FREQUENCY-RESPONSE OF PVDF NEEDLE-TYPE HYDROPHONES

This paper examines the factors governing the frequency response of ul trasonic polyvinylidene flouride (PVDF) polymer needle-type hydrophone s, in particular the sensitivity variations in the lower frequency ran ge of 1-6 MHz. A theoretical model was used to analyze the influence o f the hydrophone's diameter, the metal electrodes, thickness, PVDF mat erial properties, the adhesive layer acoustical characteristics and th e backing material, on the frequency response of the hydrophone. The r esults of the theoretical modelling differ by less than +/- 0.5 dB fro m those obtained experimentally from the reciprocity calibration in th e frequency range 1-20 MHz. It is shown that the needle hydrophone's d iameter and backing material are the main reasons for the sensitivity variations observed in the frequency range below 6 MHz.