Indust. Mater. Inst., Natl. Res. Council, 75 De Mortagne Blvd., Bouchervill, PQ J4B 6Y4, Canada
The influence of a boundary layer on the scattering of elastic waves by spherical inclusions is investigated. Based on the exact transition matrix (T) developed for layered obstacles [A. Bostrom, J. Acoust. Soc. Am. 67, 399--413 (1980)], a numerical study is performed for all values of h/a, where h is the layer thickness and a is the effective radius of the layered obstacle. For h/a << 0.1, the layer behaves like an interface, allowing one to investigate a wide range of boundary conditions. Except for high mass density interfaces, the scattered field amplitude is sensitive mainly to the normal and transverse stiffnesses and classical solutions for the so-called rigid and slip boundary conditions are recovered. For h/a<0.1, the layer acts as an interface region and property changes of the host near the obstacle can be modeled. Ultrasonic measurements with charge-filled polymers present evidence for such a layer. Finally, for h/a(approximately equal to)0.1, the layer behaves as a coating or a shell depending on the mass density. In this case, full interactions are included in the formalism.