Abstract
Underwater sensors that detect the distance and direction of acoustic sources are critical for surveillance monitoring and target detection in the water. Here, we propose an axial vector sensor that utilizes a small (~1 cm3) compressive-type piezoelectric accelerometer using piezoelectric single crystals. Initially, finite element analysis (FEA) was used to optimize the structure that comprised piezoelectric Pb(Mb1/3Nb2/3)O3-28%PbTiO3 single crystals on a tungsten seismic mass. The receiving voltage sensitivity (RVS) was enhanced through geometric optimization of the thickness and sensing area of the piezoelectric material and the seismic mass. The estimated maximum RVS of the optimized vector sensor was −212 dB. FEA simulations and practical measurements were used to verify the directivity of the vector sensor design, which exhibited a dipole pattern. The dipole beam pattern was used to obtain cardioid patterns using the simulated and measured results for comparison. The results clearly showed the feasibility of using the proposed piezoelectric single-crystal accelerometer for a compressive-type vector sensor.
Highlights
The detection of underwater targets, such as submarines and torpedoes, requires measurement of the pressure and vector components of an acoustic source
For the vector hydrophone with thickness shear mode, dual piezoelectric single crystals were mounted on a vertical metal base with dual seismic mass to improve the sensitivity
If the vector sensors developed here are aligned with the X, Y, and Z axes inside an omnidirectional hydrophone, they could be used to measure the directivity of an acoustic source for underwater sensor nodes
Summary
The detection of underwater targets, such as submarines and torpedoes, requires measurement of the pressure and vector components of an acoustic source. For the vector hydrophone with thickness shear mode (or d15 mode), dual piezoelectric single crystals were mounted on a vertical metal base with dual seismic mass to improve the sensitivity (i.e., the minimum RVS of −201.4 dB). If the vector sensors developed here are aligned with the X, Y, and Z axes inside an omnidirectional hydrophone, they could be used to measure the directivity of an acoustic source for underwater sensor nodes. A compressive mode accelerometer is used to obtain excellent reception sensitivity and a dipole beam pattern based on analysis of the vector sensor structure, i.e., the geometry of the piezoelectric material and seismic mass. The performance of the fabricated vector sensor prototype, and the simulation results are compared using the cardioid beam patterns to ensure the validity of the vector sensor design
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