The Radiation Efficiency of Finite Size Flat Panels

The radiation efficiency of an infinite flat panel which is radiating an infinite plane wave into an infinite half space can be shown to be equal to the inverse of the cosine of the angle between the direction of propagation of the plane wave and the normal to the panel. The fact that this radiation efficiency tends to infinity as the angle tends to 90° causes problems with simple theories of sound insulation. Sato has calculated numerical values of radiation efficiency for a finite size rectangular panel. This paper presents a simple analytic strip theory which agrees reasonably well with Sato’s numerical calculations for a rectangular panel. This leads to the conclusion that it is mainly the length of the panel in the direction of radiation, rather than its width that is important in determining its radiation efficiency.