9. Ultrasonics, Bulk Waves
The method of optimal truncation (MOOT), a convergent T-matrix scheme, has been applied to the computation of scattering of elastic waves from axially symmetric fluid and elastic inclusions imbedded in an isotropic homogeneous medium. Cones, pillboxes, and spheroids have been considered; an example of frequency and angular dependence of scattering from an oblate spheroid is given. Cracks may be considered as special cases of inclusions wherein the included material is identical to the host. A circular crack, for example, may be simulated by imposing free boundary conditions on the top surface of a pillbox and requiring continuity of displacements and surface tractions elsewhere. Alternatively, it may be feigned by an equatorially cloven spherical inclusion, wherein free boundary conditions are imposed on the bisecting plane and the spherical surfaces are welded.
Visscher, William M., "Application of MOOT to Scattering of Elastic Waves from Inclusions and Cracks" (1980). Proceedings of the DARPA/AFML Review of Progress in Quantitative NDE, July 1978–September 1979. 53.