谐振频率可调的环状开口谐振器结构及其效应

理论和实验研究表明，开口谐振环(SRRs)中可以激励磁谐振从而实现负磁导率.通过在SRRs结构中引入与其开口边平行的金属短杆设计并制备了新的磁谐振单元，采用波导法系统研究了短杆对SRRs和左手材料的微波透射特性以及左手效应的影响.实验和数值模拟表明：金属短杆和SRRs开口边形成附加电容，导致SRRs开口电容增大从而引起谐振频率降低.随短杆长度l和短杆与SRRs间距d的增大，SRRs谐振频率也随之减小和增加.短杆的加入不影响SRRs的负磁导率特性，改变短杆与SRRs间距d< 关键词： 开口谐振环 金属短杆 调控 左手材料     

Conversion from constitutive parameters to dispersive transmission line parameters for multi-band metamaterials

Abstract

In this study, we explain an approach including conversion from constitutive parameters to dispersive transmission line parameters using the double-band DNG (double-negative) properties of the circular type fishnet metamaterials. After designing the metamaterial structure, the numerical calculations and the composite right/left-handed (CRLH) modeling of circular-type metamaterials are realized in free space. Detailed dispersion characteristics give us the opportunity to explain the true behavior of the inclusions during the analysis stage. By combining the results coming from the standard retrieval procedure with the conventional CRLH theory, we calculate the actual values of the transmission line parameters for all frequency regimes. The constitutive parameters of an equivalent CRLH transmission line are derived and shown to be negative values. It is shown that the constitutive parameters present the same behavior for all negative refractive index regimes. The double-negative properties and the phase advance/lag behavior of metamaterials are observed based on the dispersive transmission line parameters.     

Numerical demonstration of three-dimensional terahertz metamaterials based on the causality principle

A parameter retrieval algorithm based on the causality principle and Kramers-Kronig （KK） relations is employed to calculate the effective parameters of three-dimensional （3D） metamaterials. Using KK relations, the branch selecting problem, which is the challenge of effective parameter retrieval method, can be removed. To reveal the validity of the proposed algorithm, the constitutive refractive index of a homogeneous polymide cube is extracted. The result is in excellent agreement with the intrinsic refractive index of the polymide. Finally, the two terahertz metamaterials with 3D structures are designed and their effective parameters are then retrieved using the proposed algorithm. Numerical simulations are performed using the fuiI-wave electromagnetic solver, CST Microwave Studio.     

Retrieval of effective parameters for bianisotropic metamaterials with omega shaped metallic inclusions

Bianisotropic metamaterials including Ω-shaped metallic elements are investigated experimentally and theoretically. A passband is observed for a composite metamaterial (CMM) based on an Ω-medium below the plasmonic frequency of the corresponding closed CMM. The effective parameters (refractive index, impedances, permittivity, permeability, and magnetoelectric coupling coefficient) are retrieved for the Ω-medium and the CMM based on it. Our retrieval results show that the passband observed for the CMM is a band with positive refractive indices. Our retrieval results confirm the deductions of our previous reports.     

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.     

Dielectric substrate effect on the metamaterial resonances in terahertz frequency range

We report on the effect of dielectric substrate on the resonance shift of metallic metamaterials operating in the terahertz frequency region. The resonance frequencies for various metamaterials obtained by time-domain spectroscopy agree well with calculations based on the finite-difference time-domain method. The dependencies of the resonance frequency to substrate index are studied, and are systematically determined by introducing an effective substrate index. The relative contributions of the substrate index for various metamaterials are obtained by fitting the numerically obtained effective refractive indices as a function of substrate index, which is found to be ∼0.63 regardless of the metamaterial geometry.     

Theoretical and experimental investigations of easy made fishnet metamaterials at microwave frequencies

In this work, we demonstrate theoretically and experimentally a left handed behaviour of a planar fishnet type metamaterial in the microwave regime. The fabrication procedure based on printed circuit board technology and mechanical micromachining technique is easy, unique and doesn’t involve optical lithography. The effective parameters have been extracted using the S parameter retrieval method and show a very good agreement between simulation and experiment. Using finite-element method based simulations and W-band (75 GHz–110 GHz) experiments. We measured a negative index of refraction of −4 at 85 GHz. The demonstrated left handed materials represent a step towards the easy fabrication of metamaterials with a negative refractive index that open a new path for the active manipulation of millimetre wavelengths.     

