大口径平面光学元件面形检测中激光光斑质心定位

如何快速准确计算透镜焦面上的光斑质心坐标是大口径平面光学元件面形检测系统的核心问题之一,直接决定面形检测的精度和重复性。定义一个半径为r的探测窗口,根据到中心距离建立一维卷积模板,在光斑覆盖区域中寻找窗口内能量和局部最大的位置,确定光斑有效区域;再使用传统重心法计算有效区域质心;最后应用3准则进行误差处理。实验结果表明,该算法检测精度为0.1像素,各指标比传统阈值加权质心定位法提高约1 倍,面形测量的面形相似性和PV 比阈值加权法更贴近干涉仪检测结果。目前,通过长时间的实验验证与改进,已成功运用于实际项目中。     

改进格雷码条纹投影三维测量方法

传统的格雷码加相移法已经广泛应用于三维测量,但是相位解包裹一般需要投影多幅格雷码条纹,如何实现快速、准确的三维测量仍具有一定挑战性。提出了一种基于几何约束的改进格雷码条纹投影三维测量方法,可以有效减少格雷码条纹的数量。为了实现高速条纹投影,使用二值抖动技术将8位正弦相移条纹转换为1位二值图像。总共使用六幅条纹图像,其中三幅相移条纹用于计算截断相位,三幅格雷码条纹用于对截断相位进行初步展开获得伪展开相位,最后利用几何约束对伪展开相位进行解包裹获得绝对相位。实验结果表明,所提方法可以有效地重建被测物体的三维形貌。     

大视场线结构光两轴测量系统

提出了一种由CCD摄像机、线结构光投射器和两个回转工作台构成的大视场线结构光2轴测量系统。通过两个回转工作台的转动使线结构光平面扫过被测物体1周,在1次装夹下测量出物体的1周全貌。首先建立了由二维摄像机像面坐标系向被测物体转台坐标系变换的数学模型;利用标准球作为标定器具,根据线结构光平面中标准球的球心坐标和2转台转角可确定1个"共轭对",利用多组"共轭对"求出了系统模型中的未知参数;从而根据两个回转工作台分别转动的角度和CCD二维图像可获得线结构光平面上点的三维数据。实验结果证明,这种方法具有较高的测量精度,能在1次装夹下完整测量结构复杂物体的1周全貌,同时具有视场大、结构简单和成本低的优点。     

Low-cost optoelectronic system for three-dimensional artwork texture measurement

A new optoelectronic system based on a projection unit in which light, coming from a laser diode coupled to an optic fiber impinges on a diffractive optical element (DOE) to produce sinusoidal fringes is proposed for three-dimensional (3-D) texture measurement. If the projected fringe pattern is viewed at an angle different from the projection angle, the fringe profile is phase-modulated by the 3-D object shape. The 3-D map information is obtained with the aid of a fringe analyzer based on phase-shifting synthetic moiré pattern, Fast Fourier Transform (FFT), signal demodulation techniques and a robust and fast phase unwrapping performed by a specially developed software. The proposed system is based on a simple and low cost equipment; furthermore, it is suitable for in situ measurements also by nonskilled operators. Some experimental examples illustrate its performance.     

一种用于结构光三维测量的空间标定方法

提出了一种全空间标定方法,可用于快速高精度 的三维测量。液晶屏作为标准平面显 示二维光栅以及被投射一维光栅,通过固定在平移台上在测量空间Z方向进行 移动,相机抓 拍光栅,计算截断相位后,建立截断相位和三维空间的坐标关系。通过改变光栅频率可实现 空间尺寸的标定,从而实现全空间的标定。测量时,计算出截断相位,通过查表索引可快速 得到物体的空间坐标信息。搭建了标定系统,并用测量实验验证了标定算法的有效性。     

面向复杂机械零件形貌测量的高精度三维重建方法

机械零件的精确测量可为零件的加工制造、虚拟仿真、缺陷检测等应用提供依据,基于条纹投影的双目视觉方法由于其高精度的特点广泛应用于机械零件的形貌测量中。在该方法中,绝对相位曲线的质量决定着三维重建的最终精度。由于环境噪声、场景不连续或零件表面复杂结构等的影响,绝对相位曲线往往存在着大量的噪声点和不同程度的形变。为了提高重建精度,针对绝对相位曲线存在的问题提出了相应的改进方法;针对难以去除的远离相位曲线的噪声点,提出逐区域相位校正方法,该方法将每一行的相位曲线分为若干区域,以区域内相位值的中位数为阈值,去除此类噪声点;针对相位曲线的形变区域,在基于点基元的立体匹配方法的基础上引入曲线拟合方法,并对匹配后得到的视差图进行精化,能够改善相位曲线形变区域立体匹配结果不佳的情况,提高了匹配方法的鲁棒性与精度。使用该方法对复杂零件FSW逆变器进行重建,标准偏差可降至0.1 mm以内。实验结果表明:所提方法重建精度更高,对于表面结构复杂的机械零件,能够实现精确测量。     

