Cédric Maury, Teresa Bravo
30thInternational Congress on Sound and Vibration. ICSV'30
Del 8 al 11 de julio de 2024, Amsterdam, Países Bajos
A key challenge in the building and transportation area is to enhance the acoustic absorption and insulation of porous wall-treatments over the low-mid frequency range while keeping sub-wavelength lightweight partitions. An approach is to design multi-layered thin micro-perforates with optimized constitutive parameters. However, the desired acoustic performance of the partition may often be hindered by the elasticity or the modal behavior of the thin panels. This study examines the effect of the vibrations on the sound absorption, dissipation and transmission properties of two-types of acoustic metamaterials: an acoustic fishnet made up of identical micro-perforated panels (MPP) separated by millimetric air gaps and a functionally-graded partition (FGP) composed of different MPPs with decreasing values of the holes radius across the partition. The acoustic fishnet exhibits a band gap pattern while the FGP works on impedance matching and visco-thermal dissipation through the holes as the incident wave enters the partition. Global optimization of the total power dissipated through these materials has been achieved from simulated annealing algorithm. The vibrational effects have been accounted for in an impedance translation formulation. It is found that elasticity effects broaden the first stop-band of the acoustic fishnet while lowering the dissipation peak values. They also bring added resistance to the FGP Hole-Cavity resonances that tend to merge over an extended bandwidth. The panel volumetric modes increase the absorption peaks of the acoustic fishnet if they fall just above the stop-band cut-off frequency. They also set an upper limit to the broadband properties of FGPs up to which a high dissipation, high absorption, and low transmission can be achieved. Critical coupling analysis shows how the HoleCavity resonances are redistributed due to coupling with the panel vibrations. It provides the amount of damping required for these resonances to achieve unit dissipation value.
