Electromagnetic Invisibility of Elliptic Cylinder Cloaks

Structures with unique electromagnetic properties are designed based on the approach of spatial coordinate transformations of Maxwell's equations. Thisapproach is applied to scheme out invisible elliptic cylinder cloaks, which provide more feasibility for cloaking arbitrarily shaped objects. The transformation expressions for the anisotropic material parameters and the field distribution are derived. The cloaking performances of ideal and lossy elliptic cylinder cloaks are investigated by finite element simulations. It is found that the cloaking performance will degrade in the forward direction withincreasing loss.     

Switchable directional scattering based on spoof core—shell plasmonic structures

Manipulating directional electromagnetic scattering plays a crucial role in the realization of exotic optical phenomenon. Here, we show that the spoof plasmonic structure is able to achieve the switching of directional scattering direction on a subwavelength scale by inserting a perfect electric conductor (PEC) cylinder into the hollow of the spoof plasmonic structure. Based on the modal analysis, it is found that the electromagnetic response of the core-shell structure not only is well excited, but also exhibits the directional scattering by interference between the electric and magnetic dipolar resonances. We also discuss the influence of PEC cylinder radius on the performance of the directional scattering. Finally, the active tunable directional scattering is realized by switching between the two states. This work provides a feasible pathway to the subwavelength manipulation of electromagnetic wave. Moreover, it offers a simple method to switch the directional scattering direction. The proposed design approach can be easily applied to digital electromagnetic wave communication and associated applications.     

Physical bounds on electromagnetic invisibility and the potential of superconducting cloaks

The possibility of suppressing the scattering cross section of an object is subject to fundamental physical bounds imposed by causality and passivity. Global cloaking limitations have been recently derived, which imply that any linear, causal and passive cloak necessarily increases the global scattering, integrated over the whole electromagnetic spectrum, compared to the uncloaked object. Here, we expand on this topic, discussing in detail an interesting exception to this limit represented by cloaks with static diamagnetism. In this context, we explore the potential of superconducting materials to realize global and local reduction of the scattering cross section. The concepts of plasmonic and mantle cloaking are extended to superconductors, realizing strong and tunable invisibility, with some unique properties stemming from the peculiar electrodynamics of superconductors. We conclude by qualitatively discussing a possible method to derive more stringent local bounds on cloaking.     

Cloaking an object in a half space without reflection

A novel cloaking scheme to hide an object in a half space from electromagnetic (EM) detection without reflection is firstly presented. The proposed cloaking scheme contains a couple of matching strips, which consist of an isotropic material layer and an anisotropic UPML layer, located right under the bottom surface of a semi-cylindrical cloaking shell. Simple expressions for the material parameters of the cloaking scheme are derived. Numerical simulations are also performed, and a good cloaking effect is achieved. The cloaking scheme is effective to hide the local object with strong scattering characters placed on mobile carriers, such as the radar antenna system on an aircraft.1     

Impedance-Matched Reduced Acoustic Cloaking with Realizable Mass and Its Layered Design

We present an impedance-matched reduced version of acoustic cloaking whose mass is in a reasonable range. A layered cloak design with isotropic material is also proposed for the reduced cloak. Numerical calculations from the transfer matrix methods show that the present layered cloak can reduce the scattering of an air cylinder substantially.     

Controlling light with plasmonic multilayers

Recent years have seen a new wave of interest in layered media – namely, plasmonic multilayers – in several emerging applications ranging from transparent metals to hyperbolic metamaterials. In this paper, we review the optical properties of such subwavelength metal–dielectric multilayered metamaterials and describe their use for light manipulation at the nanoscale. While demonstrating the recently emphasized hallmark effect of hyperbolic dispersion, we put special emphasis to the comparison between multilayered hyperbolic metamaterials and more broadly defined plasmonic-multilayer metamaterials A number of fundamental electromagnetic effects unique to the latter are identified and demonstrated. Examples include the evolution of isofrequency contour shape from elliptical to hyperbolic, all-angle negative refraction, and nonlocality-induced optical birefringence. Analysis of the underlying physical causes, which are spatial dispersion and optical nonlocality, is also reviewed. These recent results are extremely promising for a number of applications ranging from nanolithography to optical cloaking.     

Approximate optical cloaking in an axisymmetric silicon photonic crystal structure.

