Primary reciprocity-based method for calibration of hydrophone magnitude and phase sensitivity: complete tests at frequencies from 1 to 7 MHz

Abstract

A primary reciprocity-based method for calibration of hydrophone magnitude and phase sensitivity is proposed. The method starts determining the transmit transfer function of an auxiliary transducer, based on the self-reciprocity method and using a stainless steel cylinder as reflecting target. Afterwards, the hydrophone, to be calibrated, is positioned facing the auxiliary transducer. The pressure field waveform, calculated at the hydrophone spot and based on the transmit transfer function of an auxiliary transducer, is used together with the output end of cable voltage waveform signal from the hydrophone to yield the calibrated hydrophone sensitivity. The method was tested with two similar membrane hydrophones, at frequencies within the 1.0-7.0 MHz range, in steps of 1.0 MHz. Results for magnitude sensitivity agree, within a confidence level of 95%, with those from previous calibration of same hydrophones at the National Physical Laboratory, in the UK (Enor⩽1.0). Phase sensitivity results agree with literature reported ones concerning the achieved uncertainty. Additionally, the phase sensitivities measured at 5.0 MHz for two similar hydrophones and employing two distinct auxiliary transducers presented no statistical significant difference. The method yielded a relative expanded uncertainty (p=0.95) for the sensitivity magnitude ranging between 6.6 and 7.0%, and an expanded uncertainty (p=0.95) ranging between 12° and 17° for the phase sensitivity. The results obtained so far lead to conclude that the proposed hydrophone calibration method is a validated alternative to the different existing methods.

Keywords: Calibration; Hydrophone; Magnitude sensitivity; Phase sensitivity; Transducer.