EM Metasurfaces [Guest Editorial]

Metasurfaces (MTSs) [1], [2], [3], [4], [5] are the surface equivalent of metamaterials (MTMs): artificial materials composed of subwavelength inclusions embedded in a host medium tailored to exhibit unconventional electromagnetic (EM) properties. In contrast to MTMs, which are characterized in terms of homogenized material parameters, the EM responses of MTSs are often characterized by homogenized boundary conditions (BCs). MTSs can be designed to exhibit abrupt amplitude and phase discontinuities to perform extreme wavefront transformations. Classical 'surface EMs' [3] took on fresh and exciting research directions with MTSs, revealing fascinating phenomena and new applications.