Topic
Transformation optics
About: Transformation optics is a research topic. Over the lifetime, 2687 publications have been published within this topic receiving 102378 citations.
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TL;DR: In this article, the magnetic and electric resonances of cut wire pairs of metamaterials were manipulated to produce a negative refractive index at optical frequencies. But the negative index was not shown at microwave frequencies.
Abstract: Metamaterials made of exclusively metallic cut wire pairs have been experimentally demonstrated to exhibit a negative refractive index at optical frequencies. However, other related works have not shown a negative index. In this paper, we propose an easy way to manipulate the magnetic and electric resonances of these metamaterials to produce a negative index. We show that judiciously breaking the symmetry of the structure allows tuning of both resonances leading to an overlapping between the negative permeability and negative permittivity regions. Numerical and experimental parametric studies of several cut wire pairs metamaterials are presented to validate our method at microwave frequencies.
44 citations
TL;DR: In this article, the authors proposed a quasi-conformal coordinate transformation (QCCT) based lens design for conformal array antenna applications, where a physically linear array can be transformed into a virtual curved array, or vice versa, using a lens having only nonmagnetic medium parameters.
Abstract: Based on quasi-conformal coordinate transformation, lens designs for conformal array antenna applications are presented. Potentially over a broad bandwidth for the two-dimensional TE polarization, a physically linear array can be transformed into a virtual curved array, or vice versa, using a lens having only nonmagnetic medium parameters. Lens designs for transforming between linear and cylindrical arrays in conformal conducting ground planes as well as their predicted scanning performances are shown. Such lenses can be designed and applied to existing array antennas to enable new scanning capabilities.
43 citations
TL;DR: In this article, a waveguide simulation of a unit cell is used to retrieve the effective permittivity and permeability with which they compute the far-field radiation of a monopole embedded in a metamaterial substrate using an analytic method.
Abstract: Simulations have been carried out on metamaterials in the microwave regime. S-parameters obtained from waveguide simulations of a unit cell are used to retrieve the effective permittivity and permeability with which we compute the far-field radiation of a monopole embedded in a metamaterial substrate using an analytic method. We find that the analytic method is able to predict features of the experimental results, implying that within a certain frequency range, we can treat the metamaterial as being anisotropically homogeneous. Based on the methodology, a structure is optimized for the application of metamaterials as antenna substrate to enhance directivity by minimizing its refractive index. The experimental results are presented and compared with the analytic calculations. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 680–683, 2006; Pubished online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.21441
43 citations
TL;DR: A recent theoretical proposal to achieve omnidirectional, reflectionless absorption in inhomogeneous media with a spatially varying permittivity is implemented, showing that this approach is experimentally feasible.
Abstract: As a fundamental phenomenon in electromagnetics and optics, material absorption has been extensively investigated for centuries. However, omnidirectional, reflectionless absorption in inhomogeneous media has yet to be observed. Previous research on transformation optics indicated that such absorption cannot easily be implemented without involving gain media. A recent theory on wave propagation, however, implies the feasibility to implement such absorption requiring no gain, provided that the permittivity profile of this medium can satisfy the spatial Kramers–Kronig relations. In this work, we implement such a profile over a broad frequency band based on a novel idea of space–frequency Lorentz dispersion. A wideband, omnidirectionally reflectionless absorption is then experimentally observed in the gigahertz range, and is in good agreement with theoretical analysis and full-wave simulations. The proposed method based on the space–frequency dispersion implies the practicability to construct gain-free omnidirectionally non-reflecting absorbers. Reflectionless absorption independent of the angle of incidence usually requires the introduction of gain media into the system. Here, Ye et al. implement a recent theoretical proposal to achieve this with a spatially varying permittivity, showing that this approach is experimentally feasible.
43 citations
TL;DR: In this article, the coordinate transformation method is applied to bounded domains to design metamaterial devices for steering spatially confined electromagnetic fields, and two approaches in non-magnetic realization of these structures are examined.
Abstract: The coordinate transformation method is applied to bounded domains to design metamaterial devices for steering spatially confined electromagnetic fields. Both waveguide and free-space beam applications are considered as these are analogous within the present approach. In particular, we describe devices that bend the propagation direction and squeeze confined electromagnetic fields. Two approaches in nonmagnetic realization of these structures are examined. The first is based on using a reduced set of material parameters, and the second on finding nonmagnetic transformation media. It is shown that transverse-magnetic fields can be bent or squeezed to an arbitrary extent and without reflection using only dielectric structures.
43 citations