磁单负材料板附近的原子的自发辐射场分布

本文研究了磁单负材料板附近的两能级原子通过自发辐射激发的表面模式及场强分布. 磁单负材料是有效介电常数大于零而磁导率小于零的人工微结构材料. 根据麦克斯韦方程及边界条件, 这种材料板只支持TE极化的表面模式. 本文分析了具有不同磁导率和厚度的磁单负材料板所支持的表面模的性质, 如模式数目和模式的对称性, 进而讨论了这些特性对原子自发辐射场的空间分布的影响. 结果表明原子与磁单负材料板的距离可影响辐射场中表面模的比重, 当表面模起主要贡献时, 在材料板左表面上原子辐射场呈定向发射的分布. 而材料板右表面的辐射场分布取决于表面模的对称性和比重, 如果同时存在对称和反对称的表面模, 右表面的场很弱甚至完全消失, 而如果只存在对称或反对称的表面模, 右表面会有与左表面等强度的辐射场分布. 这些性质与原子在金属表面的辐射场分布明显不同, 我们的结果对原子辐射场的空间控制以及实现简单结构的单光子源有积极意义.     

Numerical simulations of negative-index refraction in a lamellar composite with alternating single negative layers

Negative-index refraction is demonstrated in a lamellar composite with epsilon-negative (ENG) and mu-negative (MNG) materials stacked alternatively. Based on the effective medium approximation, simultaneously negative effective permittivity and permeability of such a lamellar composite are obtained theoretically and further proven by full-wave simulations. Consequently, the renowned left-handed metamaterial comprising split ring resonators and wires is interpreted as an analogy of such ENG--MNG layers. In addition, beyond the effective medium approximation, the propagating field squeezed near the ENG/MNG interface is demonstrated to be left-handed surface waves with backward phase velocity.     

Scattering from a coated nihility circular cylinder placed in chiral metamaterial

The scattering of electromagnetic plane wave from a coated nihility circular cylinder placed in chiral metamaterial is investigated. The nihility cylinder is coated with chiral or chiral-nihility metamaterial and the medium hosting the coated cylinder is also considered as chiral or chiral-nihility metamaterial. The vector wave equation is used to find out the solution for the fields scattered from the concentric chiral ciruclar cylinders immersed in chiral metamaterial. Inner chiral cylinder is reduced to nihility cylinder taking permittivity and permeability approaching to zero with chirality parameter equal to zero. Coated perfect electric conductor (PEC)/perfect magnetic conductor (PMC) are obtained by taking very large value of permittivity/permeability of the inner cylinder. Numerical results for fields reflected from coated nihility cylinder are compared with those obtained for coated PEC/PMC cylinder. Our results for the special case of dielectric coated nihility/PEC cylinders in free space are shown to be in agreement with already published results thus validating the scheme of analysis.     

Trapping of electromagnetic wave in single-negative metamaterial waveguides

We study the trapping properties of transverse magnetic (TM) waves in single-negative metamaterial waveguides including epsilon-negative (ENG) metamaterial and mu-negative (MNG) metamaterial. The relationship between effective refractive index and reduced core width is analyzed when the permittivities of ENG and MNG metamaterials are different, and the inflection on this curve can be regarded as the trapping point. Simulation results show that the properties in an ENG–MNG–ENG metamaterial waveguide are contrary to that in a MNG–ENG–MNG metamaterial waveguide. The sensitivity of trapping point to the change of permittivity makes the single-negative metamaterial waveguides to be an effective method to detect the permittivity variation and can be used as a new kind of waveguide sensor.     

A novel structure for a broadband left-handed metamaterial

A low absorptivity broadband negative refractive index metamaterial with a multi-gap split-ring and metallic cross (MSMC) structure is proposed and investigated numerically and experimentally in the microwave frequency range. The effective media parameters were retrieved from the numerical and experimental results, which clearly show that there exists a very wide frequency band where the permittivity and permeability are negative. The influence of the structure parameters on the magnetic response and the cut-off frequency of the negative permittivity are studied in detail. This metamaterial would have potential application in designing broadband microwave devices.     

