瞬态电磁场对多孔洞目标耦合规律的数值研究

 运用时域有限差分（FDTD）方法,用数值方法研究了瞬态电磁场对开有多个孔洞的长方体的耦合规律。分别分析了不同极化方向、不同入射方向及不同带宽的瞬态电磁场的耦合效应。入射波极化方向与孔洞的短边平行时耦合入腔体的能量最多;相同振幅、不同上升前沿和带宽的入射波以窄带、快前沿耦合入的能量为多;多孔洞腔体内场衰减很快。     

各向异性有耗介质板介电系数和电导率的反演

简述了各向异性介质FDTD方法，并用FDTD方法分析了三维各向异性有耗介质板的瞬态后向散射.根据各向异性介质板后向散射与入射电磁波极化方向有关的特点，利用其后向RCS的谐振特性和后向散射场的时域波形特点反演有耗介质板的横向介电系数和电导率.数值模拟结果表明本反演方法可行，且方便、快捷. 关键词： 各向异性板 FDTD方法 有耗介质 谐振 反演     

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。     

层状介质时域有限差分方法斜入射平面波引入新方式

应用二维时域有限差分方法分析层状介质中的目标散射时,在总场-散射场边界斜入射平面波源用常规方法难以引入,因为在总场-散射场边界处设置的入射波实际上包含了入射脉冲以及各分层界面的反射和多次反射.为解决这个问题,提出了斜入射平面波的混合引入方式,即对总场-散射场的四个边界面采取不同的处理方式.对于总场-散射场的纵向侧边界,用含有斜入射角度的修正一维时域有限差分方法,只要在自由空间位置加入入射脉冲就会自行产生由各分层界面形成的反射波,包括多次反射.同时,把纵向总场-散射场侧边界向下延伸,使得总场-散射场下边界位于完全匹配层内,这样透射波和散射波均为外向行波而被吸收.对于总场-散射场的上边界,由于完全位于自由空间中,边界上各点的入射波将是总场-散射场纵向边界角点处入射波的带有时间延迟的复制.数值模拟结果表明了本文所提出方法的正确性和有效性. 关键词： 时域有限差分 层状介质 斜入射平面波 修正一维麦克斯韦方程     

垂直极化平行板有界波电磁脉冲模拟器辐射近场的快速估算方法

为快速估算出垂直极化平行板有界波电磁脉冲(EMP)模拟器的时域近场,将散射传递函数法应用于该类型模拟器近场的时域计算中,即对于给定的脉冲源,先寻找有效频谱范围能覆盖该源的高斯脉冲源,并应用时域有限差分(FDTD)方法计算该高斯脉冲源激励时模拟器中测试点场的时域响应,再利用傅里叶变换、系统的传递函数及傅里叶逆变换计算得到给定脉冲源激励时各测试点场的瞬态响应。所得计算结果与直接使用给定脉冲源激励时FDTD方法的计算结果符合较好。所述方法可用于同一模拟器在不同脉冲源激励时辐射近场的快速估算,能大大减少FDTD模拟计算的次数,尤其对于中大型模拟器能有效减少计算时间和内存。     

V型纳米金球阵列天线侧向散射方向性的数值模拟

纳米天线侧向散射的方向性在生物感测以及表面增强光谱学等领域都有重要研究价值。侧向散射方向性的产生需要破坏纳米天线相对于平面波极化方向的镜像对称,由纳米粒子阵列构成的纳米天线排列灵活,易于实现非镜像对称结构。采用T-matrix方法对V型纳米金球阵列天线进行数值模拟,研究了其侧向散射的方向性,分别讨论了不同阵元数目构成的不同臂长、不同臂间开角、不同球形阵元半径、不同阵元球心间距对V型天线侧向散射方向性的影响。研究表明V型纳米阵列天线具有侧向散射方向性的可调性。     

微波脉冲与圆柱腔体耦合的时域有限差分模拟

给出了微波脉冲与腔体上孔洞线性耦合的物理模型,讨论了数值模拟的时域有限差分方法以及吸收边界条件,计算了不同大小和位置孔洞的耦合过程,分析了耦合对孔洞大小和入射场偏振方向的依赖关系.     

微波脉冲与孔阵矩形腔体耦合的数值模拟研究

利用时域有限差分(FDTD)方法对微波脉冲与孔阵矩形腔体的耦合过程进行了数值模拟研究. 当孔缝阵中的孔缝长边垂直于入射电场方向时, 详细分析了微波脉冲与孔缝阵矩形腔体的耦合过程中孔阵面上各个孔缝中心点的电场分布情况. 结果表明, 在平行于入射电场方向上排列的孔缝中, 处在中心的孔缝场增强效应最弱, 孔缝场增强效应由中心向两侧依次对称的增强; 在垂直于入射电场方向上排列的孔缝中, 处在中心的孔缝场增强效应最强, 孔缝场增强效应由中心向两边依次对称的减弱. 同时, 讨论了孔缝孔阵中孔缝个数、间隔等因素对各孔缝中心点的场增强效应和腔体内的耦合场分布的影响.     

