A Full-Band Piezoelectric MEMS Microphone with a Single Diaphragm

This work presents a piezoelectric microphone with a single diaphragm to detect both infrasonic ($0.2-50 \text{Hz}$) and audible ($20 \text{Hz}-10 \text{kHz}$) frequency regimes with a dual sensing scheme (resonant and non-resonant output). The proposed methodology offers a universal solution to low-frequency attenuation in high-performance piezoelectric microphones, which is often caused by slit design and packaging constraints. For infrasound detection, the membrane is actuated piezoelectrically at its resonant frequency by a closed-loop frequency-tracking system, which provides frequency ($0.12 \text{Hz} / \text{Pa}$) and amplitude ($893.94 \text{nV} / \text{Pa}$) outputs modulated by the infrasound inputs. For the audio band, the membrane is not actuated and demonstrates a baseline sensitivity of -45.14 dB (re$1 \mathrm{V} / \text{Pa}$) and an SNR of 65.28 dB at 1 kHz. The proposed technique enables piezoelectric MEMS microphones to enhance their ultralow-frequency detection without modifying their structure or compromising audio-band performance. That renders considerable potential for multiplexed-division full-bandwidth acoustic systems.