Effects of oblique incidence on terahertz responses of planar split-ring resonators

Effects of oblique incidence of terahertz waves on the response of planar split-ring resonators are investigated, both experimentally and by simulation. It is found that the incident angle dependent phase delay and coupling conditions of neighboring split-ring resonator （SRR） units play important roles and greatly change both the transmission and reflection spectra for the resonant feature of linear charge oscillations. Our results show that the SRR structure-supported magne- toelectric couplings at oblique excitation are trivial and can be ignored. A highly symmetric response is found in the cross-polarization effects, which may manifest the bianisotropic properties of the SRR system but this needs further study.

Band-stop optical nanofilters with split-ring resonators based on metal–insulator–metal structure

Novel band-stop filters with circular split-ring resonators based on the metal-insulator-metal （MIM） structure are presented, with their transmission properties of SPPs propagating through the filter simulated by the finite-difference time-domain （FDTD） method, The variation of the gap of the split ring can affect the transmission characteristics, i.e., the transmission spectrum of SPPs exhibiting a shift, which is useful for modulating the filter. Linear and nonlinear media are used in the resonator respectively. By varying the refractive index of the linear medium, the transmission properties can be changed obviously, and the effect caused by changing the incident intensity with a nonlinear medium is similar. Several resonant modes that are applicable can be enhanced by changing the position of the gap of the split ring. Thus, the transmission properties can be modulated by adjusting the size of the gap, varying the refractive index, and changing the incident intensity of the input light. These methods may play significant roles in applications of optical integrated circuits and nanostructural devices.

Expanding the bandwidth of planar MNG materials with co-directional split-ring resonators

An effective approach to expand the bandwidth of negative permeability of small-sized planax materials is proposed. Based on qualitative analysis of equivalent circuit models, the fractional bandwidth of an μ-negative （MNG） material is expanded from 3.53% up to 12.87% by adding split-ring resonators （SRRs） and arranging them by proposed steps. Moreover, the experimental results validate the effectiveness of bandwidth-expanding methods, which is promising for the extensive application of metamaterials in the microwave field.

Experimental Study on Split-Ring Resonators with Different Slit Widths

Metamaterial one-dimensional periodic structures are composed of split-ring resonators, which can display electric permittivity and magnetic permeability simultaneously negative, are studied experimentally. In the present study, each resonator is made up of two concentric circular copper rings patterned on a substrate of kapton, with slits diametrically opposite each other and with the line of the splits along the longitudinal direction of the periodic array containing seven split rings evenly spaced. The experiments consist in inserting the metamaterial slab into a square waveguide of side length 6 mm, corresponding to a cutoff frequency of 25 GHz. Transmission bands due to magnetic and electrical responses are identified for slits with aperture widths of 1 mm and 2 mm, centered at 5.67 and 6.12 GHz frequencies, respectively, values well below the 25 GHz frequency cutoff, so characterizing a medium with negative permeability and permittivity.

Design of Multi-band Small Antenna Based on Single Split-Ring Resonator

To use the single split-ring resonator （SRR） as a basic unit cell for small antenna with multi-band frequency response is proposed. The structure of antenna is consisted of a single spilt-ring resonator and a coupled microstrip line. The designed antenna is numerically optimized with CST Microwave Studio. The radiation properties of the antenna show that there are three frequency bands among which two bands are 1.3 GHz and 2.1 GHz ultra-widehand （UWB）, respectively, where Sll is less than - 10 dB. The gain at every frequency for the multi-hand antenna is above 2.6 dBi, and it increases monotonously with the frequency in the two UWB.

Permittivity Measurement of Low-Loss Substrates Based on Split Ring Resonators

In this paper, we present the complex permittivity measurement of low-loss substrates based on a microstrip-line-excited split-ring resonator (SRR). Permittivity of an unknown substrate is calculated based on the change in oscillation frequency of SRR caused by the material-under-test (MUT) above the SRR. Theoretical analysis and results of the simulations and experiments demonstrate the microstrip-line-excited SRR can be used to effectively improve measurement sensitivity. Simple equations for measurement of low-loss substrates using SRR are proposed and experimentally verified.

Polarization Insensitivity in Double-Split Ring and Triple-Split Ring Terahertz Resonators

A modified double-split ring resonator and a modified triple-split ring resonator, which offer polarization-insensitive performance, are investigated, designed and fabricated. By displacing the two gaps of the conventional double- split ring resonator away from the center, the second resonant frequency for the 0° polarized wave and the resonant frequency for the 90° polarized wave become increasingly close to each other until they are finally identical. Theoretical and experimental results show that the modified double-split ring resonator and the modified triple-split ring resonator are insensitive to different polarized waves and show strong resonant frequency dips near 433 and 444OHz, respectively. The results of this work suggest new opportunities for the investigation and design of polarization-dependent terahertz devices based on split ring resonators.

