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Based on the constitutive tensor of the perfect regular polygonal cloak, the effects of different kinds of losses on the performance of regular polygonal cloak are investigated. The cloak is modeled and simulated using full wave ...
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Based on the constitutive tensor of the perfect regular polygonal cloak, the effects of different kinds of losses on the performance of regular polygonal cloak are investigated. The cloak is modeled and simulated using full wave package COMSOL MULTIPHYSICS. It is found that if the loss tangents are imposed on one or more components of constitutive tensors, especially on the off-diagonal components, the performance of the cloak in the backward region is significantly different from the results of the traditional case, in which losses are the same in all components of magnetic and electric loss tangents. We believe that the results are helpful for the practical situations.
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A theoretical study of a cylindrical anisotropic optical fiber filled inhomogeneously by an anisotropic metamaterial is carried out. Nanoporous alumina microtubes obtained recently by acid anodization techniques are physical manif...
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A theoretical study of a cylindrical anisotropic optical fiber filled inhomogeneously by an anisotropic metamaterial is carried out. Nanoporous alumina microtubes obtained recently by acid anodization techniques are physical manifestations of such optical waveguides. In these microtubes, the nanopores are aligned radially outward and the nanopore diameters vary radially, rendering the system inhomogeneous. By considering the radial variation of the nanopore size, a local permittivity tensor is obtained by a Maxwell-Garnett homogenization theory. The cylindrically anisotropic and inhomogeneously filled fiber is shown to support propagating modes of hybrid polarization character (EH or HE modes). The salient feature of this system is that the modal fields are extremely confined near the center of the waveguide due to the refractive inhomogeneity. The anisotropy plays a relatively minor role in the localization. The easy control over the dielectric anisotropy and the inhomogeneity made possible in the nanoporous alumina fiber makes it an attractive candidate for nanophotonic applications. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)
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Complete transparency and zero reflection condition in anisotropic materials are investigated, and are undertaken in an analytical study. First, the relations related to multilayer anisotropic media in linear structures are stated...
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Complete transparency and zero reflection condition in anisotropic materials are investigated, and are undertaken in an analytical study. First, the relations related to multilayer anisotropic media in linear structures are stated, and then, through these relations, zero reflection from layered structures composed of conventional materials and/or metamaterials are studied. The authors have formulated a rule for zero reflection from anisotropic media, and have presented various aspects of such structures from the viewpoints of frequency and the angle of incidence, and have created complete transparency in them.
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The design of arbitrarily controlled multi-beam antennas is investigated by using the technique of optical transformation. Based on the optical transformation, cylindrical waves emitted from a line source can be converted to plane...
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The design of arbitrarily controlled multi-beam antennas is investigated by using the technique of optical transformation. Based on the optical transformation, cylindrical waves emitted from a line source can be converted to plane waves through a metamaterial layer which has a circular shape in the inner outline and a polygon shape in the outer outline. Hence the line source together with the metamaterial layer constructs a high-performance multi-beam antenna. The number of sidelines and the shape of polygon are used to control the number and directions of beams. Analytical formulas of the permittivity and permeability tensors are presented for the metamaterial layer in the antenna. The designed multi-beam antennas are validated by full-wave simulations using the finite-element method. The proposed multi-beam antennas will be very useful in the intelligent traffic system.
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Several applications of a cylindrical waveguide filled with inhomogeneous materials have been demonstrated. Analytical solutions for modes, an inhomogeneous cylindrical waveguide, are available only for a few material parameters a...
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Several applications of a cylindrical waveguide filled with inhomogeneous materials have been demonstrated. Analytical solutions for modes, an inhomogeneous cylindrical waveguide, are available only for a few material parameters and those are also mostly approximations. We have obtained exact analytical solutions for cylindrical waveguides filled with different inhomogeneous and anisotropic material parameters. Different sets of material parameters are obtained using the geometric transformation method. The analytical and numerical modal field distributions, the value of cutoff frequencies and effective mode indices for different propagating modes are well matched to each other. The inhomogeneity can be used to miniaturize the radial dimensions of the waveguide. This is highly desirable for many applications like sensing, near-field coupling and magnetic resonance imaging (MRI).
