一种合成孔径雷达的快速数据处理方法

简要介绍了合成孔径雷达相关积累的数字实现方法。在满足实时成像和一定分辨率的条件下，分析了系统对运算速度的要求，提出了一种改进的快速傅里叶算法及其实现方法。分析证明，这种算法是快速有效的。     

空间目标逆合成孔径成像实验研究

逆合成孔径雷达(ISAR),由于其良好的空间分辨能力,非常适合于空间目标的探测研究。它通过采用宽带信号来获得高距离分辨能力,通过对目标不同方向上接收回波进行相干处理来获得精细的横向距离(方位)分辨能力。这种雷达得到的高分辨二维图像提供了更好的目标特征探测性能。文中给出了一种用于空间目标逆合成孔径成像的实验研究。     

Measurement Geometry and Hydrostatic Pressure-Dependent Magnetoresistance in All-Oxide-Based Synthetic Antiferromagnets

The electronic structure of constituent layers and the spin channel of propagating electrons are critical factors that affect the magnitude and sign of magnetoresistance (MR) in synthetic antiferromagnets (SAFMs), which are important for spintronic applications. However, for all-oxide-based SAFMs, where there is strong coupling between multiple degrees of freedom, spin transport becomes more complex and remains elusive. Here, using ultrathin half-metallic manganite/doped ruthenate SAFMs as a model system, three sign reversals of MR are demonstrated accompanied by the crossover between underlying spin-dependent transport mechanisms. Electron tunneling produces normal MR in the current-perpendicular-to-plane (CPP) geometry at low temperatures, whereas carrier confinement causes inverse MR in the current-in-plane (CIP) geometry. Strikingly, CPP MR can undergo a temperature-driven sign reversal due to resonant tunneling via localized states in the spacer. Moreover, hydrostatic pressure can modulate the interlayer exchange coupling and induce an asymmetric interfacial response to dramatically facilitate electron tunneling, driving a controllable sign reversal of CIP MR. These results provide new insights into understanding and optimization of MR in all-oxide-based SAFMs.     

实现浅地层探地雷达快速合成孔径成像的一种有效方法

通过分析浅地层探地雷达回波数据的特点,提出通过基于回波数据的方差与A scan能量的特征来确定目标回波数据在整个回波数据中的分布区域,并只用该区域数据参与探地雷达合成孔径成像运算,从而排除非目标回波数据对合成孔径成像的影响,减少合成孔径运算量,实现快速合成孔径成像。通过对实测数据进行处理,结果表明,所提快速实现方法的成像效果与普通实现方法的成像效果相当,而处理速度与普通实现方法相比有了极大的提高。     

基于改进CLEAN算法的毫米波综合孔径成像重建方法研究

在毫米波综合孔径成像中,当处理对象是扩展源时,得到的图像存在着条纹现象。提出了一种改进的CLEAN算法,将经过窗函数加权的阵列点散布函数用于CLEAN算法的解卷积过程。仿真结果表明,采用该算法对被点散布函数副瓣和噪声污染的毫米波综合孔径图像进行重建时,图像质量得到了进一步改善。     

机载合成孔径雷达对运动目标的检测与成像

机载合成孔径雷达对地面运动目标的检测与成像已成为现代雷达技术发展的一个重点。首先介绍了运动目标成像的特点,接着就这一技术的发展过程和研究现状进行了全面的综述,最后指出这一领域今后的发展方向。     

CLEAN算法在机载毫米波综合孔径成像中的应用

该文将非即时u-v覆盖的综合孔径射电天文观测中的CLEAN算法应用到即时u-v覆盖的机载二维被动毫米波综合孔径成像中,避免因空间频率覆盖的不完整而产生对图像质量的影响,以达到消除高旁瓣对图像产生的负面影响。该文主要分析了CLEAN算法中具体处理时的清洁脉冲类型、脉冲半峰值宽度和迭代比例因子对处理后的图像的影响。研究结果表明：当清洁脉冲半宽度峰值等于系统脉冲响应图的半峰值宽度时、迭代比例因子为1/256时以及清洁脉冲类型为高斯脉冲时有利于改善图像的质量,该结论对实际的机载被动毫米波综合孔径成像的工程研究具有重要的参考价值。     

逆合成孔径成像激光雷达微多普勒效应分析及特征提取

 研究了基于逆合成孔径成像激光雷达的目标微多普勒效应,分析了激光信号高载频和大带宽对目标微动点一维距离像的影响,在此基础上建立了相应的微多普勒特征参数方程并讨论了快时间对微多普勒效应的影响.针对逆合成孔径成像激光雷达系统目标微多普勒效应的特点,提出了一种结合二值数学形态学腐蚀膨胀运算和推广Hough变换的目标微多普勒特征提取方法.仿真实验验证了文中微多普勒效应理论分析和微多普勒特征提取算法的正确性,并证明了逆合成孔径成像激光雷达对厘米或毫米量级微动观测的有效性.     

