MEMS UNDERWATER DIRECTION FINDING ACOUSTIC SENSOR

Abstract

Acoustic sensors operating in underwater environments were designed and fabricated based on the ear structure of the parasitic fly, Ormia ochracea. The design was executed using COMSOL Multiphysics, including mass loading and viscous damping. The optimized sensors were fabricated using MEMSCAP commercial foundry service. The testing was performed using NPS water tanks and TRANSDEC’s San Diego underwater testing facility. For underwater characterization, a custom housing was made to immerse the sensors in a non-conducting fluid with acoustic impedance close to water. Measurements showed that the sensors could detect underwater sound with a narrow-band spectral response. Directional response of the sensors showed the expected cosine dependence, indicating their ability to detect the bearing of underwater sound sources. The sensor enclosure affected the measurements due to its non-uniform response to the incident sound. A reference hydrophone was similarly enclosed and COMSOL simulations performed to reduce and understand this effect. The results show that the enclosure produces unwanted resonance frequencies. For uniquely determining sound-source bearing, it is necessary to use two sensors at a canted angle. The circuit boards affected directional responses. COMSOL simulations were performed with actual-sized circuit boards. Several approaches to determine the optimal angle based on these observations are presented in this thesis.