Diffraction of an acoustic plane wave by a rectangular hole in an infinitely large rigid screen

The method of the Kobayashi potential (KP) is applied to evaluate an acoustic field diffracted by a rectangular hole in an infinite rigid screen. The screen thickness is assumed to be negligibly small. The KP method yields an eigenfunction expansion of the present geometry, and the expansion coefficients are obtained from the matrix equation. The intensity pattern of the far diffracted field, the velocity distribution on the hole, and the transmission coefficient are numerically evaluated. The intensity pattern results are compared with those obtained from the Kirchhoff’s diffraction integral. The agreement between them is fairly good. Since no existing method has provided transmission coefficients for a rectangular hole in a rigid screen, these results are compared with the total scattering cross section of the soft disk, which is analogous to a circular hole in a rigid screen. Their frequency characteristics are found to show a similar variation.