Calibration of laser beam direction based on monocular vision

In the laser displacement sensors measurement system,the laser beam direction is an important parameter.Particularly,the azimuth and pitch angles are the most important parameters to a laser beam.In this paper,based on monocular vision,a laser beam direction measurement method is proposed.First,place the charge coupled device(CCD)camera above the base plane,and adjust and fix the camera position so that the optical axis is nearly perpendicular to the base plane.The monocular vision localization model is established by using circular aperture calibration board.Then the laser beam generating device is placed and maintained on the base plane at fixed position.At the same time a special target block is placed on the base plane so that the laser beam can project to the special target and form a laser spot.The CCD camera placed above the base plane can acquire the laser spot and the image of the target block clearly,so the two-dimensional(2D)image coordinate of the centroid of the laser spot can be extracted by correlation algorithm.The target is moved at an equal distance along the laser beam direction,and the spots and target images of each moving under the current position are collected by the CCD camera.By using the relevant transformation formula and combining the intrinsic parameters of the target block,the2D coordinates of the gravity center of the spot are converted to the three-dimensional(3D)coordinate in the base plane.Because of the moving of the target,the3D coordinates of the gravity center of the laser spot at different positions are obtained,and these3D coordinates are synthesized into a space straight line to represent the laser beam to be measured.In the experiment,the target parameters are measured by high-precision instruments,and the calibration parameters of the camera are calibrated by a high-precision calibration board to establish the corresponding positioning model.The measurement accuracy is mainly guaranteed by the monocular vision positioning accuracy and the gravity center extraction accuracy.The experimental results show the maximum error of the angle between laser beams reaches to0.04°and the maximum error of beam pitch angle reaches to0.02°.

Generation and Detection of a Directed Monoenergetic Neutrino Beam with Hydrogen-Like Ions

We consider two possible schemes for generation and detection of a monoenergetic directed beam of neutrinos which may have application to neutrino communication. First, we consider generation of a directed neutrino beam using electron capture beta decay in hydrogen-like ions. Next, we suggest detection of a directed neutrino beam using resonant absorption of a neutrino by a bare nucleus with the generation of a bound electron. This reaction is inverse to electron capture beta decay, and we call it “Bound State Inverse Beta Decay (BSIBD)”. We show that the recoil effect can be eliminated by an appropriate choice of velocities for the ions and bare nuclei. Finally, we consider a combination of a solid state source of a directed mono-energetic neutrino beam and its detection using BSIBD.

Design of a compact polarization beam splitter based on a deformed photonic crystal directional coupler

In this paper a compact polarization beam splitter based on a deformed photonic crystal directional coupler is designed and simulated. The transverse-electric （TE） guided mode and transverse-magnetic （TM） guided mode are split due to different guiding mechanisms. The effect of the shape deformation of the air holes on the coupler is studied. It discovered that the coupling strength of the coupled waveguldes is strongly enhanced by introducing elliptical airholes, which reduce the device length to less than 18.Sttm. A finite-difference tlme-domain simulation is performed to evaluate the performance of the device, and the extinction ratios for both TE and TM polarized light are higher than 20 dB.

Full-vectorial finite-difference beam propagation method based on the modified alternating direction implicit method

A modified alternating direction implicit algorithm is proposed to solve the full-vectorial finite-difference beam propagation method formulation based on H fields. The cross-coupling terms are neglected in the first sub-step, but evaluated and doubly used in the second sub-step. The order of two sub-steps is reversed for each transverse magnetic field component so that the cross-coupling terms are always expressed in implicit form, thus the calculation is very efficient and stable. Moreover, an improved six-point finite-difference scheme with high accuracy independent of specific structures of waveguide is also constructed to approximate the cross-coupling terms along the transverse directions. The imaginary-distance procedure is used to assess the validity and utility of the present method. The field patterns and the normalized propagation constants of the fundamental mode for a buried rectangular waveguide and a rib waveguide are presented. Solutions are in excellent agreement with the benchmark results from the modal transverse resonance method.

Acoustic beam splitting in a sonic crystal around a directional band gap

Beam splitting upon refraction in a triangular sonic crystal composed of aluminum cylinders in air is experimentally and numerically demonstrated to occur due to finite source size, which facilitates circumvention of a directional band gap. Experiments reveal that two distinct beams emerge at crystal output, in agreement with the numerical results obtained through the finite-element method. Beam splitting occurs at sufficiently-small source sizes comparable to lattice periodicity determined by the spatial gap width in reciprocal space. Split beams propagate in equal amplitude, whereas beam splitting is destructed for oblique incidence above a critical incidence angle.

