微型曲面发光二极管阵列照度一致性研究

为提高微型曲面发光二极管(LED)阵列在显示及照明使用方面的舒适度,针对微型曲面LED阵列照度分布的均匀性问题进行研究.采用TracePro光线追迹法分别计算了柱面显示阵列及球面照明阵列的照度分布.计算结果表明,曲面弯曲半径R和光源辐射参数m是影响柱面阵列照度分布的主要因素.通过合理排布阵列像素单元位置,可以增强器件显示均匀度,提高能量利用效率.10×10柱面LED阵列最大平坦化照度均匀度为90.5%.对球面环形阵列照度分布计算结果表明,单环形LED阵列照度均匀性与像素数量无关.影响球面多环LED阵列照度分布的参数主要包括环线分布系数K、环法线与第一环阵列光源法线夹角(?)_0及各环线像素光通量之比φ.以双环LED阵列为模型进行计算,获得最大平坦化照度均匀度为94.8%.调整球面多环阵列位置参数可实现不同照度分布模式.实验对比了微型LED像素单元夹角θ分别为13°,15°和17°时的照度分布,实验结果与理论计算较为一致.本文取得的理论与实验结果可以为微型曲面LED显示及多模式智能照明设计提供参考.     

微带阵列天线的时域散射特性

本文用时域有限差分方法(FDTD)研究了微带阵列天线的时域散射场,分析了入射脉冲极化方向不同以及入射方向不同时的散射场的分布情况;讨论了时域散射场的时域波形以及频谱与微带阵列天线结构的关系;用散射场分离算法讨论了地板对于微带贴片阵列散射场的影响.研究发现,有限大地板的微带阵列天线的散射场主要是由地板的边沿电流产生的,同时微带贴片阵列的谐振频率与入射脉冲的极化方向有关,因此不同的极化方向对应于不同的散射频谱. 关键词： 时域散射 微带天线 FDTD     

脉冲镜反射回波及其表面曲率效应

本文由刚性球目标的回波时域结构与反射面的空间分布之间的关系,研究了刚性目标表面曲率对脉冲镜反射回波波形的影响和棱角反射回波的特性。在高频反射区域,镜反射回波同人射波波形相同;在低频或谐振散射区域,光滑曲率表面的脉冲镜反射回波特征是在主回波后有时间扩展,它是由曲率反射面产生的,称为回波的曲率效应;曲率效应与频率、反射角度有关。棱角是表面曲率的特殊情况,弯曲棱角的传递函数与频率的1／2次方成反比,因此,脉冲反射波形产生畸变,称为回波的棱角效应;直棱角的传递函数与频率无关,反射波形与入射波形相同。     

飞秒激光诱导自组织纳米光栅偏振散射特性研究

实验证实飞秒激光在透明材料内部诱导的周期性纳米条纹具有特殊的光学特性。采用时域有限差分方法(FDTD)分别对单元纳米光栅和纳米光栅阵列的散射特性进行研究,分析结果显示纳米光栅的散射对入射激光的偏振方向敏感;散射强度与入射激光波长相关,波长越长、散射越弱。对于纳米光栅阵列,平行于纳米光栅的散射强度比垂直于纳米光栅的散射强度小两万倍。最后从理论上验证了Ⅱ类波导和纳米光栅偏振导光是由纳米光栅的散射引起的而不是双折射效应。     

Compton散射强光子流在等离子体通道中的传输特性

给出了冷等离子体中高阶相对论下多光下非线性Compton散射的光子流在等离子体通道中的传输方程,研究了高阶相对论效应对散射光子流传输的影响。在近轴近似下,散射强光子流依然有较浅的“势阱”方程。当散射强光子流强度较大时,高阶相对论效应变得更加重要：它减小了散射光束宽的振荡幅度,同时加快了散射光束宽的振荡速度。当散射强光子流功率大于或等于相对论临界功率时,高阶相对论效应避免了散射强光子流强度随传输距离出现无限大的奇异性。给出了散射强光子流的平衡解存在的条件。     

考虑互耦的半波振子线阵辐射和散射方向图综合

对于半波振子阵列天线,可用感应电动势法算得其阻抗矩阵,依据等效电路原理计入单元间的互耦计算辐射场.将其推广至考虑互耦的散射场计算,基于此辐射场和散射场的计算公式,提出一种考虑互耦同时综合半波振子阵列天线辐射和散射方向图的新方法.运用粒子群优化算法,通过优化振子的间距,同时综合指定辐射和散射方向图.运用该方法,通过对中心工作频率处的辐射和散射特性以及在威胁角度给定频带内的散射特性优化,有效降低半波振子阵在中心工作频率处的辐射和散射方向图的副瓣电平,并减小其在威胁角度给定频带内的雷达散射截面.计算结果与FEKO仿真结果吻合良好,验证方法的正确性.     

