The acoustic transmission properties of anisotropic sandwich panels with perforations

Abstract

A rectangular sandwich panel, consisting of two thin plane shells on either side of a cellular structure, has perforations in one of the bounding shells so that some or all of the cells may act as Helmholtz resonators. The compound panel is set in an otherwise rigid plane baffle and is irradiated by a plane wave travelling from the unperforated side of the system. An estimate is presented, in integral form, for the acoustic power transmitted through the panel, averaged with respect to time and with respect to all possible directions of incidence, in the limit of large values of ka and kb, where k is the acoustic wavenumber and a, b denote the plate dimensions. For operating frequencies below a certain critical coincidence value, the basic estimate is supplemented by an additional contribution from the resonantly driven but acoustically inefficient modes, which become significant at modest values of ka and kb if the mechanical loss factor ϵ is sufficiently small. There is good agreement between the numerical evaluation of the estimates and the available experimental data.