Vibroacoustic analysis and design of cavity-backed microperforated panel absorbers for environmental noise abatement

Abstract

The advantage of Micro-perforated Panels (MPP) is its ability to withstand severe working environments in which traditional absorption materials fail due to flammability and contamination. An MPP consists of a sheet panel with a lattice of sub-millimetre sized holes distributed over its surface. By reducing the hole size to the sub-millimetre scale, an MPP with an appropriate perforation ratio provides enough acoustic resistance and a sufficiently low acoustic mass reactance for an absorber, without the use of any porous material. An effective Micro-Perforated Panel Absorber (MPPA) usually has a cavity at the back, so it achieves a Helmholtz resonance effect and provides a wide sound absorption band. At present such a device is usually designed in an intuitive and empirical manner, due to a number of factors. The first is the lack of a thorough understanding of the sound absorption mechanism of MPPA. The second is the lack of a suitable design tool to streamline and optimise the development of such devices. Both of them require a reliable simulation model, which allows the thorough analysis and characterisation of the sound absorption properties of MPPA. Therefore a model of an MPPA flush-mounted on an infinite baffle is established in the current work. The model also incorporates panel flexibility into the system and enables an oblique plane wave incidence impinging on MPP. Based on this model, a systematical vibroacoustic analysis is carried out, which aims to provide an essential and fundamental understanding of the working mechanism of this device. It is found that the coupling mechanisms are different when the MPPA is subjected to the incidence wave at different angles. A clear physical view of this device opens the door to many practical applications. As an example, MPPA can be integrated with a traditional rectangular barrier to form a so-called Wave Trapping Barrier, which is used to reduce the performance deterioration of the barrier due to the presence of a reflecting wall.