Topological logical elements based on defect-mediated sound-wave manipulation

Growing interest in acoustic topological insulators arises from their robust edge states, which are resistant to defects and backscattering. Traditionally, the edge states of topological insulators are believed to be nearly immune to subwavelength-sized defects. As a result, there have been few studies focusing on utilizing defects to enhance wave control. Here, we investigate the impact of introducing periodic defects into acoustic pseudospin systems on the band structures and extend our analysis to nonperiodic structures. We discover that even a single subwavelength defect can significantly affect the topological boundary states, providing a platform for controlling and switching pseudospin edge states using defects. Expanding on this discovery, we develop a broadband topological sound switch (TSS) that achieves a high transmission ratio before and after switching by simply rotating a single scatterer. Additionally, we design three topological logic gates based on this TSS and experimentally verify their functionality. Our theory and experiments demonstrate that the spatial arrangement of defects can serve as a means of manipulating sound waves, potentially advancing acoustic computing and information processing.