P2C-2 A New PVDF Membrane Hydrophone for Measurement of Medical Shock Waves

Calibration of medical shock wave sources is critical and challenging. Aside from the fiber optic probe hydrophone, there are few if any commercially available hydrophones designed for measuring medical shock waves. We have developed a new PVDF membrane hydrophone and compared it to measurements with a fiber optic probe hydrophone (FOPH) in several lithotripters. One part of the hydrophone held the 5 cm times 5 cm times 25 mum PVDF film with geometrical element size 0.5 mm. The other part housed the preamplifier. By substitution comparison to FOPH and an NTR hydrophone, the sensitivity was found to be 0.035 MPa/mV at 2 MHz. Initial spot frequency comparisons showed the response to be fairly flat from 1-20 MHz but showed an elevated sensitivity at 15-20 MHz, and lithotripsy waveforms indicated some high-pass filtering. The impulse response of a 25 mum membrane was calculated and used to de-convolve the signal after which agreement with waveforms from the other hydrophones was excellent. The hydrophone is sufficiently robust to measure 1000 s of lithotripter shock waves. It is inexpensive, sensitive, and has a lower signal to noise ratio than the FOPH