激光测月回波探测器位置控制系统设计

激光测月(LLR)具有测量距离远和回波光子少的特点,观测中需要适当更新回波探测器的位置以提高回波探测概率。采用现场可编程门阵列(FPGA)技术研制多步进电机同步控制系统,并结合VC++软件开发工具开发其计算机控制程序,最终实现回波探测器在xoy探测平面上位置的计算机控制。测试结果表明,两个步进电机可以各自单独运行或同时运行,使回波探测器可以单独沿着x轴或y轴移动,也可以同时沿着x轴和y轴移动,最小移动步长为2.5μm,实现对探测器位置的精准控制。     

任意单模光纤的微弯损耗与模场半宽之间的关系

本文导出了任意单模光纤的微弯损耗与近场二阶矩模场半宽W_(x1)、W_(y1)的关系式,在圆对称情况下我们的公式将简化为已有结果。     

旋转对称性对红外超材料完美吸收器特性的影响

研究了超材料完美吸收器的旋转对称性对其吸收特性的影响.吸收器由金属颗粒/电介质/金属薄膜三层结构组成.以最上层是方形金属块为例,并通过在其y方向不同边沿处引入空气孔研究了四重、二重和非旋转对称吸收器的吸收特性.理论结果表明,当入射光偏振平行于x轴或y轴时,四重旋转对称结构有一个完全相同的吸收峰;二重旋转对称结构吸收峰会在入射光偏振平行于x轴时劈裂成两个峰;而无论入射光偏振平行于x轴或y轴,非旋转对称结构的吸收峰都会劈裂成两个峰.不同重数旋转对称性对吸收峰特性影响的结果将有助于设计新型的偏振无关的吸收器.     

CRT偏转线圈结构设计中的磁场测量与控制

本文在对ＣＲＴ偏转线圈进行实测的基础上，运用南开大学丁守谦教授发明的双线圈加测试原理并将其加以推广，使双线圈测在测量磁场参数Ｈ２、Ｈ４、Ｖ２、Ｖ４时，沿Ｘ轴或Ｙ轴能以任意步长进行测量，并根据偏转线圈的特殊形状，当测头越接近开口部，沿Ｘ轴或Ｙ轴的测点也越多、跨距也越大，这样 就克服了所测数据只适应近轴范围的不足，充分发挥了双线圈回归测试原理适应较远轴范围的特性。     

双曲正弦平方-高斯光束在单轴晶体中垂直于光轴的传输

基于光束在单轴晶体中的傍轴矢量传输理论,对双曲正弦平方-高斯光束在单轴各向异性晶体中垂直于光轴的传输做了研究,得到了一般的解析传输公式,并用数值计算方法分析了该光束的传输特性。研究表明:由于晶体的各向异性,其原来的偏振特性将不再保持,仅沿x方向偏振的初始场分量衍生出y分量;随着传输距离的增加,非寻常光沿x轴和z轴的偏振场慢变振幅均减小,光强峰值也随之减小。此外,双曲正弦平方-高斯光束在单轴晶体中垂直于光轴传输时,光束参数β取值不同,光强呈现不同的分布状态。     

一种基于方差融合的双均匀线阵阵列测向算法

本文提出了一种基于双均匀线阵的快速高精度测向算法。针对双均匀线阵不同轴上的接收噪声互不相关的特点,可以得到理论上不含噪声的互相关矩阵。并且由于在两个轴上的阵列流型均具有移不变特性,因此本文所提的快速算法首先利用x轴上最大不重叠的两个子阵列对y轴上最大不重叠的子阵列做互相关,利用y轴上最大不重叠的两个子阵列对x轴上最大不重叠的子阵列做互相关,接着对上述两个相关矩阵采用旋转不变子空间算法,分别计算出目标的角度,再利用方差融合的方法,将两次求得的角度信息进行融合,最后得到较高精度的角度信息,理论分析表明该算法是无偏的,并且在较高信噪比下趋近于克拉莫罗界。最后利用蒙特卡洛仿真验证了本算法的有效性。      

基于多FBG组网的智能装配修正系统研究

工况环境下为了稳定地获取工件状态信息,采用多光纤布喇格光栅(FBG)组网监测的方法,将多光纤光栅传感器分布于装配结构的工装上,在获取敏感位置实时应变场数据的基础上,分析了不同装配误差与应变场分布的函数关系,并给出了合适的修正参数.结果表明,在工件上分别施加100N的应力时,x轴方向的最大形变值为0.86mm,y轴方向的...     

