Design and implementation of dual pressure variation chambers for bone conduction microphone

Abstract

This study presents a bone conduction microphone (BCM) to detect the variation of air pressure resulted from the skull vibration. The presented BCM consists of a commercial MEMS microphone, the sensing circuits, the bulk metal, the deformable polymer diaphragm, and two printed circuit board (PCB) covers. In this design, two chambers and a vibrating spring-mass structure are hermetic sealed by two PCB covers. As the spring-mass structure vibrates, the pressure of one chamber will increase and that of another will decrease. Thus, the vibration could introduce a higher pressure load as well as a larger sensing signal for the BCM. In application, the device with the dimensions of 3.5 × 2.65 × 1.48 mm3 is implemented. Measurements show the device has a sensitivity of −38.8 dBV, THD < 0.48% at 1 kHz with 1 g excitation, and ±5 dB bandwidth for 100 Hz∼6.7 kHz. Frequency responses of different samples show good repeatability. Furthermore, air leakage effect and crosstalk of the skull vibration sensing module have also been investigated in this paper. The results demonstrate the feasibility of the presented BCM.