Sound transmission properties of a porous meta-material with periodically embedded Helmholtz resonators

The main scope of this work is to study the effect of embedding a periodic pattern inside a porous material, in order to passively improving its acoustic performance in terms of sound transmission loss. A contemplated application is the improvement of classical aeronautical soundproofing packages. In order to reach this goal, numerical models of an acoustic package including periodic patterns are implemented using the finite element method and the Transfer Matrix Method. Firstly, some of the proposed configurations are experimentally tested, providing a comparison and validation of the obtained numerical results. Afterwards, several configurations of inclusions are numerically studied, and incorporate hollow cylindrical inclusions, half-cut hollow cylindrical inclusions and cylindrical Helmholtz resonators. The improvements in terms of transmission loss, essentially brought by a periodicity peak, are evaluated under plane wave excitation with various incidence angles. The main novelties of the present work are represented by an experimental validation of the proposed acoustic meta-materials that were only numerically studied in previous works. The effect of the inclusion of a periodic pattern of Helmholtz resonators inside the foam core is also considered. The presented numerical results are also evaluated for different incidence angles of an exciting acoustic plane wave.

Automated summary

The aim of this study is to investigate the effect of embedding periodic patterns in porous materials to passively enhance their acoustic performance. The focus is on improving sound transmission loss in classical aeronautical soundproofing packages. Numerical models of acoustic packages with periodic patterns were implemented using the finite element method and the Transfer Matrix Method. Experimental testing of some proposed configurations was conducted for comparison and validation of numerical results. Various configurations of inclusions were numerically studied, including hollow cylindrical inclusions, half-cut hollow cylindrical inclusions, and cylindrical Helmholtz resonators, to evaluate the improvements in transmission loss under plane wave excitation with different incidence angles. The main contributions of this work include experimental validation of proposed acoustic meta-materials previously only studied numerically, and consideration of the effect of including a periodic pattern of Helmholtz resonators in the foam core. Numerical results were also evaluated for different incidence angles of an exciting acoustic plane wave.