John G. Harris
Theor. Appl. Mech., Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801
Gerry Wickham
Brunel Univ., Uxbridge, Middlesex UB8 3PH, UK
The imaging of thin solid films or interfaces by a confocal arrangement of ultrasonic transducers is modeled in both a two-dimensional and a three-dimensional context. In the first model, an antiplane shear, focused beam is directed across an interface comprised of an array of cylinders, with contrasting material properties. Its periodicity is destroyed by removing cylinders arbitrarily. In the second, a thin solid film, having quite general mechanical properties, is immersed in a fluid and scanned by a three-dimensional acoustic beam. This last work is only partially completed. An approximate integral representation of wave fields scattered by these thin regions of heterogeneity in terms of a Green's function for the host media, and the stress and momentum polarizations averaged through the thickness of the film or interface is the starting point. The stress polarization measures the change in elastic properties and the momentum polarization that in inertial properties, both changes being with respect to the properties of the host media. The scattered waves are calculated by formulating and solving integral equations. Those received are estimated using a measurement model that mimics the receiving transducer. [Supported by the NSF, MSS 91-14547.]