Equivalence-Principle-Based Active Metasurfaces

Considered a pillar of electromagnetic theory, the Huygens' principle draws a fundamental link between geometric optics and wave theory. This insight has led to the formulation of the equivalence principle which postulates that a field distribution within a region can be represented by fictitious equivalent sources on its boundary. While the equivalence principle remains a vital theoretical model, the advent of metasurfaces has provided a means of physically realizing such equivalent sources. To demonstrate the capabilities and potential of this technological development, this paper reviews recent work performed in the area of active Huygens' metasurfaces; composed of electric and magnetic radiating sources. These constituent sources can be used to replicate equivalence principle boundary conditions, enabling one to arbitrarily generate electromagnetic waves or control existing fields within a given region at will.