一种新型SRR缺陷地面结构低通滤波器

该文提出一种新型开口谐振环(Split-Ring Resonator,SRR)缺陷地面结构(Defected Ground Structure,DGS)。这种结构与传统哑铃形DGS结构相比,具有陡峭的带隙和平坦的低通特性。文中详细分析了开口谐振环DGS单元的等效电路以及结构参数与电参数之间的关系。在此基础上提出一种加载开路枝节的SRR DGS单元模型以提高带外抑制,采用这种单元的级联周期结构设计并制作了一种紧凑的S波段低通滤波器。测试结果表明,该滤波器带内插损小于0.5dB,带外抑制度在30 dB以上。

基于缺陷地和开口谐振环的三频段小型化天线

提出了一种新型三频段工作的小型微带贴片天线,天线采用不对称结构,在接地板上引入缺陷地结构(DGS)改变了天线表面电流分布,改善工作频率,衍生在无线局域网(WLAN)(2.4 GHz)处的频带。加载开口谐振环(SRR)金属环结构在独立控制WLAN(5.8 GHz)的频带的同时,减小了12%的天线体积。天线结构紧凑,整体尺寸为12.5 mm×28.5 mm×1.5 mm。结果表明,天线覆盖3个独立的阻抗带宽,分别为800 MHz(1.96~2.76 GHz),200 MHz(5.65~5.85 GHz)和1 460 MHz(7.64~9.1 GHz),在频段内的回波损耗均小于-10 dB,具有良好的方向性和增益,支持WLAN(5.8/2.4 GHz)频段和国际电信联盟(ITU)(8.0~8.7 GHz)频段的应用。

基于SRR-DGS新型高选择性带通滤波器的设计

通过在阶梯阻抗谐振器（Stepped Impedance Resonators,SIR）上加载开口谐振环缺陷地结构（SplitRing Resonator Defected Ground Structure,SRR-DGS）,设计了一款具有高选择性和较好带外抑制性能的带通滤波器。测试结果表明,该滤波器的3 d B工作频带为2.56~2.77 GHz（7.9%）,带内最大插入损耗为0.8 d B。此外,在通带两侧各有两个传输零点,分别位于2.17 GHz、2.48 GHz、2.86 GHz和3.81 GHz,带外抑制均大于30 d B,表明该滤波器具有较好的带外抑制特性。同时,仿真与测试结果吻合较好,验证了该滤波器设计方法的有效性。

基于SRR结构的多频带频率选择表面

为实现频率选择表面(FSS)的多频带特性,将开口谐振环(SRR)结构引入多频带FSS的设计中。基于等效电路和仿真模型分析了单个SRR的电磁谐振特性,及其作为FSS结构单元而产生的电磁耦合。最后,利用有限元仿真软件HFSS计算了理想状态下无穷大周期性结构的多频带FSS,并通过对FSS的传输和反射频谱研究,揭示这种FSS谐振频率与SRR结构基本几何参数的内部关系。

Terahertz radiation enhancement in photoconductive antennas with embedded split-ring resonators

This Letter proposes a novel method for enhancing terahertz(THz) radiation from microstructure photoconductive antennas(MSPCA). We present two types of MSPCA, which contain split-ring resonators(SRRs) and dipole photoconductive antennas(D-PCAs). The experimental results reveal that when the femtosecond laser is pumping onto the split position of the SRR, the maximum THz radiation power is enhanced by 92 times compared to pumping at the electrode edge of the D-PCA. Two π phase shifts occur as the pumping laser propagates from the negative electrode to the positive electrode. Analysis shows that photoinduced carrier charges move within the split position of the SRR.

基于拓扑变换的共形超材料高增益微带贴片天线

微带贴片天线具有体积小、重量轻、剖面低、成本低、易于集成等优点,被广泛应用于各种通信、遥测和探测系统中。但是,微带贴片天线也存在定向增益低的缺点。为此,提出了一种加载共形超材料的高增益微带贴片天线。将方形开环谐振器(Split-ring resonator,SRR)拓扑变换为符合圆形衬底的SRR单元,SRR赋予抑制天线表面波的超材料效应。仿真结果表明,初始的圆形微带贴片天线的谐振频率为10 GHz,增益为6.12 dBi。加载10个拓扑SRR单元的天线的近场参数保持良好,远场增益为7.88 dBi,比初始天线增加了近2 dBi。

Tunable multiband terahertz metamaterials using a reconfigurable electric split-ring resonator array

