Scattering by small defects in the neighbourhood of a fluid-solid interface

The scattering of incident plane elastic waves by a variety of different de fects that lie upon a fluid-solid interface is considered here using matche d asymptotic expansions. The expansion scheme is developed in terms of a pa rameter epsilon, the ratio of a typical defect length scale to a typical wa velength of the incident field, taken to be small. Three different canonical situations occur and these are illustrated via th ree specific examples treated here: a rigid strut, an edge crack, and a rig id strip. In each case the leading-order matching is performed to identify the leading-order contribution of the defect to the acoustic field in the f ar field. In particular, each defect is identified with a source or dipole response in interfacial stress or displacement. It is shown in the limit as epsilon << 1 that in the inner problems the flu id and solid pieces uncouple in a particularly convenient manner allowing a nalytical solutions to be deduced. These are then matched with appropriate outer solutions.