Design, Fabrication and Characterization of a Biologically Inspired MEMS Directional Microphone

A Directional Microphone is a special type of acoustic sensor which has the capability of sensing the direction of acoustic pressure. In this paper a capacitive sensing Directional MEMS Microphone is presented. The design of the Directional MEMS Microphone is inspired by the parasitoid Ormia Ochracea. The capacitive sensing is achieved by using comb drives on either side of the microphone membrane. The Directional Microphone has been fabricated using SOIMUMPs process. The characterized results have been verified analytically and simulated using COMSOL Multiphysics and Coventorware. The measured frequencies of Rocking and Bending modes were found to be around 3.4 kHz and 7.9 kHz respectively which matches with the simulated results. The base capacitance on either side of the interdigital fingers was found to be 1.5pF. The sensitivity of the microphone was estimated to 0.7pF/ Pa. The novelty of the design lies in the fact that the microphone structure has been modified by splitting the middle
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beams and improving the sensitivity by the spring action, thereby increasing the sensitivity from 0.lpF/ Pa as reported earlier to 0.7pF/ Pa. The device has also been tested with the readout circuitry based on MS3110. A voltage sensitivity of 0.04mV/Pa was obtained.