The Design Of Broadband Reflective And Transmissive Electromagnetic Invisibility Cloaking Based On Phase Abrupt Metasurface

With the emergence and development of metamaterials and metasurfaces in recent years,the invisibility technology has come to life from a dream.However,metamaterials have some disadvantages such as harsh material parameters,large structures,and difficulty in integration and processing,the use of metasurfaces to achieve cloaking devices has received widespread attention.The metasurface is actually a two-dimensional metamaterial.Compared with the former,it has ultra-thin,lightweight,easy to integrate and process,and can be extended to large size invisibility cloaks.The metasurface has a unique ability to control the phase,amplitude,and polarization of the incident electromagnetic waves.By adjusting the size of the metasurface resonance unit,the phase of the metasurface unit can be arbitrarily changed,local phase compensation can be provided on the surface of the hidden object,and the near-field wavefront of the electromagnetic wave can be restored,so that the incident electromagnetic wave acts as if it hit a plane mirror to achieve invisibility.However,the development time of metasurface cloak is still short,and some existing problems need to be further explored.For example,the existing metasurface cloaks generally have narrow band and relatively small angle response problems,and the current application scenarios of metasurfaces are only to achieve carpet-type invisibility device.Regarding how to improve the cloaking performance of the metasurface cloak and how to realize the transmissive cloak based on metasurface,this paper has carried out the research on the following schemes:(1)Firstly,a THz metasurface cloak with wide-band and wide-angle response was proposed.By introducing antireflective high-refractive-index dielectric layer and antireflective "moth-eye-like" microstructure,with its high permeability and wide response ability to angles,greatly enhanced the cloaking performance on the basis of the traditional metasurface invisibility cloak.At the beginning of the design,we proposed two schemes,by covering a layer of high refractive index material and adding a layer of "moth-eye-like" microstructure on the basis of the traditional metasurface cloaking unit cell.Then,by scanning the parameters of the metasurface resonance unit,the size of basic unit cell that satisfies the local phase compensation under the two schemes is found.Through numerical simulation,we found that after the antireflective layer was introduced in the unit design,the metasurface cloak can realize a significant reconstruction of the wavefront in the wideband range of0.65 THz to 0.9THz and still work effectively when the angle of incidence deviates from 15 ° working angle。(2)A dual-wavelength metasurface cloak based on a single-layer metasurface is proposed.Achieving dual-wavelength or multi-wavelength cloaks has been an important research direction to solve the problem of narrowband about the traditional metasurface invisibility cloaking.The difficulty in realizing dual wavelength is that the phase response of a basic unit can usually only satisfies a single working wavelength.In this paper,we design a basic unit with a large difference in structural period.Using the low coupling of the internal and external structures in the metasurface basic unit,a dual-wavelength cloak capable of operating independently at 9.6GHz and 21.6GHz is realized.(3)A novel transmissive invisibility cloak based on transparent metasurfaces was proposed.Since the emergence of metasurfaces,the research about metasurface cloak has never stopped.However,most of the current metesurface cloaks are carpet-type invisibility cloaks,but how to utilize metasurface to achieve transmissive space cloaks is rarely involved.We introduced a transparent metasurface,which has the both ability to manipulate electromagnetic waves and super high permeability.We propose a transmissive cloaking device based on transparent supersurface.By three layers of transparent metasurfaces to control the incident electromagnetic waves,the incident waves can propagate around the surface of the obstacle,so that it does not cause unexpected scattering and forms an ideal hidden space.