Reciprocity-based method for magnitude and phase calibration of hydrophone sensitivity

Two-transducer reciprocity is a traditional, long time validated and well known ultrasonic transducer calibration method used in the calibration of hydrophone sensitivity magnitude. The method uses a reciprocal auxiliary transducer, whose transmission and reception sensitivities are related by a reciprocity parameter. Typically, reciprocity calibration is done at discrete frequencies. Reasonable simple measurement setup is used, once it demands basically electrical measurements. Other methods for measuring hydrophone complex sensitivity have been described, and some examples, with intrinsic drawback, include: optical methods, nonlinear acoustic wave propagation, and time-delay spectrometry. The present work proposes a novel method for magnitude and phase calibration of hydrophone sensitivity based on the reciprocity method. Two membrane hydrophones of the same model were calibrated at 3 MHz in repeatability conditions. Their sensitivity magnitudes were compared with previous calibrations undertaken in an independent laboratory (National Physical Laboratory, UK), and their sensitivity phases were compared to each other. All results are statistically identical within 95% of confidence level.