光缆转输e指数脉冲系统

一、前言在许多物理量的测试中,常碰到e指数(自然指数)脉冲信号。例如,在核反应的大部分时间内r射线与中子增殖速率的关系是按自然指数规律变化的。自然指数的数字表达式为: y=e~x (1) 这个公式表明,y是指数x的函数,x可以是正值或负值,但y都是正值。也可将(1)式表示为y=N_0e~x,并且电流或电压信号可以用e指数函数的形式表示,则     

一种快速简便测定单轴晶体x(y)轴及半波电压的方法

KDP,DKDP等单轴晶体在激光技术中通常被作为激光器的Q开关使用,在实际应用中,晶体的x(y)轴及其半波电压的标定为激光器的调试带来很大方便,我们介绍一种快速简便测定单轴晶体x(y)轴及其半波电压的方法。     

C型MEMS平面微弹簧弹性系数研究

设计了一种新型的C型微机电系统(MEMS)平面微弹簧,用卡氏第二定律和胡克定律推导出这种平面微弹簧在3个方向(即x,y和z方向)上的弹性系数计算公式,用ANSYS进行有限元仿真,结果验证了公式推导的正确性。在公式计算和仿真的基础上,研究了各种结构参数对其弹性系数的影响规律。     

差值感应法测量电视偏转线圈的空间磁场

本文扼要地介绍了测量磁场的各种电测方法并作了比较。详细论述了测量偏转线圈磁场的原理及方法。提出了三探针的测场机构及切实可行的测量装置。测出了电视偏转线圈的磁场参数曲线H0(z)、H2(z)及H4(z)。     

关于无重复分解产生树的定理

本文定义了一种二分图,称之为互补划分图。利用此图容易证明有关互补划分的定理,并可得到一个判别是否是本性互补划分的较弱的条件。     

Electrodynamics of waveguide junctions with anisotropic loading

An electrodynamic model for the calculation of waveguide junctions with anisotropic loading has been built in this study. A wave equation for longitudinal components of hybrid electromagnetic field and a system of linear algebraic equations (SLAE) were obtained. The conditions were found under which the SLAE for HE _mnp -oscillations (indexes indicate the number of variations of the field in terms of coordinates x, y, z, respectively) disintegrated into two independent systems corresponding to H _mno — and E _klo -oscillations. The developed algorithm and the software programs were used to carry out numerical analysis for these modes of oscillations that are of practical interest. The recommendations are given on the use of waveguide junctions for measuring components of the dielectric permittivity tensor of anisotropic crystals.     

Electric-field-controlled effects of spatial recurrence and multiplication of electron waves in two-dimensional semiconductor nanostructures

Effects of recurrence and multiplication in the spatial distribution of the probability-flux density j _x(x, z) (or the quantum-mechanical current density ej _x(x, z), where e is the elementary charge), which arise from electron-wave interference in two-dimensional semiconductor nanostructures, are analyzed, and the possibility of controlling these effects by the application of a dc transverse electric field is examined. A type of nanostructure represented by two rectangular quantum wells (a wide one and a narrow one) whose widths are measured in the direction of the z axis (the quantum-confinement axis) with the wells arranged sequentially in the direction of propagation of the electron wave (the x axis) is considered. It is shown that, for an electron wave entering the wide well from the narrow well, the initial transverse distribution peak j _x(0, z) is reproduced with some accuracy at distances X _p = pX ₁ (recurrence) and, in nanostructures symmetric along the z axis, splits at distances X ₁/q into q identical peaks of magnitude reduced by a factor of q (multiplication) (here, p and q are integers). It is demonstrated that these effects can be controlled by a dc electric field applied in the transverse direction (along the z axis) in the region of the wide quantum well. A reduction in the effective well width and appearance of asymmetry in the transverse potential profile upon application of the electric field cause a radical change in the j _x(x, z) distribution in this quantum well and make possible inverse population of the quantum-confinement subbands.     

Investigation of the scattering field under the low-frequency resonance conditions of screw helices

The frequency-selective properties of small screw helical coils are investigated. It is shown that, in a frequency band of 2–4 GHz, such coils have two resonances. The scattering patterns of helical coils are measured in the E and H planes. It is found that, at the zeroth-order resonance, a coil scatters a circularly polarized field with the maximum in the plane perpendicular to its longitudinal axis and that, at the frequency of the first resonance, the maximum of the scattered field is oriented along the longitudinal axis of the coil.     