太赫兹波段谐振频率可调的开口谐振环结构

开口谐振环(SRRs) 结构可以激励磁谐振, 实现负的磁导率. 提出在SRRs两环间隙内引入相对交错的金属短线, 并研究了金属短线对谐振频率的影响. 结果表明: 随着金属短线数目的增多, 谐振频率显著降低, 同时金属短线的结构参数如长度、宽度及间距也会对谐振频率产生影响. 最后验证了金属短线的引入对减小器件尺寸有明显作用, 且不因介质基底的存在而受到影响. 新型磁谐振单元可为今后超材料的设计及实际应用提供新的参考. 关键词： 左手材料 开口谐振环 太赫兹 小型化     

Tunable dual-band infrared chiral metamaterials based on double-layered asymmetric U-shape split ring resonators

We have numerically demonstrated chiral metamaterials based on double-layered asymmetric U-shape split ring resonators. Dual-band circular dichroism is found in the whole frequency regime from 50 to 250 THz by studying the transmission properties. Huge optical activity and the induced negative refractive index are obtained at resonance by calculating the optical activity and ellipticity of the transmitted E-fields. Chirality parameter and effective refractive index are retrieved to illustrate the tunable optical properties of the metamaterials. The underlying mechanisms for the observed circular dichroism are analyzed. These metamaterials would offer flexible electromagnetic applications in the infrared regime.     

同时实现介电常数和磁导率为负的H型结构单元左手材料

基于用一种结构同时实现材料介电常数和磁导率为负的思想，提出了H型结构单元左手材料模型.采用矩形波导法测试表明，H型结构单元在微波频率范围出现左手透射峰，并且可以由参数t对左手特性区域进行调控.同时利用相位法、棱镜折射法和散射参量法从实验和理论证明了在左手透射峰区域材料的折射率为负值，介电常数和磁导率亦同时为负.相对由金属开口谐振环与金属线两种结构组合实现的左手材料，H型结构集磁谐振与电谐振于一体，结构简单、制备方便，对微波器件左手材料表现出更多的优越性.     

二维负磁导率材料中的缺陷效应

研究了以金属铜六边形开口谐振环为基元的二维负磁导率材料的缺陷效应.利用电路板刻蚀 技术制备了二维负磁导率材料样品.采用波导法测量了点缺陷和线缺陷对二维负磁导率材料X 波段(8—12GHz)微波透射行为的影响.实验发现，无缺陷的二维负磁导率材料样品存在一个 谐振频率，在稍大于该谐振频率的极窄区域内表现为负磁导率.点缺陷和线缺陷SRR的引入导 致材料主谐振峰的强度下降、谐振频率发生移动，品质因数Q显著下降.缺陷的存在破坏 了材料的周期性结构，从而引起其谐振峰的谐振强度和谐振频率发生变化.缺陷效应的研究 不 关键词： 负磁导率 缺陷效应 开口谐振环     

The influence of pressure on the refractive index of castor oil up to 0.8 GPa

Abstract

The application of a novel fiber-optic technique for the determination of the refractive index of liquids under high pressure is outlined. The present method is based on th measurements of the scattered light intensity on certain types of rough surfaces. Here we present the effect of pressure on the refractive index of castor oil. A significant increase of the refractive index has been observed in the whole range of pressure up to 0.8 GPa.     

MICROWAVE PROPAGATION IN ROUND GUIDING STRUCTURES BASED ON DOUBLE NEGATIVE METAMATERIALS

This paper presents a theoretical study of guided propagation in a waveguide containing ordinary and negative refractive index (NRI) media. The cut-off frequency of positive/negative combined media is examined. It is calculated for each propagating mode as a solution of a characteristic equation that is solved in terms of Bessel functions, taking into account the implications of the negative refraction. In contrast to what happens in ordinary propagation, mode mixing and crossing and no cut-off modes are found for negative values of ε, μ and refractive index n. The investigation considers the range 1-80 GHz where metamaterials have been demonstrated to work with negative parameters. The results are also compared with the negative core/negative cladding case. Some applications are suggested for devices operating in the microwave frequency domain.     

