Effective electromagnetic response of nanostructured metal-dielectric metamaterials

The optical properties of metamaterial layers have been analyzed by the scattering matrix method. The properties of effective ɛ and μ, reconstructed from the transmittance and reflectance of metamaterial layers of finite thickness using the inverse Fresnel formulas, are discussed. It is shown that the optical response of nanostructured metal-dielectric metamaterials is strongly nonlocal and dissipative. Original Russian Text ? S.G. Tikhodeev, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 1, pp. 95–97.     

A method to determine effective metamaterial properties based on stratified metafilms

Metamaterials’ properties may be quantified through the assignment of bulk material parameters such as magnetic permeability and electric permittivity. These assignments rely on the assumption that metamaterials are effective media, in this context meaning that their electromagnetic properties are independent of the sample size. This assumption is not always valid, particularly for metafilms, the surface equivalents of metamaterials. However, metamaterials comprised of numerous metafilm and dielectric layers can be uniquely characterized in the effective medium approximation when all aspects of the metamaterial are properly integrated. We present a simple model based on stratified systems to illustrate this fact. The model further assists in the interpretation of novel metamaterial behaviors and offers a rapid and accurate method to determine the functionality of bulk metamaterial-based devices.     

交指电容加载的周期性对称负磁导率人工材料研究

利用二端口网络理论和弗洛奎定理, 详细分析了周期性对称磁谐振人工材料的相对布洛赫磁导率与散射矩阵参数的关系, 利用这个关系提取了四种形式的开口谐振环布洛赫磁导率. 全波仿真和磁导率数值提取结果表明, 在开口谐振环的开口处加载交指电容, 磁谐振频率将显著降低. 这些成果将为提取周期性人工材料的布洛赫磁导率提供理论依据, 同时为小型化磁谐振特异人工材料提供新的设计思路.     

Absorption and dispersion in metamaterials: Feasibility of device applications

We present a quantitative study of the effects of losses in layered media with a metamaterial layer as the constituent. The metamaterial is modelled by a causal isotropic effective medium (Lorentz-type) response. The parameters for the model are picked from a recent experiment. Two specific examples, namely, that of resonant tunnelling (RT) and imaging are chosen to demonstrate the devastating effects of losses in the present day metamaterials. It is then shown how large delays in RT, as well as near perfect imaging can be restored in gain-doped metamaterials. We also point out yet another use of metamaterials for achieving near perfect absorption, and its use for probing strong atom-field interaction.     

Effective material parameter retrieval for thin sheets: Theory and application to graphene,thin silver films,and single-layer metamaterials

An important tool in the field of metamaterials is the extraction of effective material parameters from simulated or measured scattering parameters of a sample. Here we discuss a retrieval method for thin-film structures that can be approximated by a two-dimensional scattering sheet. We determine the effective sheet conductivity from the scattering parameters and we point out the importance of the magnetic sheet current to avoid an overdetermined inversion problem. Subsequently, we present two applications of the sheet retrieval method. First, we determine the effective sheet conductivity of thin silver films and we compare the resulting conductivities with the sheet conductivity of graphene. Second, we apply the method to a cut-wire metamaterial with an electric dipole resonance. The method is valid for thin-film structures such as two-dimensional metamaterials and frequency-selective surfaces and can be easily generalized for anisotropic or chiral media.     

一种基于3D打印技术的结构型宽频吸波超材料

设计了一种三层宽频吸波超材料,其表层和中间层为单元尺寸不同的周期阵列结构,底层为吸波平板结构,优化后的总厚度仅为4.7 mm,并采用三维(3D)打印技术成功制备了该吸波超材料.吸波体反射率测试结果表明,在电磁波垂直入射条件下,宽频吸收峰分别出现在5.3和14.1 GHz,两峰叠加使得其在4-18 GHz频率范围内反射损耗均小于-10 dB.采用S参数反演法计算了每一层的等效电磁参数,并利用多层结构反射率公式推导得出该模型的理论反射率,理论计算结果与实测结果基本一致.通过研究能量损耗、电场分布和磁场分布揭示了吸波机理,分析表明该吸波体的宽频吸收效果源于三层结构产生的吸收带宽叠加.本文提出的吸波超材料具有良好的宽频吸收效果,尤其在低频范围吸波性能较佳,结合3D打印快速成型技术,可获得结构精细的三层吸波超材料,具有重要的实际应用价值和广阔的应用前景.     

