Low-frequency sound absorption of elastic micro-perforated plates in a parallel arrangement

Abstract

In this paper, the low-frequency sound-absorbing performance of parallel-arranged micro-perforated plates (MPPs) is investigated, where elastic MPPs with different MPP parameters and cavity depths are set in a parallel-arrangement with a checkerboard pattern. Under the plane wave condition, a low-frequency formula for sound absorption coefficient is derived by means of a structural-acoustics analysis with two different elastic MPPs in the aforementioned parallel-arrangement. The accuracy of the proposed method is confirmed by comparisons with finite element method (FEM) results. The present method is based on the velocity average over different MPPs and does not assume any interactions among different MPPs. However, the FEM considers interactions among MPPs. The basic arrangement of the MPPs consists of two different MPPs and cavity depths in parallel. To smooth out the interactions, the cross-section of the MPPs is subdivided into small sections like a checkerboard pattern so that no immediate neighboring sections would have the identical MPPs and cavity depths. As the number of the sections increases, the FEM results converge to the prediction due to the cancelling out of the interaction. When two rigid MPPs are arranged in parallel, the equivalent impedances are derived by modeling the MPPs as equivalent electrical circuits. When a partition between two different MPPs exists, the equivalent impedance using the analytical method is found to be identical to that based on an equivalent electrical circuit analogy. However, in the absence of a partition, the two results show a small difference, which is negligible in the plane wave approximation. The effect of the partition is discussed. When the partition between two MPPs is removed, acoustic fields separated by the partition form a single field, which in turn yields a single peak.