Axisymmetric photonic crystal structures may be designed to possess interesting optical properties, particularly when the photonic band structure of the material is highly anisotropic. We use finite element calculations to demonstrate an approximate electromagnetic cloaking effect imparted by a structure consisting of concentric silicon photonic crystal layers. The results show that it is possible to bend light around an object by simply using anisotropy. The calculations show that the cloaking mechanism is fundamentally different from Pendry's approach. This design may work as a practical solution for optical cloaking.     

Modeling of arbitrary cross-sectional cylinder using N circular cylinders for the scattering calculations

Exact solution of the electromagnetic wave scattering by N dielectric cylinders is presented by using matrix formulation. To check this present method, two comparisons between exact solutions for a single circular conducting and dielectric cylinder and this model composed of N=25 circular cylinders are made. Numerical results of conducting and dielectric square cylinder has been also checked with well-known result (B.E.M). The scattering patterns and the near field distributions in space are presented for the concave, convex and dielectric circular cylinder with conducting reflector.     

Mathematical Simulation of Cloaking Metamaterial Structures

In this paper we present a rigorous derivation of the material parameters for both the cylinder and rectangle cloaking structures. Numerical results using these material parameters are presented to demonstrate the cloaking effect.     

Electromagnetic analysis of cylindrical invisibility cloaks and the mirage effect

We present a finite-element analysis of a diffraction problem involving a coated cylinder enabling the electromagnetic cloaking of a lossy object with sharp wedges located within its core. The coating consists of a heterogeneous anisotropic material deduced from a geometrical transformation as first proposed by Pendry [Science 312, 1780 (2006)]. We analyze the electromagnetic response of the cloak in the presence of an electric line source in p polarization and a loop of magnetic current in s polarization. We find that the electromagnetic field radiated by such a source located a fraction of a wavelength from the cloak is perturbed by less than 1%. When the source lies in the coating, it seems to radiate from a shifted location.     

Electromagnetic beam wave scattering by arbitrary cross-sectional conducting cylinder using N circular cylindrical models

Rigorous expression of the electromagnetic beam wave scattering by N circular cylindrical models is described. To check this method, comparison between exact solution and this model composed of N=24 circular cylinders is presented for a single circular conducting cylinder. Numerical results of conducting square cylinder has been also checked with well-known result (B.E.M).     

微波超材料隐形结构及其新型快速实验方案

基于Maxwell方程组在坐标变换下的协变性,利用柱坐标变换以及开口谐振环周期排列而形成的超材料设计了一个工作于10.14GHz频率下的隐形结构.采用一种新型快速实验方案测量微波信号强度.实验结果表明在外围增加了隐形结构之后,圆柱金属的阴影和散射效应都被削弱,得到了预期的隐形效果.该实验系统降低了系统的结构复杂性并缩短了实验周期,为该领域的研究提供了一种新的简单有效的实验方案.     

Theoretical and experimental validation of UTD applied to electromagetic-wave scattering by circular cylinders

The scattering of obliquely incident electromagnetic waves by a perfectly conducting circular cylinder is analyzed. In this paper the accuracy of a high-frequency asymptotic model based on the Uniform Theory of Diffraction (UTD) is investigated by comparing UTD simulations with results obtained from the exact eigenfunction solution for plane-wave incidence.UTD results are also compared with results from experiments carried out at 50 GHz, for various cylinder radii and for different linear wave polarizations. Excellent agreement between the measurement results and the theoretical ones is obtained.     

Scattering theory derivation of a 3D acoustic cloaking shell

Through acoustic scattering theory we derive the mass density and bulk modulus of a spherical shell that can eliminate scattering from an arbitrary object in the interior of the shell--in other words, a 3D acoustic cloaking shell. Calculations confirm that the pressure and velocity fields are smoothly bent and excluded from the central region as for previously reported electromagnetic cloaking shells. The shell requires an anisotropic mass density with principal axes in the spherical coordinate directions and a radially dependent bulk modulus. The existence of this 3D cloaking shell indicates that such reflectionless solutions may also exist for other wave systems that are not isomorphic with electromagnetics.     

On-axis Gaussian beam scattering by an eccentrically coated conducting cylinder

Based on the generalized Lorenz–Mie theory (GLMT) framework, an exact analytic solution to electromagnetic scattering by an eccentrically coated conducting cylinder is constructed, for oblique incidence of an on-axis Gaussian beam described by a localized beam model. The solution is found by the classical separation of variables technique and the translational addition theorem. For a tightly focused Gaussian beam propagating perpendicularly to the cylinder axis, numerical results of the normalized differential scattering cross section are presented, and the scattering characteristics are discussed concisely.     

