Rajagopal, S; Robinson, S P; Ablitt, J; Miloro, P; Wang, L; Zeqiri, B; Hurrell, A (2023) On the importance of consistent insonation conditions during hydrophone calibration and use. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 70 (2). pp. 120-127.

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Abstract

Hydrophones are generally calibrated in acoustic fields with temporally localized (short pulse) or long duration (tone bursts) signals. Free-field conditions are achieved by time gating any reflections from the hydrophone body and mounting structures arriving at the active sensing element. Consequently, the sensitivity response of the hydrophone is a result of direct wave incident on its active element free of any contaminating effects of reflections. However, when using tone bursts below 400 kHz to calibrate hydrophone, it may not be possible to isolate the direct wave from reflection artefacts. This means the sensitivity responses derived at these frequencies using different acoustic fields might not be comparable as they are characteristic of the acoustic field interaction with the hydrophone active element alone or hydrophone active element and the body. Therefore, there is a need to consider an appropriate calibration method for a given hydrophone type depending on the insonation conditions in which it is eventually used. This article presents the findings from a short study comprising four needle type hydrophones of active element diameters in the range 1 mm to 4 mm. These hydrophones were calibrated from 30 kHz to 1.6 MHz using established calibration methodologies employed at NPL. For the 4 mm hydrophone where the largest discrepancy was observed, results were supported by theoretical analysis facilitated by a validated acoustic wave solver. The work contained within illustrates the need to ensure that method of calibration is carefully considered in the context of the subsequent measurements for which the hydrophone will be used.

Item Type:	Article
Subjects:	Acoustics > Ultrasound
Divisions:	Medical, Marine & Nuclear
Identification number/DOI:	10.1109/TUFFC.2022.3205851
Last Modified:	02 May 2023 12:49
URI:	https://eprintspublications.npl.co.uk/id/eprint/9693