折射率浅释

折射是光入射介质的多种光学现象之一,而折射率是表征各种介质(材料)物理、化学性质的重要参数。科学界对其了解伴随着光学发展的整个历程。文章从折射率的定义出发,介绍了它的物理含义、测量方法、应用以及关于"负折射率"的研究发展。     

A modified split ring resonator based printed compact monopole UWB antenna with spiked elliptical radiator having five band rejection features

A coplanar waveguide (CPW) fed printed compact monopole antenna with five band rejection features is presented. Wide bandwidth was achieved by beveling the lower part and adding a modified ellipse on the upper portion of the patch. An inverted circular arc, single circular split ring resonator (SRR) with wide opening and two symmetrical circular single SRRs were embedded for obtaining three stop‐band characteristics. Two symmetrical slits were inculcated in the ground forming defected ground structure (DGS) to get another stop‐band characteristic. Two concentric rectangular modified SRRs were etched to obtain a higher frequency stop‐band feature. The proposed antenna was designed, fabricated, and experimentally tested for the validation of results. The overall dimensions of the proposed antenna were 29 mm × 24 mm × 1.6 mm. The measured impedance bandwidth of the antenna was 2.87 to 13.3 GHz at | S₁₁ |< ? 10 dB. The measured results show that the proposed antenna has five band notches centred at 3.96, 4.35, 5.7, 8.54, and 9.95 GHz to reject WiMAX band (3.65‐4.04 GHz), ARN band (4.29‐5.18 GHz), WLAN band (5.5‐6.9GHz), ITU‐8 band (7.37‐8.87), and amateur radio band (9.2‐10.3 GHz) respectively. The proposed antenna maintains omnidirectional radiation pattern in H‐Plane and dumbbell‐shape radiation pattern in E‐plane. Further, stable gain over the whole UWB except at notched frequency bands was reported.     

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。     

基于太赫兹亚波长超材料的偏振不敏感调制器的理论研究

对太赫兹波超材料调制器的偏振响应进行了研究.提出并计算仿真了两种特殊结构的调制器,包括中心十字结构和双开口环结构.传统的开口环结构的调制器是偏振敏感的,而所研究的两种结构都是偏振不敏感的.中心十字结构是一个完全对称的金属结构,并具有完美的偏振不敏感特性.对于双开口环结构,它没有达到完全的偏振不敏感,但从太赫兹偏振透射率曲线来看,这种差别可以忽略不计.此外还模拟了双开口环的表面电流分布,并提出了产生两个谐振吸收波谷的主要机制.     

Estimating sustainable crop residue removal rates and costs based on soil organic matter dynamics and rotational complexity

The government of Ontario, Canada, has committed to stopping the use of coal for electrical generation by 2014 and agricultural biomass is being considered as replacement. However, there is limited information on whether the annual 2 million Mg of biomass required to replace coal could be sustainably supplied by agriculture and at what costs. This study assesses the sustainable availability and the farm-gate break-even cost of residue biomass from three crops (corn, soybean and winter wheat) grown under two common rotation scenarios in Ontario. Sustainably removable residue (SRR) rates are determined using a five-step approach that accounts for maintenance soil organic matter (MSOM) in the presence of yield and rotation variations across counties. Under typical SOM formation and decomposition conditions and assuming typical corn-soybean and corn-soybean-winter wheat rotation scenarios, about 1.1 million Mg of residue could be sustainably removed each year, primarily from the major agricultural counties in the province. While rotational complexity enhances SRR, the inclusion of soybean decreases available residue compared to corn and winter wheat. The break-even price for crop residues, representing the minimum price necessary to cover all variable and fixed costs for the farmer, is between $57 Mg⁻¹ and $87 Mg⁻¹. However, the actual amount supplied for each biomass price depends critically on the opportunity costs associated with not growing typical crops in the conventional manner.     

提高遥感图像空间分辨率方法的研究

图像空间分辨率是评价图像质量的一个关键指标,它表示图像细节清楚程度,在保证图像一定信噪比的前提下,高空间分辨率一直是成像系统追求的目标.研究从提高遥感成像仪空间分辨率的原理出发,详细分析各种提高遥感成像仪图像空间分辨率的方法,并对最有应用前景的方法—SRR（Super Resolution Reconstruction）,进行了的理论分析与实验研究。     

基于左手材料的复合单极子天线研究

为了改善单极子天线的辐射特性,通过对左手材料开路电流环谐振器(Split Ring Resonator,SRR)的结构及其电磁特性研究,提出一种新的复合天线设计思路,即将单个SRR或多个SRR与单极子天线复合。利用电磁理论和HFSS软件仿真得到工作频率为3.52GHz的这种复合天线的各项参数。仿真结果表明复合天线中SRR的个数对谐振天线的频率影响很小,其增益也基本不变。与单独的单极子天线相比,复合天线尺寸更小,类似电小天线,因此可被应用在电性能类似单极子天线,而天线尺寸又要求较小的领域。     

高斯波束在异向介质棱镜中的折射

为了验证异向介质的左手特性,分别采用棱镜实验和时域有限差分法(FDTD)模拟的方法对高斯波束透过异向介质棱镜的传播特性进行研究.异向介质采用周期排列的金属棒和金属环谐振器(SRR)结构,棱镜实验放在平板波导中测量.异向介质中的金属棒与平板波导上下电壁保持电连续,从而产生很好的电等离子效应.在数值模拟中采用高斯波束代替平面波研究能更好的符合实验中的入射波条件.实验和模拟研究结果都显示,折射波束与入射波束位于法线的同一侧,从而表明高斯波束在异向介质/空气交界面处发生了负折射,并且通过测量折射角求出了异向介质的等效折射率.     

基于液态金属的柔性频率可重构CPW天线设计

针对固态金属天线在受力弯曲后易产生裂纹导致功能失效的问题,本文提出一种频率可重构的柔性液态金属共面波导馈电天线.该天线由四个不同半径的开口谐振环（Split-Ring Resonators,SRR）构成,利用紫外光刻技术（ultraviolet lithography）制备天线的SU-8负模结构,其次浇注聚二甲基硅氧烷进行倒模并键合,最后将液态金属合金注入至微流沟道,完成天线的制作.通过机械施压方式改变不同谐振环间的通断状态,可在1GHz~6GHz范围内实现频率可重构,满足WLAN、WiMAX和部分C波段的通信要求.弹性体和液态金属的特性使天线具有更好的灵活性和耐久度,可应用于集成电子设备的弯曲表面.     

Modelling and validation of microwave LPF using modified rectangular split ring resonators (SRR) and defected structures

We propose a design of lowpass filter (LPF) using modified rectangular split ring resonator (SRR) that acts as a unit cell of metamaterials. Initially, a conventional LPF of 4.5 GHz is designed and the low impedance line is replaced to produce a sharp cut-off with a modified SRR structure. A brief parametric study is done to establish a relationship between the inner perimeter of the SRR to the cut-off frequency of the proposed LPF. Same study is also done for the outer perimeter. Using this relationship, another LPF of 2.4-GHz cut-off frequency is obtained. Defected ground structures (DGS) and microstrip structures (DMS) are incorporated with the 2.4-GHz LPF structure for the removal of harmonics and better pass-band characteristics. The IE3D simulation results and the circuit simulation results are in good agreement with the measured results. The obtained structure can thus be used for several useful applications such as in Bluetooth, Wi-Fi, cordless phones, computers, and other wireless communication devices.