The virtues of geometrical diffraction theory and of uniform asymptotic methods can be combined. Instead of merely matching the local geometry with the geometry of a canonical problem, the exact solution to the canonical problem is used as an approximation to the problem at hand. The wave equation is not employed directly, but the principle of energy conservation is used to determine certain amplitudes. This idea is illustrated by applying it to WKB solution of an ordinary differential equation, deriving the equation for geometrical optics, finding whispering gallery modes, finding the whispering gallery waves excited by a source, and by constructing creeping waves and their excitation coefficients.
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