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.

Very Compact Bandstop Filters Based on Miniaturized Complementary Metamaterial Resonators

In this paper, a design of very compact microstrip bandstop filters based on complementary split ring resonators (CSRRs) is proposed. Two techniques of metamaterial miniaturization are used to optimize the physical and electrical size of the CSRR. The bandstop filter is produced by an array of miniaturized loaded CSRRs etched on the center line of a microstrip. The size of the proposed filter, is as small as 0.58 cm2, and its electrical length is very small with only 0.08 λ0), compared to a conventional bandstop filter, a miniaturization of a factor 5 while the bandstop performance is maintained. A very good agreement obtained between the measurement and the simulation results.

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.

A Modified Split⁃Ring Resonator Antenna for Radio Frequency Identification Tag

A compact antenna formed by three concentric split rings for ultra-high frequency(UHF)radio frequency identification(RFID)tag is proposed in this paper.The antenna is composed of two parts,an outer short-circuited ring modified from a traditional split-ring resonator(SRR)antenna and an inner SRR load,so the antenna can be regarded as a short-circuited ring loaded with SRR.According to the transmission line theory,to conjugate match with the capacitive input-impedance of a tag chip,the length of the short-circuited ring isλg/4 shorter than that of an open-circuited dipole of a traditional SRR antenna,whereλg is the wavelengh of the operating frequency.Hence,the size of the proposed antenna is more compact than that of the traditional SRR antenna.Thereafter,the proposed antenna is simulated and optimized by ANSYS high-frequency structure simulator(HFSS).The impedance,efficiency,and mutual coupling of the fabricated antenna are tested in a reverberation chamber(RC).The results show that the size of the presented antenna is 83%smaller than that of the traditional SRR antenna and the proposed antenna can cover the whole UHF RFID operating frequency band worldwide(840—960 MHz).The measured read range of the tag exhibits maximum values of 45 cm in free space and 37 cm under dense tag environment.

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.

基于慢波基片集成波导的小型化移相功分器

针对移相器和功分器的功能融合设计,提出了一种基于慢波基片集成波导(Slow-Wave Substrate Integrated Waveguide,SW-SIW)的小型化移相功分器,两个输出分支等长带宽,可实现30°相移量.其中一个输出分支通过基片集成波导(Substrate Integrated Waveguide,SIW)实现,而另一个输出分支将互补开口谐振环(Complementary SplitRing Resonator,CSRR)加载在上层金属表面,代替传统SIW连续的金属表面,该CSRR由经典CSRR结构演变而来,同时为了降低由CSRR加载所造成的相位上的不稳定,在CSRR内部添加金属化通孔,实现SW-SIW,使得截止频率和相速度降低.测试结果表明,移相功分器在9.0~11.8 GHz频带范围内反射系数|S11|小于-10 d B,相对工作带宽为26.9%,插入损耗小于1.3 d B.两个输出端口的相位差稳定在30°±3°,幅度差小于1.4 d B,实现了等功率分配.所设计的移相功分器具有较小的尺寸和低制造成本,适合应用在相控阵天线中.

用于测量材料介电常数的高精度微波传感器

提出了一种用于测量材料介电常数的微波传感器,其特点是成本低、测量精度高。在传统的互补裂环结构上进行优化设计,实现了更大范围的测量区域;并加载了金属通孔结构,将电场限制在测量区域内,达到了更好的测量效果。结果显示传感器的测量灵敏度为2.89%。传感器在空载时谐振频率为2GHz;当样品加载到测量区域时,测量区域的电场将发生变化,从而导致频移。选取了介电常数值为1~10的样品进行了模拟加载试验,得到了介电常数与谐振频率的拟合经验关系式,同时采用5种常见的高频板材对拟合公式进行了验证。结果表明:传感器具有很高的测量精度,整体测量误差为0.8%,证实了利用该传感器测量材料介电常数的可行性。

波导谐振环微带阵列多裂纹检测传感器设计

针对飞行器机翼的大面积壁板等金属结构的多形态裂纹分布难以同时检测、检测精度低等问题,设计了一种互补开口波导谐振环微带阵列多裂纹检测传感器。该传感器群阵列中不同尺寸的互补开口波导谐振环微带传感器能够检测直裂纹、针孔、星型3种裂纹的特征参数。实验结果表明,传感器对3种裂纹的参数变化的最大检测灵敏度达到了150 MHz/mm,传感器可检测出的最小直裂纹尺寸为10 mm×1 mm×0.1 mm。该传感器结合了互补开口谐振环辐射能力强、易于表面共形和基片集成波导低损耗、品质因数高、尺寸小的特性,能够实现对金属材料上多形态裂纹的同时检测,具有灵敏度高、检测范围大等优点。

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.

