左手材料的反射特性与负折射率行为

利用平板波导法研究了不同入射角度下周期排列开口谐振环负磁导率材料、周期排列金属杆负介电常数材料以及左手材料微波反射特性，并利用劈尖法研究了左手材料的负折射特性.实验结果表明：负磁导率材料反射率曲线形成反射峰，其对应的反射峰频率与材料的谐振频率一致；负介电常数材料反射率接近0dB；左手材料出现单个反射较小的反射峰，其峰值反射率随入射角度的增大而变大，即反射能力增强，且反射峰与透射峰有相对频移.劈尖法测量还表明，左手材料在9800MHz频率附近出现负折射现象，其折射率n为-0.796. 关键词： 左手材料 反射 负折射率     

High transmittance left-handed materials involving symmetric split-ring resonators

We present theoretical and experimental results for a new design of highly symmetric, multigap split-ring resonators (SRRs), as well as for left-handed materials of a broad and high transmittance left-handed band, achieved by combining those symmetric SRRs with continuous wires. Studying in detail, both theoretically and experimentally, our proposed symmetric SRRs, we proved that they avoid the electric field excitation of the magnetic SRR resonance; thus they are appropriate for the creation of two-dimensional and three-dimensional left-handed materials. Finally, we propose critical design rules for the development of low-loss and broad-band left-handed materials.     

Fabrication of terahertz metamaterials by laser printing

A laser printing technique was used to fabricate split-ring resonators (SRRs) on Si substrates for terahertz (THz) metamaterials and their resonance behavior evaluated by THz time-domain spectroscopy. The laser-printed Ag SRRs exhibited sharp edge definition and excellent thickness uniformity, which resulted in an electromagnetic response similar to that from identical Au SRR structures prepared by conventional photolithography. These results demonstrate that laser printing is a practical alternative to conventional photolithography for fabricating metamaterial structures at terahertz frequencies, since it allows their design to be easily modified and optimized.     

Experimental analysis of true left-handed behaviour and transmission properties of composite metamaterials

We report the true left-handed transmission of a composite metamaterial (CMM) consisting of periodically stacked split-ring resonator (SRR) and wire elements. The negative permeability (μ < 0) gap is demonstrated explicitly by comparing SRR and closed-ring resonator structures. We confirm experimentally that the plasma cut-off frequency of the CMM is determined by the combined dielectric response of SRR and wire elements, and it is much lower than that of the wire-only medium. This is crucial to identify the left-handed transmission bands of the CMM. We further investigate the effect of intralayer and interlayer disorder on the transmission spectrum of CMM arising from misaligned fabrication and stacking of the SRR layers. We found that the intralayer disorder affects the μ < 0 gap of SRRs and the left-handed transmission band of CMM significantly, whereas the SRR transmission is rather immune to interlayer disorder.     

Transmission properties of terahertz pulses through subwavelength double split-ring resonators

We present a terahertz time-domain spectroscopy study of the transmission properties of planar composite media made from subwavelength double split-ring resonators (SRRs). The measured amplitude transmission spectra reveal a resonance near 0.5 THz, the central frequency of most ultrafast terahertz systems, for one SRR orientation in normal-incidence geometry. This resonance is attributed to the effect of electric excitation of magnetic resonance of the SRR arrays. In addition, the influences of background substrate, lattice constant, and the shapes of the SRRs on the terahertz resonance are experimentally investigated and agree well with the results of recent numerical studies.     

人工异向介质调控电磁波极化特性的实验与仿真研究

电磁波的极化特性在通信、导航和雷达等方面已逐渐得到应用.为了有效控制电磁波的极化状态, 本文设计了一种基于开口环结构的人工异向介质.该人工异向介质由开口环结构,电介质基底和金属背板组成, 可以将入射的线性极化波完整地转换为圆极化波,椭圆极化波以及和入射波极化方向垂直的线极化波. 本文通过实验和仿真验证了本文的设计,实验结果和仿真结果符合较好.     

