Diffraction and Radiation
Diffraction relates, in general terms, to a characteristic wave phenomenon within regions of space not directly insonified or illuminated by a given source < e.g., the shadow of an object interposed in a beam of light >; and is manifest by a non-zero level of excitation in such regions. This, and the kindred phenomena of reflection and refraction, is explicable by means of superposed wave functions that are separately linked with the primary or given source and the secondary effect of its environment < resulting from the presence, say, of a material object nearby >. The classical development of diffraction theory envisaged configurations without any relative motion between the primary source and its surrondings; and invoked the abstractions inherent in time-periodic or aperiodic point sources and plane waves for purposes of mathematical simplicity. Thus, Sommerfeld obtained the first explicit and exact analytical solution for a diffraction problem in linear wave theory, relating to a plane wave incident upon a thin opaque semi-infinite screen with a straight edge; afterwards, Macdonald, Herglotz and others derived the corresponding solution for a point source and a wedge formed by two semi-infinite intersecting plane surfaces.
KeywordsVortex Refraction Acoustics
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