有耗异向介质层覆盖普通介质圆柱电磁特性的研究

研究了线电流源平行放置在有耗异向介质层覆盖的无限长介质圆柱附近模型的电磁特性.首先,提出电磁模型并给出此电磁模型的精确解.其次,利用精确解进行数值计算,得到不同电磁参数情况下该电磁模型的近场分布图形,并通过方向性系数和归一化辐射阻抗研究其远场特性.由于有耗异向介质的负折射特性和损耗的同时作用,相比于无耗异向介质层以及有耗普通介质层,得到了有耗异向介质层覆盖普通介质圆柱模型在近场和远场特性上极为不同的电磁特性. 关键词： 线电流源 异向介质 方向性系数 辐射阻抗     

线电流源激励下无耗异向介质层覆盖导体圆柱电磁特性的研究

研究了线电流源平行放置在无耗异向介质层覆盖的无限长导体圆柱附近模型的电磁特性.首先，给出了电磁模型描述，求出此电磁模型的精确解.其次，利用精确解进行数值计算，得到几何参数和电磁参数不同情况下电磁模型的近场图形，并通过方向性系数和归一化辐射阻抗研究其远场特性.利用异向介质的负折射特性，在异向介质层的近场图形内得到明显的“焦点”，这个焦点在普通介质层中是不存在的.该电磁模型同前人方法进行了比较，验证了本电磁模型的有效性. 关键词： 线电流源 异向介质 方向性系数 辐射阻抗     

Properties of Near and Far Fields for the Electric Line Source Illumination of a Lossy Metamaterial Covered Dielectric Cylinder

The electric field properties of the electric line source radiation in the presence of a lossy metamaterial covered dielectric cylinder are investigated. Firstly, the electromagnetic model configuration is given. The exact solution of the electromagnetic is presented. Secondly, the near field and the far field properties are investigated according to the electromagnetic and geometrical parameters. The different “focus” phenomenon, the directivities and the normalized radiation resistance are discussed and important conclusions are obtained. During all the numerical computation, the lossy conventional material covered dielectric cylinder is utilized as the reference.     

The Property of the Horizontal Dipole Radiating in the Presence of a Single Lossless Metamaterial Sphere

The electric field properties of the horizontal dipole radiation in the presence of a lossless metamaterial sphere are investigated. First, the solution of the electromagnetic field of the model could be obtained. Second, the near field properties are investigated according to the electromagnetic and geometrical parameters. It could be seen that in the metamaterial sphere, the focusing phenomenon is obviously observed. It is in consistent with the analysis. Throughout the article, the conventional sphere is utilized as reference. No focus is observed in the conventional material sphere as it does not have the characteristic of negative refraction.     

单负材料异质结构中损耗诱导的场局域增强和光学双稳态

光学双稳态的阈值取决于非线性材料中的场局域程度, 场局域越强阈值越低. 而材料的损耗是影响场局域强弱的重要因素. 之前, 人们普遍认为, 增加损耗会削弱场局域, 不利于降低阈值. 本文研究了由磁单负材料和电单负材料组成的异质结构中光学双稳态现象, 发现随着损耗的增大, 其阈值可以呈现先降后升的非单调变化. 进一步研究表明, 异质结构界面处的电磁场强度随着损耗增大呈现先降后升的非单调变化, 即增加损耗也有可能增强场局域. 研究结果揭示了场局域程度与材料损耗之间的非单调依赖关系, 为设计开发非线性功能器件提供了新的思路.     

Designing polarization insensitive negative index metamaterial for operation in near infrared

Hexagonal arrays of gold nanoelements with C₃ symmetry are studied as a metamaterial slab of reduced anisotropy. Tri-dimensional (3D) finite-difference time domain (FDTD) simulations are used to calculate the reflected and transmitted electromagnetic field for two waves normally incident to the slab with mutually perpendicular polarizations. S-parameter method is used to retrieve the constitutive parameters for each polarization. While dipolar plasmonic resonance in the case of one layer metamaterial slab leads only to negative values of permittivity, using two layers of asymmetric nanoelements leads to a negative refractive index metamaterial in the near infrared range (158–172 THz) as a result of hybridized plasmonic states inversion.     

