Spot poled reflector style hydrophone for shock wave measurements

The membrane style hydrophone commonly used to calibrate lithotripters is found to have a fast rise time and mediocre sensitivity but a very short life span. A new style of hydrophone that overcomes the longevity problem by employing a spot poled ceramic active element backed by a matched acoustic impedance is proposed. This robust hydrophone is shown to have a fast rise time (<50 ns) together with a high sensitivity. It has been successfully used to measure pressures in excess of 100 MPa for over five thousand shots without any serious degradation in sensitivity or pulse shape. Furthermore, it is shown that such a hydrophone reproduces negative (rarefactional) pressures faithfully. The benefit of having well-defined and potentially very small (less than 0.5-mm-diameter) active areas is gained by the technique.<>