Optical Sensing Inadirectional Memsmicrophone Inspired by the Ears of the Parasitoid Fly, Ormia Ochracea

Abstract

The fabrication and characterization of a biomimetic MEMS directional microphone with integrated optical readout is presented. The use of diffraction-based optical interferometric detection with this novel microphone diaphragm avoids key limitations imposed by capacitive sensing, which is commonly used in miniature microphones. In this study, a biologically-inspired microphone with inter-digitated fingers is fabricated on a silicon substrate using a combination of surface and bulk micromachining techniques. The 1mm × 2mm microphone diaphragm is made of polysilicon and has stiffeners and carefully designed hinge supports to ensure that it responds like a rigid body on flexible hinges. The diaphragm is designed to respond to pressure gradients, giving it a first-order directional response to incident sound. This mechanical structure is integrated with a compact optoelectronic readout system. The directivity measurements show the expected figure-8 directivity pattern with a 21dB difference between the maximum and minimum at the first diaphragm resonance frequency of 2 kHz. This concept has the potential of allowing the fabrication of low noise, directional miniature microphones with high sensitivity for hearing aid applications.