Sound absorption of porous materials perforated with holes having gradually varying radii

A multiscale theoretical model and a finite element (FE) model are established to investigate the sound absorption of porous materials perforated with holes having gradually varying radii. Experimental measurements are carried out to favorably validate the theoretical and numerical models. In the theoretical model, the double porosity material is divided into multiple thin layers and each layer is modeled by adopting the double porosity theory; the transfer matrix method is further applied to establish the relationship of the sound pressure and velocities between the connected layers. The FE simulations give a more detailed explanation for the sound absorption mechanism of the double porosity materials through the distributions of sound pressure, particle vibration velocities, sound energy flow and sound energy dissipation in the material. The influences of the static airflow resistivity of the micro-pore matrix, perforation hole dimensions and hole shapes on the sound absorption of the double porosity materials are analyzed. Results show that the radius gradually varying perforation holes can substantially improve the impedance match between the material and air, and thus enhance sound absorption. Also, the perforation hole shapes have a significant effect on the sound absorption of the double porosity materials. This work provides a helpful guidance to improve the sound absorption of the microporous materials by employing the multiscale design approach.