Ray acoustic analysis of plane‐wave coupling into large open waveguides: Plane parallel geometry

Abstract

When a plane sound wave impinges on a wide open‐ended baffled or unbaffled plane parallel waveguide, the behavior of the sound field coupled into the interior differs from that when the waveguide is tubular [H. Shiral and L. B. Felsen, this meeting]. The difference is due to the fact that plane waves retain their integrity between wall reflections. By application of ray theoretic, modal, and hybrid ray‐mode methods, one may establish the connection between the geometrically sharply delineated multiple reflected sheet beam, the edge diffracted‐multiple reflected ray fields, and the guided modes. For very strongly overmoded conditions, the significantly contributing modes are those whose plane‐wave congruences have directions near that of the incident plane wave. Invoking ray‐mode equivalences, a hybrid form is found to describe the propagation phenomena in a physically incisive and numerically efficient manner, especially the diffusion of the initially well‐collimated sheet beam after undergoing multiple reflection. [Work supported by ONR.]