A new method of ultrasonic hydrophone calibration using KZK wave modeling

Most commercially available ultrasonic transducers exhibit finite amplitude distortion in water during hydrophone measurements needed to comply with regulatory requirements. The frequencies observed due to finite amplitude distortion can easily exceed ten times the transducer center frequency and 100 MHz. Typically, hydrophone calibrations are supplied only up to 15 or 20 MHz and do not exhibit a flat response. The frequency response above 15 MHz should be known to accurately represent the acoustic information, especially for high-frequency transducers ranging between 7.5 and 15 MHz. A new hydrophone calibration technique has successfully predicted the frequency response of hydrophones up to 100 MHz. A circular source transducer was first characterized and then modeled using the KZK wave propagation model. This model accounts for diffraction, absorption, and nonlinearity. The transducer frequency response was measured with a hydrophone and compared to the simulation. This difference characterized the frequency response of the hydrophone and was used to estimate the hydrophone calibration. The estimated calibration at 20 MHz was checked and provided good agreement with the manufacturer calibration supplied. Acoustic measurement accuracy will be improved if the hydrophone frequency response is deconvolved from the actual acoustic transducer response.