Research On Complementary Invisibility Cloak Based On Coordinate Transformation Theory

Controlling electromagnetic field theory has always been one of the hot issues of research for people.The basis of this theory is the invariant form of Maxwell's equations,that is,Maxwell's equations have similar structures in different space.One of the most widely applications of this theory is the invisibility cloak,which directs smoothly electromagnetic waves through the invisibility cloak and then recovers the original trajectory,making the object appear to be "disappeared".At the early time of the design,this method can only realize the invisibility,but it is “blind” for the inside of the invisibility cloak,namely,it prohibits electromagnetic wave from penetrating into the cloak,and the interior of the cloak can not exchange information with the outside world.In the following years,there have been many of open cloaks.One of the most attractive designs is an external invisibility cloak using complementary media theory,which enables the objects inside the cloak to communicate with the outside world.However,it must be embedded a specific "anti-object" in the complementary layer.Considering the difficulty of actual manufacturing,an idea of discretization is applied to study the multi-layered complementary invisibility cloak,and this paper also proposes a non-conformal complementary cloak that can adjust the axial ratio to contain the different shape objects.Two different invisibility cloaks are proposed in this paper,which combine the theory of coordinate transformation and the concept of complementary media.The main research works as following:1.Firstly,this paper introduces briefly the theory of controlling electromagnetic field and complementary media theory,derives the material parameter expression,and verifies the validity of the above expressions by using simulation software.The above theoretical knowledge is the basis of the following multi-layered complementary invisibility cloak and non-conformal invisibility cloak.2.Secondly,considering the difficulty of actual manufacturing and based on an idea of the discretization,this paper separates all continuous and complete regions into a number of smaller finite regions,whilst ensuring that the material parameters of the same small region are identical.The parameter expressions of different regions are derived,and the correctness of the above expressions are verified by the simulation software Comsol which is based on finite element analysis.The invisibility performance of the proposed cloak can be illustrated from the near-field distribution and the far-field RCS distribution.And the communication performance is also verified by the electric field distribution when object is placed the inside of the cloak.At last,two-dimensional(2D)space can be extended to three-dimensional(3D)space,and obtain the designed process of 3D multi-layered complementary cloak.Similar to 2D case,the electric field distributions of the different layered cloak are simulated,communication effects are also verified,and the constitutive parameter distributions of different regions are also given as it is helpful in analyzing the possibility of manufacturing such a cloak.3.Finally,on the basis of multi-layered complementary cloak,this paper studies a non-conformal complementary cloak that can adjust axial ratio to adapt to different shapes object.Draw upon the boundary equation of the ellipse,the general formula of the parameter expression of different regions are obtained.Combining the near-field distribution that simulation software gives,far-field distribution of arbitrary geometrical size,and the constitutive parameter distributions,this paper verify the possibility to implement this invisibility cloak.At the same time,the invisibility performance and communication effect of this cloak are confirmed by placing different shapes object inside the invisibility cloak.At last,the two-dimensional case can extend to the three-dimensional case,and the material parameter expressions are also given.Invisibility effects are verified by simulation software,and it further shows that the invisibility performance is basically not affected whatever incident angles are.