for single diaphragm/dual backplate architecture and even 73 dB for dual diaphragm architecture. Similarly, AOP has improved from 130 dB to 135 dB, and in some cases, up to 140 dB.

Our studies, however, indicate that conventional MEMS microphones with a single diaphragm/dual backplate architecture are more sensitive to vibrations than those with a single diaphragm/single backplate architecture. There is essentially no difference in Effective SNR between a 65 dB SNR single diaphragm/single backplate architecture MEMS microphone and a 70 dB SNR single diaphragm/dual backplate architecture MEMS microphone.

The vibration-resistant MEMS microphone utilizes a dual-differential mechanism to mitigate the effects of vibration on microphone sensing, making it insensitive to mechanical vibrations. Its Effective SNR is typically 10 to 15 dB better than that of conventional MEMS microphones. Additionally, its Effective AOP remains consistent with its nominal AOP measured in an anechoic chamber. Conversely, the Effective AOP of conventional MEMS microphones may deviate by 20 to 30 dB from the nominal AOP due to their sensitivity to vibrations.