微波脉冲与孔阵矩形腔体耦合的数值模拟研究

利用时域有限差分(FDTD)方法对微波脉冲与孔阵矩形腔体的耦合过程进行了数值模拟研究.当孔缝阵中的孔缝长边垂直于入射电场方向时,详细分析了微波脉冲与孔缝阵矩形腔体的耦合过程中孔阵面上各个孔缝中心点的电场分布情况.结果表明,在平行于入射电场方向上排列的孔缝中,处在中心的孔缝场增强效应最弱,孔缝场增强效应由中心向两侧依次对称的增强;在垂直于入射电场方向上排列的孔缝中,处在中心的孔缝场增强效应最强,孔缝场增强效应由中心向两边依次对称的减弱.同时,讨论了孔缝孔阵中孔缝个数、间隔等因素对各孔缝中心点的场增强效应和腔体内的耦合场分布的影响.     

电磁脉冲斜入射时对孔缝耦合效应的数值分析

 利用时域有限差分法（FDTD）研究了电磁脉冲对不同孔洞的耦合规律。分别分析了电磁脉冲对正方形、长方形和多孔洞的耦合效应，讨论了不同极化方向的电磁脉冲对孔洞的耦合能量的规律。研究表明：电磁脉冲对正方形孔洞的耦合能量较小；而对长方形，当脉冲极化方向与长方形短边平行时，耦合能量最大；在孔洞面积相同的条件下，对多孔洞的能量耦合要比单孔洞小。     

X波段4单元微带天线阵辐照响应

采用时域有限差分法,并结合导体边缘奇异性处理技术,在不降低计算效率的情况下,保证了计算精度,得到了高功率电磁脉冲辐照下X波段4单元微带天线阵的响应。计算结果表明:馈电点最大响应电压峰值由天线阵各阵元接收的入射脉冲在馈电点叠加引起,且天线阵中主要存在与馈电点激励天线阵不同模式的波。响应电压峰值随着入射脉冲波矢量与正z轴夹角的减小而增大,随着入射脉冲波矢量xOy平面投影与正x轴夹角的增大而增大,频谱随着上述两个夹角的增大均向低频转移。     

Rectangular patch antennas over electromagnetic band gap structures

In this paper, I propose a new design of a defected structure (DS) for use as an electromagnetic band gap (EBG) configuration to enhance the performance of low profile microstrip antennas. The proposed defected structure embodies a honeycomb lattice of cylindrical air holes. The proposed DS is applied to three different configurations using a dielectric substrate (dielectric constant 6 and thickness 1.5 mm); namely: a dielectric substrate backed by a defected ground plane, a defected dielectric substrate backed by a normal substrate and a defected dielectric substrate backed by a defected ground plane. The simulated values of the transmission coefficient S ₂₁ for the last one show two well-defined stop bands around 8.5 and 9.5 GHz, respectively. The first band has been used to reduce mutual coupling in a microstrip array. On the other hand, the stop band defined around 9.5 GHz has been applied to enhance the characteristics of a rectangular patch antenna and improve the operational 10-dB bandwidth.     

一种新型的低散射微带天线阵设计

本文将电磁表面(electromagnetic surface, EMS)的设计思想引入到微带天线阵的设计中,在设计天线单元的同时,也将其作为EMS单元兼顾其反射特性.通过在矩形辐射贴片上开弧形缺口,得到一种新的单元结构,该单元可与原始EMS单元之间形成180°±30°有效相位差,且作为天线单元时与原始天线工作在相同谐振模式、相同频带.将两种单元以棋盘形式构成组合天线阵,在两个极化下分别基于相位对消原理和吸波原理实现了雷达散射截面(radar cross section, RCS)减缩.实测与仿真结果表明:相较于等大小的金属板,在x极化波照射下,天线阵在5.6—6.0 GHz实现了6 dB以上的RCS减缩,相对带宽为10.1%;在y极化波照射下,天线阵在5.0—7.2 GHz实现了6 dB以上的RCS减缩,相对带宽为24%.同时由于两种单元在辐射上具有较好的一致性,使得组合天线阵的辐射性能得以保持.该方法有效解决了天线阵辐射和散射难以兼顾的矛盾,为其他形式的低散射天线阵的设计提供了新的方法与思路.     