圆柱坐标系下生物组织中激光传输的七流模拟

提出了圆柱坐标系下生物组织中激光传输的七流模型,根据此模型进行的计算结果与直角坐标系下七流模型的计算结果比较,二者吻合较好.在此基础上,研究了组织光学性质对激光在组织内传输过程的影响,结果表明:散射效应使入射激光分布到更大的组织范围内,并使激光的穿透率降低,但其影响是有限的,即当散射系数增大到一定程度后,组织内的激光能量分布就不再有明显的变化.相对而言,吸收系数对组织内激光能量分布的影响比散射系数要大,各向异性系数增大使组织内的散射趋于前向散射,激光能量分布也更深入组织内部.     

基于宽波束磁电偶极子天线的宽角扫描线性相控阵列

设计并加工了两款基于宽波束磁电偶极子天线单元的宽角扫描线性阵列.首先,通过加载磁偶极子的方法拓展了天线单元的3-dB波束宽度.然后,基于该宽波束天线单元设计了两款具有良好宽角扫描特性的一维阵列天线.实测结果表明,天线单元的E面方向图3-dB波束宽度在9GHz—12 GHz均大于107°,H面方向图3-dB波束宽度在7GHz—12 GHz均大于178°.E面阵列中心单元的有源驻波比在9GHz—13 GHz小于2,相对阻抗带宽为36.36%.H面阵列中心单元的有源驻波比在9.6GHz—12.6 GHz小于2.5,相对阻抗带宽为27.03%.E面阵列在9GHz—12 GHz可实现±70°的有效宽角扫描.H面阵列在9GHz—GHz可实现±90°的有效宽角扫描.与传统的扫描阵列相比,设计的阵列可实现有效宽带宽角扫描,在X波段相控阵雷达方面具有广阔的应用前景.     

利用集总LC元件实现频率选择表面极化分离的特性

基于电磁局域谐振的路谐振理论, 将集总LC器件加载到工字形周期阵列中, 设计了一种新型频率选择表面极化分离结构. 利用等效电路法分析了不同极化时该结构的作用机制, 并采用全波分析法研究了极化方式、入射角度和集总参数对其传输特性的影响.结果表明: 所设计的结构在6.37 GHz附近具有良好的极化分离特性; 在0°–40°扫描范围内, 横电(TE) 和横磁(TM) 极化下结构传输特性均保持稳定; 通过调控集总元件LC值, 该结构在保持 TE极化方向传输特性不变的同时, 可以实现对TM传输特性的独立调节, 使设计更加灵活.该结构为极化分离器以及极化波产生器的设计提供了借鉴. 关键词： 频率选择表面 极化分离器 集总电容 集总电感     

复合振子天线阵列的数值模拟

 用时域有限差分方法模拟了由复合振子天线单元组成的天线阵列的辐射特性;计算了天线从同轴线的馈电效率，给出了天线阵列的辐射场和能量方向图;比较了不同排列方式下阵列的辐射方向图。模拟结果表明：这种天线阵列具有宽带特性和较高的馈电效率，适合于超宽带电磁脉冲的辐射应用。     

Radiation Properties of Carbon Nanotubes Antenna at Terahertz/Infrared Range

The geometric structure and the terahertz/infrared radiation characteristics of carbon nanotubes dipole antenna arrays have been investigated by CST MICROWAVE STUDIO based on finite integral methods. In terahertz and infrared frequency span, the antenna properties such as electrical field distributions, scattering parameters, standing wave ratio, gain, and two dimension directivity patterns are discussed. Our results show that N × N antenna arrays have higher radiation efficiency than single carbon nanotube dipole antenna. This work was supported by National Natural Science Foundation of China (60571026, 10396160).     

Characteristics of the statistical distribution of the current transmitted by a cathode spot of a vacuum arc in variously oriented magnetic fields

The influence of variously oriented uniform magnetic fields on the cathodic attachment of a low-current vacuum arc with electrodes made of oxygen-free copper and CuCr30 composition is studied. It is found that, if the current is fixed, cathode spots in the arc attachment are distributed by the normal law in the entire range of variation of the amplitude of magnetic induction vector B and angle α between this vector and the normal to the cathode surface. The parameters of the distribution depend on the magnetic field and cathode material. The magnetic field dependence is appreciable only when angle α exceeds some critical value α* (α* ≈ 30° and ≈45° for cathodes made of copper and CuCr30, respectively). At α > α*, the parameters of the distribution become strongly dependent on α, while the B dependence remains weak. Only when α → π/2 does the field amplitude have a pronounced effect on the parameters of the distribution. From the obtained results, we determine the statistical characteristics of the distribution of the mean current transmitted by a cathode spot in variously oriented magnetic fields. The found relationships make it possible to explain the peculiarities of the structure of the cathodic attachment of the high-current vacuum arc stabilized by an external axial magnetic field.     

Finite size panoramic optical system integrated design

Aiming at the present situation of the panoramic target detection field, one laser target panoramic optical system on finite size is designed. The laser transmission optical system proposes a partition beam layout method, namely 360° omnidirectional detection can be realized by 6 fan-shaped light beams with 60° × 1° field angle. The receiving system position and size can be determined based on calculation the transformation of the Gaussian beam through the lens. After the computing and optimizing the lens curvature radius and other optical parameters, the integrated design of the transmission and receiving optical system is completed. The system echo signal experiment is carried out, and the experimental results show the error of the actual value and theoretical value is less than 4.8%. The system works stably and the anticipated design effect is achieved.     

