Wireless Functionalities with Reflective Metasurfaces

Reflective metasurfaces act as engineered planar electromagnetic boundaries that enable deterministic scattering control of wireless fields across spatial, spectral, and polarization dimensions. This chapter structures reflective metasurface research into three operational regimes—static, reconfigurable, and time-varying—emphasizing their potential to realize wireless beam manipulation and resource-management functions. Static metasurfaces go beyond conventional beam-shaping primitives such as anomalous reflection, focusing, vortex wavefront generation, and polarization conversion, to support extreme aperture-level field control, extreme-angle scattering, spectral and wavefront selectivity, and analog spatial signal processing for enhanced feature extraction and interference-robust reception. These static capabilities are transferred to the reconfigurable domain through tunable elements—chip-scale varactors, digital phase-switching cells, and coordinated FPGA control—enabling adaptive wireless behavior including real-time beam scanning, dynamic polarization tuning, optimized relaying, interference suppression, and link-loss compensation. When biased with temporal or joint space-time modulation, reflective metasurfaces exit linear time-invariant constraints, unlocking additional wireless functions such as frequency translation, phase-conjugated, nonreciprocal reflection, wave amplification, and momentum-frequency control inspired by time-modulation and time-interface physics and photonic time-crystal-type surface dispersion. By operating as wave-manipulating boundaries instead of transmission-line radio-frequency circuit analogues (e.g., circulators, mixers, relays), reflective metasurfaces establish an expanded functional foundation for future wireless front-ends, enabling signal routing, beam combining and splitting, path-loss relief, and interference mitigation, with boundary-driven degrees of freedom positioned for 6G and beyond.