Generating flexural wave vortex with polygonal metasurfaces

Vortex wave carrying helical phase has wide applications in particle manipulation, communication, edge enhancement of image, etc. Here, we propose an efficient approach to generate vortex with polygonal metasurfaces for flexural waves. The polygonal elastic metasurfaces consist of maze-like units based on the required phase distribution. The maze-like elastic units alter the acoustic path, thereby modifying the phase of the transmitted wave. By improving the corners of the units, we enhance the transmissivity of the units while ensuring the high mode-preservation. Through the modulation for flexural waves with the metasurfaces, the elastic vortex is successfully generated within the surrounded region. We demonstrate various vortexes with integer and fraction topological charges, centered and off-center locations, based on square and trigonal metasurfaces. The proposal may have potential capability of particle and microfluid manipulations.