Tunable broadband metamaterial absorber consisting of ferrite slabs and a copper wire

A tunable broadband metamaterial absorber is demonstrated at microwave frequencies in this paper.The metamaterial absorber is composed of ferrite slabs with large resonance beamwidths and a copper wire.The theoretical analysis for the effective media parameters is presented to show the mechanism for achieving the perfect absorptivity characteristic.The numerical results of transmission,reflectance,and absorptivity indicate that the metamaterial absorber exhibits a near perfect impedance-match to free space and a high absorptivity of 98.2% for one layer and 99.97% for two layers at 9.9 GHz.The bandwidth with the absorptivity above 90% is about 2.3 GHz.Moreover,the absorption band can be shifted linearly in a wide frequency range by adjusting the magnetic bias.This metamaterial absorber opens a way to prepare perfectly matched layers for engineering applications.     

基于单面金属结构的二维宽带左手材料

利用将磁谐振器与共面短金属导线相结合的思想,设计了一种基于单面金属结构的二维左手材料. 理论分析与仿真结果均表明该结构在某一频段同时具有负等效磁导率和负等效介电常数,并且相对左手带宽达到36%. 此外,该结构具有良好的容错能力,短金属导线宽度的变化对整体结构的谐振频率及通带宽度影响很小,这不仅有利于实际加工而且对于设计红外及太赫兹频率范围下的左手材料具有参考价值. 关键词： 左手材料 磁谐振器 宽频带 容错性     

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.     

Exploring electromagnetic response of tellurium dielectric resonator metamaterial at the infrared wavelengths

We numerically investigate the electromagnetic properties of tellurium dielectric resonator metamaterial at the infrared wavelengths. The transmission spectra, effective permittivity and permeability of the periodic tellurium metamaterial structure are investigated in detail. The linewidth of the structure in the direction of magnetic field W x has effects on the position and strength of the electric resonance and magnetic resonance modes. With appropriately optimizing the geometric dimensions of the designed structure, the proposed tellurium metamaterial structure can provide electric resonance mode and high order magnetic resonance mode in the same frequency band. This would be helpful to analyze and design low-loss negative refraction index metamaterials at the infrared wavelengths.     

Dual-band asymmetric electromagnetic wave transmission for dual polarizations in chiral metamaterial structure

In this paper, we propose a chiral metamaterial structure that enables dual-band asymmetric transmission effect for different linearly polarized electromagnetic waves. The metamaterial is composed of metallic spirals with two split-ring resonators sandwiching a dielectric slab and connecting with via hole. Strong one-way transmission of two orthogonally polarized waves at different frequency bands has been confirmed through both full-wave simulation and test on fabricated prototype at the microwave band. Analysis also shows such asymmetric transmission can be attributed to the induced asymmetric current distributions in the spiral that support strong polarization conversion and cross-polarization transmission. By scaling down the metamaterial structure, the concept could also be utilized at other frequency bands, such as submillimeter or even terahertz band and find applications in designing one-way electromagnetic wave devices or polarization spectral filters.     

Dual-band polarization-independent sub-terahertz fishnet metamaterial

A dual-band and polarization-independent fishnet metamaterial for the sub-THz frequency range is proposed and investigated. Dual-band modes have two resonances in which the first one is fixed as a left-handed mode and the second one can be arranged as a left-handed or single-negative mode. We select the character of second resonance by the choice of substrate properties. The metamaterial features of the structure are analyzed using the scattering data and confirmed by applying Kramers-Kronig relations. The characteristic features are also verified by the current distribution at the inner metallic surfaces of the structure. The influence of substrate modifications is studied and the effect of this change on resonances is discussed. The design of a dual-band and polarization-independent sub-THz metamaterial presented here can serve as a model and guide to realize tunable fishnet metamaterials for other frequency regimes.     

Experimental verification of negative refraction in a double cross metamaterial

We report on microwave experiments with a metamaterial composed of pairs of metallic crosses. The transmission properties of the structure show a left-handed transmission band at frequencies around 10.2 GHz. The validity of the negative effective index of refraction is verified by a Snell’s law refraction experiment performed on a wedge-shaped sample of the metamaterial. A second measurement of a similar wedge made from blank FR4 boards is done for reference. The results of the measurements show positive refraction over the whole measured frequency band for the FR4 wedge as well as the refraction of the incident radiation to negative angles within the designated left-handed frequency band for the metamaterial sample.     

