Control Of Propagation Path Of Electromagnetic Wave And Heat Flux

By controlling the propagation path of electromagnetic wave and heat flux, numerous meaningful functional cloaks could be designed. These cloaks can be utilized to achieve electromagnetic invisibility and illusion, or thermal invisibility, illusion and protection, etc. Researches on the shapes of the cloaks and the coordinate transformations for material parameters designing can increase their flexibility and practicability in engineering applications and develop more theoretically achievable functionalities of cloaks as well.The theory of designing the material parameters of cloaks by the coordinate transformation has been presented. Then, the invariance of Maxwell’s equations and the thermal diffusion equation, which determine the propagation path of electromagnetic wave and heat flux respectively, has been shown.Employing the medium of arbitrary material properties as the object in the arbitrarily shaped electromagnetic illusion cloak, the similarity between the disturbances caused by the cloak-wrapped object and the illusion object has been discussed. Farther more, the analysis on the cloaking effect for electromagnetic irradiation in different frequencies indicates that the effect of the illusion cloak is perfect when the wavelength is equivalent to, or bigger than the cloak’s size, and it could be diminished and even vanished, with the decrease of the wavelength.The material parameters of the thermal cloak are determined by coordinate transformations of varied orders to discuss the differences between the cloaks for the thermal invisibility and protection. By analyzing the simulated results and temperature, it is concluded that the order of coordinate transformations is inadvisable to be big but appropriate to be around the order of liner transform considering the feasibility of material parameters.Based on the folded-geometry transformation and complementary media, a thermal cloak which can cloak an object at a distance outside the cloaking shell is developed and verified by a finite element solver as well as an internal-external thermal invisibility cloak. And it is demonstrated that the direction of heat flux has no influence on the invisibility effect of the two thermal cloaks.To thermally protect an object in the lasting heat flux, a nonclosed thermal cloak is proposed and three sets of parameters with an alterable coefficient are developed to construct it. By comparing simulated results of the three cloaks with a same coefficient, the cloak with best performance is selected and utilized to explore the coefficient’s influence on the thermal protection effect. Eventually, the best set of material parameters is presented to form the nonclosed thermal protection cloak.