强流电子束入射角二维分布测量方法

电子束与靶物质相互作用时的入射角测量是强流电子束热-力学效应研究中的难点问题. 提出了一种新的基于覆盖不同厚度衰减片微型法拉第筒阵列的电子束入射角测量方法, 与现有方法相比, 可获得具有时域特性和位置分布的强流电子束入射角分布. 以此方法进行了入射角二维分布(r, θ)测量实验, 结果表明, 电子束入射角二维分布与束流箍缩情况紧密相关. 如果箍缩不明显, 则电子主要在自身做回旋运动的同时沿着电力线运动, 多以垂直或者小角度(40°以下)轰击到阳极靶面; 如果箍缩明显, 受E×B漂移影响, 电子束入射角度会明显变大, 从40°以下增至60°左右.     

Magnetic scattering of neutrons in magnetic superconductors

The magnetic dipolar interaction responsible for the neutron scattering due to magnetic moments in a crystal is affected by the persistent current in the superconducting state. From this effect, the small angle scattering of neutrons is strongly depressed, and the intensity maximum of the critical scattering appears at a finite scattering wave number even in ferromagnetic superconductors.     

The observation of the localized surface plasmons and its coupling

The surface plasmons properties on gold film composed of inverted square pyramidal pits were investigated. The near‐field scanning optical microscopy image showed that the surface plasmons were mainly located in the cavity of the pits; this is consistent with the mapping image obtained using the Raman scattering intensity of Rhodamine 6G. The calculation results obtained by using the finite element method showed that the electric field mainly located in the pyramidal pits and the field distribution was not affected by the adjacent pits around it. Compared with the single pyramidal pit, the localized electric field intensity increased in the condition of the structure array because of the surface plasmons coupling effect. The surface‐enhanced Raman scattering spectra intensity decreased as the incident angle of the excited laser increased except that there are two peaks at around 5° and 17.5°, which can be attributed to the Bragg scattering of the surface plasmons. The reflectance spectra collected by a microscope at different magnifications were different. The intensity variation between surface‐enhanced Raman scattering spectra obtained using ×20 and ×50 objective illustrated that the adsorption peak in the reflectance spectra corresponded to the surface plasmons coupling effect. Copyright © 2011 John Wiley & Sons, Ltd.     

Koinzidenzexperimente zum Elementarprozeß der Bremsstrahlungserzeugung

By using a coincidence method, the angular distribution of bremsstrahlung has been measured for definite energy loss and definite angle of the outgoing electron. The incident electron energy was 300 keV. With a magnetic spectrometer, outgoing electrons with an energy of 170 keV and scattering angles of 0°, 5° and 10° were selected. The electrons and photons were both detected in scintillation counters. A gold foil of 250 Å thickness served as the target. The experimental results are compared with theoretical calculations.     

非晶Fe89.7P10.3合金纳米线阵列的磁性研究

利用电化学沉积方法在阳极氧化铝模板中制备了Fe_89.7P_10.3非晶 合金纳 米线阵列.利用x射线衍射仪、透射电子显微镜、振动样品磁强计和穆斯堡尔谱仪研究了样品的结构和磁性,发现纳米线阵列是非晶结构，且拥有垂直磁各向异性和高的矫顽力，H_c =304×10⁴A/m.纳米线内部的平均超精细场和平均同质异能移分别为2 15×10⁶ A/m和007 mm/s；而纳米线末端的平均超精细场（233×10⁶ A/m ）大于内 部的值，平均同质异能移（004 mm/s）小于内部的值.另外，纳米线内部Fe原子磁矩与线轴的夹角约为16°，而在纳米线末端Fe原子磁矩与线轴的夹角约为28°.这些结果表明，由于形状各 向异性，在纳米线中实现了无序非晶合金磁矩的有序排列. 关键词： 非晶合金 纳米线阵列 垂直磁各向异性 穆斯堡尔谱     

Electromagnetically induced transparency in novel dual-band metamaterial excited by toroidal dipolar response

We demonstrated a novel metamaterial with dual-band electromagnetically induced transparency(EIT)via simulation,experiment and numerical analysis,with resonance frequencies of the trans-parency peaks of 7.60 and 10.27 GHz.The E-εmetamaterial unit cells were composed of E-shaped and e-shaped patterns.By analyzing the surface current distribution and the magnetic field,we qualitatively verified the toroidal dipole response in the E-εmetamaterial at 10.27 GHz.Meanwhile,by calculating the multipole's radiated power,we found that the two transparency peaks were due to the excitation of the electric and toroidal dipole responses.By changing the incident angle from 0°to 60°,we observed changes in transmission spectra,and the quality factors(Q-factors)of the two transparency peaks increased.In addition,the proposed E-εmetamaterial can be designed to act as a refractive index sensor or other electronic equipment for the control of electromagnetic waves.