Diffuse field sound absorption performance of porous material with embedded periodic Helmholtz resonators

This study investigates the diffuse field sound absorption performance of acoustic metamaterial composed of a porous layer with embedded periodic Helmholtz resonators. The periodic unit cell of the metamaterial consists of a porous layer integrated with one, four and nine distinct Helmholtz resonators having extended necks. Although the resonators have cavities of the same volume, they differ in neck parameters and are arranged in parallel. The finite element method is used to evaluate the sound absorption coefficients and the surface impedance of the metamaterial under both oblique and random incidence (diffuse field) conditions. Compared to the conventional porous layer, the metamaterial exhibits significantly enhanced diffuse field sound absorption at the resonant frequencies of the resonators. With one, four and nine embedded periodic resonators, the diffuse field sound absorption shows one, four and nine resonant peaks, respectively. This metamaterial effectively attenuates low-frequency tonal noise across multiple frequencies simultaneously.