超材料谐振子间的电耦合谐振理论与实验研究

通过将两个金属开口环谐振器口对口地放置, 实现了超材料谐振子间的电耦合谐振. 对电耦合谐振的微波等效电路进行了理论分析和数值计算, 结果表明耦合后的超材料谐振子能产生两个谐振频率, 其中一个随耦合强度的增加逐渐向低频方向移动, 而另一个固定在单谐振子的谐振频率处不变. 微波透射谱的实验测试和电磁仿真结果表明, 两个谐振峰随耦合强度的增加分别向低频和高频方向移动. 分析表明: 低频谐振峰的位置主要是由超材料谐振子间的电耦合强度决定的; 高频谐振偏离单谐振子的谐振频率主要是由不可避免的磁耦合引起的, 而且在耦合间距越小时磁耦合影响越大. 提出的基于超材料谐振子间的电磁耦合实现的双频谐振及其可调性极大地增加了超材料的设计与应用空间.     

Dual-band double-negative-index fishnet metamaterial at millimeter-waves

An effective negative refractive index (NRI) is demonstrated and experimentally verified for the first two propagation bands of a fishnet-like metamaterial at millimeter-wave frequencies. The dual-band NRI behavior is achieved by engineering the diffraction order (±1, ±1) associated with the internal mode supported between holey layers to correspond with the second propagation band. In addition to the experimental interferometric technique that accounts for the handedness of the propagation, numerical results are given to predict the dual-band effective NRI and to confirm dual-band negative refraction for a prism composed of the proposed metamaterial.     

基于平行金属条的左手结构设计与仿真研究

基于双平行金属线结构,将金属线宽度增大,变为金属条,同时在金属条结构单元中部引入缺口,使中部变细.由于等离子体效应,该双平行金属条结构在一定频段等效介电常数为负;又由于单元结构中部较细,使得该结构在一定频率会发生强烈的磁谐振.通过模拟仿真研究发现这种结构在X波段可以实现ε和μ同时为负.出现双负（ε<0,μ<0）的频段会随着谐振频率的变化而变化.理论分析表明谐振频率与金属条宽度、缺口高度及中部宽度有关,仿真结果同分析一致. 关键词： 左手材料 磁谐振 负磁导率 平行金属条     

Dual-band tunable negative refractive index metamaterial with F-Shape structure

This paper presents a negative refractive index tunable metamaterial based on F-Shape structure which is capable of achieving dual-band negative permeability and permittivity, thus dual-band negative refractive index. An electromagnetic simulation was performed and effective media parameters were retrieved. Numerical investigations show clear existence of two frequency bands in which permeability and permittivity both are negative. The two negative refractive index bandwidths are from 23.8 GHz to 24.1 GHz and from 28.3 GHz to 34.9 GHz, respectively. The geometry of the structure is simple so it can easily be fabricated. The proposed structure can be used in multiband and broad band devices, as the band range in second negative refractive index region is 7 GHz, for potential applications instead of using complex geometric structures and easily tuned by varying the separation between the horizontal wires.     

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     

一种基于旋转调谐的超材料

数值仿真研究了一种可调谐的双开口谐振环(DSRR)超材料.在平行入射的电磁波激励下,这种DSRR单元可以在不同的频段分别表现出磁谐振和电谐振.当外加电场E与DSRR的双开口平行时,DSRR受激励得到的磁谐振和电谐振强度最大.随着DSRR超材料沿外加磁场H方向顺时针旋转,其磁谐振和电谐振频率基本保持不变,但谐振强度均发生显著下降,同时对应透射相位的突变也逐渐降低.提出的超材料调谐方法只需要简单地旋转材料,而不需要改变原有超材料单元的结构或者增加额外的激励场,极大地简化了可调谐超材料的制备及应用,在电磁开关、相位调制等方面具有潜在的应用.同时,这种简单的方法有希望应用于更高频段的超材料调谐,可以有效地拓展太赫兹频段和光频段超材料的实际应用.     

Simulations of ferrite-dielectric-wire composite negative index materials

We perform extensive finite difference time domain simulations of ferrite based negative index of refraction composites. A wire grid is employed to provide negative permittivity. The ferrite and wire grid interact to provide both negative and positive index of refraction transmission peaks in the vicinity of the ferrite resonance. Notwithstanding the extreme anisotropy in the index of refraction of the composite, negative refraction is seen at the composite air interface allowing the construction of a focusing concave lens with a magnetically tunable focal length.     

基于石墨烯振幅可调的宽带类电磁诱导透明超材料设计

基于石墨烯的电控特性提出了一种由金属线谐振器和"H"型谐振器组成的宽带可调的类电磁诱导透明(类EIT)超材料结构.首先,利用CST Microwave Studio软件对该超材料结构的透射特性进行了仿真.该结构在1.05—1.46 THz内的透射窗由金属线谐振器的等离子谐振和"H"型谐振器的电感-电容谐振干涉相消引起,且暗模式谐振器的数量增多导致了透射窗带宽的增加.其次,仿真模拟了该结构在不同石墨烯费米能级下的透射特性.当石墨烯费米能级由0 eV逐渐增加到1.5 eV时,该结构透射窗在1.05—1.46 THz内的平均透射振幅由87%逐渐减少到25%,实现了宽带可调.同时,通过仿真模拟该结构在1.26 THz下的电场分布对其透射机理进行了分析,并实验制备了类EIT超材料结构样品,且利用太赫兹时域光谱对样品进行了透射性能测试,测试结果与仿真分析的趋势基本一致.     

