同轴型激光器焊后偏移的理论与实验研究

为了研究同轴型激光器激光焊接产生的焊后偏移(PWS),采用基于有限元热-结构耦合理论的分析方法,建立了同轴型激光器3束激光焊接模型,分析了激光焊接工艺参量对焊后偏移的影响规律,并进行了激光锤校正实验研究,获得了同轴型激光器激光焊接前后及校正后的耦合光功率值。结果表明,同轴型激光器的焊后偏移受到3个焊点功率分布和位置分布等因素的影响;耦合光功率在激光锤校正后整体呈上升趋势,最大耦合光功率可恢复至94%,有限元仿真分析对PWS的方向预测合理。这一结果对激光焊接同轴型激光器的生产具有一定的指导意义。     

Ohmic selection in open coaxial resonators: An experimental study

A study of ohmic selective properties of open coaxial cylindrical resonators has been conducted experimentally and compared with theory. The resonator consists of an inner cylinder made of silicon carbide symmetrically located inside an outer cylindrical, tube shaped waveguide. Several fundamental TE modes were identified over the range 9 to 17 GHz through measurements of the resonant frequencies and the associated quality factors. Mode discrimination is achieved both by exploring selective ohmic effects and examining the electrodynamical properties of the coaxial cylindrical waveguide. The effectiveness of a silicon carbide coaxial insert in providing ohmic mode selection is demonstrated in that the totalQ factors of TE _mp modes with radial indexp≥2 become well below the quality factors for surface TE _m1 modes. It has been verified that both structure and number of resonant modes are strongly dependent on the diameter and the resistivity of the coaxial insert.     

Theoretical and experimental study of the forces between different SNOM probes and chemically treated AFM cantilevers

A shear-force mechanism between a chemically etched scanning near-field optical microscope tip and different chemically treated atomic force microscope cantilevers has been experimentally and theoretically investigated as a function of the tip-to-sample distance for different amplitudes of the tip oscillation. The experimental results show, in agreement with the theoretical predictions, that as the tip approaches the cantilever, the electrostatic force is the most influential in the shear-force mechanism, independently of the nature of the tip or the sample. As the tip-to-sample distance decreases, other forces come into play, and the type of interaction depends on the chemical nature of tip and sample surfaces. Thus, for hydrophobic cantilevers, the decrease in the vibration amplitude is mostly due to the solid friction forces resulting from electrostatic interactions. However, if the sample surface is hydrophilic, there is a decrease in the electrostatic force, a water meniscus is formed, and the decrease in the tip amplitude is mostly due to dynamic friction related to capillarity.     

Theoretical and experimental study of radio coverage in tunnels using radiating cables

The purpose of this paper is to study radiowave retransmission in confined areas using leaky coaxial cables. First, the theoretical approach determining the radiation of this type of structure is described. To show the tunnel walls’ impact on electromagnetic field propagation, we give computed results for a cable in free space and in a tunnel. The study is conducted initially in the space domain to evaluate the variation of the electric field versus distance along the cable, and secondly in the time domain to estimate the spread or distortion of a short pulse due to reflection off the walls. Comparisons between theoretical and experimental results are also presented.     

Theoretical simulation and experimental investigation on a WDMsurvivable unidirectional open ring network using tunable channelselecting receivers

In this paper theoretical and experimental investigations on a wavelength-division-multiplexed (WDM) reconfigurable open ring network are reported. The theoretical study is focused on network component characteristics and ring network structure. These aspects will form the basis of numerical modeling. A powerful computer aided design software “COMSIS” is used for the simulation. The simulation takes into account the most important parameters: node structure, link losses, EDFA characteristics, optical powers of the channels, and signal wavelength arrangements. The power of a new channel added at each node and its wavelength with respect to those present before the node are two important parameters in the performance analysis of this open ring network. If the performance criterion is to receive the channels with high signal to noise ratios (SNR) and a narrow spread ΔSNR, the optimal length of this ring network can reach 366 km for 4 nodes and 565 km for 8 nodes. The experimental demonstrator is composed of 4 secondary nodes incorporating tunable channel selecting receivers (TCSR's) and erbium doped fiber amplifiers (EDFA's). The reconfiguration and the protection of the ring is computer controlled. Experimental results of a fully connected testbed demonstrator are also presented     

Broad-band simultaneous measurement of complex permittivity andpermeability using a coaxial discontinuity

