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The low frequency characterisation of underwater material properties in a pressure vessel via single, dual and multiple hydrophone techniques.

Martin, M J*; Hugin, C T*; Robinson, S P; Beamiss, G A; Haymanb, G*; Smith, J D*; Humphrey, V F* (2007) The low frequency characterisation of underwater material properties in a pressure vessel via single, dual and multiple hydrophone techniques. In: 2nd International Conference & Exhibition on "Underwater Acoustic Measurements: Technologies & Results", June 2007, Crete.

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Abstract

The underwater acoustic properties of materials are typically assessed by insonifying a large panel of the test material and measuring the reflected and transmitted pressure via a single hydrophone. This is usually conducted in open water, which allows measurements to be made down to low kilohertz frequencies, but is reliant on ambient conditions. It is desirable to conduct these experiments in a controlled laboratory environment, thus reducing significantly both the cost and inconvenience of measurements which would otherwise be conducted at sea. The Acoustic Pressure Vessel at the National Physical Laboratory in the UK allows the simulation of ocean conditions through varying temperature and pressure, and can accommodate a measurement system which permits panels of a moderate size to be assessed. The physical dimensional constraints of the system place limits on the suitability of the traditional single hydrophone pressure technique, particularly at low kilohertz frequencies, due to diffracted and reflected secondary signals which cannot be time gated out of the primary signal during analysis. Measurements conducted by QinetiQ and NPL show that through employing either a dual hydrophone intensity probe or hydrophone array it is possible to discriminate against these undesirable signals, thus reducing the error in these measurements at low frequencies. This provides a very cost efficient and convenient measurement facility to undertake materials assessment which otherwise could be prohibitively expensive.

Item Type: Conference or Workshop Item (UNSPECIFIED)
Keywords: Underwater acoustics, panel measurements, materials properties
Subjects: Acoustics
Acoustics > Underwater Acoustics
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/3934

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