Lumped-Parameter Modeling and Performance Analysis of Fluid-Backed Piezoceramic Flexural Disc Acoustic Sensors

A two-port lumped-parameter equivalent circuit model is presented to analyze the electroacoustic characteristics of piezoelectric flexural-mode acoustic sensors with fluid backing. The circuit parameters are determined from the measured electrical admittance spectra in water. Expressions for frequency-dependent receiving sensitivity are derived in terms of the equivalent circuit parameters under two extreme boundary conditions, namely, clamped and simply supported edges. The effect of geometric parameters of the composite flexural discs on the acoustic performance is analyzed. The model is validated by constructing flexural disc hydrophones of several dimensions and configurations, in which the overall thickness is much smaller than the radius. The model results agree well with the experimental data, validating the model. It is found that the receiving sensitivity of practical sensors lie in between clamped edge and simply-supported edge conditions which are the theoretical lower and upper bounds, respectively. Among all the sensors studied, the sensor with the lowest radius ratio (
${R}_{p}/{R}_{s}$
) has the highest measured receiving sensitivity of −173 dB (ref. 1V/
$\mu $
Pa) at low frequencies and −150 dB (ref. 1V/
$\mu $
Pa) at resonance. The self-noise characteristics of these sensors are also analyzed with reference to underwater applications. The largest sensor has the highest Figure-of-Merit (
FoM
) with the measured
${M}^{2}{C}$
value of
$743\times10$
⁻²⁸
V
²
F/
$\mu $
Pa
²
, which is about three orders of magnitude higher than typical sensors. Piezoelectric sensors with high
FoM
is required to design acoustic systems with high Signal-to-Noise Ratio (
SNR
) with enhanced acoustic receiver characteristics.