Customizable multiband second-order sonic topological insulators via inverse design

The second-order sonic topological insulators (SSTIs) with topologically protected corner states offer promising opportunities for developing novel acoustic devices. However, most of the current SSTIs are designed via trialand-error and are only able to host the second-order topological phases within a single bandgap, leaving the topic of second-order topological phases within multiple bandgaps rarely studied. Here, we exploit a topology optimization method to customize and optimize multiband SSTIs. To begin with, we create multiple dual-band SSTIs with customizable dual bandgaps for hosting dual-band corner states. On that basis, a three-band SSTI with three bandgaps is constructed for hosting three-band corner states. Experimental validation is performed to prove the existence of the three-band corner states. This study ushers in a route for customizing high-performance multiband SSTIs, and the designed multiband SSTIs have potential for designing robust multiband acoustic devices.

Automated summary

In this study, a topology optimization method is used to customize and optimize multiband second-order sonic topological insulators (SSTIs). Multiple dual-band SSTIs and a three-band SSTI with customizable bandgaps for hosting corner states are successfully constructed and experimentally validated. This research opens up a route for customizing high-performance multiband SSTIs, and the designed multiband SSTIs have the potential for designing robust multiband acoustic devices.