Wideband calibration of PVDF hydrophones by an electromagnetic hydrophone using theoretical spectra of overtones
L. Filipczyński, T. Kujawska, Janusz Wójcik · The Journal of the Acoustical Society of America · 1999
PVDF hydrophones are limited in their frequency band, thus distorting measured pulses. For nonlinear effects, caused by propagation of ultrasonic pulses with finite amplitudes, the frequency characteristics are of particular importance. One can correct those distortions knowing the sensitivity characteristics of the hydrophone. To find the sensitivity of the PVDF hydrophone, focused pressure pulses were at first measured by themselves and compared with those measured by the electromagnetic hydrophone (EMH) at low source pressure (linear propagation conditions). So due to the narrow frequency band, one avoided frequency distortions in the EMH, where the absolute pressure was obtained from only two measurements: electrical and magnetic. To discover the sensitivity frequency characteristics, a wideband pulse spectrum of overtones (at known high source pressure) was obtained. Multiplying the theoretical spectrum by the expected sensitivity characteristics, to match theoretical and measured spectra, one obtained the true frequency characteristics. Finally, the averaging effect occurring on the surface of the sensitive electrode of the PVDF hydrophone was computed and eliminated, to obtain the sensitivity for the incident plane wave. For determination of theoretical pressure pulses and their spectra, a special numerical code was elaborated, based on numerical solutions of the nonlinear wave propagation.