Design And Study Of Novel Electromagnetic Devices Based On Metasurfaces

Metamaterial is a kind of artificial composite material, its medium property is irrelevant to the component material and is decided by the microscopic structure. So metamaterials have a lot of physical properties which do not exist in nature, and can control electromagnetic waves with extraordinary ability. Metasurfaces can be regarded as special metamaterials which can produce a series of fascinating electromagnetic properties by controlling the phase gradient or impedance matching. In this dissertation, as a representative electromagnetic device, the ultrathin carpet cloak based on metasurface is studied deeply.The research background and the developing trend of metamaterials, cloaking devices and metasurface are introduced. We present two basic theory, the transformation optics and geometrical optics, which are widely used to design devices of metamaterials. Then we design a lens for collimating illumination based on geometrical optics and full wave simulation is executed to show its performance. The high impedance surface and frequency selective surface are introduced, their properties and operating principle are analyzed in detail.The generalized Snell’s law on the surface of metamaterials is derived, which establishes the foundation for designing devices of metamaterials.Using the high impedance surface as unit cells, an ultrathin directional carpet cloak is designed based on generalized Snell’s law. We realize the directional cloaking by controlling reflected electromagnetic wavefront, and its performance is verified with simulation and experiment. Based on the above work, we find that the carpet cloak can realize the effect of cloaking when the direction of incident electromagnetic wave changes in a certain range. Then we change the operation frequency and find that it can work well in a certain frequency range, the simulation and discussion are made.Our work shows that applying metasurfaces into the study and design of cloaking devices has a considerable advantage over the traditional design methods, because it is much simpler and easier to realize, and it also opens a new mentality in designing. Since the traditional cloaking devices are related to anisotropic, inhomogeneous materials, they are often bulk and difficult to realize. However, the metasurfaces using in this paper are easy in fabrication and can be ultrathin. The superior performance of metasurfaces has important theoretical and practical application value, and they will certainly provide the potentials in various fields.