The modification of the initial susceptibility of dilute binary ferrofluids based on γ-Fe2O3/ZnFe2O4 nanoparticles

This paper presents a multi-band metamaterial absorber comprising three multi-gap split-ring resonators (SRRs) with different radii and ring widths, designed in combinatorial approach. Experiments demonstrate that it can perform absorption peaks at three resonant frequencies 7.10 GHz, 10.04 GHz, and 17.44 GHz with the absorption of 99.90%, 99.91%, and 99.68%, respectively. The physical mechanism of metamaterial absorber was explained through numerical calculation and simulation, which showed that three absorption peaks were caused respectively by the three four-gap SRRs. The absorber is insensitive to incident angles and polarization states, so it has broad prospect of application.     

Selective mode suppression in coplanar waveguides using metamaterial resonators

In this paper, it is shown that split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs) can be used to selectively suppress the odd (slot) mode or the even (fundamental) mode, respectively, in coplanar waveguides. To this end, it is necessary to symmetrically etch the SRRs and the CSRRs in the line. An interpretation of this behavior is reported. The paper is also supported by experimental results, and some applications are highlighted.     

Magnetic response of split-ring resonators in the far-infrared frequency regime

We report on the fabrication, through photolithography techniques, and the detailed characterization, through direct transmission measurements, of a periodic system composed of five layers of photolithographically aligned micrometer-sized Ag split-ring resonators (SRRs). The measured transmission spectra for propagation perpendicular to the SRRs plane show a gap around 6 THz for one of the two possible polarizations of the incident electric field; this indicates the existence of a magnetic resonance, which is verified by detailed theoretical analysis. To our knowledge this is the first time that a system of more than one layer of micrometer-sized SRRs has been fabricated. The measured optical spectra of the Ag microstructure are in very good agreement with the corresponding theoretical calculations.     

Experimental observation of left-handed behavior in an array of standard dielectric resonators

We demonstrate that by utilizing displacement currents in simple dielectric resonators instead of conduction currents in metallic split-ring resonators and by additionally exciting the proper modes, left-handed properties can be observed in an array of high dielectric resonators. Theoretical analysis and experimental measurements show that the modes, as well as the subwavelength resonance, play an important role in the origin of the left-handed properties. The proposed implementation of a left-handed metamaterial, based on a purely dielectric configuration, opens the possibility of realizing media at terahertz frequencies since scaling issues and losses, two major drawbacks of metal-based structures, are avoided.     

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.     

Symmetric and antisymmetric modes of electromagnetic resonators

In this paper, we numerically study a new type of infrared resonator structure, whose unit cell consists of paired split-ring resonators (SRRs). At different resonant frequencies, the magnetic dipoles induced from the two SRRs within one unit cell can be parallel or antiparallel, which are defined as symmetric and antisymmetic modes, respectively. Detailed simulation indicates that the symmetric mode is due to magnetic coupling to resonators, in which the effective permeability could be negative. However, the antisymmetric mode originating from strong electric coupling may contribute to negative effective permittivity. Our new electromagnetic resonators with pronounced magnetic as well as electric responses could provide a new pathway to design negative index materials (NIMs) in the optical region. PACS 78.20.Ci; 73.20.Mf; 42.25.Bs     

Photoexcited Blueshift and Redshift Switchable Metamaterial Absorber at Terahertz Frequencies

We propose a design and numerical study of an optically blueshift and redshift switchable metamaterial(MM)absorber in the terahertz regime. The MM absorber comprises a periodic array of metallic split-ring resonators(SRRs) with semiconductor silicon embedded in the gaps of MM resonators. The absorptive frequencies of the MM can be shifted by applying an external pump power. The simulation results show that, for photoconductivity of silicon ranging between 1 S/m and 4000 S/m, the resonance peak of the absorption spectra shifts to higher frequencies, from 0.67 THz to 1.63 THz, with a resonance tuning range of 59%. As the conductivity of silicon increases, the resonance frequencies of the MM absorber are continuously tuned from 1.60 THz to 1.16 THz, a redshift tuning range of 28%. As the conductivity increases above 30000 S/m, the resonance frequencies tend to be stable while the absorption peak has a merely tiny variation. The optical-tuned absorber has potential applications as a terahertz modulator or switch.     