等离子体覆盖立方散射体目标雷达散射截面的时域有限差分法分析

采用分段线性电流密度递归卷积时域有限差分（PLJERC-FDTD）算法计算了均匀非磁化等离子体覆盖三维立方体目标的散射特性.分析了等离子体厚度、密度和碰撞频率对雷达散射截面（RCS）的影响.计算结果表明：等离子体包层能有效地减小雷达目标的RCS，当等离子体频率比入射电磁波频率小得多时，主要靠增大等离子体的厚度使立方散射体目标的RCS值减小，增大等离子体碰撞频率对立方散射体目标的RCS值影响不大；当等离子体频率约为入射电磁波频率的一半时，增大等离子体厚度和碰撞频率都对立方散射体目标的RCS值减小有影响；当等 关键词： FDTD算法 电磁波 等离子体隐身 雷达散射截面     

Scattering-free plasmonic optics with anisotropic metamaterials

We develop an approach to utilize anisotropic metamaterials to solve one of the fundamental problems of modern plasmonics--parasitic scattering of surface waves into free-space modes, opening the road to truly two-dimensional plasmonic optics. We illustrate the developed formalism on the examples of plasmonic refractor and plasmonic crystal, and discuss limitations of the developed technique and its possible applications for sensing and imaging structures, high-performance mode couplers, optical cloaking structures, and dynamically reconfigurable electroplasmonic circuits.     

Manipulating surface plasmon waves by transformation optics:Design examples of a beam squeezer,bend,and omnidirectional absorber

We present several design examples of how to apply transformation optics and curved space under coordinate transformation to manipulating the surface plasmon waves in a controlled manner.We demonstrate in detail the design procedure of the plasmonic wave squeezer,in-plane bend and omnidirectional absorber.We show that the approximation method of modifying only the dielectric material of a dielectric-metal surface of the plasmonic device could lead to acceptable performance,which facilitates the fabrication of the device.The functionality of the proposed plasmonic device is verified using three-dimensional full-wave electromagnetic simulations.Aiming at practical realization,we also show the design of a plasmonic in-plane bend and omnidirectional absorber by an alternative transformation scheme,which results in a simple device structure with a tapered isotropic dielectric cladding layer on the top of the metal surface that can be fabricated with existing nanotechnology.     

Scattering response of featured uniaxial anisotropic chiral medium-coated twisted PEC cylinder

Scattering of electromagnetic waves from a perfectly electrical conducting (PEC) cylinder of circular cross-section, coated with uniaxial non-magnetic chiral anisotropic medium, was discussed. A conducting sheath helix structure with adjustable pitch angle exists over the outer surface of coated cylinder, which is interfaced with the free-space. Under the uniform parallel polarized plane wave with fixed oblique incidence angle, the echo widths were determined emphasizing the other relevant scattering-related parameters (e.g. scattering/extinction efficiency etc.), taking into account different pitch angle values (of the sheath helix) and the kinds of coating mediums. The results revealed that the coating of negative uniaxial chiral medium causes enhancement in scattering efficiency (of the scatterer). Also, the scattering efficiency was found to be the same as the extinction efficiency, thereby yielding vanishing absorption of the medium. The obtained results were also compared with the situation of vanishing chirality of coating medium over the PEC cylinder; the echo width and scattering efficiency both decrease in this case.     

Manipulating surface plasmon waves by transformation optics: Design examples of beam squeezer, bend, and omnidirectional absorber

We present several design examples of how to apply the transformation optics and curved space under coordinate transformation to manipulating the surface plasmon waves in a controlled manner. We demonstrate in detail the design procedure of the plasmonic wave squeezer, in-plane bend and omnidirectional absorber. We show that the approximation method of modifying only the dielectric material of a dielectric-metal surface of the plasmonic device could lead to acceptable performance, which facilitates the fabrication of the device. The functionality of the proposed plasmonic device is verified using three-dimensional full-wave electromagnetic simulations. Aiming at practical realization, we also show the design of plasmonic in-plane bend and omnidirectional absorber by an alternative transformation scheme, which results in simple device structure with a tapered isotropic dielectric cladding layer on the top of the metal surface that can be fabricated with the existing nanotechnology.