Application of Sound-Conducting Polymeric Pellicle for Hydrophone Calibration by Means of Optical Interferometry

Hydrophone calibration is carried out via optical interferometry using a thin sound-transparent polymeric pellicle (membrane). A major issue associated with implementing this calibration method consists in estimating the correspondence between the oscillations of the metalized side of the pellicle and water particle displacements under the action of the acoustic wave incident on the pellicle. On the basis of a simplified theory of plane acoustic waves propagating through the layers of dissimilar materials, the authors developed methods for measuring the speed of sound through the applied pellicle together with an algorithm for calculating the frequency dependence of the acoustic wave transmission coefficient (in terms of particle velocity) from water, through the pellicle, and into water/air. An introduced correction of the hydrophone calibration results to take the acoustic wave transmission coefficient into account is justified along with its estimated uncertainty.