Numerical Study of the Vibrations of Beams with Variable Stiffness under Impulsive or Harmonic Loading

The behavior of beams with variable stiffness subjected to the action of variable loadings (impulse or harmonic) is analyzed in this paper using the successive approximation method. This successive approximation method is a technique for numerical integration of partial differential equations involving both the space and time, with well-known initial conditions on time and boundary conditions on the space. This technique, although having been applied to beams with constant stiffness, is new for the case of beams with variable stiffness, and it aims to use a quadratic parabola (in time) to approximate the solutions of the differential equations of dynamics. The spatial part is studied using the successive approximation method of the partial differential equations obtained, in order to transform them into a system of time-dependent ordinary differential equations. Thus, the integration algorithm using this technique is established and applied to examples of beams with variable stiffness, under variable loading, and with the different cases of supports chosen in the literature. We have thus calculated the cases of beams with constant or variable rigidity with articulated or embedded supports, subjected to the action of an instantaneous impulse and harmonic loads distributed over its entire length. In order to justify the robustness of the successive approximation method considered in this work, an example of an articulated beam with constant stiffness subjected to a distributed harmonic load was calculated analytically, and the results obtained compared to those found numerically for various steps (spatial h and temporal τ ¯ ) of calculus, and the difference between the values obtained by the two methods was small. For example for ( h=1/8 , τ ¯ =1/ 64 ), the difference between these values is 17%.

Effect of beam-pointing errors on bistatic SAR imaging

The purpose is to conduct a research in the energy variation of echo wave and the imaging effect caused by the aero bistatic SAR pointing errors. Based on the moving geometry configuration of aero bistatic SAR, a model of beam pointing errors is built. Based on this, the azimuth Doppler frequency center estimation caused by these errors and the limitation to the beam pointing synchronization error are studied, and then the imaging result of different errors are analyzed. The computer＇s simulations are provided to prove the validity of the above analysis.

Silicon detector array for radioactive beam experiments at HIRFL-RIBLL

A new and innovative detector system based on a silicon strip detector dedicated to the study of the reaction induced by lighter radioactive beams is described herein.The detector system consists of five sets of three types of telescopes,which are successfully used to measure the angular distributions of both elastic scattering and breakup simultaneously, on the Radioactive Ion Beam Line in Lanzhou at Heavy Ion Research Facility in Lanzhou. This silicon detector array is used to measure the elastic scattering angular distributions of ^(11) Be on a ^(208) Pb target at E_(lab) = 140 and 209 MeV. A comparison of the Monte Carlo simulations with the experimental results shows a reasonable consistency.

可见光波段多路激光合束及闭环校正技术研究

为了实现可见光波段多路不同波长激光的周期性闭环校正,设计了一种具有光束指向和位置偏差独立监测与调节的激光合束系统。首先,根据系统的应用需求,提出了合束系统的设计指标与整体合束方案。然后,在合束方案的基础上,建立了合束系统的光束控制模型,并通过数值仿真得到了合束系统光束控制的解算方法。闭环合束系统通过光束指向和位置监测装置分别实现合束激光指向偏差与位置偏差的独立监测,并根据监测结果进行光束调节装置控制量的解算;进而通过两维摆镜和一维平移台分别实现光束指向和位置偏差的独立高效调节。最后,采用两路不同波长的激光束,配合光束监测与调节装置,搭建了闭环合束模拟实验平台,对周期性闭环合束系统的合束效果进行了验证。实验结果表明:在长时间的工作过程中,两路激光均实现了与基准光路的精密合束,合束指向精度优于±7μrad,位置精度优于±0.84 mm。本研究所组建的激光合束系统不仅具有合束精度高、校正速度快、光路扩展性强的优势,而且可实现激光束的周期性闭环校正,能够有效保证合束激光的长期工作稳定性。

Space Charge Effect of Bunched Beam With Gaussian Distribution

The nonlinear space charge effect of a bunched beam with Gaussian distribu-tion in the longitudinal direction is discussed.Some useful formulae are derived for cal-culating the potential induced by a cylinder model of space charge in the waveguide of alinac with different combinations of density distribution:Gaussian distribution in thelongitudinal direction versus Kapchinskij Vladimirskij,waterbag,parabolic andGaussian distribution in the transverse direction,rcspectively.

