Advance in micro-perforated-panel sound absorbers

Theoretical and experimental investigations on the performance of micro-perforated- panel sound absorbers are reviewed in this paper. These absorbers are robust to adverse environments as they can be made with a wide choice of materials. They are clean, nonpolluting and transparent for indoor-lighting. Moreover, for these absorbers there are analytical solutions to their sound absorption. However, for a commonly used micro-perforated-panel absorber, the absorption frequency bandwidth usually covers only 1-2 octaves. Reviewing recent research work, this paper reveals the relationship between the maximum absorption coefficient and the limit of the absorption frequency bandwidth. It has been demonstrated that the absorption frequency bandwidth can be extended up to 3-4 octaves as the diameters of the micro-holes decrease. This has become possible with the development of technology for manufacturing micro-perforated panels, such as laser drilling, powder metallurgy, welded meshing and electro-etching to form micrometer order holes. In this paper, principles of how to choose parameters of a micro-perforated panel are presented. In addition, non-linear absorptive-characteristics of such panels are discussed both theoretically and experimentally in the case of high intensity sound field. This review shows that the micro-perforated-panel absorber has potentials to be one of the 21st century ideal absorbing materials.