Topological design of phononic crystals for unidirectional acoustic transmission

The realization of unidirectional acoustic transmission (UAT) has recently aroused great attention owing to the versatile possibility in acoustics-based applications. This paper extends the bi-directional evolutionary structural optimization (BESO) method to the design of phononic crystal (PC) for achieving UAT. The optimization objective is to enlarge the minimum imaginary part of wave vectors along Γ-X while keep that along Γ-M less than the constraint value. We systematically studied the design of symmetric and asymmetric PCs at various frequencies. Numerical examples demonstrate that the proposed optimization algorithm is effective for creating the partial band gap at the specified frequency. The UAT with high rectifying efficiency is then successfully realized by placing the optimized PC in a bend wave guide. The results also show that the asymmetric PCs are more favorable for the design of broadband UAT devices compared with symmetric ones.