Design And Validation Of The Electromagnetic Invisibility Cloaks

With the emergence and development of left-handed materials, the stealth material also entered a new stage of development—the design and investigation of invisibility cloaks. Most of the electromagnetic invisibility cloaks designed by the existing methods have the following problems: the material parameters of invisibility cloaks in local places have the singularity; Almost all invisibility cloaks are composed by nonuniform anisotropic media, so it is difficult to make invisibility cloaks satisfy theoretical requirements in engineering applications. Therefore, looking for the nonsingular, isotropic even uniform medium for the invisibility cloaks is a very important work now. Aiming at the existing problems in the electromagnetic stealth field, some new methods and extension of existing works will be proposed in this paper.Firstly, the isotropic cloak medium defined by exponential function is proposed to overcome the anisotropic defect in the invisibility claoks. The method of variable separation is used to study the electromagnetic scattering problem when the cloak medium is isotropic. The distributions of all the field quantities are obtained by rigorously mathematical derivations. Furthermore, the relationship between the scatteing cross-section and geometry size of the cloak is given by the MATLAB software. The present results indicate that the cloak designed by simple isotropic material can not accomplish the purpose of invisibility.Secondly, to avoid the singulatity appeared in most invisibility cloaks, a new method of designing the invisibility cloak is proposed by combining the coordinate transformation with the conformal mapping method. Then an elliptic cylindrical cloak without any singularity is designed by the method developed in this paper. The COMSOL Multiphysics software is used to solve elliptic cylinders with different sizes and the elliptic cylinders with or without a loss tangent. The numerical results proved that the elliptic cylindrical cloak designed by the present method can not only accomplish the purpose of invisibility, but also can avoid the singularity of invisiblity cloaks. Therefore, the present method is valid and practical.Finally, the application scope of the existing outside stealth cloaks and the internal and external cloaks will be extended. The shapes of the outside cloak and the internal and external cloak are transformed from the axisymmetric cylinder to the arbitrary polygon cylinder. This paper not only gives the strict theoretical derivations for the two different cloaks, but also gives the simulation examples by using the COMSOL Multiphysics software. The simulation results verify the effectiveness of the theoretical derivation.