基于石墨烯编码超构材料的太赫兹波束多功能动态调控

提出了一种基于石墨烯带的太赫兹波段的1 bit编码超构材料,可以实现太赫兹波束的数目、频率、幅度等参数多功能动态调控.该结构由金属薄膜、聚酰亚胺、硅、二氧化硅、石墨烯带组成.通过对石墨烯带施加两种不同的电压,可以实现一定频率范围内相位差接近180?的"0"和"1"数字编码单元,进而构成1 bit动态可控的编码超构材料.全波仿真结果表明,不同序列的编码超构材料能够实现波束数目从单波束、双波束、多波束到宽波束的调控.相同序列的编码超构材料,通过施加石墨烯带的不同电压能够实现宽频段波束频率的偏移.对于000000或者111111周期序列的编码超构材料,通过施加石墨烯带的不同电压还能够实现波束幅度的调控.因此这种基于石墨烯带的编码超构材料为灵活调控太赫兹波提供了一种新的途径,将在雷达隐身、成像、宽带通信等方面具有重要的意义.     

Design of an acoustic bending waveguide with acoustic metamaterials via transformation acoustics

Transformation acoustics is employed to design an acoustic bending waveguide. A two-dimensional square area with anisotropic and homogeneous material properties is transformed into a fan-shaped area with anisotropic and inhomogeneous material properties to rotate the direction of beam propagation. An alternating layered structure is considered to approximate a medium with anisotropic material properties. From the calculation results, the transformation medium can be realized by an alternating layered structure consisting of water and fluid with negative mass density. We propose that an acoustic metamaterial composed of three layers in water background can be designed to replace negative mass density fluid. The effective mass density and bulk modulus of the system that is composed of the acoustic metamaterial and water are dependent on the incident frequency and the geometric size of the acoustic metamaterial. We tune the geometric size of the acoustic metamaterial to approach the corresponding mass density distribution of the negative mass density fluid at a specific frequency. Thereby, the acoustic bending waveguide designed by using transformation acoustics can be achieved by the acoustic metamaterials.     

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.     

Plasmonic nanoparticle monomers and dimers: from nanoantennas to chiral metamaterials

We review the basic physics behind light interaction with plasmonic nanoparticles. The theoretical foundations of light scattering on one metallic particle (a plasmonic monomer) and two interacting particles (a plasmonic dimer) are systematically investigated. Expressions for the effective particle susceptibility (polarizability) are derived, and applications of these results to plasmonic nanoantennas are outlined. In the long-wavelength limit, the effective macroscopic parameters of an array of plasmonic dimers are calculated. These parameters are attributable to an effective medium corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial where plasmonic monomers or dimers have the function of “meta-atoms”. It is shown that planar dimers consisting of rod-like particles generally possess elliptical dichroism and function as atoms for planar chiral metamaterials. The fabricational simplicity of the proposed rod-dimer geometry can be used in the design of more cost-effective chiral metamaterials in the optical domain.     

Circular polarization converters based on bi-layered asymmetrical split ring metamaterials

In this paper, a kind of bi-layered asymmetrical split ring metamaterial was proposed as a circular polarization converter. Simulations and experiments at the microwave regime showed that the proposed structures can achieve the conversions from right-handed circularly polarized electromagnetic waves to left-handed ones and the reversed conversions in the opposite propagating direction. The linear to circular polarization transmission coefficients and the surface currents were investigated to understand the mechanism of the circular polarization conversions. Moreover, we optimized the proposed metamaterials by increasing the distance between the two metal layers. The proposed circular polarization converters have applications in microwave wave plates and metamaterial antennas.     

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.     

