Simulation sample.

Anechoic coatings are of significance for enhancing the acoustic stealth of underwater equipment. Acoustic coatings with multi-layers of periodic solid inclusions are proposed and investigated for broadband sound absorption. Firstly, an analysis model is derived to calculate effective material and geometric parameters of the layer of solid scatterers. Thereafter the acoustic absorption properties can be obtained by the transfer matrix method. Compared with the finite element method, the analytical model is proven to be viable and efficient. The effect of different geometrical parameters on the acoustic performance is investigated when there is one layer of steel inclusions. In addition, the genetic algorithm is used to quickly achieve the broadband absorption for the two-layer case. The optimized structure, featuring subwavelength thicknesses, has significantly improved its sound absorption performance across a wide frequency range spanning from 1780 Hz to 8890 Hz, covering over two octaves. Finally, the influence of different materials of scatterers on the sound absorption is investigated. This study can provide theoretical guidance for the design and optimization of acoustic coatings with multi-layer solid inclusions.