Continuous Tera-Hertz wave transmission spectroscopy of Nb double superconducting split-ring resonator array

Transmission spectroscopy of two Nb double superconducting split-ring samples with different thicknesses on MgO substrates was measured by a continuous Tera-Hertz spectrometer.The transmission curves of two different samples with the thicknesses of 50 and 150 nm at 7.5 K show dips at 480,545 GHz,respectively,which origin from the different capacities and inductances of the samples.For the sample of 50 nm,the dip shifts to lower frequency,also decreases in depth and increases in width with temperature or field increasing below T c of Nb film,while the sample of 150 nm does not show such a phenomenon.This thickness-dependent transmission behavior is due to the kinetic inductance and conductivity change of superfluid electrons in Nb film and may suggest a practical tunable THz filter based on the thinner samples.

互补开口谐振环微带传感器介电常数的测量

介电常数是材料的重要特性之一,采用互补开口谐振环微带传感器实现了不同厚度待测物质介电常数的无损测量。方形互补开口谐振环蚀刻在微带线接地平面上,与微带线耦合实现谐振,分析了谐振器的等效电路,讨论了介电常数与谐振频率之间的关系。通过有限元分析,谐振频率的负二次方与待测物质的介电常数实部值存在线性关系,且线性关系受待测物质的厚度影响;介电常数的虚部值对谐振频率的影响可忽略不计;最终建立了介电常数实部值与谐振频率和样本厚度之间的数学解析式。实验测试结果表明,当待测样品的厚度大于2 mm时,实部介电常数的相对测量误差小于3.5%。

逆开环谐振器在微带天线谐波抑制中的应用

介绍了一种利用逆开环谐振器实现微带天线谐波抑制的方法。在传统逆开环谐振器的开口处添加一对缝隙,可有效的降低传输零点的位置。提出了加载逆开环谐振器微带线的等效电路模型,电路模型结果与仿真结果相吻合,证明了所提电路模型的正确性,并从等效电路模型的角度分析了传输零点下降的原因。将不同传输零点的结构单元级联起来制作在微带线的接地板上,很好地实现了微带天线的谐波抑制。仿真结果与测试结果相吻合,证明了所采用方法的有效性和正确性。该设计方法结构紧凑,简单易行。

基于二维互补随机共振的轴承故障诊断方法研究

一维随机共振(One-Dimensional Stochastic Resonance,1DSR)被广泛用于轴承故障诊断中。针对传统1DSR对微弱信号的检测效果不够理想,输出信号噪声大,不能准确获得轴承故障特征频率(Fault Characteristic Frequency,FCF)等问题,提出一种新的二维互补随机共振(Two-Dimensional Complementary Stochastic Resonance,2DCSR)方法并应用于轴承故障诊断。将采集到的轴承故障信号根据共振带位置进行带通滤波并解调,随后将解调信号对半分成两个子信号并输入2DCSR的两个输入端,利用输出信号的加权功率谱峭度(WPSK)指标对2DCSR系统参数进行自适应调节优化,得到最优的滤波输出信号及频谱,以识别轴承FCF并诊断轴承故障类型。数值仿真及实验结果表明,提出的方法可以有效地增强轴承FCF并提高轴承故障诊断效果。

利用互补天线原理求解孔缝的共振性能

利用互补天线原理从理论上推导了真空、介质窄缝的共振频率公式,在理想窄缝长度小于5倍波长、辐射角度偏离垂直方向小于30°的情况下,孔缝的共振频率点仍然可以用半波振子的辐射情况来解释,共振点满足孔缝长度等于入射波的半个波长;介质窄缝等效为半个孔缝深度的微带贴片天线,不同介电常数介质填充时的共振频率理论公式推导值和数值模拟值基本一致,相对误差在5%以内。进一步分析了窄缝阵列的耦合性能,结果表明互补天线原理可以很好地应用于分析和求解孔缝的共振性能。

基于CSRR改进的双陷波超宽带天线

针对超宽带系统易受窄带信号干扰的问题,提出了一种基于互补金属开口谐振环(CSRR)改进的双陷波超宽带缝隙天线。在现有文献中,单个CSRR只能实现单陷波功能,要想增加陷波频段,只能通过增加CSRR个数的方法来实现,这就增加了设计的复杂性。通过天线辐射贴片上的表面电流分布图分析了CSRR内外环与两个陷波频段的对应关系。对所设计的超宽带天线进行了制作和测量,实测结果与仿真结果吻合较好,证明了该设计方法的正确性。

平面左手结构在微波器件及天线设计中的应用

自从2001年首次实现人工左手媒质以来,人们一直致力于制作大带宽、低损耗、易集成且具有左手特性的微波器件与天线.本文着重介绍两种基本的左手结构在平面微波电路中的应用,其一是左右手复合结构,其二为互补开口谐振环结构.近年来,这两种结构在微波器件及天线设计中得到广泛研究与应用.本文总结了国内外在这两个方面的研究进展,并结合我们在这方面所取得的成果,对平面左手电路的原理和应用进行了详细分析和说明.