A technique for simultaneously measuring the real and imaginary parts of both the permittivity and the permeability of a given material is discussed. A gap in a coaxial line is filled with the material under test. Complex permittivity and permeability are computed from the S-parameter (S₁₁ and S₂₁) measurement made on the gap, taking into account higher-order modes excited at the discontinuity. Measured ϵ_r and μ_r data for several materials are presented from 45 MHz up to 18 GHz. This technique shows good agreement between calculated and generally accepted values     

Theoretical and experimental study of nematic liquid crystaldisplay cells using the in-plane-switching mode

In this paper a two-dimensional (2-D) dynamic model, based on a tensor formulation and solved numerically by combining finite elements and finite differences, is proposed and used for analyzing nematic liquid crystal (LC) test cells with interdigital electrodes. We compare theoretical and experimental results concerning the switching behavior, response mechanism, and viewing angle characteristics of nematic LC pixel structures which use the in-plane-switching (IPS) mode. The good agreement observed between theory and experiment in terms of electro-optical properties validates our modeling and demonstrates its potential for design optimization. We show that the proposed LC test cells, using the in-plane-switching mode, ensure switching-ON and -OFF response times of 22 and 28 ms, respectively, and excellent viewing angle characteristics     

Theoretical and experimental study of transverse-horizontal convolver

The letter presents the results of theoretical and experimental studies for the transverse-horizontal convolver (THC) fabricated on LiNbO3. First, the definition of the figure of merit for the THC is proposed and, secondly, the existence of the crystal orientation and the direction of propagation with high efficiency and large electromechanical coupling coefficient for an LiNbO3 SAW THC is shown.     

填充多层介质的共焦椭圆同轴线传播特性

采用在椭圆柱坐标系中分离变量的方法,得到了填充多层介质共焦椭圆同轴线模式特征方程.研究表明:当椭圆退化为圆时,利用角向和径向马修函数的渐进关系,可得到填充多层介质的圆形同轴线的模式特征方程,由此可见,圆形同轴线可看作椭圆形同轴线的特例;当椭圆同轴线内导体半长轴大小为零时,则椭圆同轴线就变成椭圆波导,同样的方法,可得到填充多层介质的椭圆波导模式特征方程.当填充一层介质时,得到了椭圆同轴线和椭圆波导的模式特征方程,结果和相关文献所得结果相同.作为示例,对填充一层介质和两层介质的椭圆同轴线中一些模式色散特性进行了数值计算,分析了椭圆同轴线中介质参数的变化以及椭圆同轴结构的变化等对其传播特性的影响.     

点阵光栅全息图的研究

作者根据衍射光栅的原理讨论了点阵光栅全息图的产生和重现衍射效率,重现色彩以及视觉效果。根据理论结果,作者装备了一套简化的,能制作出丰富色彩的点阵光栅全息图的实验系统。为了增强点阵光栅全息图的闪耀效果和获得奇妙的动态视觉效果,作者在实验中采用了两项特有的单元技术,即光斑整形和像元移位。     

Theoretical and experimental study of beveled thyristor structures

The design of power semiconductor devices requires a theoretical and technological understanding of the problems associated with surface conditions. A reduction of the breakdown voltage occurs if sufficient attention is not devoted to the surface during the fabrication of these devices. It is possible to realize nearly true bulk breakdown voltages with positively beveled P-N junctions by proper selection of the bevel angle, the permittivity of the passivation dielectric and by control of the charges at the dielectric-silicon interface. The analysis has been performed with a two-dimensional computer program model for P? junctions protected by a bevel. Poisson's equation is solved by an optimized successive overrelaxation method. The theoretical results are verified by means of a local carrier injection method using a laser beam, in order to measure the width of the surface depletion region.     

激光熔覆孔式同轴送粉系统设计及实验研究

为了解决送粉激光熔覆系统中因重力作用发生偏聚及水冷效果差等问题,采用以激光束轴心为中心轴圆周均匀分布送粉孔的方法,没计了一系列孔式同轴送粉喷嘴(主要结构包括激光束通道、保护气体通道、水冷通道、气载送粉通道),从而获得良好的粉末流形态,提高送粉激光熔覆的质量。用该系列喷嘴在竖直(90),60,30和水平(0)等工况下进行粉末汇集性实验,发现粉末汇集效果良好。通过对Ti和Ni粉末、工具钢和等材料进行熔覆实验,送粉系统输送的粉末稳定、均匀,得到的熔覆样品表面光滑、熔覆层组织均匀,熔覆层与基体呈冶金结合。结果表明,孔式同轴送粉系统较好地满足了激光熔覆对送粉喷嘴的要求,并且能用来进行多种元素粉末的材料合成。所开发的送粉系统适用于材料表面改性和熔覆3维制造。     

