Topology optimization of acoustic mirror-symmetric waveguides for interface states in Bragg and non-Bragg gaps

Topology optimization, as a scientific and efficient intelligence algorithm, can be used to distribute the structures or materials with periodic units within the design domain to obtain the desired properties or functions. To induce interface states with high transmission and localization at the specified objective frequency, we propose a topology optimization design of the mirror-symmetric periodic waveguides based on the combination of the multiple population genetic algorithm and the finite element method. In addition to the traditional Bragg gaps, which are generated by the same low-order mode resonances, interface states can also be induced through the proposed topology optimization method in the non-Bragg gaps formed by the resonances of the more complex modes. The non-Bragg interface states possess higher localization due to the involvement of high-order modes in the non-Bragg resonances. This topology optimization method is expected to realize the wavefield manipulation of sound wave localization from a new perspective and provide a novel method for the design of devices for intense localization and high transmission.