Thermal broadband tunable Terahertz metamaterials

A thermally tunable metamaterial comprising a periodic array of metallic split-ring resonators with an embedded semiconductor has been proposed. The resonance frequencies of the metamaterial are demonstrated to be continuously tuned in the terahertz regime by increasing the temperature. The tunability is attributed to the temperature-dependent permittivity of the embedded semiconductor and well analyzed by an equivalent capacitor-inductor model. The proposed designs ensure broadband thermally tunable terahertz devices.     

Flexural wave suppression by an acoustic metamaterial plate

A new acoustic metamaterial plate is presented for the purpose of suppressing flexural wave propagation. The metamaterial unit cell is made of a plate with a lateral local resonance (LLR) substructure which consists of a four-link mechanism, two lateral resonators and a vertical spring. The substructure presents negative Young’s modulus property in certain frequency range. We show theoretically and numerically that two large low-frequency band gaps are obtained with different formation mechanisms. The first band gap is due to the elastic connection with the foundation while the second is induced by the lateral resonances. Besides, four-link mechanisms can transform the flexural wave into the longitudinal vibration which stimulates the lateral resonators to vibrate and to generate inertial forces for absorbing the energy and thus preventing the wave propagation. Frequency response function shows that damping from the vertical spring has little influence on the band gaps, although the damping can smooth the variation of frequency response (see the dotted line in Figs. 10 and 11). Increasing the damping of the lateral resonators may broaden the second band gap but deactivate its effect. This study provides guidance for flexibly tailoring the band characteristics of the metamaterial plate in noise and vibration controls.     

多频与宽频超材料吸收器

提出了多频与宽频超材料吸收器结构模型, 该吸收器是由刻蚀在介质基板两面的金属图案组成, 其正面是由不同大小的金属铜圆片和金属铜圆环结构组合而成, 反面完全覆盖金属铜. 由于不同几何大小的圆片或圆环结构的谐振频率不同, 且是相互独立的. 因此通过将两种不同几何大小的圆片与圆环结构组合, 使其在不同频率谐振, 便可得到双频吸收器; 而将三种不同几何大小的圆片和圆环结构组合便可得到三频吸收器; 同理可得到四频吸收器. 同时, 通过研究吸收器的电场分布, 验证了不同几何大小的圆片或圆环结构在不同频率谐振. 若通过优化组合圆片和圆环结构, 使其谐振频率紧密相连则可得到宽频吸收器. 关键词： 吸收器 超材料 多频 宽频     

Multi-band left-handed metamaterial inspired by tree-shaped fractal geometry

We report an alternative method of designing a new metamaterial with left handed (LH) characteristics over multi-band (MB) frequencies at microwave frequency regime. The resultant LH metamaterial (LHM) consisting of a single-sided tree-shaped fractal structure features triple magnetic resonances and one electric resonance apart from the lower metal plasma response, which is responsible for the three bands of negative refraction. The multi-resonant mechanism has been systematically studied to account for all electromagnetic behaviors, and capacitor–inductor circuit models are put forward for quantitative analysis. The LHM is balanced in the fundamental passband when only one layer is utilized, whereas the balanced condition is slightly broken when a collection of sub-wavelength cells are cascaded. The negative-zero-positive refraction of the fundamental LH band and the negative refraction of the higher LH band have been numerically validated by a prism-like LHM. For demonstration, a three-layer LHM slab sample is fabricated and measured. Consistent numerical and experimental results are observed. The method not requiring individual resonant particles and electrically continuous wires paves the way for a new route to compact MB LHM design.     

Band structure of two-dimensional square lattice photonic crystals of circular dispersive metamaterial rods

By virtue of the efficiency of the Dirichlet-to-Neumann map method, the details of the band structure of a two-dimensional square lattice photonic crystal composed of dispersive metamaterial circular rods in air background has been studied. We show that there are two flat bands at the band structure of the system for both H-polarization and E-polarization. These flat bands are created around the magnetic resonance frequency, surface plasmon frequency and magnetic surface plasmon frequency. We realized that the modes with frequencies lying above the resonance frequency behave like resonant cavity modes created in a single metallic cylindrical waveguide. While, due to the relatively large and imaginary refractive index of the metamaterial rods at the frequencies lying below the resonance frequency, the modes are localized modes with negligible penetration into the rods. Moreover, the modes are localized at the interface of the cylindrical metamaterial rods and the air background for the frequencies around the surface plasmon frequency and the magnetic surface plasmon frequency.