极化轨道约束下的最优极化（一）

本文针对极化测量过程中干扰和噪声对接收效果的影响，提出一种极化轨道约束下的变极化接收方法，以改卷接收系统的SINR（信号干扰噪声比）。在极化轨道约束下的SINR最大化问题是一个寻求局部最优的问题，本文在任意的信号与干扰极化条件下，解决了任意给定的极化轨道上SINR的最大化问题，并对极化轨迈上最优极化与其他两种最优极化得到的SINR进行了比较。     

用Fourier分解法测量材料表面的Mueller矩阵

测量系统采用双旋转延迟器结构,通过两个1/4波片的周期变化,对入射光、散射光的偏振态进行调制.由探测光强的25个Fourier分解系数可以计算得到样品的Mueller矩阵.为了检测测量系统的准确性,将测量的16个自由空间Mueller矩阵分量和理想情况下的自由空间Mueller矩阵分量进行比较,并给出了每个矩阵分量的标准误差.最后,通过测量聚四氟乙烯样品板的Mueller矩阵,定量地分析样品的退偏效应.     

Dirac Cone Spin Polarization of Graphene by Magnetic Insulator Proximity Effect Probed with Outermost Surface Spin Spectroscopy

The effects of the proximity contact with magnetic insulator on the spin‐dependent electronic structure of graphene are explored for the heterostructure of single‐layer graphene (SLG) and yttrium iron garnet Y₃Fe₅O₁₂ (YIG) by means of outermost surface spin spectroscopy using a spin‐polarized metastable He atom beam. In the SLG/YIG heterostructure, the Dirac cone electrons of graphene are found to be negatively spin polarized in parallel to the minority spins of YIG with a large polarization degree, without giving rise to significant changes in the π band structure. Theoretical calculations reveal the electrostatic interfacial interactions providing a strong physical adhesion and the indirect exchange interaction causing the spin polarization of SLG at the interface with YIG. The Hall device of the SLG/YIG heterostructure exhibits a nonlinear Hall resistance attributable to the anomalous Hall effect, implying the extrinsic spin–orbit interactions as another manifestation of the proximity effect.     

In Situ Formation of Copper‐Based Hosts Embedded within 3D N‐Doped Hierarchically Porous Carbon Networks for Ultralong Cycle Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are promising energy storage systems due to their large theoretical energy density of 2600 Wh kg^?1 and cost effectiveness. However, the severe shuttle effect of soluble lithium polysulfide intermediates (LiPSs) and sluggish redox kinetics during the cycling process cause low sulfur utilization, rapid capacity fading, and a low coulombic efficiency. Here, a 3D copper, nitrogen co‐doped hierarchically porous graphitic carbon network developed through a freeze‐drying method (denoted as 3D Cu@NC‐F) is prepared, and it possesses strong chemical absorption and electrocatalytic conversion activity for LiPSs as highly efficient sulfur host materials in Li–S batteries. The porous carbon network consisting of 2D cross‐linked ultrathin carbon nanosheets provides void space to accommodate volumetric expansion upon lithiation, while the Cu, N‐doping effect plays a critical role for the confinement of polysulfides through chemical bonding. In addition, after sulfuration of Cu@NC‐F network, the in situ grown copper sulfide (Cu_xS) embedded within Cu_xS@NC/S‐F composite catalyzes LiPSs conversion during reversible cycling, resulting in low polarization and fast redox reaction kinetics. At a current density of 0.1 C, the Cu_xS@NC/S‐F composites' electrode exhibits an initial capacity of 1432 mAh g^?1 and maintains 1169 mAh g^?1 after 120 cycles, with a coulombic efficiency of nearly 100%.     

