metasurface

A metasurface is a two-dimensional analogue of a metamaterial, consisting of an array of subwavelength scattering elements, or meta-atoms, arranged on a planar substrate. By designing the geometry, orientation, and arrangement of these elements, metasurfaces impart spatially varying amplitude, phase, and polarization to incident electromagnetic waves. The result is control of the wavefront with a thickness much smaller than the wavelength, enabling flat, compact devices for optics, microwaves, and terahertz applications.

Control mechanisms include resonant phase delays from individual scatterers and geometric, or Pancharatnam–Berry, phase achieved by rotating anisotropic elements to convert polarization while imposing phase shifts. Many metasurfaces are designed to be transmissive or reflective and may use high-refractive-index dielectrics to reduce losses. Advanced designs aim for high efficiency and tailored dispersion over designed bandwidths.

Fabrication typically relies on lithography, nanoimprint, and thin-film deposition, using materials such as silicon, titanium dioxide, gold, or other dielectrics. Metasurfaces span radio to optical frequencies and also include acoustic and elastic variants. Some metasurfaces are active or tunable, incorporating varactors, microelectromechanical systems, liquid crystals, or phase-change materials to adjust their response in real time.

Applications include flat optical lenses (metalenses), beam steering and shaping for communications, holography, polarization control, imaging, sensing, and antenna design. Challenges remain in bandwidth, dispersion, losses, and large-area fabrication, but progress toward programmable and multifunctional metasurfaces continues to expand their use in photonics, sensing, and radar systems.