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Underwater ultrasonic field characterisation using laser Doppler vibrometry of transducer motion.

Cooling, M*; Humphrey, V*; Theobald, P; Robinson, S P (2010) Underwater ultrasonic field characterisation using laser Doppler vibrometry of transducer motion. In: ICA 2010: 20th International Congress on Acoustics, 23-27 August 2010, Sydney, Australia.

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Abstract

The full far-field characteristics of an underwater ultrasonic transducer can be predicted from either a 2-D planar scan of the complex pressure in the near-field of the source or a transducer surface velocity scan. A Laser Doppler Vibrometer (LDV) can provide such a scan of the radiating surface and hence has the potential to be a fast, non-invasive method for source characterisation and, in turn, field prediction. Such measurements are, however, significantly complicated by the acousto-optic interaction - that is, the effect on the measurements of the acoustic field through which the laser beam passes. Initial examples of surface velocity measurements and field predictions are presented to show the possibilities of the approach. The results of a theoretical study of the effect of the acousto-optic artefact on LDV measurements for a circular, plane-piston transducer are also presented. The use of a transient pressure field is important both for simulation and experiment, such that measurements are made over a time window which ends before any acoustic signal reaches the water tank boundaries. The simulation results show a significant acousto-optic artefact in the surface velocity data, but also that in spite of this useful field predictions may be made for some applications

Item Type: Conference or Workshop Item (UNSPECIFIED)
Keywords: Nearfield, optical scanning, laser vibrometer, acousto-optic effect
Subjects: Acoustics
Acoustics > Underwater Acoustics
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/5330

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