PVDF hydrophone for the measurement of shock waves [lithotripsy]

Focused fields of finite-amplitude ultrasonic pulses occurring in lithotripsy can be measured with hydrophones made of the piezoelectric polymer polyvinylidene fluoride. Extreme requirements for the hydrophones-peak pressure of more than 20 MPa with a risetime of less than 50 ns (shock pulses)-lead to a special construction of the hydrophone where sensitive area and metal electrodes are well separated spatially. The signal from the sensitive area is capacitively coupled to the metal electrodes by a dielectric liquid medium. With a thin, 25-μm PVDF foil, and an unmetalized sensitive area of 3 mm diameter, a hydrophone of 2×10^-2 V/MPa sensitivity with a bandwidth near 20 MHz is achieved. More than 10⁵ focused shock pulses of ≈20 MPa were measured without a significant decrease in sensitivity of the hydrophone