Simulation of High-Transmission Chiral Metamaterial with Impedance Matching to a Vacuum

For a previously simulated eight-broadband negative-refraction-index chiral metamaterial,we use S-parameter retrieval methods to determine the complex effective permittivity,permeability,and the impedance.We also calculate the figure of merit,which is defined as the ratio of the real and the imaginary refraction components,and compare it with those of fishnet metamaterials.The simulation results show that our chiral metamaterial exhibits high transmission and impedance matching to a vacuum.Also,we determine that the electric and magnetic dipoles of the surface plasmons play an important role in determining the nine resonance frequencies.Therefore,this investigation provides an experimental basis for developing metamaterial devices with multiple and broad resonance frequency bands.     

色散负折射特异介质的1维光子晶体缺陷态

在1维光子晶体中引入色散负折射特异介质,分析了其介电常数和磁导率在微波区（1～10 GHz）与频率的关系。分别对以色散负折射介质为缺陷的正折射率介质光子晶体及以正折射率介质为缺陷的正负折射率介质光子晶体进行了数值仿真,得出了均匀平面电磁波在正入射和斜入射时的透射谱。结果表明:在介电常数和磁导率均为负值的不同禁带中,分别出现了单、双缺陷模。利用透射谱的这一特点,可实现单、双通道滤波。     

1.7—2.7GHz宽频带小单元异向介质设计及其介质参数提取

提出一种单元电尺寸小、工作频带宽、损耗小、结构简单的异向介质设计方案，在1.7—2.7 GHz上所设计的异向介质结构单元电尺寸小于0.035，相对带宽达到45.5%，在整个工作频带上单个结构单元传输损耗小于0.75 dB.对由上述异向介质单元构成的半无限大异向介质平板的电磁波反射、透射特性进行了数值仿真分析，并提取出了电磁波在该异向介质平板中传播时的波数、相速、折射率以及该异向介质平板的有效介电常数和有效磁导率等一系列电磁特性参数，仿真与计算结果表明复波数的实部、相速以及折射率的实部在1.7—2.7 GHz的范围上为负值，并且在相同频带上，有效介电常数和有效磁导率的实部同时为负值，从而有效地验证了“后向行波效应”、“负折射效应”、“双负效应”等异向介质特有的电磁特性，对上述异向介质的存在性给予有力证明. 关键词： 异向介质 宽频带 小单元 介质参数     

An incident-direction-selective transmission filter based on anisotropic metamaterial

We construct an incident-direction-selective transmission filter based on anisotropic metamaterial, and explore the possibility of complete tunneling when elements of permittivity and permeability tensors of the anisotropic metamaterial are totally or partially negative. We first deduce the expressions of field distribution, reflection and transmission amplitudes in our filter and then study the influence of anisotropic metamaterial on the tunneling incident angle of light, including seven subcases of different combinations of positive and negative permittivity and permeability components. At last we conclude the principle of appearance of complete tunneling.     

Effect of backward radiation of electromagnetic waves by a metamaterial waveguide structure

The anomalous properties of electromagnetic radiation from an antenna in the form of a rectangular section waveguide tube made of a metamaterial with the negative real parts of permittivity and permeability have been demonstrated. The metamaterial is an isotropic two-dimensional array of left and right-twisted coils placed on a thin polyurethane substrate. The coils of the sample are directed in equal numbers along the x, y, and z axes. The possibility of the preferential backward radiation of the structure has been shown on the basis of numerical calculations with the use of the method of moments and the measurements of the radiation pattern of the antenna in an anechoic chamber at frequencies close to the 3-GHz resonance frequency of the metamaterial. The causes and existence conditions of the effect have been revealed.     

A novel structure for broadband left-handed metamaterial

A low absorptivity broadband negative refractive index metamaterial with multi-gap split-ring and metallic cross (MSMC) structure is proposed and investigated numerically and experimentally in the microwave frequency range. From the numerical and experimental results, the effective media parameters were retrieved, which clearly show that there exists a very wide frequency band where the permittivity and permeability are negative. The influence of the structure parameters on the magnetic response and the cut-off frequency of the negative permittivity are studied in detail. This metamaterial would have potential application in designing broadband microwave devices.     

