激光尘埃粒子计数器信号幅度概率密度函数

为了研究激光尘埃粒子计数器计数信号幅度概率分布,对激光尘埃粒子计数器计数信号幅度概率分布与传感器光敏区光强分布、采样气流中的粒子数密度、气体层流速度分布之间的关系进行了理论分析。采用自行设计的带保护气套的光电传感器测定粒子计数信号幅度概率分布,给出的分布模型与理论分析相吻合。结果表明,尘埃粒子计数器计数信号幅度概率分布由传感器光敏区光强分布和粒子数密度空间分布共同决定,这为尘埃粒子计数器的设计提供了理论依据。     

液体粒子计数器测量原理及校准方法

液体粒子计数器广泛的应用于高纯水,高纯化学溶液中对不溶性微粒子进行测量,本文介绍了两类液体粒子计数器（光障碍式液体粒子计数器和光散射式粒子计数器）的测量原理和校准方法,为用户正确选择和使用仪器提供依据。     

净化室内单个亚微米悬浮粒子的实时测量

本文介绍五种类型的亚微米悬浮粒子测量仪器的工作原理:(1)光学粒子计数器(OPC),其中包括激光光谱仪;(2)气动粒子分选机;(3)粒子电迁移率分析仪;(4)扩散电解槽;(5)冷凝核子计数器。光学粒子计数器主要用来测量0.5～5.0μm尺寸的粒子,是半导体厂内净化室最常用的粒子监测设备,气动离子分选机测量的粒子的尺寸与前一种仪器相同,但它是迄今尚未广泛使用的一种较新的设备,能直接测量与净化室类似的连续流动系统内的气动粒子,对直径最大的粒子最适用。电迁移率分析仪和扩散电解槽均为尺寸分选设备,当在冷凝核子计数器上游使用时,它们能够测量0.02～0.2范围内的悬浮粒子的分布状况。不过,对静止状态下净化室内的典型粒子浓度的统计性计数测量不够精确。     

基于匹配滤波的激光尘埃粒子计数器信号处理方法研究

为提升激光尘埃粒子计数器的计数准确率，基于匹配滤波器设计粒子计数器信号预处理方法。分析粒子信号的特征，通过归一化后累加的方法获得粒子的典型波形。以该典型信号作为匹配模板，将激光粒子尘埃计数的原始信号与匹配模板进行离散卷积操作，得到高信噪比的输出信号。试验结果表明，针对原始幅值在55～262 mV、噪声均方根值约为6.74 mV的粒子信号，经该匹配滤波方法后，信噪改善比均优于1.56。该方法对比数字滤波器方案，能更有效提升输出信号信噪比，为粒子的准确检测和识别提供良好基础。     

稀释器采用流量比标定方法的不确定度分析

分析了稀释器的不同标定方法和由其产生的稀释比偏差,得出采用流量比标定稀释器的方法较好,同时建议采用粒子计数器计算稀释器上下游的粒子浓度比,以评估标定稀释器时两种稀释比测量结果的允许误差。     

脉冲激光测距中时间间隔测量的新方法

提出脉冲激光测距中时间间隔测量的新方法。传统数字法的测时误差主要是开始和结束2个脉冲周期的计数误差，为此利用FPGA芯片中集成锁相环（PLL）单元产生N路同频且相位均匀分布的时钟脉冲，用N个计数器在这2个周期进行计数，用计数结果均值作为最终结果。这相当于将脉冲周期T细分为N等份，每份相当于1个脉冲，其周期为T／N。实现了在不增加测量时间和盲区的前提下，测量精度提高了N倍，解决了传统脉冲激光测距系统中提高精度、缩短测量时间和盲区的矛盾。     

不同光源对激光尘埃粒子计数器性能的影响

使用Beam Profile2350 光束诊断仪测量了氦氖激光和半导体激光两种典型光源的光束特性,并分析了将它们作为激光尘埃粒子计数器的光源时,其在光敏区所产生光场的不均匀性。同时讨论了光场不均匀对计数器性能的影响,计算了两种不同光源下,计数器计数效率和分辨比率的差异。结果表明,以半导体激光作为计数器光源时,光敏区的光强均匀性更好,计数效率更高,粒径的分辨比率较氦氖激光作用时提高了17 % ,增大了粒径的有效测量范围。     

