Properties of a PVDF Hydrophone with 100 MHz Bandwidth for Studying Medical, Nonlinear and Other Fields

A broadband hydrophone made from a pvdf membrane is described. It has a smooth frequency response, flat to ? 3 dB up to 100 MHz, and gives accurate waveform reproduction. The hydrophone's performance characteristics have been studied to allow c onfident interpretation of the signals obtained under appropriate experimental conditions, and to provide a clear understanding of the physical basis of its behaviour. The frequency response, inferred from direct calibrations and measurements of nonlinear fields, agrees excellently with the p redictions of a theoretical model, clarifying the piezoelectric behaviour of the pvdf film used. Its directionality, which shows limited agreement with that ofa stiff disc receiver, can be better understood by considering the three-dimensiona l piezoelectric properties of the pvdf film. Measurements of these characteristics, the hydrophone's electrical properties and the performance of the cable and detection circuitry give the information necessary for its reliable practical use. The hydrophone is shown to be ideally suited for many practical applications, including the measurement of medical and nonlinear fields containing high frequency components. The use of nonlinear acoustic fields in conjunction with this hydrophone for the convenient calibration of other hydrophones is also illustrated.