Deposited metamaterial thin film with negative refractive index and permeability in the visible regime

Thin films are fabricated from arrays of silver nanorods with thicknesses of 160?nm and 200?nm, to function as a metamaterial. The negative refractive index and negative permeability are retrieved from measured reflection and transmission coefficients using walk-off interferometer in the visible regime. A negative-index-material thin film with negative permittivity or (and) permeability can be produced by glancing angle deposition.     

磁电耦合超材料本构矩阵获取方法的研究

单负(仅介电常数或仅磁导率小于零)超材料以及由导线-开口谐振环组成的双负超材料本构参数的提取通常采用传统的S参数方法. 由于磁电耦合超材料存在交叉极化现象, 仅用介电常数和磁导率两个本构参数无法准确描述其电磁特性. 传统的S参数提取方法一开始就假定超材料仅具有介电常数和磁导率两个本构参数, 所以采用该方法提取磁电耦合超材料本构参数存在明显局限性. 将磁电耦合超材料中的电元件和磁元件分别等效为面电流和面磁流, 通过推导平均电通密度和磁通密度与外加电磁场的相互关系, 从理论上获取了磁电耦合超材料2×2 的本构参数矩阵, 确定了磁电耦合超材料这四个本构参数与磁元件的磁导率、电元件的介电常数、空间色散项和耦合系数之间的关系解析公式, 进而获得了折射率理论计算公式. 利用该折射率公式对折射率提取值进行了非线性拟合, 发现提取值和理论值之间的误差很小, 这个结果很好地验证了所给出的本构矩阵解析式和折射率公式的正确性. 根据拟合结果, 获得了磁电耦合超材料本构矩阵中四个电磁参数的频率响应曲线. 所提出的磁电耦合超材料本构矩阵参数获取方法将为研究磁电超材料中电元件和磁元件的耦合现象提供重要的理论参考.     

Imaging with a metamaterial ＂Im-Perfect＂ lens

There is widespread and strong interest in trying to fabricate a metamaterial in which both the permittivity and permeability are equal to - 1 in order to achieve sub-wavelength imaging. Several metamaterial constructs have been proposed with varying degrees of suceess because of inherent losses, limited bandwidth and scattering from the abstracted circuit elements constituting the artificial material itself. A further limitation is the need to capture evanescent components from the object to be imaged that requires the lens to be located near the object. We have studied the underlying models and constraints that influence the design of a negative index lens and present this analysis as well as reviewing the opportunities. There are inevitable and well-known trade-offs between lens thickness, wavelength, dispersion and absorption. However, these can be eharaeterized both numerically and experimentally, suggesting that a computational imaging approach to the recovery of sub-wavelength features might be effective. Depending on the specific details of the metamaterial employed for imaging, one can consider the data acquired to represent a set of coded apertures.     

基于铁氧体基板的开口谐振环的可调微波左手特性研究

利用铁氧体的外场调制特性,提出采用铁氧体作为金属环线结构的介质基板,实现频率可调左手材料. 首先采用时域差分有限元方法数值模拟了基板材料参数变化的条件下,开口谐振环的频率可调性规律. 随基板材料的介电常数或磁导率升高,与开口谐振环负磁导率对应的透射谷频率将显著降低. 实验制备了一系列超高频软磁六角铁氧体,利用外加磁场有效调制了其磁导率. 并通过实验表明,通过调控外加磁场可以有效地调控开口谐振环负磁导率对应的透射谷频率. 关键词： 左手材料 开口谐振环 铁氧体 可调     

Optical metamaterials at near and mid-IR range fabricated by nanoimprint lithography