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We have investigated specific features of reflection of a plane elliptically polarized electromagnetic wave that is incident from an isotropic nonabsorbing medium onto a plane-parallel layer of a hyperbolic metamaterial the optica...
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We have investigated specific features of reflection of a plane elliptically polarized electromagnetic wave that is incident from an isotropic nonabsorbing medium onto a plane-parallel layer of a hyperbolic metamaterial the optical axis of which is parallel to the interface, while the diagonal values of the dielectric permittivity are smaller than the dielectric permittivity of the isotropic medium. Depending on the angle of incidence and the angle between the plane of incidence and the optical axis of the hyperbolic metamaterial, regimes are possible in which either an ordinary wave or an extraordinary wave, or both waves decay outward from the interface, and, in the latter case, for some values of these angles, the decay may be nonexponential. For these three regimes, the reflection coefficient from a layer of an ITO/Ag nanostructure has been calculated numerically. Upon variation in the polarization of the incident wave, the energy reflection coefficient changes from minimum to maximum values, which depend on the layer thickness. As distinct from conventional anisotropic media, in all cases, the maximum value of the reflection coefficient tends to unity with increasing layer thickness. If the amplitude of an ordinary or extraordinary wave does not decrease outward from the interface boundary, the minimal reflection coefficient periodically turns to zero with increasing layer thickness due to interference. In the case in which both waves decay, with this decay being nonexponential under certain incidence conditions, the minimum reflection coefficient turns to zero at a certain layer thickness, and then tends to unity.
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By means of the commonly used transformation optics, and a general transformation function, new sets of external cylindrical invisibility cloaks are proposed. For the proposed cloaks, a rigorous analysis is performed and the resul...
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By means of the commonly used transformation optics, and a general transformation function, new sets of external cylindrical invisibility cloaks are proposed. For the proposed cloaks, a rigorous analysis is performed and the results indicate zero scattering coefficients outside of the cloaks. Later, a numerical investigation shows that the material dynamic range (MDR) of the proposed cloaks can be as small as half of that of the previously introduced cloak which was based on a simple linear transformation function. The obtained analytical results are verified using a Finite-Element computational analysis.
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A mixed-structure form of one-dimensional metamaterial structure composed of single negative permittivity material and anisotropic metamaterial has been investigated in this paper. Such a multi-layer metamaterial structure constit...
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A mixed-structure form of one-dimensional metamaterial structure composed of single negative permittivity material and anisotropic metamaterial has been investigated in this paper. Such a multi-layer metamaterial structure constitutes special resonant structures, which can be used to control wave propagation and realize the complete separation of TM and TE wave by choosing specific parameters. Theoretical analysis and numerical calculations have been performed to confirm the above results. Specifically, augments in incident angles of TM and TE waves make complete transmission frequencies right shift, and the thicknesses of this resonant structure determine propagation modes and propagation frequencies.
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Metamaterials are composed of structural elements and derive their properties mainly from the inner structure of the elements, rather than the properties of their constituent material. By designing an unstable structural element a...
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Metamaterials are composed of structural elements and derive their properties mainly from the inner structure of the elements, rather than the properties of their constituent material. By designing an unstable structural element as the building block of a metama-terial, many interesting effective material properties can be obtained. The deformation and dissipation mechanisms of such a material built from unstable structural elements is studied in detail. To do so a combination of analytical, semi-analytical, and numerical models are applied to a single buckling element, a periodic cell, and finite size combinations of buckling elements including gradients in the properties of the building blocks. This not only provides insight into the micromechanics and the resulting effective behavior of such metamaterials, but also makes them accessible on the different relevant length scales. A metamaterial built from these building blocks shows programmable or switchable properties and can display energy dissipation with fully reversible deformation, distinguishing it from plastic materials, and timescale independent behavior, distinguishing it from vis-coelastic materials.
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