Measurement of shock waves in the focus of a lithotripter

For the measurement of ultrasonic shock waves with amplitudes near 40 MPa, two different hydrophones were constructed. The first is a high-bandwidth PVDF membrane hydrophone with a capacitively coupled signal. The second is a small acousto-optic fiber hydrophone which measures the shock-wave-induced variation of the refractive index of a liquid at the front end of the fiber. The properties of the hydrophones are compared. The first, with a sensitivity of 6 mV/MPa, demonstrates high durability and a 20-MHz bandwidth. The second has equally good characteristics and additionally measures the creation and the time dependence of cavitation bubbles in the liquid.<
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