Information metamaterials and metasurfaces

Traditionally, ''metamaterials'' have been described by effective medium parameters due to the sub-wavelength nature of unit particles. The continuous nature of medium parameters makes traditional metamaterials behave as analog metamaterials. Recently, the concept of coding metamaterials or metasurfaces'' has been proposed, in which metamaterials are characterized by digital coding particles of 0'' and 1'' with opposite phase responses. It has been demonstrated that electromagnetic waves can be manipulated by changing the coding sequences of 0'' and 1''. The coding particles provide a link between the physical world and digital world, leading to digital metamaterials and even field programmable metamaterials, which can be used to control electromagnetic waves in real time. The digital coding representation of metamaterials or metasurfaces can also allow the concepts and signal processing methods in information science to be introduced to physical metamaterials, thereby realizing extreme control of electromagnetic waves. Such studies have set the foundation of information metamaterials and metasurfaces. In this review article, the coding, digital, and field programmable metamaterials and metasurfaces are systematically summarized and analyzed with particular emphases on the information and digital convolution aspects. The future trend of information metamaterial/metasurface is predicted, including software-defined metamaterials/metasurfaces and cognitive metamaterials/metasurfaces.