Fast Computation of Diffraction in General Anisotropic Media by Use of the Geometrical Theory of Diffraction

Abstruct-The “geometrical theory of diffraction” (GTD) provides a remarkably simple means for computing the diffracted field from an aperture in terms of a geometric optics beam plus contributions from scattering centers at the edges of the aperture. To our knowledge this method has not previously been applied to anisotropic media, except for the special case of a uniaxial medium in regions away from the beam edges. (At the beam edge a singularity occurs in the GTD solution unless corrections are added.) A method has been found for applying the GTD to general anisotropic media such as YZ LiNb03. Also, methods for removing the beamedge singularities, which were developed for isotropic media, have been adapted for the anisotropic case. Comparisons of results computed by the GTD with results obtained by the plane-wave spectrum method for the case of YZ LiNb03 show good agreement. The GTD provides a means for rapidly computing diffraction patterns of SAW transducers on media like YZ LiNbO3, where the parabolic anisotropic approximation is not valid. The numerical data needed for making computations is provided for the case of YZ LiNbO,, and some sample calculations are shown.