A 2.4 GHz Switched Beam Antenna for Indoor Applications Using Angle of Arrival Estimation

This study introduces a new design of planar antenna array for ISM band applications at 2.4 GHz. This prototype is switched beam antenna, namely planar antenna with four meandered slotted triangular elements (PAFMSTE), which is proposed for wireless indoor applications. The Base Station (BS) equipped with this planar antenna is preferred to be at the center position on the room ceiling to cover all sectors of the room. It is designed to use four directional triangular elements arranged to form a square planar antenna array. The PAFMSTE is used to obtain optimal directivity in four directions in azimuth plane with 3 dB beamwidth of 90°at a specific orientation of 30°in elevation plane. Switched parasitic technique is used to enable PAFMSTE to steer a directional beam through four locations by using four PIN diodes switches. The High Frequency Structure Simulator (HFSS) is used as an efficient simulation tool to optimize the performance of the PAFMSTE antenna. The fabrication and measurements of the PAFMSTE antenna are introduced. The proposed antenna enable radio positioning via Angle of Arrival (AOA) information collected from nearby devices. Then, the Cramér-Rao Bound (CRB) is presented for AOA estimation using identically and equally spaced antenna elements. The CRB depends on the directivity, where the maximum values of CRB are 1.35 × 10-3 and 8 × 10-3 at HPBW of 60° and 90°, respectively.

Instability of functionally graded micro-beams via micro-structure-dependent beam theory

This paper focuses on the buckling behaviors of a micro-scaled bi-directional functionally graded （FG） beam with a rectangular cross-section, which is now widely used in fabricating components of micro-nano-electro-mechanical systems （MEMS/NEMS） with a wide range of aspect ratios. Based on the modified couple stress theory and the principle of minimum potential energy, the governing equations and boundary conditions for a micro-structure-dependent beam theory are derived. The present beam theory incorporates different kinds of higher-order shear assumptions as well as the two familiar beam theories, namely, the Euler-Bernoulli and Timoshenko beam theories. A numerical solu- tion procedure, based on a generalized differential quadrature method （GDQM）, is used to calculate the results of the bi-directional FG beams. The effects of the two exponential FG indexes, the higher-order shear deformations, the length scale parameter, the geomet- ric dimensions, and the different boundary conditions on the critical buckling loads are studied in detail, by assuming that Young＇s modulus obeys an exponential distribution function in both length and thickness directions. To reach the desired critical buckling load, the appropriate exponential FG indexes and geometric shape of micro-beams can be designed according to the proposed theory.

基于机器视觉的带式输送机高精度煤流检测研究

针对现有基于机器视觉的带式输送机煤流检测方法存在的图像细节缺失、在多处断裂或断裂间距较大区域拟合效果较差的问题,基于直射斜收式激光三角测量原理,提出了一种基于机器视觉的带式输送机高精度煤流检测系统,将线激光发射器布置在带式输送机测量位置正上方并垂直照射煤堆,煤堆随带式输送机匀速运动,利用相机在斜上方实时拍摄包含激光条纹的煤堆表面图像。对煤流检测系统进行标定,包括相机内参数标定和激光平面标定,得到煤堆的高度信息;对煤流截面激光条纹图像进行处理,从提取精度、算法实时性等角度对比分析了灰度重心法和区域骨架法,根据对比结果选用区域骨架法提取激光条纹中心;针对利用图像膨胀操作进行激光条纹断裂修补拟合效果较差的问题,提出采用最小二乘法作为激光条纹断裂修补算法,相较于闭运算,最小二乘法拟合处理的平滑效果更好,精度较高;建立煤流截面积计算模型,通过计算每一帧上煤堆的横截面积,即可得出不同带速下的煤流体积。实验结果表明,当带速分别为0.25,0.5,1 m/s时,煤流检测系统误差均较小,最大误差分别为2.78%,3.61%和3.89%,验证了煤流检测系统具有较高的准确性。

冷弯薄壁卷边C形不锈钢梁的力学性能试验

为了研究冷弯壁薄卷边C形钢受弯构件的力学性能,以冷弯薄壁不锈钢梁为研究对象,重点研究加载条件、跨度对构件屈曲模式和受弯承载力的影响。结果发现:试件的加载条件和跨度对冷弯薄壁卷边C形钢受弯构件屈曲模式和极限承载力的影响显著,纯弯加载下的短梁极限承载力高达169.1 kN,破坏模式为畸变屈曲,其余试件破坏模式也为畸变屈曲;腹板V型加劲能够有效抑制腹板鼓曲的产生,提高试件的极限承载力。利用现有直接强度法修正公式的计算结果与试验结果进行对比,以验证公式的准确性。