Field-Free Spin-Orbit Torque Switching in Synthetic Ferro and Antiferromagents with Exchange Field Gradient

Deterministic switching of perpendicularly magnetized synthetic antiferromagnets using spin-orbit torque (SOT) usually requires an in-plane auxiliary magnetic field, which limits its practical applications. Here, an exchange field gradient is introduced into perpendicularly magnetized synthetic ferro- and antiferromagnets (SFs and SAFs) through the insertion of a slightly wedged Ru between two thin ferromagnetic layers, which induces field-free switching of perpendicular SFs and SAFs with a switching ratio up to 81% regardless of the nature of the coupling. Temperature-dependent measurement shows a robust field-free switching even at low temperature. The experimental results show that the field-free switching ratio and the effective SOT field are directly related to the exchange field gradient. The theoretical model and numerical simulation indicate that the dynamic noncollinear spin textures induced by the exchange field gradient lead to the field-free switching, while the sign of the exchange field gradient determines the field-free switching polarity. It is further revealed that the SOT efficiency is positively correlated with the antiferromagnetic exchange field for both Ru wedged and non-wedged samples. These results provide a new avenue for simultaneously achieving field-free switching and high SOT efficiency of perpendicularly magnetized SAFs for highly stable, high-density, low-stray-field, and low-power magnetic memory devices.     

杂波环境下多被动传感器单目标跟踪算法

由于被动传感器只能获得目标的角度量测,因此杂波环境下基于被动传感器的关联问题较主动传感器更为困难。针对杂波环境下纯方位多被动传感器系统的单目标跟踪问题,提出了一种基于扩展卡尔曼滤波的模糊综合贴近度关联跟踪方法。该方法采用直角坐标系下多被动传感器系统的扩展卡尔曼滤波对目标进行跟踪。首先利用目标航迹的预测信息,针对每个传感器建立确认跟踪门;在获得候选关联组合后,直接利用角度信息建立各候选关联组合与角度预测值间的模糊综合贴近度,通过在所获得的全部模糊综合贴近度中寻求最优解完成量测到航迹的关联。仿真实验表明,该方法可以有效地解决杂波环境下多被动传感器系统的单目标跟踪问题。     

在低速风洞中红外热图诊断技术的实验研究

文章介绍了NF－3风洞应用红外热图技术和热丝加热方法实施的一项综合研究结果。该项研究对等弦长直机翼和无人机机翼进行了附面层流态诊断，分析出不同攻角、不同风速（雷诺数）下机翼表面的层流区、紊流区及转捩线位置。结果表明，在低速风洞中，用红外热像仪进行实验模型的附面层状态的诊断，是一种简便、快捷、可信的方法。     

An efficient method for monitoring the shunts in silicon solar cells during fabrication processes with infrared imaging

, and energy dispersive X-ray spectroscopy. Approaches for diminishing shunts are presented. The methods are beneficial for the optimization of the cell fabrication processes and the improvement of the cell performances.     

一种用红外热像监测硅太阳能光伏电池生产工艺的新方法

为了监测硅太阳电池生产工艺,设计了一套红外热像系统对单晶硅太阳电池的漏电情况进行研究。外加直流偏压时,太阳电池的漏电区域会明显发热。红外热像仪可以发现这些发热区域,从而确定漏电的位置。结合金相显微镜、扫描电子显微镜和能量色散谱等分析手段,总结了刻边、镀膜、丝网印刷和烧结工艺所造成的七种常见漏电形式。本文还提出了解决各类型漏电的可能方案,为进一步优化太阳电池生产工艺提供指导。     

[Cp*W(dmit)2]•: An Organometallic 15‐Electron Neutral Radical (d1) with Optical Limiting Properties in Solution and an Antiferromagnetic Ground State in the Solid State

The synthesis of the organometallic d² [Cp*W(dmit)₂]^1– complex (where Cp* is pentamethylcyclopentadienyl and dmit is 1,3‐dithiole‐2‐thione‐4,5‐dithiolate), and its oxidation to the paramagnetic d¹ [Cp*W(dmit)₂]^• species, is described and their X‐ray crystal structures given. Geometrical evolutions upon oxidation, characterized by a variable folding of the WS₂C₂ metallacycles along the S–S hinge, are rationalized by density functional theory (DFT) calculations and by comparison with the molybdenum analogs; as is also the evolution in the UV‐vis‐NIR absorption spectra. In solution, only the d¹ complexes exhibit positive optical density variations in transitory nanosecond spectroscopy after 10 ns laser pulses. A weak optical limiting effect was observed on these d¹ species, stronger in the W than in the Mo complex. In the solid state, the interacting, paramagnetic [Cp*W(dmit)₂]^• species (θ_{Curie–Weiss} = –20 K) orders antiferromagnetically below T_Néel = 4.5 K with a spin‐flop field, B_SF(W) of 8000 G. Compared with the molybdenum analog, the weaker θ_{Curie–Weiss}(W) and T_Néel(W) values, and larger B_SF(W) values reflect weaker intermolecular interactions due to a decreased spin density on the dithiolene ligands and stronger spin–orbit coupling with the W atom, as confirmed by DFT calculations on the d² and d¹ Mo and W complexes.     

An exhaustive criterion for estimating quality of images in electrical impedance tomography with application to clinical imaging

This study proposes a versatile criterion for estimating quality of images in electrical impedance tomography. The point spread function (PSF) is calculated throughout the domain based on the scattering of energy as responses to a small anomaly spirally moved from the centre to the boundary. The proposed PSF is a measure of weighted spatial variance (WSV) of the conductivity over the whole domain. For each element, the weighting factor is a normalized multiplication of the area of that element by its square intensity. The WSV collectively incorporates all image attributes, i.e., spatial resolution, artifact, amplitude response, positioning error and shape deformation. The location of artifacts, which significantly influences reconstructed images in reality, is taken into account as well. The results illustrate that the proposed measure is more tolerant than existing criteria in evaluating performance of EIT systems in both theory and practice.