Study And Design Of Electromagnetic Functional Devices Based On Transformation Optics Method

Transformation optics was introduced to design electromagnetic materials in recent years and is based on the form-invariance of Maxwell’s equations under a coordinate transformation. The difference exists between transformation optics and the traditional optical. Fermat’s law is used to describes the effect of the change of the refractive index to light path in traditional optical, but in transformation optics it is through the design of material properties to manipulate electromagnetic wave in desired manner. The shape is dominant in transformation optics, and the design process of electromagnetic devices is greatly simplified at the cost of increasing the complexity of materials parameters through coordinate transformation. Transformation optics methodology provides a totally new and powerful tool to us to manipulate electromagnetic wave, which is achieved through the application of appropriate coordinate transformations. Transformation optics can be interpreted as appropriate scaling of the material parameters are compressed and dilated in different coordinate directions. The most salient example of the transformation-based device design is the invisibility cloak by which incident light will be guided around the object smoothly and return to its original trajectory outside the cloak. Generally, the materials derived through transformation optics are inhomogeneous and anisotropic. Even some time we will achieve the metamaterial with negative-index, which is not realizable in nature. With metamaterial, a new class of electromagnetic materials, arbitrarily manipulating electromagnetic wave comes true. Metamaterial owe their properties to sub-wavelength details of structure rather than to their chemical composition, which can be designed to have properties difficult or impossible to find in nature. And metamaterial enables transformation optics methodology to rapidly develop.Metamaterial plays an important role in the development of transformation optics and the resulting revolution is progressing around the world. Owing to their ability to support the surface waves in the infrared and visible regimes, the noble metals, such as silver and gold, have been popular materials for constructing optical metamaterial. However, the difficulty in varying parameters of noble metals and the existence of material losses especially at visible wavelengths limit the relative propagation lengths of SPP waves along the interface between such metals and dielectric materials. In 2004, graphene is firstly isolated. Graphene owns a single atomic layer of sp2 hybridized carbon atoms and is tightly packed in a symmetric hexagonal honeycomb lattice. From then on, there has produced a vast body of literature on graphene. The interest in graphene is due to its outstanding physical, electrical and optical properties, which originate from the unique smooth-sided conical band structure. And graphene is regarded as a material to realize a large variety of devices. At same time, graphene can also serve as a good platform for further exploration of plasmonic devices. Graphene is thought to be a kind of material which can promote the great development of science.Under this background, this dissertation carefully studies and discusses several electromagnetic functional devices based on transformation optics method. And the main work of the dissertation is detailed as follows:1. The major strategies are summarized and described for several electromagnetic functional devices. One can crush the concealed object to a point or a sheet to achieve perfect invisibility. With different idea, the transformation optics technology consists in compressing or expanding a certain space and the apparent size of a cross section can be changed. In order to make the appearance of an object is equivalent to a larger or smaller one, and the appropriate transformation function needs to be employed. At the same time, the proper material’s parameters can be gained and the impedances at the inner and the outer boundaries of the device are matched. The results are validated by numerical simulations by using different cross sections. And in the limited cases, the proposed material shell will be a cloak. In addition, by using Laplace’s equation, the coordinate relationship between original space and transformed space can be achieved with a finite element software. Based on this a design of a planar focusing antenna is presented.2. Plasmonic cloak using graphene at infrared frequencies is proposed. A design for one-atom-thick cloak is presented in this paper. It is achieved by utilizing an approximate hemispherical geometry with graded index to create a perfect, isotropic, and omnidirectional cloak. A curved surface with given refractive index will modify the effective distance seen by a SPP wave. The conductivity profile will ensure that the propagation characteristics of a flat surface are emulated by the hemispherical one, and this makes the curvature invisible to SPP waves confined to the hemispherical surface.3. Graphene-based infrared lens with tunable focal length is proposed. In modern information and communication technologies, manipulating focal length has been hot topic. Considering that the conductivity of graphene layer can effectively be tuned by purposely designing the thickness of the dielectric spacer underneath the graphene layer, a graphene-based lens with tunable focal length is proposed in this paper, and it can be used to collimate waves. The fabrication of the proposed graphene-based lens is purposed, and the performance of the lens is verified with finite-element method. The simulation results demonstrate that the graphene-based lens has excellent tunability and confinement. At the same time, the lens exhibits low loss in certain rang and large frequency bandwidth.