Small Sensitive Hydrophones

Guide-lines are given for optimum choices of sensitively and capacitance of piezoelectric hydrophones of small size, suitable to detect extremely weak signals. The sensitivity level of such a hydrophone shall be higher than −180 dB below 1 V/μPa. The frequency of mechanical resonance of the hydrophone can be chosen as high as 60 kHz and its capacitance of the order of 50 pF or more. The required load resistance will be not higher than 1000 MΩ.

The frequency range of these hydrophones extends easily downward to below 10 Hz. The capacitance of a hydrophone shall preferably be equal to its external load capacitance caused by the cable or the input circuit of the preamplifier.