Dual-band metamaterial with windmill-like structure

A broadband negative refractive index metamaterial based on a windmill-like structure is proposed, and investigated numerically and experimentally at the microwave frequency range. From the numerical and experimental results, effect media parameters are retrieved, which clearly show that there exist two broad frequency bands in which the permittivity and permeability are negative. The two negative bands are from 9.1 GHz to 10.5 GHz and from 12.05 GHz to 14.65 GHz respectively, and the negative bandwidth is 4 GHz. Due to the good bandwidth performance, the metallic cell with double negative property obtained in this paper is suitable for use in the design of multiband or broadband microwave devices.     

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.     

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.     

新型负模量声学超结构的低频宽带机理研究

提出了一种具有负模量特性的新型声学超结构,并揭示了其低频带隙的形成及拓宽机理.通过理论推导给出了该新型结构的归一化有效模量表达式,由于有效模量的零值点与系统参数密切相关,可以调节合适的参数使得零值点降低或带隙下界降低,进一步实现低频带隙.理论结果表明,在一定的频率范围内,系统的弹性模量为负且负模量区域进一步拓宽,从而通过负模量区域的放大而拓宽带隙.这种新的实现低频带隙的方法克服了传统局域共振附加质量过大及惯性放大结构带隙较窄的缺点.同时,通过有限元法得到的周期结构的传输率随着结构参数的变化趋势与理论分析的变化趋势基本一致,并得到了约40—180 Hz的低频宽带.这种实现低频带隙的新思路对低频声波的控制具有很重要的理论指导意义.     

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。     

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。     

基于特异材料的非完美透镜成像

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 success 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 ...     

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.     

Propagation of a localized wavepacket in a metamaterial with a negative index of refraction

Propagation properties of electromagnetic waves in a medium with a negative index of refraction are investigated. A model of a physical signal that combines simultaneously qualities of both a spatially-localized beam and a wavepacket was used as the incident wave. Such a choice was necessary because of the strong frequency dispersion of metamaterials in the spectral region with a negative index of refraction. An approximate analytical solution was derived that describes the propagation dynamics of such a signal through a slab made of material showing simultaneously a negative dielectric permittivity and magnetic permeability. Presented at the XIIIth International Conference “Physics of Pulse Discharges in Condensed Media,” August 21–25, 2007, Nikolaev, Ukraine. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 187–193, March–April, 2008.     

一种新型异向介质设计及实验验证

本文提出了工作在X波段的单面双S型异向介质结构,在仿真、实验两个方面对这种新型异向介质的异向特性进行了验证.实验和仿真结果均表明,这种新型的异向介质结构在这一工作频率下具有负折射特性.这种新型的异向介质具有两个优势:更加便于制造和便于添加可控器件使单面异向介质成为可控异向介质.     

Membrane-based acoustic metamaterial with near-zero refractive index

We investigate a one-dimensional acoustic metamaterial with a refractive index of near zero(RINZ) using an array of very thin elastic membranes located along a narrow waveguide pipe. The characteristics of the effective density, refractive index, and phase velocity of the metamaterial indicate that, at the resonant frequency fm, the metamaterial has zero mass density and a phase transmission that is nearly uniform. We present a mechanism for dramatic acoustic energy squeezing and anomalous acoustic transmission by connecting the metamaterial to a normal waveguide with a larger cross-section. It is shown that at a specific frequency f_1, transmission enhancement and energy squeezing are achieved despite the strong geometrical mismatch between the metamaterial and the normal waveguide. Moreover, to confirm the energy transfer properties, the acoustic pressure distribution, acoustic wave reflection coefficient, and energy transmission coefficient are also calculated. These results prove that the RINZ metamaterial provides a new design method for acoustic energy squeezing,super coupling, wave front transformation, and acoustic wave filtering.     

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.     