复合左右手技术的二元阵天线的计算及测量

为了克服微带天线的横向尺寸需要满足半个波长的限制,本文提出了一种基于复合左右手传输线技术的二元阵天线.该天线阵由结构相同的两个天线阵单元构成:天线阵单元由3个辐射片、辐射片之间的交指电容和导通辐射片和接地板的短路针组成.辐射片、短路针、天线阵的基片和接地板构成了复合左右手传输线结构.天线阵单元之间通过弓形连接线连接,通过调节弓形连接线两个端口到馈源之间的距离来调节天线阵单元之间的初始相位差.在关心频段内,数值计算得到的二元阵天线的S参数与实际测量结果符合得很好,并且零阶谐振频率与用等效电路理 关键词： 天线 异向介质 左右手传输线 增益     

宽带高增益双层硅基MEMS微带天线阵列

针对传统微带天线带宽窄和增益低等问题,设计了一种易与射频（RF）前端集成的硅基微带天线。该天线设计结合MEMS工艺,将高阻硅和低阻硅通过键合工艺形成双层硅基底,来改善微带天线介质基板的等效介电常数,有效增大了天线的带宽。同时通过在地面引入缺陷地结构（DGS）,有效的抑制谐波的产生。在此基础上设计了中心频率为10 Hz,22天线辐射阵列。仿真结果表明,天线相对阻抗带宽达到15.9%,增益超过10.9 dB,比传统微带天线有明显提升,同时满足引信中天线抗干扰的要求。     

Tight focusing of partially polarized vortex beams by binary phase Fresnel zone plates

Based on vectorial Debye theory, the focusing properties of partially polarized vortex beam by high numerical aperture Fresnel zone plate are investigated. The effects of the numerical apertures of and the phase difference of binary phase Fresnel zone plates, the topological charge of vortex beam and the degree of polarization of incident beam on the intensity distribution and degree of coherence in the focal plane are investigated in detail. It is shown that elliptical light spots and the flat top beam can be obtained by selecting certain parameters. Studies of degree of coherence reveal that the degree of coherence between x and y components of the electric field, which is zero in the source plane, is improved in the focal plane for vortex beam, but it is hardly changed for the nonvortex beam. It is also proved that any two of the three electric field components E_x, E_y and E_z are completely coherent everywhere in the focal region if the incident light beam is linearly polarized.     

Scattering Properties of Cylindrical Ferrite Posts and Their Applications

The scattering field of a ferrite post and a cylindrical ferrite post containing conducting post illuminated by a plane wave is analyzed. The special interest is the scattering property of the ferrite posts, which is resonating at certain modes such as TM₁₁ mode. We hope to know the speciality it shows and find its applications. It is found that the scattering field pattern of a resonating ferrite post is similar to the rotation of the scattering field pattern of a dielectric cylindrical post, which has the same dimension as ferrite. The scattering properties of the ferrite may give us some inspirations to explore its applications in microwave components. This property is utilized to explain the mechanism of the operation of the circulators. It also may be used in microstrip patch antenna, coupler and filter to control their properties. Other applications may be possible too. Some calculation results are presented.     

Analysis and design of optically transparent antenna on photonic band gap structures

An optically transparent microstrip patch antenna is designed on photonic bandgap structures and its radiation characteristics are computed and analyzed in the visible spectrum region. The proposed antenna consists of indium tin oxide, a transparent conducting material used both as a radiating patch and a ground plane separated by the 5 μm thin glass substrate. The introduction of periodic cylindrical air cavity structures in the glass substrate leads to the formation of photonic band gap. The patch thickness is carefully selected based on the analysis of the optical transmission coefficient with respect to patch thickness. The effective dielectric constant of the photonic band gap loaded glass substrate is computed using the effective medium approach. The refractive index of the proposed antenna is presented and discussed. The radiation efficiency of the antenna is shown to improve significantly due to insertion of proposed photonic band gap structures. The proposed design has yielded a bandwidth of 2–2.3 THz for a return loss (S₁₁) of less than −15dB and achieved a peak gain of 4.97dB at 2.27 THz.     

Infrared lattice vibration spectra of tetragonal ZnP2

Infrared reflectivity spectra of tetragonal ZnP₂ are measured in the frequency range from 40 to 600 cm^-1 for both polarization directions E ⊥ c and E 6 c. The parameters of 9 E modes and 4 A₂ modes are determined by a dispersion analysis of the spectra. Three additional A₂ modes are detected by infrared transmission measurements. The results obtained are compared with previous Raman scattering and two-phonon combination mode spectra.     

Effect of spiral left-handed material with near-zero index on rectangular microstrip antenna

In this paper, spirals are arranged periodically on the surface of the substrate, making a left-handed material (LHM) with a near-zero index of refraction. A radiation patch is etched on the surface of this substrate, making an antenna. The finite difference time domain method is used to study the effect of this LHM with a near-zero index of refraction on the microstrip. At f=13.78 GHz, the equivalent permittivity and permeability of the proposed spiral materials are both negative; at f=28.02 GHz, the equivalent permittivity and permeability are both negative and the refraction index is near zero. Compared with conventional microstrip antenna, the radiation gain of the antenna is much higher and the return loss is much lower due to the near-zero-index effect.