Symmetric waves in a circular metal waveguide containing an anisotropically conducting coaxial cylindrical surface

Symmetric waves propagating in a hollow metallic waveguide that contains a coaxial cylindrical surface which conducts perfectly along helical lines with a small twist angle are investigated. It is found that, at certain ratios between the structure’s geometric parameters, there exist two modes with close propagation constants. It is shown that the superposition of these modes results in a field that, during propagation along the waveguide, periodically coincides either with the field of the E ₀₁ mode of the inner cylindrical channel (in this case, the field is zero in the coaxial area) or with the field of the H ₀₁ mode of the outer channel. A circular-waveguide E ₀₁ ? H ₀₁ mode converter has been developed and experimentally investigated. It is shown that the conversion loss does not exceed 0.8 dB.     

Magnetic Field And Field Gradient Corrections within a Nonconducting Sensor Enclosure in a Conducting Fluid?Part III: Current Exclusion Contribution for an Arbitrary Axisymmetric Enclosure

Neglecting the velocity field perturbation, we examine the current exclusion contribution to the magnetic distortion field H?1 along the symmetry axis of a ?streamlined? enclosure in the shape of a general body of revolution. In contrast to the case of a spherical enclosure where all orientations of the (unknown) unperturbed current density J?o relative to the enclosure surface are equivalent, for the present geometry the relative orientation of J?o must be specified. On the symmetry axis (z-axis) the component of the distortion field parallel to that axis vanishes independent of the orientation of J?o. In regard to field gradients, all diagonal elements of the gradient dyad similarly vanish. However, only the combination ?H?x/?y + ?H?y/?x vanishes independent of orientation. Here (x, y) denote any two orthogonal directions perpendicular to the symmetry axis.     

A New Technique for Measuring an Electromagnetic Field by a Coil Spring

A thin coil spring whose length can be varied periodically by mechanical means has been used as a probe to measure the electric field intensity. The vibrating probe acts as a reradiating antenna with periodically varying length that modulates and scatters the component of the E/sup bar/ field which is parallel to the axis of the spring. The scattered signal is picked up by a receiving antenna (the sending antenna was used also as a receiving antenna) and amplified with an amplifier that is locked-in with the frequency of the mechanical vibration of the coil. Measurements were made with coil springs of three different dimensions, and a gain constant K, which should be independent of the product of the axial length of the coil and the magnitude of the vibration, was experimentally checked. Measurements of the field of a half-wave dipole antenna as measured with the spring probe are in general agreement with theory. An expression for the ratio between the scattered and incident waves is obtained based upon the field-pattern method and the approximations involved in the reciprocity-theorem method are clarified. It is also demonstrated (in the appendix) that the effective length of a thin helical antenna with a triangular current distribution equals one-half of the axial length of the helix.     

Growth and characterization of lead-tin-ytterbium-telluride for diode lasers

PbSnYbTe is a new and potentially useful material for fabricating double hetero junction PbSnTe diode lasers by molecular b<sam epitaxy. These lasers should have improved carrier and photon confinement, resulting in improved external quantum efficiency and higher device operating temperature. It is found from room temperature optical transmission studies that the band gap of Pb_1−x Yb_x Te increases approximately as dEg/dx =; 3.3 eV for x < 0.04, and that the index of refraction decreases with increasing x. Doping studies of (Pb_1−y Sn_y )_0.97 Yb_0.03Te indicate that> it can be doped heavily p-type at low temperatures for y ∼ 0.10. The lattice constant of (Pb_0.85 Sn_0.15)_1−x Yb_x Te is independent of x up to x ∼ 0.10. these characteristics make (Pb_1−y Sn_y )_1−x Yb_x Te well-suited for the fabrication of lattice-matched double heterojunction lasers with y∼ 0.10.     

Superconducting magnet system containing Bi-2212/Ag Coil Generates 21.8 T at 1.8K

We fabricated a Bi-2212/Ag double stacked pancake coil of 13 mmØ) in inner bore and of 46.5 mmØ in outer diameter, by using Bi-2212/Ag tapes prepared by the combination of continuous dip-coating process and melt-solidification technique. This small superconducting magnet was used as an insert magnet of a conventional superconducting magnet system and tested at saturated superfluid helium temperature (～ 1.8K) in various bias fields. The generated field of Bi2212/Ag coil was 0.9 T, with I_c of 310 A(criterion 10^-13Ω·m), in the bias field of 20.9 T. Thus, this superconducting magnet system achieved generation of magnetic field of 21.8 T in the full superconducting state.