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Acoustic Properties of Sonar Dome Materials

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Technical Report

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Guigne International Limited Paradise, Newfoundland Canada

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The acoustic properties of composite panels made from high strength polyethylene Spectra Fiber were compared to conventional glass fiber composites, and to the double-walled stainless steel design currently used in the C5 Sonar Dome . Characterization consisted of insertion loss measurements from 0-40 kHz using a parametric array projector, and self noise measurements from 0-6 kHz. All the panels but the cyanate-based 4H Spectra Fiber composite panel tested had very low insertion losses 1 dB below 10 kHz at normal incidence. Apart from the epoxy-based 4H panel, the SpectraFiber composite panels had lower insertion losses, and less angular dependence of the insertion loss, than both the glass fiber composites and the double walled stainless steel panel in the 0-40 kHz range. Of the two different resin systems examined, epoxy and cyanate ester, the cyanate ester resin based composite panels had slower water uptake rates than the epoxy panels, but there was no significant difference in the insertion losses below10 Hz. In general, the angular dependence of the insertion losses below 10 kHz was minimal with the exception of the 4H epoxy Spectra Fiber panel, which had a slightly higher angular dependence. Aging the composite panels in water resulted in some slightly reduced insertion losses, with the exception of the 4H cyanate Spectra Fiber panel. The self noise experiments consisted of measuring the radiated sound produced by a mechanically excited panel placed at the airwater interface in a reverberant tank.Comparison of the composite panels to the stainless steel dome section was complicated by the rigidity of the stainless steel structure, which produced few modes in the frequency range studied.

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