PACKAGING AND CHARACTERIZATION OF BIO-INSPIRED UNDERWATER MEMS DIRECTIONAL SOUND SENSOR

Abstract

The thin-line towed array hydrophones and vector sensors are commonly used to determine the bearing of sound sources in underwater environment. In this thesis, a MEMS-based directional underwater acoustic sensor (inspired by the ears of the fly Ormia Ochracea) is explored. The sensor operates in a narrow frequency band where the mechanical resonance frequency determines the operating frequency. The sensor consists of two wings connected by a bridge and the assembly is pivoted to a substrate using two torsional legs. The electronic readout of the response is obtained using a pair of interdigitated comb finger capacitors attached to the wings. The MEMS sensor was designed using COMSOL finite element modeling and a suitable package was developed for underwater testing. The performance of the sensor was characterized in air using an anechoic chamber, and underwater testing was done using NPS and TRANSDEC water tanks. Measurements showed that the operating frequency of the sensor in air is about 1600 Hz while underwater it shifted to a lower frequency (285 Hz), primarily due to mass loading from the fluid used for immersing the sensor. The peak sensitivity of the MEMS sensor was found to be about -160 dB (re 1V/uPa), which is about 30 dB higher than conventional broadband hydrophones. The sensor showed good directional response with dipole pattern. The results show the potential of MEMS sensors for underwater applications to detect the bearing of sound sources.