Archives of Acoustics, 23, 2, pp. 251-266, 1998

Acoustical distortions in capacitance hydrophones and the effect of diaphragms in measurements of shock wave pulses

L. Filipczyński
Department of Ultrasound, Institute of Fundamental Technological Research, Polish Academy of Sciences, 00-049 Warszawa, ul. Świętokrzyska 21
Poland

J. Etienne
Department of Ultrasound, Institute of Fundamental Technological Research, Polish Academy of Sciences, 00-049 Warszawa, ul. Świętokrzyska 21
Poland

T. Kujawska
Department of Ultrasound, Institute of Fundamental Technological Research, Polish Academy of Sciences, 00-049 Warszawa, ul. Świętokrzyska 21
Poland

J. Wójcik
Department of Ultrasound, Institute of Fundamental Technological Research, Polish Academy of Sciences, 00-049 Warszawa, ul. Świętokrzyska 21
Poland

B. Zienkiewicz
Department of Ultrasound, Institute of Fundamental Technological Research, Polish Academy of Sciences, 00-049 Warszawa, ul. Świętokrzyska 21
Poland

The shock wave pulse measured by means of a membrane PVDF hydrophone was compared with the pulse obtained by means of the capacitance hydrophone showing distortions in the pulse trailing edge. The mechanism of distortions in the capacitance hydrophone was explained and confirmed by experiments as caused by transverse waves generated on the surface of the hydrophone's metal plate by compressional incident waves. The effect of the rise time of the measured shock wave pulses was interpreted and analysed by means of diaphragms with various apertures. Interaction of the applied diaphragms with the measured acoustic fields was explained showing their equivalence to the high pass filtering. The differentiating circuit used for determination of the particle velocity from the displacement, measured by the capacitance hydrophone, was analysed. Also an improved capacitance hydrophone was applied in measurements.
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