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The dependence of the resonant frequency of a piezoelectric microcantilever sensor (PEMS) on electrostatic discharge (ESD), oscillating voltage, dc bias and time was measured from its electrical response. Linear and nonlinear characteristics of the PEMS were analyzed using a lumped parameter model. In particular, the Duffing model-a nonlinear phenomenological model-was adopted to analyze the effects of varying oscillating voltage. The results showed that the ESD can produce a variation in resonant frequency, but can be prevented by earth grounding. In addition, an increase in the oscillating voltage led to a decrease in the resonant frequency owing to the nonlinear spring effect. The resonant frequency exhibited hysteretic behavior with varying dc bias and increased with time. The resonant frequency changed by approximately 18.5 kHz when the oscillating voltage was increased from 0.05 V to 1 V, approximately 9 kHz when the dc bias voltage was increased from 0 V to 20 V and approximately 3.062 kHz over 12 h owing to time drift. The time drift over a period of 30 min remarkably reduced from approximately 0.09% to 0.0049% after a stabilizing time period of approximately 6 h.

Directional sound detection using vector sensors rather than large hydrophone arrays is highly advantageous for target detection in SONAR. However, developing highly sensitive and compact vector sensors for use in a system whose size is limited has been a challenging issue. In this paper, we describe a miniaturized acoustic vector sensor with piezoelectric single crystal accelerometers for the application in towed line arrays. A mass-loaded cantilever beam accelerometer with a [011] poled PIN-PMN-PT single crystal shows a better signal-to-noise ratio compared to accelerometers with other piezoelectric materials because of its superior piezoelectric properties in the 32 direction. We suggested a sufficiently compact vector sensor by using a cylindrical hydrophone with 10 mm in diameter as a housing of the single crystal accelerometers. Two single crystal accelerometers were orthogonally mounted inside the cylindrical hydrophone to detect direction of sound in the transverse plane of the line array. The receiving voltage sensitivity of the accelerometers and hydrophone was −199 and −196 dB, respectively, at 3 kHz. The directional cardioid beams generated by summing the omnidirectional beam from the hydrophone and the dipole beam from the accelerometers were validated over the entire operating frequency.