非均匀缺陷环对微波左手材料的影响

以金属铜六边形开口谐振环(SRRs)与金属铜线的组合为结构单元，研究了三维左手材料中的 缺陷效应. 利用电路板刻蚀技术制备了左手材料样品，采用波导法测量了SRRs构成的点缺陷 和线缺陷对左手材料X波段（8—12 GHz）微波透射行为的影响. 实验结果表明，引入不同尺 寸SRRs构成的点缺陷，材料谐振峰强度下降，最多达6 dB，相当于原来的186%，谐振频率 移动，通频带宽在630—720 MHz范围变化；引入不同尺寸SRRs构成三种取向的线缺陷时，材 料谐振峰强度下降，最多达11 dB，相当于原来的34 关键词： 左手材料 缺陷效应     

Nonlinear phenomena of left-handed nonlinear split-ring resonators

We theoretically analyze a two-dimensional periodic structure consisting of period nonlinear split-ring resonators (SRRs) with varactor diode. The diode is loaded into the slit of the SRRs. Then, we demonstrate nonlinear phenomena of left-handed nonlinear SRRs. This paper introduces nonlinear SRRs based on left-handed (LH) media and simulates self-tuning mechanisms, bistable effects in the microwave frequency range. In addition, with the increase of input power, the nonlinear response of the SRRs becomes multi-valued, paving a way for creating bistable tunable metamaterials.     

利用集总L-C元件构造的一维metamaterials特性的实验研究

在普通微带传输线中周期性地加载集总L C元件能够构造一维特异性材料(metamaterials)，它具有与众不同的特异性质.通过实验证实了波在这种结构中传播具有相速度与群速度方向相反的左手性通带，其折射率为负值，并发现平均折射率为零的能隙.这种结构具有结构紧凑，参数可调，制作简单的优点. 关键词： 负折射率 特异性材料 周期性结构 微带线     

磁电超材料折射率特性分析

基于麦克斯韦旋度方程, 将磁电超材料板中的电元件和磁元件分别等效为面电流和面磁流, 通过计算这些周期性面电流和面磁流在某个磁电超材料板上产生的总电场和总磁场, 获得了关于面磁流密度和面电流密度的两个方程, 进而推导出了周期性磁电超材料折射率与磁元件的磁导率、 电元件的介电常数和空间色散项之间关系的解析公式. 与传统的折射率计算公式不同, 该解析公式充分考虑到了空间色散以及磁电超材料的电元件和磁元件的相互作用. 折射率理论曲线和基于仿真实验数据的提取值曲线能很好地符合, 这说明文中推导的折射率公式能够正确地描述磁电超材料的负折射特性. 本文的结果将为分析电磁元件之间的相互作用以及设计负折射率符合一定要求的磁电超材料提供重要的理论参考. 关键词： 磁电超材料 周期性结构 负折射率     

Phase retrieval in two-wavelength DSSI using a combined filtering method

Phase retrieval in two-wavelength DSSI (digital speckle shearing interferometry) using a combined filtering method is proposed for small deformation derivative measurement. A simultaneous two-wavelength illumination and 3-CCD camera are employed in the experimental setup. The proposed method, which uses a two-wavelength technique does not require the conventional spatial phase unwrapping and has the advantage of good noise suppression for phase retrieval. Experimental results obtained show that using the proposed combined filtering method sensitivity similar to the single wavelength technique can be achieved.     

Metamaterials: electromagnetic enhancement at zero-index transition

Resonant enhancement of electromagnetic waves propagating at oblique incidence in metamaterials, with dielectric permittivity and magnetic permeability linearly changing from positive to negative values, has been predicted and theoretically studied. This effect occurs for both TE and TM polarizations near the point where a refractive index changes its sign. Our model elucidates the unique features of the resonant enhancement in "positive-to-negative transition" metamaterials for a broad frequency range from microwaves to optics.     

Manipulating electromagnetic resonances in meta-molecules with double split ring resonators

We proposed meta-molecules structure composed of stacked double split ring resonators (DSRRs) and studied its electromagnetic resonances in the optical frequency range. We demonstrated that, for the first order plasmonic modes, the coupling between the outer and the inner SRRs in plane strongly influences on the resonant frequency splitting of the stacked DSRRs. And their resonant dips change with the arrangement of SRRs. However, the resonant frequencies for the high order plasmonic modes always remain immobile as the configuration varies. Our investigation offers an effective way to manipulate the resonant behavior in metamaterials.