Sound absorption enhancement in poro-elastic materials in the viscous regime using a mass–spring effect

Abstract

This paper investigates the mechanisms that can be used to enhance the absorption performance of poro-elastic materials in the viscous regime. It is shown that by adding small inclusions in a poro-elastic foam layer, a mass-spring effect can be introduced. If the poro-elastic material has relatively high viscous losses in the frequency range of interest, the mass-spring effect can enhance the sound absorption of the foam by introducing an additional mode in the frame and increasing its out-of-phase movement with respect to the fluid part. Moreover, different effects such as the trapped mode effect, the modified-mode effect, and the mass-spring effect are differentiated by decomposing the absorption coefficient in terms of the three energy dissipation mechanisms (viscous, thermal, and structural losses) in poro-elastic materials. The physical and geometrical parameters that can amplify or decrease the mass-spring effect are discussed. Additionally, the influence of the incidence angle on the mass-spring effect is evaluated and a discussion on tuning the inclusion to different target frequencies is given.