Research Of Static Field And Electromagnetic Wave Cloaking Device Based On Metamaterials

Invisibility has been a long-standing dream of mankind as a miraculous physical phenomenon.Over this century,researchers have developed the metamaterial structures to control physical fields.These metamaterial structures can be realized by designing microscopic unitcells,or by matching materials in nature.In this thesis,the author focuses on problems in the field of invisibility and carries out some cutting-edge exploratory research.The contents of this thesis are summarized as follows:1.The experimental verification of three-dimensional omnidirectional direct current invisibility cloak.Present direct current cloaking devices are mostly focused on two-dimensional or cylindrical cases.In addition,the conventional resistor network model cannot be directly applied to the cloak of natural bulk material.To solve these above problems,the author experimentally realized a three-dimensional omnidirectional cloaking device in analogy to the electromagnetic field scattering cancellation model.The cloaking device uses a bilayer structure,where all composite materials are homogeneous and isotropic,and can be manufactured by developed industrial processes.By matching the boundary conditions,the layers,object and background material cancel each other’s "distortion" effect on the background electric field,and finally conceal the target object.Since there is no higher-order scattering term in the direct current field,such cloak does not need to satisfy electric small and the metamaterial structure can be very thin comparing to the cloaks in electromagnetic field.This work successfully promotes the experimental realization of direct current cloak from two-dimension to three-dimension for the first time.2.The experimental verification of remote cloaking device based on multi-folded transformation optics.In conventional transformation optics,the needed inhomogeneous anisotropic materials are difficult to prepare,and such cloak need to wrap the object inside the cloak.In order to solve these problems,our group proposed the multi-folded transformation optics method,which can achieve omnidirectional remote cloaking feature.However,the multi-folded transformation optics method involves materials with negative permittivity and permeability,which are also difficult to achieve in experiment.In this thesis,by the metamaterial structure of the resistor network,we achieve a variety of materials with anisotropic but homogeneous conductivity materials and equivalent negative resistance required by multi-folded transformation optics.After optimizing the original multi-folded transformation optics model,an actual remote cloaking device in direct current field is fabricated.This work is the first experimental demonstration of the remote cloaking theory.3.A greyscale metasurface hologram illusionary cloaking device.Metasurface is a twodimensional metamaterial structure that plays an important role in electromagnetic wave modulation devices due to its small dimension,thin thickness,and ease of fitting shape.In order to take advantage of the precise modulation of electromagnetic waves by metasurface,it is possible to build an illusion device.The illusion device can create an electromagnetic illusion of another object to the detector rather than just conceals the cloaked object.In this work,a grayscale tunable metasurface can be achieved by integrating a varactor diode with continuously tunable capacitance into the unitcell.Such metasurface can be programmed real time to control the phase response by digital signal processing instruments,which is able to create an electromagnetic illusion image of an arbitrary nonexistent object in the detector.