Comparison of hydrophone calibration by reciprocity and heterodyne interferometer in the frequency range 500 kHz to 15 MHz

This paper presents a comparison of high-frequency hydrophone calibration by a heterodyne interferometer and two-transducer reciprocity method respectively. For the calibration using the heterodyne interferometer, a vertical arrangement is applied to avoid the acousto-optical interaction which is a major uncertainty source in previous studies. For the demodulation of the acoustic displacement, a PC-based digital demodulation using arctangent algorithm is applied which has overcome the drawback of analog demodulation and achieved a higher demodulation accuracy. The demodulation is independent of the intensity of the carrier signal and thus can avoid the correction for the frequency response of the photodiode which is another uncertainty source. Comparison results between these two methods showed a good agreement. Owing to the optical measurement is independent of the acoustic field generating by the transducer, it has wider usage compared to the reciprocity method and can be easily extended to higher frequency and higher acoustic power application.