Design, fabrication, and characterization of a microelectromechanical directional microphone

• Main Author: Touse, Michael.
• Other Authors: Karunasiri, Gamani
• Published: Monterey, California. Naval Postgraduate School 2012
• Online Access: http://hdl.handle.net/10945/10762

A series of micro-electromechanical system (MEMS) based devices for acoustic direction finding have been designed and fabricated which mimic the aural system of the Ormia ochracea fly and its extraordinary directional sensitivity. To overcome the minimal spatial separation between its ears, a flexible hinge mechanically couples the fly's two tympanic membranes. Because of this coupling, the phase differences due to the time difference of arrival (TDOA) are greatly amplified and sound source direction is determined with unparalleled speed and accuracy. This unique system allows the fly to acoustically locate crickets, which chirp with wavelengths two orders of magnitude greater than the dimensions of the hearing system. In this thesis, MEMS sensor design using finite element modeling and experimentation to characterize the physical phenomena that affect the performance will be described. Specific investigations reported include damping effects, device linearity to sound pressure, and the effects of various packaging schemes on device performance. Results include successful demonstrations of several directional sensors responsive to both sinusoidal and impulsive sources, an electronic readout scheme using capacitive comb fingers, an asymmetric design for dual frequency use, and devices effective into the ultrasonic range, all of which could ultimately contribute to a millimeter-scale device for sniper-location or a number of other defense applications.