A modeling and optimization approach to sound absorbers based on porous materials

Porous materials with interconnected pores are widely used for sound absorption. Under the assumption of a perfectly rigid frame, the interconnected pore structure can absorb freely propagating sound energy via coupled inertial-viscous and thermal dissipation mechanisms. This study numerically and experimentally investigates relationships between the structural characteristics and the absorption response of typical porous materials and their combinations. To examine the micro-macroscopic link, representative elementary volumes are introduced based on the microstructure of material samples (e.g., foams and fibers), including their shape and arrangement as observed in morphological analyses. Subsequently, the macroscopic transport parameters of these virtual samples are calculated by numerical homogenization. A comparison between numerical predictions and experimental measurements provides a good assessment of their correlation and accuracy. Using the established structure-property relationships, the design of advanced sound absorbers with desirable acoustic performance is explored by tailoring the local morphology and the placement configurations of both single-layer and multilayer absorbers. Specifically, for individual porous layers, expressions among the optimal cell or particle size, the layer thickness, and the target frequency of 100 % sound absorption have been demonstrated. From the perspective of designing and optimizing sound absorbers, it is shown that design parameters can be adjusted within manufacturing and operational conditions and explored in a high-dimensional space.