Realization of equivalent gradience of porous materials with periodic macro void structure

Abstract

In this paper, a periodic macro void (PMV) design of porous materials is proposed, through which different acoustic properties can be obtained with uniform porous materials. The proposed PMV structure is an alternative to realize gradient sound absorbers, which experimentally shows the potential to enhance the sound absorption performance of porous materials. Based on the wave finite element (WFE) method and a homogenization procedure, the equivalent density and bulk modulus of PMV porous materials are obtained, which are validated by finite-unit’s simulation and experiment. These equivalent acoustic parameters are between that of uniform porous materials and air, which are controlled by the macro porosity, but independent of void position and shape. The proposed PMV porous material with gradient macro voids is used to optimize the anechoic chamber performance with an optimization procedure provided. For a chamber with size of 9 m × 8 m × 7 m, and cut-off frequency of 100 Hz, the performance of gradient PMV design is compared with the classic wedge design. It is found that the optimized gradient PMV design can achieve better performance than the classic wedge design with the same thickness of 0.8 m. Moreover, the thickness of gradient PMV design can be reduced up to 15% (0.68 m) while keeping better performance than the wedge design.