Optimal design of subwavelength broadband acoustic porous composite metasurface based genetic algorithm

A 3D composite acoustic metasurface (CAM) is proposed to achieve broadband sound absorption in subwavelength thickness. The designed structure consists of a parallel configuration multicomponent resonant structure (MRS) for the low frequency band and a metaporous layer (ML) with periodic array components for the high frequency band. Genetic algorithm is adopted to construct an optimal design method to obtain the appropriate parameters of the CAM. The optimized result is got accurately and quickly in this way and the acoustic properties satisfy the target design. In the low frequency range, the parallel configuration of different microperforated panel systems (MPPSs) broadens the resonant frequency band. The ML based on polyurethane (PU) foam consists of four subunits with a linear phase gradient in one period, which improves the absorption of uniform porous foam with the same thickness by converting the reflected wave into the surface wave. The sound energy in high frequency range is mostly dissipated in this way. The acoustic performance of CAM is predicted theoretically and demonstrated by numerical simulation and experiment. The sample with 50 mm achieves remarkable absorption, over 80 %, in the overall frequency range from 500 Hz to 3000 Hz. Even though the thickness of the sample is reduced to 30 mm, it still presents a better sound absorption than the PU foam with same thickness in the range from 500 Hz to 3000 Hz. No matter what the azimuthal angle of incident wave is, the 3D CAM shows quasi-perfect sound absorption which the PU foam cannot provide at the design frequency 2000 Hz in this study. This work provides a method to design broadband sound absorbers efficiently, which has good application value in cabin noise control.