Abstract
In this work, microelectromechanical systems (MEMS)-based directional acoustic sensors operating in an underwater environment are explored. The studied sensors consist of a free-standing single wing or two wings pivoted to a substrate. The sensors operate in a narrow frequency band determined by the resonant frequency of the mechanical structure. The electronic readout of the mechanical response is obtained using interdigitated comb finger capacitors attached to the wings. The characteristics of MEMS sensors immersed in silicone oil are simulated using finite element modeling. The performance of the sensors is evaluated both in air and underwater. For underwater testing and operation, the sensors are packaged in a housing containing silicone oil, which was specially developed to present near unity acoustic transmission. The measurements show that the resonant frequency of the sensors obtained in air shifts to a lower frequency when immersed in silicone oil, which is primarily due to the mass loading of the liquid. The peak sensitivity of the MEMS sensors is approximately 6 mV/Pa or −165 dB re 1 V/μPa, and the directional response shows a dipole pattern. The signal-to-noise ratio was found to be about 200 or 23 dB at 1 Pa incident sound pressure. The results show the potential of MEMS sensors to be used in underwater applications for sound source localization.
Highlights
IntroductionThe bearing of underwater sound sources is typically obtained using a linear array of omnidirectional hydrophones spaced proportionally to the wavelength of the source to be located [1]
The bearing of underwater sound sources is typically obtained using a linear array of omnidirectional hydrophones spaced proportionally to the wavelength of the source to be located [1].These arrays require time delay, amplitude difference, or phase-weighting algorithms to determine the direction of the detected sound [2]
The sensor sensor readout electronics were programed with the same parameters used to obtain the results readout electronics were programed with the same parameters used to obtain the results shown shown in in MEMS-based directional sound sensors with two different configurations were studied for potential application in an underwater environment
Summary
The bearing of underwater sound sources is typically obtained using a linear array of omnidirectional hydrophones spaced proportionally to the wavelength of the source to be located [1] These arrays require time delay, amplitude difference, or phase-weighting algorithms to determine the direction of the detected sound [2]. The most common method to determine the direction of sound is the measurement of pressure gradient [8] or particle velocity due to the volumetric motion of the medium [9]. Multiple other techniques have been studied and combined to produce a directional response from underwater acoustic sensors These include a combination of omnidirectional hydrophones to measure the pressure and an accelerometer to acquire particle velocity [10]. The Wilcoxon vector sensor uses three lead magnesium niobate-lead titanate (PMN-PT)
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