We demonstrate micromachined reconfigurable metamaterials working at multiple frequencies simultaneously in the terahertz range.The proposed metamaterial structures can be structurally reconfigured by employing flexible microelectromechanical system-based cantilevers in the resonators,which are designed to deform out of plane under an external stimulus.The proposed metamaterial structures provide not only multiband resonance frequency operation but also polarization-dependent tunability.Three kinds of metamaterials are investigated as electric split-ring resonator(eSRR)arrays with different positions of the split.By moving the position of the split away from the resonator’s center,the eSRR exhibits anisotropy,with the dipole resonance splitting into two resonances.The dipole–dipole coupling strength can be continuously adjusted,which enables the electromagnetic response to be tailored by adjusting the direct current(DC)voltage between the released cantilevers and the silicon substrate.The observed tunability of the eSRRs is found to be dependent on the polarization of the incident terahertz wave.This polarization-dependent tunability is demonstrated by both experimental measurements and electromagnetic simulations.

加载谐振环的新型宽带准八木天线设计

设计了一种新型宽带准八木天线,该天线采用微带线进行馈电,通过一种新型的巴伦结构实现了微带线到共面带状线的转换。天线有一个辐射振子和两个引向振子,介质板背面的金属地板作为反射器,具有较宽的带宽。为了进一步提高增益,在引向振子前端加载两组开口谐振环单元。改进后天线的-10 dB阻抗带宽为53.7%(5.9~10.2 GHz),增益达到了5.7~9.3 dB,相比改进前平均提高了2 dB。对原型天线和改进后天线分别进行了加工测量,测量结果与仿真结果基本吻合。

基于裂缝谐振环周期结构的频率选择表面

介绍了一种利用裂缝谐振环构成的缝隙型频率选择表面。使用有限元法对这种频率选择表面的电波传输特性进行了全波仿真分析。同时,提出了简单的L-C等效电路模型,并结合巴比涅原理分析预测了这种频率选择表面的谐振频率。分析结果表明,频率选择表面的谐振频率由单元结构决定,受单元周期的影响较小,而且透射波具有沿垂直于裂缝方向的极化选择性。实验测量结果与理论分析吻合。

一种新颖的开口环地面缺陷结构低通滤波器

提出了一种新颖的具有陡峭边带和宽阻带的小型化低通滤波器。通过把开口谐振环地面缺陷结构(Split-Ring Resonator Defected Ground Structure,SRRDGS)与阶梯阻抗梳状谐振器结合,提高了滤波器的选择特性,同时获得了宽阻带。对所提出的结构作了加工并进行了实物测量,测试结果表明:滤波器选择特性大于160dB/GHz,在2.98GHz到8.2GHz范围内抑制度大于20dB,而占用面积仅为20×25mm2。

一种新颖的双陷波超宽带天线设计

针对超宽带系统易受窄带信号干扰的问题,设计了一种新颖的基于金属开口谐振环结构的双陷波平面超宽带天线。通过在天线的辐射贴片上加载U形槽和在接地板上引入寄生条带的方法实现了双陷波特性。利用仿真软件研究了U形槽和寄生条带的物理尺寸对陷波特性的影响,并对所设计的超宽带天线进行了制作和测量。仿真和测试结果表明,天线在超宽带系统3.1～10.6GHz工作频段内的电压驻波比小于2,在WiMAX和WLAN频率范围具有良好的陷波特性,有效地抑制了超宽带通信系统与窄带通信系统之间潜在的干扰。

一种超材料的平面型频率选择反射面特性研究

为降低频率选择反射面的设计维度和制造成本,研究了开口谐振环的结构尺寸对谐振点的影响,提出了一种双面印制型开口谐振环(Split-Ring Resonators,SRR)结构.利用负磁导率超材料,设计了一种双面印制型SRR结构,在平面内对SRR正交排列形成双面印制型频率选择反射面,对馈源频段的垂直极化波反射,而对其它频段来波透射.通过对新型频率选择反射面的测试,测试结果表明符合设计频率选择反射面(Frequency Selective Reflector,FSR)的反射性能.

一种准光带阻滤波器的仿真与实验研究

对中心频率为225GHz的谐振环结构(SRR)带阻滤波器进行了仿真分析和实验研究。采用HFSS仿真模拟技术,研究了SRR开口宽度、线宽、加载介质以及极化角度等相关参量对其谐振特性的影响。结果表明,该带阻滤波器的频率响应特性对场极化角度的敏感性很低,具有较好的稳定性;实验中测试到样品的中心频率为225.6GHz,与仿真结果有一定的偏差。通过进一步分析发现,影响频率偏移的主要因素是样品的实际尺寸偏小和介质的介电常数偏大,导致实际测试响应频率小于设计值。