Topology optimization of anisotropy hierarchical honeycomb acoustic metamaterials for extreme multi-broad band gaps

Acoustic metamaterials (AMMs), especially based on hierarchical honeycomb structure and topology-optimized design with suitable mechanical properties and low-frequency band gaps (BGs), have been studied recently. The present work reports a series of anisotropy hierarchical honeycomb structure lattices composed of the cell walls and vertices of regular hexagonal lattice replacement honeycombs of various sizes, as well as improved BG evaluation indicators. The band structures of three different types of unfilled hierarchical honeycomb lattices are calculated and the mechanism of BGs generation is analyzed. To obtain multi-broad BGs in the low-frequency range, the scatterers filling schemes are optimized by using a genetic algorithm (GA). Additionally, the effects of structural/material parameters on the BG characteristics of the optimized structures are discussed. Finally, the transmission loss (TL) experiment verified the optimization of the structures. This paper aims to promote the application of hierarchical honeycomb metamaterials with low-frequency vibration isolation in the industrial field.