Effect of raindrop size distribution and rain rate inhomogeneity on the relationship between attenuation and depolarization

In addition to attenuation, depolarization due to rain is another factor that degrades satellite propagation signals, especially in the higher frequency bands and in places that have high rates of rainfall. A formula to predict cross‐polarization as a function of attenuation has been proposed, and it is derived by a theoretical calculation using frequency, the forward scattering amplitude of raindrops, rainfall rates, the raindrop size distribution (DSD), and various other propagation parameters. In this paper, a formula for predicting cross‐polarization is derived on the basis of the assumption of a gamma‐type DSD up to 100 GHz. These results are compared with conventional exponential‐type DSDs, such as the Marshall‐and‐Palmer DSD. Moreover, for a more realistic propagation situation, we consider the effect on the aforementioned relationship of rainfall rate inhomogeneity along the propagation path. It is shown that, for practical purposes, this inhomogeneity does not have a significant effect on satellite propagation. Copyright © 2017 John Wiley & Sons, Ltd.     

一种图像校正的偏振光罗盘系统的研究

导航传感器在探险、应急、精确制导武器、船舶、航空器导航和定位系统中起着关键作用。针对偏振光罗盘在倾斜状态下误差较大的问题,提出了一种利用加速度计和陀螺仪对偏振光罗盘进行图像校正的方法,设计了一种基于陀螺仪校正的偏振光罗盘系统。首先利用加速度计和陀螺仪计算得到载体姿态角,对偏振光图像数据进行图像校正,采用Stokes矢量法解算大气偏振模式分布,进而提取导航特征点,最后对特征点进行拟合解算出航向角信息。并且进行了静态和动态测试实验,实验结果表明,该算法能够有效的对偏振光罗盘姿态变化引起的误差进行补偿,可以将偏振光罗盘的航向角测量误差控制在1.86°之内,平均误差为0.09°。     

基于狄拉克半金属宽带的可调谐太赫兹偏振器

提出了一种基于狄拉克半金属超材料的双开口环结构的宽带偏振器,研究了狄拉克半金属费米能级以及中间介质厚度对偏振转换性能的影响。结果表明:当中间介质厚度为22μm,费米能级为70meV时,在1.44THz和1.95THz两个谐振频率处,偏振转换效率为100%;当中间介质厚度为22μm时,随着狄拉克半金属费米能级从64meV增加到70meV,高低两个谐振峰均产生蓝移;当狄拉克半金属费米能级为70meV时,随着基底介质厚度从19μm增加到22μm,低频处的谐振峰未移动,高频率点处的谐振峰红移。     

基于波长敏感的耦合器动态增益平坦L波段EDFA理论与实验

掺铒光纤放大器(EDFA)的增益平坦化是波分复用(WDM)系统的重要问题,文章通过理论和实验提出一种新型的增益平坦滤波器,即一种耦合比随波长变化的耦合器与偏振控制器(PC)构成光纤环形镜,调节光纤环形镜内的PC的状态,从而改变光纤环形镜的反射谱线的位置和深度,使其匹配EDFA的增益谱,实现对L波段EDFA增益平坦,实验结论得出,平坦后的光谱在1562nm~1605nm带宽内增益平坦度为±0.7d B。     

"动中通"变极化系统研究

根据任意极化波可由空间两个正交的线极化波合成的理论,提出了一种终端电控变极化的方案,通过控制两个正交线极化波的幅度和相位,可以获得任意取向线极化波,可实时对极化角进行稳定性处理,有效解决移动通信中的极化失配现象,改善通信质量。     

电磁矢量传感器阵列相干信号源波达方向和极化参数的同时估计:空间平滑方法

研究如何利用电磁矢量传感器阵列中隐含的冗余空域信息解决多个相干极化信号源的二维波达方向(DOA)和极化参数的同时估计问题。基于整个阵列中所隐含的多个空域旋转不变结构,将组成阵列的单个或多个电磁矢量传感器单元看作一个无模糊子阵,利用空间平滑方法对阵列数据进行预处理,以恢复信号协方差矩阵的秩特性。在此基础上,利用多信号分类方法(MUSIC)和旋转不变参数估计方法(ESPRIT)完成多个相干极化信号源的二维 DOA 和极化参数的同时估计。文中还讨论了成功进行信号解相干的必要条件,并通过计算机仿真验证和比较了所给方法的有效性及其辨识能力。