凝聚核粒子计数器(CNC)

当今技术还不能提供灵敏度高于0.05微米的光学粒子计数器,因为低于此值时,光分子的散射会大于干扰粒子测量。对于此种超细微粒的测量必须采用凝聚核粒子计数器(CNC)。凝聚核粒子计数器的测量原理是利用在超细微粒子周围产生凝聚作用,从而使被测微粒子粒径扩大,以便于采集测量。美国MetOne出产的凝聚核粒子计数器专门用来测量超细微粒,对超纯气体的测量灵敏度可高达0.005微米,远远高于普通光学粒子计数器。全部MetOneCNC-1100系列的计数器除了可用来采样洁净室内的空气,还可采样氮气和惰性气体,如:氩气、氦气。其中CNC-1107型的计数器…     

不同光源对激光尘埃粒子计数器性能的影响

使用Beam Profile2350光束诊断仪测量了氦氖激光和半导体激光两种典型光源的光束特性,并分析了将它们作为激光尘埃粒子计数器的光源时,其在光敏区所产生光场的不均匀性。同时讨论了光场不均匀对计数器性能的影响,计算了两种不同光源下,计数器计数效率和分辨比率的差异。结果表明,以半导体激光作为计数器光源时,光敏区的光强均匀性更好,计数效率更高,粒径的分辨比率较氦氖激光作用时提高了17％,增大了粒径的有效测量范围。     

并行计数法脉冲激光测距的研究

提出脉冲激光测距中利用并行计数法测量时间间隔。传统数字法测时误差主要是开始和结束两个脉冲周期的计数误差。为此利用CPLD高速缓冲的延迟特性产生多路同频且相位均匀分布的时钟脉冲,用多个计数器在这两个周期并行计数,用计数结果均值作为最终结果。相当于将脉冲周期T细分为多份,每份相当于1个脉冲。实现了在不增加测量时间和盲区的前提下,提高测量精度;解决了传统脉冲激光测距系统中提高精度与缩短测量时间和盲区的矛盾。     

扩束型光纤连接器损耗机理研究

介绍了扩束型光纤连接器的基本原理,定量分析了它的损耗机理,即包括可变损耗和固定损耗。可变损耗主要是由于系统各单元之间的对准误差引起的,包括径向偏移损耗、纵向偏移损耗以及轴向倾角损耗,其中影响最大的是径向偏移损耗;其次是轴向倾角损耗、固定损耗、纵向偏移损耗。固定损耗是由系统自身所用材料、表面处理决定的,包括菲涅耳损耗、球差损耗、衍射损耗、色散损耗、吸收损耗等。给出了降低损耗的有效方法。     

Effect of wire vibration on the materials loss in sapphire slicing with the fixed diamond wire

Sawn kerf, wafer profile error and wafer subsurface damage were systematically measured and were used to evaluate the materials loss for the sapphire slicing with the fixed diamond wire. The vibration of saw wire was also measured during the slicing process. The impact of each part on the materials loss was discussed. The effect of the wire vibration on the materials loss was explored. It was found that the sawn kerf loss and the wafer profile error loss were the main forms of the materials loss during the slicing process. Wire vibration has significant influence on sliced wafer morphology. Influence of slice parameters on the kerf loss is similar with the case on the vibration amplitude, which indicates that the wire vibration is the key factor to cause the kerf loss. Wire slicing model with the wire vibration is established to understand the influence of wire vibration on the materials loss.     

Longley-Rice等效散射模型的建立

研究了Longley-Rice电波传播模型以及各参数的实际意义,指出了Longley-Rice模型没有考虑接收机附近的因素对传播损耗的影响,因此会导致接收机附近的电波传播损耗的计算误差。对Longley-Rice模型做了改进,建立了等效散射模型,描述了接收机附近的损耗情况。改进的模型能够减小计算误差,在一定程度上提高预测的精度。     

A Combined Techniques of PC + MPC + APC to Achieve Higher Error Correction Probability and Throughput over APC and MPC Techniques

