Recent Developments in the Acoustical Proper- Ties of Perforated and Porous Materials Con- Taining Dead-end Pores – Applications to Low Frequency Sound Absorption

It was shown recently in Nevers, France, Sherbrooke, Canada and Salford, UK, that porous materials with semi-opened pores or materials with open pores bearing lateral cavities or resonators at the microscopic scale of the pores can result in peculiar sound absorption properties. Various examples of these materials can be found in engineering and in everyday life including bio-based materials. The cavities and resonators can be assimilated to dead-end pores, which are opened at one end and closed at the other. The deadend pores are known to geophysicists. We studied them more recently in the field of engineering acoustics where the saturating fluid is air. The closed ends prevent the fluid to flow in the dead-end pores so that a crucial assumption usually made in the classical models of the acoustics of porous media based on Biot’s theory is not fulfilled for these materials. In some dead-end pore materials, it was observed that the frequency of the absorption peak was lowered and that the absorption was increased. This has led to the development of new materials with controlled microstructure for low frequency sound absorption applications. Perforated materials with dead-ends were designed and built and their low frequency performances were confirmed experimentally. Absorption peaks around 0.9 were measured at a few hundred Hz for materials of a few centimeters thickness. Future developments of dead-end pore materials are concerned with the optimization of the microstructure, new designs of the microstructure, the use of dead-end pore materials in muffler applications, the interaction with the black hole effect, the behavior under high sound level and the use of vibroacoustic properties of perforated plates for low frequency sound absorption.