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 virtually all 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 due to the sound-induced flow. This viscous force then rotates the movable structure around a middle central hinge and creates a change in capacitance due to a relative motion between neighboring beams on the movable and fixed electrodes which creates an electronic signal through a charge amplifier circuit. The whole structure is made of one layer of silicon using a Silicon-on-Insulator (SOI) wafer using photolithography technology consisting of moving and fixed electrodes with a thickness of 5µm. The movable part has dimensions of 0.7mm×1.2mm and is placed above a cavity inside the bulk silicon that facilitates the flow of sound particles. Because this microphone responds to flow (a vector) rather than pressure (a scalar), this design has an output that depends on the sound propagation direction and can cancel out sound from unwanted directions. Experimental results show that it has very promising capabilities for achieving the next generation of MEMS microphones that respond to acoustic flow rather than pressure and can be integrated with other sound sensors for consumer electronics and hearing aids.