Directionality Patterns for Acoustic Radiation from a Source on a Rigid Cylinder

Abstract

The directionality patterns produced by an acoustic source located on a rigid cylinder of infinite length have been investigated. Assuming that the source strength may be represented as a separable function of azimuth angle and axial dimension, expressions for these patterns are obtained using the method of steepest descent as applied by Silver and Saunders to the electromagnetic analog of this problem. It is observed that the pattern in a plane orthogonal to the axis of the cylinder is independent of the axial distribution of the source, and is, in fact, identical with the pattern given by Morse for a source of infinite axial extent. For the particular case in which the ratio of circumference to wavelength is 14, patterns in this plane have been computed numerically using an IBM-Card Programmed Calculator. Some properties of these patterns are qualitatively explained. Patterns in a plane containing the axis of the cylinder have also been investigated. Experimental patterns confirm the general features of the theoretical patterns and seem to indicate the validity of the theory.