A new combined technique of Packet Combining (PC), Modified Packet Combining (MPC) and Aggressive Packet Combining (APC) is presented for improving the performance of MPC and APC. The proposed protocol consists of three blocks; PC block, MPC block, and APC block. Two copies of the same packet are sent from transmitter to receiver (Rx). If both the copies are found as erroneous then PC technique is used to correct the original copy in the PC block and if it is not obtained a successful copy then the Rx requests for a third copy. Again, if the third copy is found as erroneous then MPC and APC techniques are implemented in the MPC and APC blocks respectively. In order to get fast error correction and also to utilize the half-corrected or resultant copies instead of discarding the received erroneous copies, MPC block uses the resultant copies of the PC block and APC block also uses the resultant copies of MPC block. Thus, the proposed protocol is simulated using MATLAB and the simulation results obtain better performance by adopting the evaluation metrics of the probability of packet error correction, packet throughput and energy consumption over conventional MPC and APC techniques.

     

Excess Loss of the Coupling System to Double-Function Optical Circulators Utilizing Lens Twice and Two-Fiber Tips

1 Introduction An optical circulatoris useful in advanced optical fibercommunication systems such as full duplex transmissionsystems[1 ~10]. With the development of fiber opticalcommunication,there is anincreasing demand for opti-cal circulators that are suitable for use with fiber opticsystems .Incomplexfiber optic systems ,there may be amultiplicity of fibers ,each requiring a si milar function.A conventional optical circulator cannot provide suchfunctions[11]. In addition,the circulator re…     

影响波束合成信噪比若干因素的研究

针对实际工作中波束合成性能下降的问题,推导了理想情况下数字波束合成信噪比相对输入信噪比的增益,研究了通道失效、幅度加权和幅相误差分别对波束合成信噪比的影响,并推导了信噪比损失的解析式。理论分析和仿真结果表明:在失效通道比例小于30%的条件下,信噪比损失与失效通道比例近似成线性关系;在同时存在通道失效、幅度加权和幅相误差的条件下,信噪比损失近似等于通道失效、幅度加权和幅相误差各自引入的信噪比损失之和。     

光纤带光纤接头损耗的探讨

阐述了传输波长对光纤接头损耗的影响以及光纤带光纤接头存在芯轴横向错位时模场直径对接头损耗的影响,引入了模场重叠率概念.探讨了纤芯与包层同心度误差、光纤带翘曲度对光纤带光纤接头损耗的影响.     

Open-loop power control error in a land mobile satellite system

In order to combat large scale shadowing and distance losses in a land mobile satellite system, an adaptive power control (APC) scheme is essential. Such a scheme, implemented on the uplink ensures that all users' signals arrive at the base station with equal average power as they move within the satellite spot beam-an important requirement in a CDMA system. Because of the lengthy round-trip delay on a satellite link, closed-loop power control systems are only of marginal benefit. Therefore, an open-loop APC scheme is proposed to counteract the effects of shadowing and distance loss. A fairly general channel model, consisting of log-normal shadowing and Rician fading, is assumed. This can be applied to a specific two-state land mobile satellite channel model, involving shadowed intervals with Rayleigh fading and unshadowed intervals with Rician fading. It is found that the power control error can be approximated by a log-normally distributed random variable. To quantify the performance of the APC, the standard deviation of the power control error in decibels is analyzed as a function of the specular power-to-scatter power ratio, the measurement time and the vehicle velocity. To illustrate the usefulness of the results, we analyze the effect of the power control error on the system capacity of a CDMA mobile satellite link     

天线卓介质损耗的精确测量

提出了一种测量天线罩介质损耗的方法,对其工作原理、测试程序及测量误差作了论述和分析。本方法适用于高性能天线罩介质损耗的精确测量,可以为天线罩的研制提供有效的判据。应用本方法对某夹层型雷达天线罩的材料和制作工艺进行了优化,实验结果良好。     

无线视频错误控制技术研究

无线视频传输中误码和丢包会导致视频质量的严重下降,研究了视频传输中的错误控制相关技术。对已有的无线视频错误控制方法进行了详细分析,在此基础上提出了一种更加有效的无线视频传输中的错误控制框架。将无线误码丢包和拥塞丢包准确区分,改进了以往算法带宽估计公式不准确的问题。并且对视频内容根据在解码端重要性的不同区分保护。在错误控制的同时进行了拥塞控制。