Radial field retrieval for current reconstruction from sphericalacquisition

An iterative algorithm for the retrieval of the radial component of the electric field is presented in conjunction with an efficient reconstruction algorithm to calculate an equivalent magnetic current (EMC) distribution from the electric field components obtained in a spherical acquisition     

Improved spherical and hemispherical scanning algorithms

A probe-corrected hemispherical-scanning algorithm has been developed which is applicable when the antenna under test radiates negligibly into its rear hemisphere. For a hundred-wavelengths diameter antenna, hemispherical scanning would be about three times more efficient computationally than prior full-sphere scanning algorithms. Improvements have also been made to full-sphere scanning, significantly increasing that algorithm's computational efficiency.     

球面近远场和远近场变换算法

天线的远场对于研究天线辐射特性具有重大意义，近场测量技术因其能够避免直接测量远场而得到广泛应用，该技术采用近远场变换获得远场，然而，检验该远场的准确性也是很重要的.为了解决此类问题，文中以球面近场测量为例，提供了一种解决方案.该方案主要探讨了球面波模式展开理论，该理论是实现球面近远场变换算法的关键，其将待测天线在空间建立的场展开成球面波函数之和，天线的加权系数既包含了远场信息也包含了近场信息.因此，不仅能够利用近场测量信息获得远场辐射特性，同样能够利用远场辐射特性反推得到近场处电场，这样就能检验由近远场变换算法得到的远场是否准确.文中首先推算得到了近远场变换公式，随后进一步推算得到远近场变换的公式，最后将本文算法计算结果与FEKO测量结果进行比较，二者吻合良好，从而证实了本文两种算法的有效性.     

Formulation of spherical near-field scanning for electromagneticfields in the time domain

Spherical near-field scanning techniques are formulated for electromagnetic fields in the time domain so that a single set of time-domain near-field measurements yields the far field in the time domain or over a wide range of frequencies. Probe-corrected as well as nonprobe-corrected formulations are presented. For bandlimited time-domain fields, sampling theorems and computation schemes are derived that give the field outside the scan sphere in terms of sampled near-field data     

Improved algorithm for probe-corrected spherical near-field/far-field transformation

The technique for computation of antenna far fields from spherical near-field measurements has been improved, allowing large antennas to be treated. The efficiency and accuracy is demonstrated for an antenna without rotational symmetry and about 50 wavelengths in diameter.     

Deep supervised hashing using quadratic spherical mutual information for efficient image retrieval

Several deep supervised hashing techniques have been proposed to allow for extracting compact and efficient neural network representations for various tasks. However, many deep supervised hashing techniques ignore several information-theoretic aspects of the process of information retrieval, often leading to sub-optimal results. In this paper, we propose an efficient deep supervised hashing algorithm that optimizes the learned compact codes using an information-theoretic measure, the Quadratic Mutual Information (QMI). The proposed method is adapted to the needs of efficient image hashing and information retrieval leading to a novel information-theoretic measure, the Quadratic Spherical Mutual Information (QSMI). Apart from demonstrating the effectiveness of the proposed method under different scenarios and outperforming existing state-of-the-art image hashing techniques, this paper provides a structured way to model the process of information retrieval and develop novel methods adapted to the needs of different applications.     

A scanning spherical tri-reflector antenna with a moving flatmirror

Spherical reflector systems can achieve pattern scanning without rotation of the main reflector through the use of multiple subreflectors that can move. Also, two subreflectors can be shaped to correct for spherical aberration and to control the aperture distribution on the spherical main reflector. In a previous paper (see ibid., vol.41, p.778, no.6, 1993) we introduced a method that offers both aperture phase and intensity control and scans the main beam without an accompanying movement of the illuminated area over main reflector. The method can overcome the poor aperture utilization problem common in spherical reflector antenna systems; however, it requires motion of the entire subreflector system, including the feed, during scan. In this paper we discuss a method that does not require motion of the subreflector system during scan. This method employs a flat mirror that creates a virtual image of the subreflector system. The motion of the subreflector system in the previous design is replaced by the motion of the virtual image that is controlled by the motion of the flat mirror. The new design offers simplified mechanical motion, while maintaining beam efficiency performance comparable to that of traditional spherical tri-reflector scanning antennas, but with some sacrifice in aperture efficiency and cross-polarization performance     

激光扫描金属粉末的“球化效应”及其应用

为了利用激光束扫描金属粉末时的"球化效应"将异形金属粉末球化,通过采用正交实验法,系统探明了获得球化效果的激光工艺参量,得到相应的球形粉末。结果表明,金属粉末的球化能力决定于金属粉末的粒径、导热性、熔点和激光吸收率等因素,可用球化因子K表征;当激光扫描速度与激光功率(高于临界功率后)的比值大致等于K时,可获得球形粉末。     

基于扫描方式与球面投影的点云修补方法

激光雷达点云数据修补是三维重建工作中的重要环节.针对现有的点云修补的插值算法无法确定空洞区域缺失点具体位置和数量的问题,提出一种简便有效的缺失点云修补方法.首先,将经过球面投影的单站激光雷达数据按照扫描方式实现结构化;然后根据旋转角和俯仰角两个方向的角度分辨率来描述缺失点云的球面位置;最后根据实际地形情况选择合理的插值...     