A novel flat lens horn antenna designed based on zero refraction principle of metamaterials

In this paper, a horn antenna filled with a metamaterial structure as lens inner the aperture is presented. Unlike conventional curve lenses, the lens is designed in the present work using a fully flat structure, which results in a great improvement for the directivity of the horn antenna based on the zero refraction characteristics of the metamaterial. In this structure, a periodic-structure metamaterial with three-layer metal grids is designed using the CST Microwave Studio for optimization and its zero refraction property is validated. For the characterization of the antenna, the electric-field distribution in radiation area, reflection parameter (S₁₁), gain and radiation pattern are calculated. The results show that the gain of a wide flare angle horn antenna is enhanced with over 2 dB between 16.10–17.30 GHz after the metamaterial is utilized. Therefore, the metamaterial lens horn structure results in a miniaturized antenna design approach compared to the optimum conventional horn of the same aperture size and gain in the interested frequency band. PACS 78.70.Gq; 81.05.Zx; 84.40.Ba     

等离子体通道天线的辐射场计算

提出了一种用于高功率微波武器的等离子体通道天线(PCA),计算了该天线的辐射方向图。推导出了一般性天线的辐射方向函数;建立了PCA的近似电磁模型;给出了圆坐标系下PCA和周围空气中的电磁场,利用边界条件得出了PCA的色散方程,求出PCA的表面波波矢。重点讨论了PCA的辐射场随等离子体密度、天线长度、半径的变化,证实了PCA方向图的可控性。     

Performance improvement of organic light emitting diode using 4,4$$^{\prime }$$-N,N$$^{\prime }$$-dicarbazole-biphenyl (CBP) layer over fluorine-doped tin oxide (FTO) surface with doped light emitting region

A metallic fishnet metamaterial structure in sub-THz region is presented. The proposed structure is based on hexagonal resonators. Simulations have been performed by a 3D full-wave electromagnetic simulator and a negative refractive index has been observed at the frequency range between 0.55 and 0.70 THz with the help of the graphene layer. In order to observe the effect of the graphene layer, the metamaterial structure has been simulated and examined before and after graphene integration. Significant modification in the propagation properties has been observed after the graphene integration. Change in S-parameters with the size variation of hexagonal resonators and alteration in graphene thickness are also presented as a parametric study to show the tunability of the structure. Suitability of the metamaterial for sensor applications has been investigated. The proposed metamaterial structure is promising to be effectively used for tunability and sensor applications.     

Super-thin cloaks mediated by spoof surface plasmons

We demonstrated the possibility of designing super-thin electromagnetic cloaks based on spoof surface plasmon (SSP). Using a metamaterial layer, incident waves can be coupled into SSP efficiently at the air/metamaterial interface. Due to the strong surface confinement of SSP, EM waves are squeezed into and propagate in deep sub-wavelength scales. Implementation of an 8.2 GHz cloak less than 1/50 the cloaking diameter was presented using split ring resonator (SRR). Excellent cloaking effect was verified by simulations. Rather than isolating objects from the background, such cloaks can drastically enhance the field intensity around the cloaked object. This is of particular importance in applications such as weak wave detection and near-field sensing.     

Retrieval of the effective constitutive parameters from metamaterial absorbers

The equivalent medium theory of metamaterials provides a way to obtain their effective constitutive parameters. However, because of its non-reciprocity, the complexity of the electromagnetic coupling, and a metallic bottom layer, it has been challenging to retrieve them from a metamaterial absorber. In this paper, we propose a method without any approximation to obtain them, in which the non-reciprocity and the strong electromagnetic coupling are included. Compared with the three methods such as symmetric metamaterial method, asymmetric metamaterial method and metasurface method, our method can reveal the metamaterial absorber's electrical and magnetic resonance and show its electromagnetic coupling coefficients. To deal with a metamaterial absorber with a metallic bottom layer, four corners of the metallic bottom layer in the unit cell are removed, making it possible to retrieve the electromagnetic parameters. Surprisingly, these results show that the metamaterial absorber with a metallic bottom layer in our example operates in a negative refraction state at the half absorption frequencies, which helps further understand the absorbing mechanism of these metamaterial absorbers.     

Manipulate light polarizations with metamaterials: From microwave to visible

Polarization is an important characteristic of electromagnetic (EM) waves, and efficient manipulations over EM wave polarizations are always desirable in practical applications. Here, we review the recent efforts in controlling light polarizations with metamaterials, at frequencies ranged from microwave to visible. We first presented a 4 × 4 version transfer matrix method (TMM) to study the scatterings by an anisotropic metamaterial of EM waves with arbitrary propagating directions and polarizations. With the 4 × 4 TMM, we discovered several amazing polarization manipulation phenomena based on the reflection geometry and proposed corresponding model metamaterial systems to realize such effects. Metamaterial samples were fabricated with the help of finite-difference-time-domain (FDTD) simulations, and experiments were performed to successfully realize these ideas at both microwave and visible frequencies. Efforts in employing metamaterials to manipulate light polarizations based on the transmission geometry are also reviewed.     

