Transformation Optics Method Research Articles

Theory and Experiment of Isotropic Electromagnetic Beam Bender Made of Dielectric Materials

In this paper, we utilize the deformation transformation optics (DTO) method to design electromagnetic beam bender, which can change the direction of electromagnetic wave propagation as desire. According to DTO, the transformed material parameters can be expressed by deformation tensor of the spatial transformation. For a beam bender, since the three principal stretches at each point induced by the spatial transformation are independent to each other, there are many possibilities to simplify the transformed material parameters of the bender by adjusting the stretches independently. With the DTO method, we show that the reported reduced parameters of the bender obtained by equivalent dispersion relation can be derived as a special case. An isotropic bender is also proposed according to this method, and it is fabricated by stacking dielectric materials in layered form. Experiments validate the function of the designed isotropic bender for a TE wave; it is also shown that the isotropic bender has a broadband with low loss, compared with the metamaterial bender. The isotropic bender has much easier design and fabrication procedures than the metamaterial bender.

Design of a one-dimensional electromagnetic transparent wall

For a one-dimensional (1D) anisotropic slab, if its electromagnetic parameters satisfy certain conditions, an incident wave can be totally transmitted without any reflections. In this work, a classical method based on analytical results and a transformation optics method using an arbitrary piecewise continuous transformation function are applied to design a 1D electromagnetic transparent wall, whose presence does not disturb the field distribution in the ambient environment. Material parameters and the geometrical requirement of the layered structure using these two different methods are derived, and they agree well with each other. Full-wave simulations validate the transparency of the proposed wall. Because of the simple constitutive parameters and geometry, a transparent structure could be realized using anisotropic and homogeneous materials. The proposed structure has potential applications in radomes, anti-reflection films, and various sensor sectors.

Design of transparent cloaks with arbitrarily inner and outer boundaries

In this paper, the efficient transformation optics method has been utilized to design and analyze two-dimensional (2D) transparent cloaks, structures that can physically protect the devices inside but do not affect their electrical performances at all. The general and explicit expressions for the material parameters of the transformed space are derived. 2D transparent cloaks with arbitrarily conformal and nonconformal inner and outer boundaries and those working in gradually changing background and layered media are designed. Full-wave simulations combined with the Huygens’ principle are applied to validate the transparency of the cloaks. The simulation results under different circumstances demonstrate that the proposed method is correct and efficient. The work introduced here makes important progress in the theoretical design of the transparent cloak and expands the application of the transformation optics method.

Design method for quasi-isotropic transformation materials based on inverse Laplace’s equation with sliding boundaries

Recently, there are emerging demands for isotropic material parameters, arising from the broadband requirement of the functional devices. Since inverse Laplace's equation with sliding boundary condition will determine a quasi-conformal mapping, and a quasi-conformal mapping will minimize the transformation material anisotropy, so in this work, the inverse Laplace's equation with sliding boundary condition is proposed for quasi-isotropic transformation material design. Examples of quasi-isotropic arbitrary carpet cloak and waveguide with arbitrary cross sections are provided to validate the proposed method. The proposed method is very simple compared with other quasi-conformal methods based on grid generation tools.

Electromagnetic interaction of arbitrary radial-dependent anisotropic spheres and improved invisibility for nonlinear-transformation-based cloaks

An analytical method of electromagnetic wave interactions with a general radially anisotropic cloak is established. It is able to deal with arbitrary parameters [ epsilon r (r) , mu r (r) , epsilon t (r) , and mu t (r) ] of a radially anisotropic inhomogeneous shell. The general cloaking condition is proposed from the wave relations, in contrast to the method of transformation optics. Spherical metamaterial cloaks with improved invisibility performance are achieved with optimal nonlinearity in transformation and core-shell ratio.