An architecture for large scale Internet measurement

Historically, the Internet has been woefully under-measured and under-instrumented. The problem is only getting worse with the network's ever-increasing size. We discuss the goals and requirements for building a “measurement infrastructure” for the Internet, in which a collection of measurement “platforms” cooperatively measure the properties of Internet paths and clouds by exchanging test traffic among themselves. The key emphasis of the architecture, which forms the underpinnings of the National Internet Measurement Infrastructure (NIMI) project, is on tackling problems related to scale. Consequently, the architecture emphasizes decentralized control of measurements; strong authentication and security; mechanisms for both maintaining tight administrative control over who can perform what measurements using which platforms, and delegation of some forms of measurement as a site's measurement policy permits; and simple configuration and maintenance of platforms     

A field theoretic foundation for the representation of quality factor in terms of reactance-slope parameters for electrically large three-dimensional arbitrarily shaped resonators

The use of reactance-slope parameters for the design of RF and microwave filters was drawn from lumped-element circuit representations. This paper provides a field-theoretic foundation for reactance-slope parameters based upon the treatment of arbitrarily shaped electrically large resonators comprised of electric and magnetic conducting enclosures. Traditional representations for these parameters in terms of the reactance for series-connected network elements and susceptance for parallel-connected network elements are related to electromagnetic fields. The resulting generalized expressions for reactance-slope parameters with utility for evaluating quality (Q) factor are developed for both electric and magnetic conducting resonators using strictly surface electromagnetic fields and sources. The generalized expressions are used to evaluate the unloaded Q for TE/sub 101/-mode rectangular resonators comprised of silver, copper, aluminum, and brass based upon two different standard rectangular waveguides with enclosed ends. Q results are also presented for TM/sub 011/-mode circular cylindrical resonators comprised of the same conducting materials. Results from the method here are compared to well-established results published in the literature. These expressions are useful for either analytically or numerically evaluating the reactance-slope parameter and Q factor.     

Gaussian field expansions for large aperture antennas

An approximate theory of large aperture antennas is developed where aperture, Fresnel, and far fields are expressed in the form of Ganssian field expansions. First, aperture fields, i.e., aperture distributions, are expanded in orthogonal Hermite-Ganssian and Laguerre-Gaussian functions for antennas with rectangular and circular geometries, respectively. Then solution of the Fresnel-Kirchoff diffraction integrals yields the Fresnel and far field expansions. Care is taken to assure the direct transformability of the aperture fields. Optimal scale factors contained in the aperture field expansions are derived and lead to structured field distributions where sidelobes are added sequentially as more terms in the expansions are used in the computations. Tables of optimal scale factors and series coefficients are provided for cosine, truncated Ganssian and Taylor aperture distributions. Several examples are provided that demonstrate the usefulness of the formulas.     

Coiled-fiber sensor for vectorial measurement of magnetic field

New results on the polarization properties of a matched fiber-coil (i.e. one beat length per turn) immersed in a magnetic field are described. It is shown that both components H_y and H_z, perpendicular to the coil axis, can be simultaneously measured. Sensing coils of 1-cm diameter, with multiple turns of fiber, were fabricated. Using 100-turn heads, a sensitivity of 0.01 G was achieved for the vectorial fiber sensor     

Rapid registration for wide field of view freehand three-dimensional ultrasound

A freehand scanning protocol is the only way to acquire arbitrary large volumes of three-dimensional ultrasound (US) data. For some applications, multiple freehand sweeps are required to cover the area of interest. Aligning these multiple sweeps is difficult, typically requiring nonrigid image-based registration as well as the readings from the spatial locator attached to the US probe. Conventionally, nonrigid warps are achieved through general elastic spline deformations, which are expensive to compute and difficult to constrain. This paper presents an alternative registration technique, where the warp's degrees of freedom are carefully linked to the mechanics of the freehand scanning process. The technique is assessed through an extensive series of in vivo experiments, which reveal a registration precision of a few pixels with comparatively little computational load.     

