Controlling Electromagnetic Wavefronts Using Huygens' Metasurfaces

Abstract

An electric and a magnetic dipole that are superimposed and orthogonal to each other have interesting properties, since the dipoles can be designed to radiate primarily into one half of space only. Such a configuration is referred to as a Huygens’ source. Both active and passive configurations of Huygens’ sources can be envisioned. In this article, the properties of such arrays of passive and active Huygens’ sources are investigated for electromagnetic wavefront manipulation. These arrays are referred to as Huygens’ surfaces and are interesting because they can be designed to implement, thin, low‐profile devices that is desirable for RF/microwave hardware. The design of active and passive Huygens’ surfaces is investigated for three specific applications in the microwave frequency range: cloaking, refraction, and polarization control. For the problem of refraction, the synthesis and analysis of a passive Huygens’ surface to refract a plane wave is discussed for the application of thin microwave lenses. Equivalent circuit models and the implementation of such refracting Huygens’ metasurfaces are discussed. On the problem of polarization control, the design of passive Huygens’ metasurfaces is examined from theoretical, numerical, and measurement perspectives to demonstrate polarization manipulation. Passive Huygens’ surfaces are constructed to perform polarization conversion and chiral polarization effects (circular birefringence). This idea of implementing chiral surfaces is further examined by looking at the design and measurement of surfaces consisting of an electric response only. Finally for the problem of cloaking, active Huygens’ surfaces are investigated to implement a cloak that suppresses scattering from an object in all directions. Both theoretical and experimental aspects are examined and limitations and possible workarounds of active cloaking are briefly discussed. These kinds of Huygens’ metasurfaces have applications in radar, imaging, and point‐to‐point links such as in satellite communications.