Ultra-broadband sound absorption of a multiple-cavity metastructure with gradient thickness

Abstract

In order to achieve ultra-broadband perfect sound absorption at low and middle frequencies, a novel acoustic metastructure composed of a multiple-cavity coupled resonator and melamine foam (MF) is proposed. Firstly, the metastructure termed as MPP-AG consisting of microperforated panel (MPP) and multiple annular groove cavities (AG) is investigated. Analytical research and finite element simulation are conducted, and the sound absorption characteristics are verified through the impedance-tube test. The effects of the MPP and backing cavity parameters on the sound absorption and coupling performance of the AG are studied. In Particular, MPP-AG with gradient depth shifts the initial frequency with a sound absorption coefficient greater than 0.5 to a lower 315 Hz at the deepest depth of 95 mm. The MPP-AG is optimized with the Genetic Algorithm and the absorption lower band with an absorption coefficient greater than 0.5 is shifted towards 278 Hz. Furthermore, through filling melamine foam into the MPP-AG, the improved metastructure MPP-AG-MF is established to broaden the absorption bandwidth. A perfect absorption (α>0.8) between 255 and 1600 Hz can be obtained at a depth of 70 mm by the optimization of the MPP-AG-MF with the Genetic Algorithm. This study can provide significant guidance for noise attenuation and sound absorber design, which is promising to be used in aerospace, transportation, construction and mechanical design, etc.