表面特性光学实时检测的理论和实验研究

针对精密磨削加工中冷却液的使用使得工件表面的光学实时检测非常困难这一问题,提出了一种在冷却液环境下借助特制"透明窗"装置的光学方法。此方法使被测表面上方出现附加层,分别对附加层中的液体处于静止和流动状态时的情况进行了理论分析和实验研究。对于静态液体,利用修改的B-K(Beckmann-Kirch-hoff)散射模型,从采集到的散射光强分布图中提取出一比值参数,通过参数拟合得到表面粗糙度和比值参数间的关系曲线。对于动态液体,分析光束在流体层中的传播特性,计算通过流动液体层的光束偏移量。结果表明:静态液体时,垂直于散射光带主方向的比值参数能够用来衡量表面轮廓算术平均偏差粗糙度,它们之间可以用explinear函数拟合;动态液体时,通过流体层的光束偏移量非常小,只有0.494×10-5μm。可见,液体的流动对于光学实时检测的影响非常小,液体处于静止状态时的测量结果可以作为表面特性实时检测的最终结果。     

CAD of efficient TMmn0 single-mode elliptical applicators with coaxial excitation.

This paper suggests computational and engineering approaches to designing single-mode elliptical applicators for thermal processing of cylindrical samples of relatively small diameters. Through a systematic computational experimentation employing a 3D conformal FDTD model, we show that stable and efficient excitation of even and odd TMo modes of elliptical waveguides can be achieved by appropriate placing of two (one active and one passive) coaxial probes extended in the longitudinal direction of the cavity of relatively small height and by choosing the dimensions of the cavity. Effects produced by cylindrical loads inserted in the electric field maxima of the applicators featuring even TM010, TM110, and TM210 modes are studied for materials with different dielectric constants and the loss factors. It is shown that with the proposed excitation supported by simulation of energy coupling and dissipated power the elliptical structure is capable of operating any of these modes in a single-mode regime and generating satisfactory uniformity of the dissipated power within the cylindrical samples.     

Theoretical and experimental study of modified coupled strip coupler

A numerically efficient full-wave analysis of a modified coupled microstrip structure useful for the design of high directivity coupler sections is reported. The effect of the dispersion on the performance of the coupler is considered. An automatic design procedure has been implemented and experimental results are included.<>     

半导体抽运的叠片热容激光器理论和实验研究

报道了半导体抽运的Nd:YAG叠片热容激光器的理论与实验研究,并用热容激光器的理论模型计算了在一定的工作时间和介质温升内激光输出特性,用Zemax软件对其抽运结构进行了模拟计算。实验中采用的4片Nd:YAG晶体尺寸均为63.5 mm×38.5 mm×7 mm,抽运平均功率约110 W,重复频率为10 Hz,占空比为0.2％,获得了最大19.1 W的1 064 nm激光输出,光光效率约17.4％。最后对两种抽运结构的叠片激光器进行了比较,提出了下一步的改进方案。     

Theoretical and experimental study of the dynamics ofpolarization-mode dispersion

The dynamic distribution of the state of polarization (SOP) is studied theoretically and experimentally for aerial fibers with a finite polarization-mode dispersion (PMD). A dynamic mode coupling wave-plate model is proposed to describe the SOP correlation and account for the PMD variations. It is found that the model can closely describe the experimental dynamic correlation of the SOP for an aerial fiber. A new algorithm for PMD emulation is developed     

Theoretical and experimental study of monopole phased array antennas

A theoretical and experimental investigation of the mutual coupling in large two-dimensional periodic planar phased arrays of thin cylindrical monopoles is addressed. A plane wave representation of the active input impedance is used to analyze an infinite array of monopoles. A finite array analysis is used to compute the center element gain pattern and input impedance as a function of the array size and element position. The center element gain pattern is shown to have omnidirectional vertical polarization with a null on-axis and peak gain in the vicinity of50degfrom broadside. Measurements of the element gain pattern and mutual coupling for a 121-element passively terminated monopole square lattice array are shown to be in good agreement with the theory. The results of the infinite array analysis are compared to theoretical and experimental data in the literature for hexagonal lattice arrays.     

基于VCSELs外光反馈干涉的微小振动测量研究

利用垂直腔面发射激光器(VCSELs)的外光反馈干涉技术推出微小振动测量数学模型,由此提出一种基于外腔VCSELs的微小振动测量系统,并对正弦波形式的微小振动进行了仿真测量.结果表明,该模型的测量误差比传统微小振动测量方法的误差下降了1～2个数量级;进一步得出,合理选取外光反馈强度可使误差达到最低且能直接判断待测物体的振动方向.