Characterization of laser-induced pressure transients by means of piezoelectric PVDF films
Stefan Lohmann, Andreas Olmes, Holger Lubatschowski, Wolfgang A. Ertmer · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1996
For an interpretation of pressure signals detected by piezoelectric PVDF-foils several parameters are of importance. These are for example pressure pulse duration and rise times, active area of the film and specifications concerning the high-frequency technique of the experimental setup. Using an input-resistance of 1 M(Omega) at the storage-oscilloscope leads to reflections of the signal which superimpose each other when reflected a second time at the foil. This might cause an apparent increase of the amplitude. The utilization of a longer cable allows a separation of each reflected pulse, but it causes the problem, that the cable's input- impedance approaches its characteristic impedance of 50 (Omega) . This will lead to a time derived signal as well as using 50 (Omega) as input-resistance at the scope. Therefore a direct measurement of short pressure transients requires a very short cable and an input-resistance of 1 M(Omega) . Otherwise the measured signal allows no proportional relation between pressure transient and measured voltage signal. In the latter case a frequency-dependent correction of the signal becomes necessary. This has been developed in this paper by means of Fast Fourier Transform algorithm. After correction in the frequency-domain the signal is transformed back into the time-domain.