基于霍尔效应弱磁场测量装置的研制与应用

为了解决弱磁场强度测量困难的问题,基于霍尔效应开发了以线性霍尔元件为探头弱磁场测量装置。对磁场测量装置各部分电路模块进行了详细设计,并结合矩形线圈磁场分布特征进行了实测值与仿真理论值的对比分析。结果表明,测量结果与理论值具有较好的拟合程度,该装置测量精度为0.01 m T,测量范围为±10 m T,最大测量误差为0.29 m T,具有测量精度高、操作简单方便、设计成本低等优点,可应用于各类线圈弱磁场强度的检测及逐点测量实验中。     

Power spectral density measurement for large aspheric surfaces

To ensure the safe and normal operation of the whole optical system, it is important to test and evaluate the quality of optical components. The article explores the advantages and disadvantages of general parameters used in aspheric surface testing, the composition of the system,the principle of operation and the design of related power spectral density (PSD) software used in testing large aspheric surfaces with Shack-Hartmann and phase shifting interferometer. The results indicate that PSD can give the spatial frequency distribution of the wavefront aberration when large aperture phase shifting interferometer is used as an instrument to test the wavefront, and this can also be applied as an evaluation standard in testing the quality of optical components. In addition, this paper describes the test results of optical components in the size of 64 mm× 64 mm.     

高精度反射镜组件面形检测结构设计方法

在反射镜组件进行检测装配时,各零件加工过程中形成尺寸公差、形状位置公差会产生装配应力。装配应力通过反射镜体传到反射镜镜面使反射镜面形变差。针对该问题文中提出将柔性铰链应用于反射镜组件检测工装设计的方法。为验证该方法的可行性,针对某反射镜组件的特征参数和检测方法,应用柔性铰链设计理论及仿真分析软件设计了反射镜组件检测柔性工装。完成对反射镜组件重复性试验、拧紧力矩敏感性试验,试验结果表明柔性工装具有较好的稳定性。反射镜组件面形与反射镜单镜面形相比变化0.006 rms,满足工装设计要求。与刚性工装比,柔性铰链应用反射镜检测工装显著降低了装配应力对反射镜面形的影响。     

A three-dimensional multifrequency large signal model for helixtraveling wave tubes

A three-dimensional (3D) multifrequency large signal model of the beam wave interaction in a helix TWT is described. The beam is divided into a set of discrete rays, or “beamlets”, instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) models. The RF fields supported by the helix are represented by a tape helix model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the model. RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources. The dc space charge electric field is similarly obtained from a solution of Poisson's equation. This model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code. The full three dimensional treatment permits the accurate computation of large signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space. The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D model. Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs. drive power. Its predictions for spent beam distributions also compare very well with measurements. Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation     

Contact resistance measurement of bonded copper interconnects for three-dimensional integration technology

A novel test structure for contact resistance measurement of bonded copper interconnects in three-dimensional integration technology is proposed and fabricated. This test structure requires a simple fabrication process and eliminates the possibility of measurement errors due to misalignment during bonding. Specific contact resistances of bonding interfaces with different interconnect sizes of approximately 10/sup -8/ /spl Omega/-cm/sup 2/ are measured. A reduction in specific contact resistance is obtained by longer anneal time. The specific contact resistance of bonded interconnects with longer anneal time does not change with interconnect sizes.     

多点流场压力实时测量技术研究与系统实现

通过对多点流场压力实时测量技术的研究,提出了一种以绝对压力系统为基准的多管多点的流场压力测量方法,研制了一套流场压力实时测量系统。在系统的硬件设计中,通过采用多路复用的循环扫描方法,有效减小了系统的体积,降低了成本。在软件设计中,通过对传感器静态特性的校正和传感器零点温漂的自动补偿,实时地对系统的误差进行修正,有效减小了系统误差。试验结果表明：研制的多点流场压力实时测量系统运行稳定,数据测试准确可靠,数据精度达到了0．1％。     

Mode field diameter measurement conditions for fibers by transmitted field pattern methods

The transmitted near- and far-field pattern methods, measuring the mode field diameter of the fundamental LP01mode in a single-mode fiber are studied. On the basis of measurement error evaluation, the optimum measurement conditions for typical single-mode fibers are determined. Actual measured values for nearly ideal step-index fibers are in good agreement with the theoretical predictions (within 0.2 μm with a standard deviation of 0.05 μm). The mode field diameter measurement by the transmitted field pattern methods is useful for the study of the structural optimization of the single-mode fibers.