Highly directional radiation generated by a tungsten thermal source

We report the design of a tungsten thermal source with extraordinarily high directivity in the near infrared, comparable to the directivity of a CO2 laser. This high directivity is the signature of the long-range correlation of the electromagnetic field in the source plane. This phenomenon is due to the resonant thermal excitation of surface-plasmon polaritons.     

Composite metamaterial enabled excellent performance of microstrip antenna array

This paper reports that the split ring resonators and complementary split ring resonators are compounded to construct a novel compact composite metamaterial.The composite metamaterial exhibits a unique property of blocking electromagnetic wave propagating in two directions near the resonant frequency.An example of two-element microstrip antenna array demonstrates that the developed metamaterial enables array performance that is an improvement in comparison with the traditional one,including mutual coupling suppression of 9.07 dB,remarkable side lobe suppression and gain improvement of 2.14 dB.The mechanism of performance enhancement is analysed based on the electric field and Poynting vector distributions in array.The present work not only is a meaningful exploration of new type composite metamaterial design,but also opens up possibilities for extensive metamaterial applications to antenna engineer.     

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提出了一种用于高功率微波武器的等离子体通道天线(PCA),计算了该天线的辐射方向图。推导出了一般性天线的辐射方向函数;建立了PCA的近似电磁模型;给出了圆坐标系下PCA和周围空气中的电磁场,利用边界条件得出了PCA的色散方程,求出PCA的表面波波矢。重点讨论了PCA的辐射场随等离子体密度、天线长度、半径的变化,证实了PCA方向图的可控性。     

Role of the ionospheric plasma in the formation of a shortwave radiation field in the environment

Using a model formulation, we study how the ionospheric plasma affects the formation of a short-wave electromagnetic field in near space by an operating broadcasting network. The principles underlying the construction of the model and the methods of solution are elucidated. An analysis is made of the variation of the global distribution of anthropogenic electromagnetic background for specific heliogeophysical conditions. Zones of maximum electromagnetic energy density are distinguished in the ionospheric plasma. V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 16–23, October, 1996.     

Femtosecond laser ablation of neurons in <Emphasis Type="Italic">C</Emphasis>. <Emphasis Type="Italic">elegans</Emphasis> for behavioral studies

In this paper, the interaction between the inhomogeneous and anisotropic cloak covered infinitely long PEC circular cylinder and the parallel electric-line-source is investigated in detail. First, the permittivity and permeability tensors of the cloak are defined according to Pendry’s model, then the wave equation in the metamaterial cloak is derived; second, the far/near properties of the model are investigated, and using the boundary conditions the electromagnetic fields of the whole region are calculated analytically; finally, based on the analytical expressions, the electric fields of the whole region are demonstrated through numerical results which show the effects of invisibility. Finally, the effects of loss on the performance of the invisible cloak are investigated.     

光波辐射下正多边形异向介质柱聚焦特性分析

基于时域有限差分方法,建立了光波辐射下正三角形、正四边形和正六边形无耗异向介质柱的二维电磁模型.分析了其近场特性,并对模型的有效性进行了验证.仿真结果表明:即便对于εr和μr都很小且无耗的正多边形异向介质柱,当平面光波沿正多边形顶角角平分线方向传播时,在异向介质柱内不会发生电磁聚焦.     

Equivalent electromagnetic parameters for microwave metamaterial absorber using a new symmetry model

Transmission line theory uses the complex nature of permeability and permittivity of a conventional magnetic absorber to evaluate its absorption properties and mechanism. However, because there is no method to obtain the electromagnetic parameters of a metamaterial-absorber integrated layer(composed of a medium layer and a periodic metal array), this theory is seldom used to study the absorption properties of the metamaterial absorber. We propose a symmetry model to achieve an equivalent complex permittivity and permeability model for the integrated layer, which can be combined with the transmission line theory to calculate metamaterial absorption properties. The calculation results derived from both the transmission line theory and the high-frequency structure simulator are in good agreement. This method will be beneficial in practical investigations of the absorption mechanism of a metamaterial absorber.