Dynamic multimode OAM generation implemented by mechanically reconfigurable metasurfaces

Electromagnetic waves carrying orbital angular momentum (OAM) hold promising applications in enhanced communications by exploiting their multiple and orthogonal modes. While programmable metasurfaces offer the capability to generate OAM waves with varying modes, they come with complexities in design and elevated costs due to the heavy reliance on active devices. In this paper, we present an innovative approach for dynamic OAM generation utilizing a pair of mechanically reconfigurable metasurfaces. The phase distributions of the two metasurfaces are carefully crafted to exhibit reconfigurable characteristics upon superimposition by adjusting their relative displacement. Specifically, the designed metasurfaces feature full phase modulation and high transmittance above -3 dB within 21–24 GHz. With these metasurfaces, OAM waves with six distinct modes (topological charge $l=\pm 1,\pm 2,\pm 3$) have been dynamically achieved, with each mode being generated under a specific displacement. The proposed design is rigorously validated through numerical simulations and experimental measurements.