基于集总元件和负微分元件的有源可调谐超材料传输线

针对无源超材料高色散、高损耗和均匀性差的缺点,利用集总元件和负微分元件设计、加工了一种微波频段的有源可调谐超材料传输线,并对其进行了测试.实验获得了具有散射参数随外加偏置电压改变而变化的电控可调谐特性以及衰减常数为负值的有源超材料传输线.     

Effect of metamaterial layer on optical surface plasmon resonance sensor

In this paper an optical surface plasmon resonance (SPR) sensor with metamaterial for four and five layered structure is studied. The numerical results presented in this paper leads to a significant properties of metamaterials in sensing field. Computed results of SPR sensors using metamaterial are compared with conventional optical SPR sensors for four and five layered structure. It is seen that wider dynamic range or effective range of measurable refractive index increases when metamaterial layer is used. It is also verified that SPR sensor with metamaterial layer can dramatically enhance the resolution and reduce the reflectivity compared with conventional SPR. Validity of the magnetic field results is proved on the basis of smooth match of the fields in the different layers of the proposed optical SPR sensor.     

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.     

Elastic waves propagation in thin plate metamaterials and evidence of low frequency pseudo and local resonance bandgaps

A comprehensive numerical simulation study on elastic wave propagation for a novel engineered thin plate metamaterial structural system is presented. To enhance the accuracy of model, a mesh convergence study is validated. The wave dispersion spectra with bandgaps for three types of structures are presented. Based on local resonance phenomena, the low frequency pseudo and local resonance bandgaps are reported. Highlights are also included for the Bragg scattering induced directional bandgaps. The effects of material and geometric parameters on bandgaps are discussed. The finite element based frequency response study further validates the reported bandgaps. The conclusions provide a new perspective for designs and applications of thin plate metamaterials for subwavelength wave manipulation including seismic shielding of civil infrastructures.     

Optimization of locally resonant acoustic metamaterials on underwater sound absorption characteristics

The study of acoustic metamaterials, also known as locally resonant sonic materials, has recently focused on the topic of underwater sound absorption. The high absorption occurs only within a narrow frequency band around the locally resonant frequency. Nevertheless, this problem can be addressed through a combination of several acoustic metamaterial layers that have different resonant frequencies. In this paper, an optimization scheme, a genetic and a general nonlinear constrained algorithm, is utilized to enhance the low-frequency underwater sound absorption of an acoustic metamaterial slab with several layers. Both the physical and structural parameters of the acoustic metamaterial slab are optimized to enlarge the absorption band. In addition, the sound absorption mechanism of the acoustic metamaterial slab is also analyzed. The result shows that each layer is found to oscillate as a nearly independent unit at its corresponding resonant frequency. The theoretical and experimental results both demonstrate that the optimized metamaterial slab can achieve a broadband (800–2500 Hz) absorption of underwater sound, which is a helpful guidance on the design of anechoic coatings.     

Metamaterials and their application in microwaves: A review

A metamaterial is a composite material that has attracted the attention of researchers since the late 1990s-early 2000s. This material contains an artificial periodic structure, which modifies its permittivity and permeability and, thereby, makes it possible to control the dispersion, refraction, and reflection of electromagnetic waves in the metamaterial. Analytical and experimental studies of the properties of metamaterials, as well as their applications, cover a wide frequency range from radio waves to the visible range. In recent years, considerable progress has been made toward the application of these materials in the microwave range (1–100 GHz). Works on development and application of metamaterials in the microwave range published over the last 8–10 years are reviewed. Artificial transmission lines as 1D metamaterials are discussed. Resonators, filters, and phase shifters based on the “metamaterial philosophy” are considered. Special attention is given to the application of metamaterials in the antenna technology.     

Research technique of metamaterials with the controlled effective negative refractive index and their characteristics

A design of the two-beam hybrid microwave interferometer for measuring refractive indices of metamaterials is described. It is based on the branching of radiation using a waveguide directional coupler. Radiations of the interferometer waveguide arms are summed and the phase disbalance of the interferometer arms is counted on the waveguide measuring line. The frequency dispersion of the negative refractive indices of the metamaterial samples with a variable distance between its constituent plates is experimentally investigated. A possibility of controlling the refractive index of a metamaterial is demonstrated.