Improved TL-RLC model for terahertz circular split-ring resonators

Three geometries of split-ring resonators (SRRs) including circular geometry and two elliptical geometries were fabricated by modern photolithography process. The samples were measured by terahertz time-domain transmission spectroscopy. These spectra clearly revealed the lower-frequency LC resonances and the higher-frequency dipole resonances; meanwhile, the coupling effect between the LC and dipole resonance had played an important role in the overall response. Comparing the results shows that the LC resonance, dipole resonance, and the coupling effect can be designed. A simple transmission-line (TL) RLC circuit model was used to help us understand this coupling behavior and the extent of its effects. But the simple model has some disadvantage. For better matching TL-RLC model results with measured data, an improved model was introduced for the circular and y-direction stretched elliptical geometry SRRs. Other resonances and modes existing at higher frequencies except the typical LC and dipole resonances were revealed by the improved model.     

Extended verification of scaling behavior in split-ring resonators

We present an expanded LC-model for nanoscale split-ring resonators (SRR), including the influence of dielectric host materials. The LC-model is experimentally verified by changing the geometry of the SRR unit cell as well as by optofluidic tuning, where the SRR samples are covered with index oil. The extended model can be used as a general guideline for metal SRR structures with arbitrary dielectric host materials.     

Spectral imaging of individual split-ring resonators

We report on spectral imaging within individual silver split-ring resonators (SRRs) operating in the near infrared-visible range. We classified the optical eigenmodes from the measurement of their energies and nanometer scale spatial distributions. They are plasmonic standing waves that show great similarities with that of nanoantennas. We, however, evidenced marked differences in the near-field electric field lines' spatial distribution and the energies' dispersion. We also showed that the subwavelength defect's influence on the SRRs' eigenmodes spatial distribution is small.     

Identifying magnetic response of split-ring resonators at microwave frequencies

In this study we provide experimental methods to identify the magnetic resonance of split ring resonantors (SRR) at the microwave frequency regime. Transmission measurements were performed on both single SRR unit cell and periodic arrays of SRRs. The magnetic response of the SRR structure was demonstrated by comparing the transmission spectra of SRRs with closed ring resonators (CRR). Effects of the changes in the effective dielectric constant of the SRR medium on the band-gaps of SRR are investigated experimentally. SRRs not only exhibit a magnetic resonance band gap but also a band gap due to the electric resonance. Finally, we present the effect of electric coupling to the magnetic resonance of bianisotropic SRRs by utilizing SRRs with different orientations, and incident electromagnetic wave polarizations.     

Amplitude- and phase-resolved optical near fields of split-ring-resonator-based metamaterials

We investigate the local optical response of split-ring resonator-(SRR)-based metamaterials with an apertureless scanning near-field optical microscope. By mapping the near fields of suitably resonant micrometer-sized SRRs in the near-infrared spectral region with an uncoated silicon tip, we obtain a spatial resolution of better than lambda/50. The experimental results confirm numerical predictions of the near-field excitations of SRRs. Combining experimental near-field optical studies with near- and far-field optical simulations provides a detailed understanding of resonance mechanisms in subwavelength structures and will facilitate an efficient approach to improved designs.     

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     

Nonunity permeability in metamaterial-based GaInAsP/InP multimode interferometers

We demonstrated an InP-based optical multimode interferometer (MMI) combined with metamaterials consisting of minute split-ring resonators (SRRs) arrayed on the MMI. The MMI could operate at an optical fiber communication wavelength of 1.5 μm. Magnetic resonance occurred between the SRR metamaterial and light at 1.5 μm, and the relative permeability of the metamaterial increased to 2.4 around this wavelength. This result shows that it is possible to use new materials with nonunity permeability to construct semiconductor-based photonic devices.