Low-frequency broadband sound absorption of the metastructure with extended tube resonators and porous materials

A composite acoustic metastructure consisting of double porous materials and resonators with extended tubes is proposed to seek low-frequency broadband sound absorption, considering the low-frequency absorption of resonators and medium–high frequency absorption of porous materials. Based on the double porosity theory and finite element simulation, the sound absorption performance of the composite metastructure is investigated, and the numerical results are verified by experiments. It has been demonstrated that the metastructure with porous materials arranged vertically or horizontally can exhibit a sound absorption coefficient greater than 0.5 at 265–2000 Hz and greater than 0.8 at 760–2000 Hz, which is significantly superior to the existing sound absorption structure with resonator and porous material with the same thickness. The dependence of the sound absorption performance on the geometric parameters of the extended tubes and the porous materials is revealed. On the premise of keeping the cross-section shape of the extended tube and the arrangement of the porous material unchanged, sound absorption performance at low frequencies depends on the diameter, length, and porosity of the extended tubes, whereas sound absorption performance at medium–high frequencies is primarily determined by the percentage of porous materials. Finally, an improved multiple population genetic algorithm (IMPGA), improved by introducing a weight factor function, is used to optimize the parameters of the composite metastructure in a finite space with a thickness of 50 mm, and the sound absorption coefficient was greater than 0.5 in even lower and broader frequency range of [225,2000] Hz. Additionally, the IMPGA can be adjusted to achieve broadband sound absorption within the target frequency range. It provides a new exploration for acoustic material design for low-frequency broadband sound absorption.