一种Kongsberg EM多波束后向散射强度波束指向性残余改正方法

Kongsberg EM多波束声呐的波束指向性与出厂标定存在偏差,导致后向散射强度呈现与扇区耦合的辐射畸变,针对这个问题提出了一种基于波束指向性模型的多扇区指向性残余改正方法。该方法首先在分析波束收发过程的基础上,构建EM声呐多扇区指向性辐射模型;然后选取特定测线,采用经验性声学模型估计后向散射强度-角度曲线,分离各扇区指向性残余信号;最后对回波强度进行指向性残余改正,得到与采集扇区无关的后向散射强度。实例计算结果表明:该方法能有效降低多扇区指向性残余对后向散射强度测量的干扰,提高EM系列多波束声呐在海底底质分析中的使用价值。

波束域特征融合的浅海水平阵目标方位估计

针对实际海洋环境影响下水平阵目标方位估计性能降低的问题,提出了一种基于水平阵波束域特征融合的卷积神经网络方位估计方法。首先建立数据计算仿真模型用于生成数据集,利用常规波束形成和最小方差无失真响应两种波束形成器得到波束域特征数据。然后,利用两种波束域特征数据分别训练卷积神经网络模型,仿真和海试数据均表明,训练后的卷积神经网络模型方位估计精度优于常规波束形成、最小方差无失真响应和匹配波束处理,尤其是在端射方向性能提升明显。最后,将两种波束域特征进行前端特征融合后再训练卷积神经网络模型,海试数据测试结果表明,特征融合后的卷积神经网络模型方位估计性能进一步提升,在5°误差范围内的可靠测向概率比单一特征卷积神经网络估计结果高约4%,均方根误差降低约0.2°。

基于极化-相位调制的雷达通信一体化波束方向图设计

为进一步实现雷达与通信系统的高效协同,提出一种基于极化相位联合调制的雷达通信一体化发射波束方向图设计方法。首先,通过正交子空间投影方法将权矢量投影至指定流形空间的零空间;然后,针对通信与探测权矢量的不同指标设计目标函数并通过优化算法求解,以实现通信信息的嵌入与极化控制;最后,添加人工噪声干扰以降低非通信方向对通信信息的截获概率。仿真结果表明所提方法可以实现极化调控和旁瓣约束,通信信号相比于已有方法具有更高的传输速率和抗截获概率。

太赫兹折叠波导慢波电路及功率合成技术

针对太赫兹频段行波管输出功率较小的瓶颈以及对紧凑型设计的明确需求,提出一种管内功率合成的0.34 THz折叠波导行波管结构。首先,对太赫兹折叠波导慢波结构的高频特性进行了研究,通过仿真计算得到了其色散特性和耦合阻抗,0.34 THz处归一化相速度为0.248,耦合阻抗为0.46Ω;其次,提出了用于管内功率合成的3 dB定向耦合器结构设计,分析表明,其在0.31~0.368 THz范围内,幅度平衡度在±0.19 dB以内,隔离度优于24 dB;最后,完成了基于3 dB定向耦合器管内功率合成的折叠波导行波管基本结构设计并构建了仿真模型,仿真结果表明,最大输出功率为9.16 W,增益为26.6 dB,3 dB带宽达到21 GHz。作为对比,单个折叠波导行波管输出功率为6.18 W,故管内合成的折叠波导行波管的输出功率是单个行波管输出功率的1.48倍;此外,与采用常规外置功率合成结构的双行波管组件设计相比,管内功率合成折叠波导行波管的横向尺寸至少缩减了56.5%。

三维高增益相控阵天线阵列机相扫模式下的波束控制算法

针对在二维平面相控阵天线和椭球天线罩之间增加引向天线会使天线阵列的辐射相位中心由二维扩展到三维,经典的平面相控阵波束控制算法不再适用的问题,基于高增益引向天线阵列,提出一种三维阵列的波束控制算法,在机相扫模式下修正脉间波束指向,提高波束扫描精度,并给出了工程实现的具体流程,最后通过地面测试验证了新算法的性能优势,并通过空中配试靶机验证了新算法的探测性能。

基于压缩感知的低复杂度超分辨角度估计方法

在空域目标角度估计中,分辨率受阵列孔径的限制,依靠增加阵元数量提高分辨率会增加系统成本。为了在受限阵列尺寸中减少阵元数量,基于压缩感知(compressive sensing,CS)理论,提出了一种超分辨角度估计算法。首先建立阵列接收信号模型并构造冗余字典,然后利用目标空间域稀疏先验信息将目标角度估计问题建模为优化问题,最后设计低复杂度算法对优化问题求解。所提算法通过贝叶斯CS理论推导了正则化系数,保证了算法的噪声抑制性能,通过共轭梯度运算及Hadamard乘积提高了算法效率。所提算法可利用较少快拍在信号数目未知的条件下,实现高精度角度估计。仿真结果和实测数据验证了所提算法的有效性。