Interferometric measurements of transient ultrasonic fields. Application to hydrophone calibration

A novel method for calibrating hydrophones is presented. The hydrophone sensitivity is determined from the Fourier transform of its response to the transient plane wave radiated by an ultrasonic source at a well-defined point, where the ultrasonic pressure is perfectly known thanks to an interferometric measurement of the particle displacement. The originality of the method comes from the fact that the plane wave is exploited very close to the source. If a wideband source is selected, the sensitivity can be obtained very quickly and continuously in a broad frequency range. Two sources have been used: a thick disk cut in single crystal and a damped transducer. The sensitivities of different hydrophones are presented, and the results obtained are shown to be in good agreement with other calibration techniques. Finally, the limitations and advantages of the method are discussed