Study on the correction of the influence of thin film in the calibration of high-frequency hydrophone by laser Doppler vibration measurement

In the process of using laser interference calibration method to calibrate high-frequency hydrophones, a transparent reflective film will be used. This article studies the influence of the film on the calibration results. The theoretical calculation formula for the sound pressure transmission coefficient of thin films was derived through the impedance transfer method of multi-layer media. It can be observed that the sound pressure transmission coefficient decreases with increasing frequency, which means that the higher the frequency, the greater the influence of the thin film. When the ultrasonic frequency reaches 10 MHz, the sound pressure transmission coefficient of the thin film with a thickness of 15 μm decreases to 0.9017. The sound pressure measured by the laser Doppler vibrometer method was corrected by the sound pressure transmission coefficient and compared with the results measured by a standard hydrophone. Experiments were conducted to measure the sound pressure at frequencies of 1, 2, 3, 5, and 10 MHz. The results showed that correcting the measurement results of the laser vibrometer method by the sound pressure transmission coefficient can effectively reduce measurement errors.