共查询到20条相似文献,搜索用时 78 毫秒
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多层球对高斯波束的散射 总被引:6,自引:0,他引:6
本文根据广义米氏理论,将入射高斯波束用矢量球谐函数展开,研究多层介质球的电磁(光)散射,提出波束因子gn的改进算法以及散射系数an和bn的迭代公式和算法,并进行了数值计算与讨论。 相似文献
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基于高斯波束波形因子的局域近似解和电磁场的球矢量波函数展开方法,研究了离轴高斯波束入射均匀各向异性磁化等离子体球的电磁散射特性.数值计算了波束参数和粒子参数对雷达散射截面(RCS)随散射角分布的影响.分析了改变波束束腰半径和粒子偏离波束轴距离时,RCS的分布特点.结果表明:前向散射截面与束腰半径的变化成正比关系;束腰半径的变化对RCS随散射角分布有很大影响;球粒子偏离波束轴距离的大小影响RCS极值的位置和角分布特点. 相似文献
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激光大气散射离轴探测分析 总被引:1,自引:1,他引:1
利用Mie散射理论,通过数值计算得到了1.06 μm激光在低空大气中传输时的散射特性;不同尺度参数的粒子的散射光强分布相差极大,随着尺度参数的增加,散射光强越来越集中于前向;复折射率的变化对散射光强影响不大.通过对大气散射的辐照度理论分析和数值计算,得到大气散射的辐照度随离轴距离的增大而近似按反比规律下降的特征;同时,对不同能见度下的散射辐照度进行了数值计算,能见度的不同只影响散射强度的大小,而不影响散射强度的分布.不同散射点的散射光到达探测器所需的时间不同,延迟时间与离轴垂直距离和探测角呈简单的线性关系,这些特征为激光散射离轴探测提供了理论依据和参考. 相似文献
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为了探究z轴单层行程z与单层熔覆层高度的匹配对激光熔覆成形的影响,采用了在不同的z轴单层行程z的情况下进行激光熔覆成形试验的方法,通过理论分析和实验验证,得到了不同z轴单层行程z与单层熔覆层高度以及离焦量的关系曲线。结果表明,z轴单层行程z存在一个以第2层熔覆层高度为基准的最佳的取值范围,在此范围内,熔覆过程能够通过自身存在的反馈调节达到z轴单层行程z与单层熔覆层高度相等的稳定成形状态。该研究给出z轴单层行程z选取时的推荐值为0.5d2 z 0.6d2。 相似文献
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贝塞尔波束自产生以来,凭借其无衍射、自修复特性已经获得了越来越多学者的关注。基于广义洛伦兹米理论, 将在轴贝塞尔波束与手征介质球相互作用的入射场及散射场展开为球矢量波函数的表达式。结合球矢量波函数的正交完备性及电磁场的连续性边界条件,推导出了在轴零阶贝塞尔波束对手征介质球电磁散射的解析解。数值模拟了散射强度随散射角的分布,将在轴贝塞尔波束退化为平面波照射手征介质球的散射结果与文献比较,吻合得较好。分析了波束及介质球参数、介质球偏离波束中心位置对散射强度的影响。该理论为手征材料和手征涂覆目标在微波工程及目标隐身中的应用提供了很好的理论应用价值。 相似文献
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激光粒度测量中大角散射产生误差分析及修正 总被引:3,自引:0,他引:3
大多数散射式激光粒度仪采用样品池后置式的光路结构,依据傅里叶光学原理确定同心圆环光电探测器上每一圆环接收的散射光角范围,分析了在大角散射的情况下,这种确定散射光角范围的方法产生误差的原因、误差的大小及对粒度分析的影响。给出了正确计算散射光角范围的公式。 相似文献
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目标红外偏振特性的影响因素研究 总被引:2,自引:0,他引:2
红外偏振是近年来发展起来的一种新技术,对增强目标与背景的对比度、识别伪装目标效果明显.本文设计了一套红外偏振成像系统,并制作不同粗糙度、不同材料的样板,在不同的观测角进行偏振成像实验,研究粗糙度、材料和观测角对目标偏振特性的影响.实验结果表明,表面越光滑,目标偏振特性越明显;不同材料的目标,偏振度不同;随观测角度增加,偏振特性也越来越明显.研究初步表明,粗糙度、观测角和目标材料是决定目标偏振特性观测结果的重要因素,目标偏振特性影响因素的研究对偏振探测技术的应用具有一定的指导意义. 相似文献
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This paper investigates the feasibility of using a lanthanum oxide thin film (La_2O_3) with a high dielectric constant as a gate dielectric on GaAs pHEMTs to reduce gate leakage current and improve the gate to drain breakdown voltage relative to the conventional GaAs pHEMT. An E/D mode pHEMT in a single chip was realized by selecting the appropriate La_2O_3 thickness. The thin La_2O_3 film was characterized: its chemical composition and crystalline structure were determined by X-ray photoelectron spectroscopy and X-ray diffraction, respectively.La_2O_3 exhibited good thermal stability after post-deposition annealing at 200, 400 and 600 ℃ because of its high binding-energy (835.6 eV). Experimental results clearly demonstrated that the La_2O_3 thin film was thermally stable.The DC and RF characteristics of Pt/La_2O_3/Ti/Au gate and conventional Pt/Ti/Au gate pHEMTs were examined.The measurements indicated that the transistor with the Pt/La_2O_3/Ti/Au gate had a higher breakdown voltage and lower gate leakage current. Accordingly, the La_2O_3 thin film is a potential high-k material for use as a gate dielectric to improve electrical performance and the thermal effect in high-power applications. 相似文献
