雷达近场成像中SVM的目标识别方法

雷达近场成像中,在精确定位的基础上,为解决目标形状识别问题,提出了利用支持向量机（SVM）预测目标信息的方法.根据时域算法——后向投影（BP）算法和频域算法——频率波数域（F-K）偏移算法得到的场强值作为SVM的特征数据,并利用时域有限差分法（FDTD）进行仿真.仿真结果表明,基于BP算法的SVM识别方法具有特征数据提取时间长、SVM预测时间短、多目标时目标信息全和虚警较多等特征,基于F-K算法的SVM识别方法具有特征数据提取时间非常短、SVM预测时间非常短、多目标时目标漏检的特征;两者都能较好地识别目标的形状,且前者的识别能力高于后者,而后者更适合实时成像.     

无人机集群协同探测距离解模糊方法

与传统单平台机载雷达相比,无人机(unmanned aerial vehicle,UAV)集群协同探测具有探测范围广、探测精度高、布阵机动灵活等突出优势,因此是未来机载预警雷达发展的重要方向之一.由于UAV集群雷达阵列具有大尺寸、超稀疏孔径,因此雷达回波近似为球面波且具有较强近场效应.本文首先推导了UAV集群稀疏阵列在...     

近场光学与近场光学显微镜

近场光学是研究距离物体表面一个波长以内的光学现象的新型交叉学科。基于非辐射场的探测与成像原理,近场光学显微镜突破常规光学显微镜所受到的衍射极限,在超高光学分辨率下进行纳米尺度光学成像与纳米尺度光谱研究。本文将讨论近场光学的基本原理,非辐射场的探测与高分辨率的关系;光学限阈及隐失场在近场光学中的重要性;以及近场信息的获取方法。对近场光学显微镜的主要类型及相应的仪器发展,分辨率,衬度原理做一综述。同时简要介绍近场光学显微镜在超高分辨率光学成像,近场局域光谱,高密度数据存储,在生命科学,单分子光谱,量子器件发光机制等领域中的应用。     

改进Turner法制备光纤探针的研究

研究了化学腐蚀方法制备近场光学显微镜光纤探针时外界因素和腐蚀溶液与保护液体系本身性质对光纤探针形貌的影响。结果表明腐蚀溶液和保护液二元体系的界面在光纤上形成的弯月面的高度与界面和探针之间形成的接触角、界面张力、密度差有关,在一定范围内弯月面的高度与光纤直径成正比。通过理论分析和实验结果相结合,对比管式腐蚀方法制备的光纤探针的形貌,我们发现Turner法制备光纤探针时探针锥面蜂窝状粗糙形貌是光纤探针成尖过程的本质上缺陷造成的。通过改进Turner法制备光纤探针的工艺,结果表明采用第二次修饰性腐蚀可以有效地改进探针的粗糙锥面,并增大探针的圆锥角。     

Near-field postseismic deformation along the rupture of 2008 Wenchuan earthquake and its implications

At first time, we observed the postseismic deformation, which actually is a kind of creep after slip, along the intra-plate active fault associated with the Wenchuan earthquake. To understand the near-field postseismic deformation following 2008 Wenchuan earthquake in Sichuan Province of China, we compared the fault scarp or flexure scarp profiles measured in different campaigns. Our result shows that among total 19 observation sites, on 13 sites (68% of 19) fault scarps fall back with an average about 9.7% decrease; on 5 sites (26% of 19) fault scarps present no change; and on one site (6% of 19) fault scarp continues to uplift with 12.8% increase. The variety of fault scarp we observed results mainly from near-field postseismic deformation, after slip occurred in shallow. Based on our observations, the following are demonstrated: except for the southwestern end near Yingxiu Town where coseismic slip deficit and some elastic energy residue exist there, fall back (68%) or non-changing (26%) of fault scarp shows energy balance or energy deficit due to overthrust, implying that the likelihood of occurrence of strong aftershocks of ≥ M7 becomes very small in these energy-released areas. Moreover, we suggest that a minimum of 10% error due to near-field postseismic deformation should be considered when evaluating the magnitude of historic and paleoearthquake or slip rate based on the fault scarp dis-placement, even though the error caused by erosion has been accounted already.     

基于液相外延生长的集成式微探尖

阐述了用于超高密度光存储的集成式扫描近场光学显微术（SNOM）微探尖的液相外延选择生长方案,并给出了实验结果．此种微探尖,可直接生长在微型集成式SNOM传感器的垂直腔表面发射激光器（VCSEL）晶片出光口上,避免了探尖转移带来的探尖损坏、难以对准等技术难题．该制作过程具有重复性较好,设备简单、经济,实用价值较高等优点．     

微小圆孔的近场衍射光强的空间分布特性

采用严格的矢量衍射理论,研究了平面光波垂直入射微小的圆孔光阑后的近场衍射光强的空间分布,模拟计算了衍射光强的空间分布.Matlab仿真结果表明,近场衍射既属于菲涅耳衍射,又接近于夫朗和费衍射.     

Near-field radiative heat transfer between general materials and metamaterials

We investigated the near-field radiative heat transfer between general materials and metamaterials. We studied the effects of metamaterial parameters on the radiative heat exchange and used three kinds of natural or artificially-constructed materials such as Al, boron-doped Si and metamaterials as examples. We calculated and analyzed the near-field radiative heat transfer processes between two semi-infinite bodies. The numerical results indicate that the radiative heat exchange between the two different materials may be less or more than the radiative heat exchange between the corresponding identical materials. It was found out to depend on the radiative properties of the materials. The work would provide a valuable reference for the selection of practical materials.     

阵元非均匀高斯白噪声背景下的近场声源定位研究

为解决非均匀高斯白噪声背景下常规近场声源定位算法精度低的问题,提出一种基于噪声协方差矩阵估计的近场声源定位,预白化MUSIC算法,该方法首先从阵列输出数据中估计出噪声协方差矩阵,再利用估计出的噪声协方差矩阵预白化阵列协方差矩阵,从而提高常规算法的估计性能.仿真结果表明,在非均匀高斯白噪声背景下的近场声源定位中,预白化MUSIC算法定位性能高于常规MUSIC和Capon算法的估计性能.     

基于镜像源方法抑制混响干扰的声全息算法改进

针对实际厂房、机舱等封闭环境中,声全息成像受混响因素严重干扰的问题,在等效源近场声全息方法的基础上,采用房间脉冲响应代替自由空间格林函数建立传递函数,并利用压缩感知技术处理求解时的欠定问题,得到相对准确的等效源强度,以消除混响的干扰,提高声源定位的效果。通过初步的数值模拟,验证了方法的准确性和有效性。结果表明,与原算法相比,改进方法在混响环境中的声源定位具有明显的优势。