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This conference paper was published under licence in the Journal of Physics: Conference Series by IOP Publishing Ltd. It was delivered at the 6th Groupe De Recherche 2501 and 9th Anglo-French Physical Acoustics Joint Conference.Industrial applications are increasingly turning to modern composite layered\udmaterials to satisfy strength requirements whilst reducing component weight. An important\udgroup of such materials are fibre/resin composites in which long fibres are laid down in layers\udin a resin matrix. Whilst delamination flaws, where layers separate from each other, are\uddetectable using traditional ultrasonic techniques, the presence of porosity in any particular\udlayer is harder to detect. The reflected signal from a layered material can already be modelled\udsuccessfully by using the acoustic impedance of the layers and summing reflections from layer\udboundaries. However, it is not yet known how to incorporate porosity into such a model. The\udaim of the work reported here was to model the backscatter from randomly distributed\udspherical cavities within one layer, and to establish whether an effective medium, with a\udderived acoustic impedance, could reproduce the characteristics of that scattering. Since\udeffective medium models are much more readily implemented in simulations of multi-layer\udstructures than scattering per se, it was felt desirable to simplify the scattering response into an\udeffective medium representation.\udA model was constructed in which spherical cavities were placed randomly in a solid\udcontinuous matrix and the system backscattering response was calculated. The scattering from\udthe cavities was determined by using the Rayleigh partial-wave method, and taking the\udreceived signal at the transducer to be equivalent to the far field limit. It was concluded that\udeven at relatively low porosity levels, the received signal was still “layer-like” and an effective\udmedium model was a good approximation for the scattering behaviour

Modelling the backscatter from spherical cavities in a solid matrix: Can an effective medium layer model mimic the scattering response?