Topological optimization of hierarchical honeycomb acoustic metamaterials for low-frequency extreme broad band gaps

Due to their suitable mechanical properties and low-frequency band gaps (BGs), acoustic metamaterials (AMMs) with hierarchical honeycomb structures received extensive attention in recent years. In this paper, the author proposed a series of hierarchical honeycomb metamaterials with hexagonal and kagome sub-units. The effect of including the fully-filled scatterers in two hierarchical honeycombs types were analyzed, along with the associated generation mechanism. Aiming to obtain the low-frequency broad BGs, a genetic algorithm was used to optimize the scatterer filling scheme. Optimized lattices displayed extreme broad BGs characteristics at low frequencies. Finally, transmission loss experiments were carried out, and results verified the band structures numerical calculation in both P wave and S wave tests. The hierarchical honeycomb metamaterial structures and scatterers filling optimization method introduced in this paper are expected to promote the development of AMMs. Additionally, resulting metamaterials are expected to find their application in the practical engineering field.