Two types of optical metamaterials operating at near-IR and mid-IR frequencies, respectively, have been designed, fabricated by nanoimprint lithography (NIL), and characterized by laser spectroscopic ellipsometry. The structure for the near-IR range was a metal/dielectric/metal stack “fishnet” structure that demonstrated negative permittivity and permeability in the same frequency region and hence exhibited a negative refractive index at a wavelength near 1.7 μm. In the mid-IR range, the metamaterial was an ordered array of fourfold symmetric L-shaped resonators (LSRs) that showed both a dipole plasmon resonance resulting in negative permittivity and a magnetic resonance with negative permeability near wavelengths of 3.7 μm and 5.25 μm, respectively. The optical properties of both metamaterials are in agreement with theoretical predictions. This work demonstrates the feasibility of designing various optical negative-index metamaterials and fabricating them using the nanoimprint lithography as a low-cost, high-throughput fabrication approach. PACS 42.25.Bs; 81.16.Nd; 42.70.-a; 81.07.-b     

Metamaterial composed of wire pairs exhibiting dual band negative refraction

The design of the metamaterial that can exhibit negative refraction at two frequency bands is presented. The components of this metamaterial are cut wire pairs and continuous wires. The cut wire pairs structure in our sample can achieve the magnetic resonance at two frequency bands by appropriately designing the cut wire dimension. Through numerical simulation, the transmission property of the proposed dual band negative index metamaterial is investigated and its result shows that with the introduction of continuous wires, the stop bands for cut wire pairs (permeability μ<0) and the frequency band for continuous wires (permittivity ε<0) components would overlap and lead to the appearance of pass bands near the two magnetic resonance frequency bands. Its electromagnetic properties are then retrieved to demonstrate that the dual band left-hand behavior can be obtained in our sample structure. It is believed that our approach will be effective to make this kind of dual band negative refractive metamaterial based on the multiple magnetic resonances work at optical frequency.     

各向异性超常材料的偏振分离特性

提出了一种利用含有负介电常量和磁导率张量的各向异性超常材料实现偏振分离的方法。通过分析电磁波在无损耗各向异性超常材料中的传输性质以及透射率与入射角度的关系,分类比较了由不同符号的介电常量和磁导率张量组合而成具有不同波矢面的各向异性超常材料的偏振分离特性,比较结果表明波矢面为单叶双曲面和椭球双叶双曲面的各向异性超常材料的偏振分离特性强。前者可以实现入射波中的s分量和p分量中某一分量正折射,另一分量负折射,且在一定条件下可以同时全透射,从而实现大角度偏振分离。后者在一定条件下可实现入射波中的s分量和p分量某一分量全反射,另一分量全透射,从而实现偏振分离。最后,对从各向同性介质入射到这两种各向异性超常材料中的高斯光波的传输进行了模拟计算,结果表明这两种各向异性超常材料可以实现很好的偏振分离功能,有潜力成为新型的偏振分离元件。     

Dual bands of negative refractive indexes in the planar left-handed metamaterials

A kind of planar left-handed metamaterial (LHM) with unique configurations is demonstrated, which offers an approach in building dual-band negative-index materials. Simulated and experimental results predict two left-handed transmission bands near 11.1 and 14.6 GHz. Dual bands of negative refractive indexes are verified using the retrieval procedure. Field and current distribution at the dual magnetic resonance are also examined. The effective electromagnetic parameters show that by carefully adjusting dimensions of the unit cell, electric and magnetic resonances can be coexistent at some frequency ranges with both negative permittivity and negative permeability. The idea can help us designing planar negative-index materials with multibands.     

由同时具有磁谐振和电谐振结构组成的左手材料

为了在同一结构中同时实现负介电常数和负磁导率(双负),采用一种“巨”字形结构,利用丝网印刷技术在氧化铝基板上进行加工制作,并通过仿真和实验测试证实了这种结构的“双负”特性. 与利用磁谐振器和电谐振器组阵实现左手材料的方法相比,这种单一结构可以同时实现负介电常数和负磁导率,制作方便,等效电路简单,双负频段较宽. 利用丝网印刷技术进行样品的制作,工艺简单,成本低廉. 关键词： 左手材料 磁谐振 电谐振