Life prediction analysis on underwater acoustic sensors and its experimental validation

Abstract

An equivalent circuit analysis is presented to predict the acoustic characteristics of resonant hydrophones and the factors leading to their degradation. The circuit parameters of a Tonpilz transducer, operated as a resonant hydrophone in the receiving mode, are determined from the measured complex electrical admittance in water at frequencies in the vicinity of resonance. The parameters are refined by non-linear regression method and used to calculate the receiving sensitivity in the same band. External components such as insulation resistance, cable capacitance and input impedance of the preamplifier are included in the model and their loading effects on the receiving sensitivity are determined. The detrimental effect of drop in insulation resistance on the performance of the resonant hydrophone is studied quantitatively. The cut-off values of insulation resistance at various frequencies and capacitances are prescribed that would mark the end-of-life of the hydrophone. In the present case, the acceptable lower limit of Ri is found to be 1 MΩ at 100 Hz and 10 kΩ at 30 kHz. The model results are validated by experiments and are found to agree well with the measured data. The equivalent circuit model of hydrophones will be useful to optimize the hydrophone- preamplifier combination of underwater acoustic systems by minimizing the receiver noise and enhancing the signal to noise ratio.