Low frequency scattering through an aperture in a rigid screen—Some numerical results

The penetration of a plane wave through an aperture in a rigid screen is investigated. The first three terms of the low frequency expansion are evaluated numerically for both simply connected and annular apertures. In the numerical method use is made of a division of the aperture into arbitrary triangles. The singular behaviour at the edges is incorporated in the shape functions, which yields good accuracy and fast convergence. Special attention has been given to the thin ring which can serve as a model for, e.g., imperfectly shielded windows.