Topological valley mode separation of elastic waves and potential applications

Abstract

Topological metamaterials in condensed matter systems have shown significant potential for information and energy applications due to their novel wave propagation behaviors. Recently, there has been an increasing focus on studying topological metamaterials in classical wave systems. Elastic waves, as full-vector classical waves, possess more intricate mechanical characteristics compared to sound waves and electromagnetic waves. This complexity not only offers diverse practical application possibilities but also presents notable research challenges in the field of topological metamaterials. In this study, our main objective is to achieve the ideal mode separation of elastic waves, specifically separated into the in-plane and out-of-plane components, and explore its potential applications. Firstly, we design phononic crystals with dual Dirac cones. Through geometric perturbation, we successfully separate the valley Hall phases of in-plane and out-of-plane modes. By superimposing different topological phases, we achieve three types of topological edge states: in-plane waves, out-of-plane waves, and hybrid waves. Combining these different topological edge states enables us to effectively separate the elastic waves into in-plane and out-of-plane components. Furthermore, we investigate the potential application of mode separation in energy harvesting. We achieve the energy localization of different wave modes based on the topological whispering-gallery mode. Additionally, by utilizing piezoelectric materials, we realize the subregional energy harvesting of in-plane and out-of-plane modes. The mechanical properties resulting from mode separation and topological whispering-gallery mode hold great potential for signal filtering and energy storage, thereby opening up new possibilities for controlling and utilizing elastic waves in various engineering scenarios.