Diffraction by a screen above an impedance boundary

Abstract

This paper is aimed at solving the problem of diffraction by a screen above a locally reacting, infinitely large plane. A general solution is given in terms of an integral equation on the diffracting object. An explicit solution is obtained in the sense of physical optics. Comparisons are made with other solutions by Lindblad and Jonasson. The main disadvantage of these solutions is that their validity is unknown; for sufficiently low screens they are not applicable. The present solution avoids these problems and also extends the knowledge to screens of finite length. To improve the solution numerically, a new method of evaluating integrals of two-dimensional Fourier transforms is discussed and applied. This technique may also be used to evaluate the radiated field from a vibrating surface in a plane infinite baffle. In an experimental section, a close agreement is found between theory and experiments in model scale, indoors as well as outdoors, which also indicates that the method of measuring the ground impedance is useful. The influence of various parameters on the insertion loss is discussed in connection with the model experiments.