Ultrawide bandgap optimization of porous 3D two-material phononic crystals aided by a 2D-based PnC construction method

Three dimensional (3D) porous two-material phononic crystals (PnCs), as a type of periodic structures, are of practical significance thanks to their ability to achieve omnidirectional absorption of acoustic waves. However, the vast search space inherent in the optimization algorithm presents a major challenge in the topology optimization of 3D PnCs. To date, there has been no reported work on the topology optimization of 3D porous two-material PnCs. To address this gap, a 2D-based PnC construction method is proposed. This method produces highly-symmetrical 3D PnCs from 2D PnCs, greatly decreasing the number of design variables that make up the search space. A genetic algorithm-based topology optimization incorporating this proposal is conducted for maximizing the bandgap of porous 3D two-material PnCs. The effectiveness of the optimization framework has been demonstrated, showcasing its capability to effectively reduce the number of design variables and its applicability to two materials with various disparities. The proposed method, which represents the key innovation of this work, enables the successful topology optimization of 3D porous two-material PnCs. Various structures have been obtained by constrained topology optimization. The results reveal that the optimized porous two-material structures demonstrate more advantages over both porous single-phase and non-porous two-material optimized structures.