A range of materials are used as anechoics and isolators in underwater acoustic systems to reduce reflections or provide attenuation of sound waves. The need for improved performance is leading to the use of new innovative metamaterials, which have properties not found in natural materials. Typically these are composite materials with a complex internal structure.  The performance testing of these materials presents new challenges which will be the subject of this project.

The classic method of characterising the acoustic transmission and reflection properties of materials is to test the material in an impedance tube which requires a sample to be cut from the material; this is unsuitable for materials with complex internal structure.  An alternative approach is to use a parametric array to generate a beam with a reasonably small cross-sectional area that enables small planar samples to be tested. 

The testing of new and innovative materials, such as metamaterials, will raise particular problems as the materials are likely to have a pronounced internal structure on a scale less than a wavelength resulting in a complex near-field in the vicinity of the panel.  This will make the use of traditional measurement techniques inappropriate and hinder the development of such materials.

This project will investigate techniques of characterising the 2D field in a plane close to test panel and the use of near-field holography techniques to extract the plane wave spectrum of the field and hence predict the far-field plane wave behaviour. The same approach will also be extended to oblique incidence measurements. Possible optical measurement approaches will also be considered. 

The project will involve a mixture of theoretical modelling, experimental measurement and signal processing. The work will be performed in collaboration with external organisations and will probably involve interaction with, and visits to, a research laboratory in the USA.

If you wish to discuss any details of the project informally, please contact Victor Humphrey, Acoustics research group, Email: vh<στο>isvr.soton.ac.uk, Tel: +44 (0) 2380 59 4957.