Application of a sound-conducting polymer foil for calibration of hydrophones by optical interferometry

Modern calibration of hydrophones at megahertz frequencies is based on the method of optical interferometry, in which the vibrational velocity of an acoustic wave is measured using a thin sound-transparent polymer foil (membrane), metallized on one side to improve light reflection and installed in an ultrasonic field, followed by its replacement with a hydrophone to be calibrated. The main problem of implementing this calibration method is to assess the adequacy of tracking vibrations of the metallized side of the foil to vibrational displacements of water particles under the action of a sound wave incident on the opposite side of the foil. On the basis of the simplified theory of acoustic plane waves passing through layers of dissimilar materials, methods for measuring the speed of sound in the applied foil and an algorithm for calculating the frequency dependence of the sound wave transmission coefficient (in terms of vibrational velocity) from water through the foil to water or air, introduced as a correction to the results of hydrophone calibration, were developed. The uncertainty of the introduction of this correction is estimated.

Calibration of hydrophones taking into account the conditions of their use

A measuring facility for reproducing a unit of sound pressure at frequencies of 1–500 Hz in the temperature range of 0.5–35 °С with excessive static pressures up to 60 MPa is described. The measuring facility was created in order to expand the functionality of the State primary standard GET 55-2017. The expediency of simulated ocean conditions in GET 55-2017 under hydrophone calibration, the principles of operation and the metrological characteristics of the measuring facility are discussed. Features of the measuring procedure for calibrating the hydrophone are given.