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This paper investigates the feasibility of using a lanthanum oxide thin film (La2O3) with a high dielectric constant as a gate dielectric on GaAs pHEMTs to reduce gate leakage current and improve the gate to drain breakdown voltage relative to the conventional GaAs pHEMT. An E/D mode pHEMT in a single chip was realized by selecting the appropriate La2O3 thickness. The thin La2O3 film was characterized: its chemical composition and crystalline structure were determined by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. La2O3 exhibited good thermal stability after post-deposition annealing at 200, 400 and 600℃ because of its high binding-energy (835.6 eV). Experimental results clearly demonstrated that the La2O3 thin film was thermally stable. The DC and RF characteristics of Pt/La2O3/Ti/Au gate and conventional Pt/Ti/Au gate pHEMTs were examined. The measurements indicated that the transistor with the Pt/La2O3/Ti/Au gate had a higher breakdown voltage and lower gate leakage current. Accordingly, the La2O3 thin film is a potential high-k material for use as a gate dielectric to improve electrical performance and the thermal effect in high-power applications. 相似文献
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激光引信易受到气溶胶的干扰,造成引信的虚警,对激光抗气溶胶干扰的研究一直是亟待解决的难题。大气环境中气溶胶的组分是多样的,因此研究不同材质气溶胶的激光回波具有重要意义,而烟雾和云雾是不同材质气溶胶的典型代表。本文基于Mie散射理论和蒙特卡罗随机逻辑方法,分别建立了激光烟雾、云雾单次和多次散射模型,对比分析了不同脉冲宽度10 ns、20 ns和50 ns的光束、不同材质气溶胶烟雾和云雾、不同散射次数的回波特性,得到了不同脉冲宽度激光在不同材质气溶胶下的散射回波规律。仿真结果表明:激光发射脉冲宽度越小和气溶胶能见度越大,目标回波和气溶胶回波的区分效果越好;激光在云雾中的透过率高于烟雾,反射率低于烟雾;激光在烟雾中的衰减度高于云雾。该结论可为研究激光引信在气溶胶环境下后向散射回波特性和提高抗干扰能力提供了研究思路。 相似文献
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激光熔覆与堆焊层成分稀释度的对比研究 总被引:1,自引:0,他引:1
测定了用激光熔覆,等离子堆(喷)焊,火焰堆焊三种方式在1Cr18Ni9Ti基体上熔焊钴合金强化层时,其熔层基体成分稀释的稀释率。结果表明:激光熔层的稀释率最小。在保证与基体良好冶金结合的条件下,激光熔层还具有组织细密、晶粒高度的特点,其熔层硬度、抗蚀、抗磨抗磨性能均大大高于等离子喷焊和火焰堆焊层。 相似文献
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V. G. Kostishin R. M. Vergazov V. G. Andreev S. B. Bibikov A. T. Morchenko I. I. Kaneva V. R. Maiorov 《Russian Microelectronics》2012,41(8):469-473
The article discusses the results of efficiency improvement of wide-range nickel-zinc ferrites by increasing the role of the dielectric subsystem in the formation of radio-wave absorbing properties of material due to the action of technological factors. The influence of doping additives and gas conditions of furnace atmosphere within sintering on absorption of electromagnetic waves has been studied. The efficiency of sintering of nickel-zinc ferrites in the atmosphere with adjustable partial oxygen pressure aimed at increasing the dielectric permeability of material has been confirmed. A model is proposed, which explains the increase in losses within the sintering of ferrites in a reducing atmosphere. 相似文献
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