Bioinspired flow-sensing capacitive microphone

Abstract

Inspired by the auditory systems of small animals, such as spiders, the tachinid fly, Ormia ochracea, and mosquitoes, a novel low-noise, flow-sensing capacitive MEMS microphone capable of sensing acoustic particle velocity is introduced. Unlike conventional microphones that have a diaphragm for sensing sound pressure, this design consists of a thin, porous, movable structure that is intended to be driven by viscous forces as a result of the sound-induced flow. This viscous force then rotates the movable structure around a middle central hinge and creates a change in capacitance caused by a relative motion between neighboring beams. The whole structure is made of one layer of silicon using a silicon-on-insulator (SOI) wafer using photolithography technology with a device layer thickness of 5 μm. The movable part has dimensions of 0.7 mm × 1.2 mm and is placed above a cavity inside the bulk silicon that facilitates the flow of sound particles. This microphone responds to flow (a vector) rather than pressure (a scalar). Ultimately, experimental results demonstrate a sensitivity of approximately 5 mV/Pa, a noise floor between 10-4 and 10-5 Pa/Hz, and directivity ratios reaching up to 77 at 2000 Hz, underscoring its potential for high-performance acoustic applications.