A flexible metamaterial with negative refractive index at visible wavelength

In this paper, we demonstrated a realization of a flexible metamaterial with negative refractive index operating at visible wavelength. With the help of Finite-Difference Time-Domain (FDTD) method, we could establish design rules for the metamaterial and analyze the characteristics of it. To this end, the fishnet structure with the unit cell size 185 nm by 240 nm was fabricated. Due to the polymer dielectric spacer between the metal-layers, the metamaterial is freestanding without base substrate and additional backside etching process.     

宽带透射吸收极化无关超材料吸波体

提出了一种新的基于磁性吸波体材料的具有低频透射和高频宽带吸收特性的超材料吸波体.该超材料吸波体在1 GHz的透射系数为-0.5 dB,具有较好的低频透射特性,可以实现对低频信号的相互通信;在频率大于8.4 GHz的频段,吸收率均大于80%,基本覆盖整个X波段和Ku波段,实现高频宽带吸收.此外,由于该超材料吸波体的单元金属周期结构具有较好的四重旋转对称性,因而是极化无关的.该透射吸收超材料吸波体设计简单,实用性强,具有较强的潜在应用价值.     

Three-dimensional surface current loops in broadband responsive negative refractive metamaterial with isotropy

We propose a bulk negative refractive index (NRI) metamaterial composed of periodic array of tightly coupled metallic cross-pairs printed on the six sides of a cube for applications of superlenses. The structural characteristics of the three-dimensional (3D) metamaterial consist in the high symmetry and the superposition of metallic cross-pairs, which can increase the magnetic inductive coupling between adjacent cross-pairs and realize a broadband and isotropic NRI. The proposed 3D structure is simulated using the CST Microwave Studio 2006 to verify the design validity. The simulation results show that the proposed structure can not only realize simultaneously an electric and magnetic response to an incident electromagnetic (EM) wave, but also exhibit a broadband NRI whose relative bandwidth can reach up to 56.7%. In addition, the NRI band is insensitive to the polarization and the incident angle of the incident EM wave. Therefore, the proposed metamaterial is a good candidate material as three-dimensional broadband isotropic NRI metamaterial.     

一种超材料梁对机械波振动吸收的模拟研究

本文设计了一种能够对机械波进行吸收的超材料梁,超材料梁由若干质量-弹簧微结构系统和一根各向同性梁构成.通过对两种不同结构的质量-弹簧系统的分析,从理论上解释了"负有效质量"和"负有效刚度".根据Hamilton原理,导出了超材料梁的代表性胞元的控制方程.通过数值模拟分析了两种不同结构的有限超材料梁对机械波的吸收性能,一种是弹性系数线性变化的质量-弹簧系统在有限梁内均匀分布,另一种是由固有频率线性变化的弹簧-阻尼器子系统构成四个相同吸收器子群在有限梁内均匀分布.模拟结果表明,进入梁中的机械波与质量-弹簧振子 关键词： 超材料梁 负有效质量 负有效刚度 机械波     

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.     

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.     

基于磁/电介质混合型基体的宽带超材料吸波体的设计与制备

本文设计了一种基于磁/电介质混合型基体的宽带超材料吸波体, 吸波体基本单元由电阻膜、磁/电介质混合型基体以及金属背板组成. 采用时域有限差分法对超材料吸波体吸波性能进行了仿真, 使用遗传算法优化了反射率小于-10 dB的带宽. 仿真结果表明, 当超材料吸波体厚度为2.5 mm时, 在7.8–18 GHz频率范围内的反射率小于-10 dB, 具有厚度薄、宽带、极化不敏感等优点. 通过等效电路模型对其工作机理进行了分析与讨论. 最后制备样品进行测试, 测试结果与仿真结果一致.     

Numerical simulations of terahertz double-negative metamaterial with isotropic-like fishnet structure

The isotropic-like fishnet metamaterial with an array of cross-shaped holes penetrating through the multiple layers has been numerically studied in the terahertz regime. Its left-handed properties are described by the retrieved effect media parameters and validated by the simulation of a wedge-shaped model. The influences of the various geometrical parameters on the electromagnetic response and the left-handed performance are investigated. This isotropic-like fishnet metamaterial has the advantage of lower losses and higher transmission and holds potential for further applications at higher frequencies.