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Phase calibration of hydrophones by the free-field reciprocity method in the frequency range 10 kHz to 400 kHz.

Hayman, G; Robinson, S P (2007) Phase calibration of hydrophones by the free-field reciprocity method in the frequency range 10 kHz to 400 kHz. NPL Report. AC 1

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Abstract

In this report, a description is given of work carried out at the National Physical Laboratory to investigate phase response calibration of hydrophones by the free-field reciprocity method. A co-linear arrangement of hydrophones, based on the method of Luker and Van Buren, is used in order to eliminate some of the difficulties in the measurement of the device separation and the speed of sound in water. The experimental implementation of this method in the NPL open tank facility is described, along with the use of a laser alignment system to accurately set the position of the central hydrophone. The results of calibrations of three hydrophones are presented and these are compared to phase response measurements, performed on the same three hydrophones, using an optical vibrometry method, at Hangzhou Applied Acoustic Research Institute (HAARI) in China. Agreement between the two methods is shown to be generally good, with typical differences of less than 8° throughout the majority of the frequency range. However, the Type A uncertainty for the reciprocity measurements is relatively large at higher frequencies, with 95% confidence level uncertainties reaching 30° at 400 kHz. The major sources of error in the reciprocity method as implemented are discussed, along with possible explanations for some of the disagreements seen when the results are compared to calibrations by the optical method.

Item Type: Report/Guide (NPL Report)
NPL Report No.: AC 1
Keywords: phase, calibration, hydrophones, reciprocity
Subjects: Acoustics
Acoustics > Underwater Acoustics
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/3981

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