Guiding Acoustic Waves Via a Gradient Index Meta-Layer

In this work, we propose an efficient approach for controlling acoustic waves through guided mode conversion within a single meta-layer comprised of gradient index metamaterials. By harnessing the subwavelength localization characteristics of acoustic surface waves, the meta-layer can be properly shaped to accommodate arbitrary and prospective trajectories, thus enabling flexible guidance and routing of acoustic waves. Utilizing such a mode conversion mechanism, the acoustic directional transmitter and beam splitter have been devised and numerically demonstrated based on Archimedean spiral structures. These acoustic devices can exhibit a broadband response, achieving transmission efficiency exceeding 80% over a specific bandwidth that can be controlled by the geometry design. The proposed gradient index meta-layer may open new possibilities for acoustic wave manipulation, enabling some promising applications in noise control, information transmission, and energy harvesting.