激光扫描球形偏心引起误差的理论分析

为了研究激光测距扫描仪在测量过程中,由于激光扫描中心与被测球形中心存在一定偏心距时对激光扫描精准度的影响,采用数形结合与公式推导的方法,对偏心距e导致的激光扫描偏差值进行了理论分析,建立了数学模型和公式推算验证,分析了影响激光扫描轮廓偏差几个因素之间的相互关系,得到了当随着半径R增大,偏心引起的误差不会超过2e的结论。结果表明,通过对提出的偏心误差修正方法进行公式验证,将扫描中心与被测球形中心两坐标轴等效变换至同一坐标系下,可减小偏心距e对激光扫描轮廓造成的偏差影响。     

彩电场扫描电路故障分析与检修

本文是以我校用厦华XT-5680R型彩色电视机机型教学为例,在教学过程中,通过对该机型场扫描电路原理进行详细分析及记录常见故障检修过程,并结合本人几年来的维修经验,谈谈彩色电视机场扫描电路常见故障的检修方法。     

Probe uncompensated near-field to far-field transformation for scanning over an arbitrary surface

A new technique of transforming the probe uncompensated near-field data to the near or far field is presented, which is useful in nearfield antenna measurements, when the probe antenna scans over an arbitrary surface enclosing the test antenna. The technique presented is analytically simple and sufficiently accurate.     

Analysis of the time-reversal operator for a small spherical scatterer in an electromagnetic field

The time-reversal operator (TRO) for a planar array of crossed dipole elements illuminating a small conducting and/or dielectric sphere is investigated in order to determine the general properties of an electromagnetic time-reversing array system. The behavior of such a system for a given frequency is analyzed by studying the eigenvalues and eigenvectors of the TRO. Each eigenvector specifies a set of complex driving currents for the array elements that produce received voltages that are proportional to the conjugates of the drive currents. The proportionality constant is equal to the square root of the associated eigenvalue and is the same for all elements. The eigenvalues and eigenvectors can be determined by performing a singular value decomposition (SVD) on the multistatic data matrix of the array. The eigenvalues of the TRO are the squares of the singular values, and the eigenvectors are identical to the singular vectors. We have shown that the maximum number of singular vectors associated with the sphere is equal to the number of orthogonal orientations of the dipole moments induced in the sphere when irradiated by the array, so there is a maximum of six for a conducting sphere but only three are significant when the conductivity is small and the sphere may be considered being just a dielectric. Numerical results are presented for linear and circular arrays to show the general behavior of the system.     

Experimental evaluation of the spherical near field test range

In aircraft manufacturer firms there is the need for measuring antenna patterns of large beamwidth communication/navigation antennas with the scale modeling technique. A series of tests has been carried out to verify the use of the spherical near field (SNF) test range for this purpose. The comparison is made between measured and calculated data of stub and waveguide antennas installed on a cylinder. From the results it appears that the agreement is reasonable. The advantages and disadvantages of the SNF test range for this particular application are discussed.     

直接探测多普勒激光雷达的光束扫描和风场测量

介绍了直接探测多普勒激光雷达的系统结构和主要参数,给出了该系统进行大气风场测量的光束扫描方法,详细推导了三维风场的计算公式,给出了其风速和风向误差的求解方法。在径向风速均为1 m/s和扫描角度误差均为1°的情况下,水平风速和风向的误差分别为1.155 m/s和0.707°。给出了合肥地区对流层风场的测量结果,结果表明,采用该方法测量大气风场是切实可行的。     

会聚球面波照明下由菲涅耳衍射实现分数傅里叶变换

提出了在会聚球面波照明下,用菲涅耳衍射实现分数傅里叶变换的光学装置。定量得出了为实现分数傅里叶变换系统结构参数应满足的条件。分析表明,利用该系统可实现任意阶分数傅里叶变换。     

相干测风激光雷达VAD风场反演的数据质量控制方法

相干测风激光雷达扫描测量模式下使用速度方位显示（VAD）方法反演水平风场时,若不进行质量控制,会使拟合数据精度大幅降低。基于最小二乘VAD拟合算法,通过分析相干测风激光雷达扫描测量模式中的多种误差源,设置了信噪比、数据残差、扫描区间有效数据、数据有效率四个判据对参与拟合的数据质量进行控制,进而提出了基于以上判据的VAD逐级拟合质量控制方案,设计了数据质量控制流程,并对该方法进行了实验验证。通过对2 955组10 min平均激光雷达测风数据与高精度风杯数据进行对比分析,结果表明:经VAD逐级拟合质量控制流程后,风速均方根偏差从0.97 m/s降低到0.54 m/s,比对偏差降低约44%,风向均方根偏差从7.47降低到5.55,比对偏差降低约26%。     

单晶硅摩擦致相变的SEM研究

自从Jamieson发现单晶硅的高压相变现象以来，有关单晶硅的高压相变的研究逐步开展起来，其最终目的之一就是通过金属延性相的出现来解决单晶硅的加工问题。Pharr、Gogotsi、zhang liangchi等人利用纳米压入技术系统研究了单晶硅的压力致相变问题。本文旨在研究单晶硅在滑动摩擦过程中的相     

利用场发射扫描电镜的低电压高性能进行材料表征

场发射扫描电子显微镜（FESEM）是一种高分辨扫描电镜,在材料分析中得到广泛应用。尤其是良好的低压高空间分辨性能和低压下良好的SE像相互结合使用,使SEM应用范围得到扩展。