Two-dimensional flexural wave vortices based on ring-shaped and partitioned acoustic black hole metasurface

Vortex beams carrying orbital angular momentum have been extensively investigated and applied in acoustics and electromagnetics, but the generation of flexural wave vortices in thin plates still lacks a simple and feasible method. Here, this work proposes an elastic metasurface based on ring-shaped and partitioned acoustic black holes (RPABH). By tailoring the residual thickness of RPABH unit cells, full 0-2π phase shift control with high transmittance is achieved. Numerical and experimental studies confirm that this metasurface converts incident cylindrical waves into flexural wave vortices. The topological charge is linearly related to the number of supercells, and the vortex rotation direction is programmably controllable. This design provides a passive and effective approach for flexural wave vortices generation and may offer new insights into particle manipulation and structural health monitoring.