渐近法高频场线耦合分析中等效短线长度的影响

深入研究了用于高频场线耦合分析的渐近法中等效短线长度取值对渐近法计算精度的影响。首先通过大量计算分析了不同等效短线长度对传输线上感应电流分布计算结果的影响,结果表明当任一等效短线长度为半波长时,渐近法计算结果不再可靠。其次对等效短线长度选择与导线长度的关系进行了分析,发现当传输线长度相对于导线间距较大时,必须适当增加等效短线的长度才能得到较为准确的沿线感应电流分布。这些研究结果为工程应用提供了有益指导。     

多导体传输线高频场线耦合渐近法分析

基于理想地面上单导体传输线渐近法,提出了改进的多导体传输线渐近法。与已有多导体传输线渐近法相比,所提方法步骤简单,求解效率高。利用所提方法计算电磁波与不同结构多导体传输线网络之间的耦合,结果与全波分析方法计算结果吻合很好。在此基础上,分析了多导体传输线导线间距对沿线感应电流的影响。结果表明,随着导线间距变化,矩形网络和平行网络沿线感应电流波形变化趋势不同,且当间距大于一个波长后,平行网络和理想地面上相同结构的单导线具有相同的沿线感应电流。     

基于双Z形金属条的双入射型左手材料研究

提出了一种新型二维左手材料结构单元,该结构由介质板及其两侧放置的两个反向对称的Z形金属条组成.在电磁波垂直于介质板和平行于介质板入射两种情况下,这种结构单元于X波段均表现出左手通带特性.通过模拟仿真,提取等效电磁参数,建立等效磁谐振电路模型,分析验证了该结构的左手特性.并将双Z形结构与相似的工字形结构相比较,发现在电磁波垂直入射时两种结构均出现相似的左手通带,而在电磁波平行入射时,只有双Z形结构实现了双负特性.结果表明这种双Z形左手单元结构具有更优越的电磁波入射适应特性,即实现了双入射型左手结构单元. 关键词： 双Z形结构 二维 左手材料 双入射     

基于BLT方程的微带线电磁耦合终端响应

为定量研究电磁波与微带线的耦合终端响应问题,提出一种基于BLT方程的电磁波与微带线耦合分析方法,相比传统方法计算效率高、占用内存少。将PCB板上微带线等效为有耗传输线模型,对辐照平面波进行矢量分析并求解等效激励源,运用BLT方程研究不同入射方式、脉冲波形对微带线终端的影响,并对入射波与终端响应进行了时域、频域分析。研究表明:当入射波频率与微带线长度满足一定关系式时对微带线的耦合最强,耦合电压峰值达2.4 mV;电场平行微带线入射比垂直PCB入射时的终端电压峰值大一倍;且同幅同脉宽的矩形脉冲较高斯脉冲和三角脉冲对微带线的耦合峰值电压大;不同波形的脉冲通过调节脉宽都可对微带线耦合终端电压达到mV量级。     

基于蘑菇型结构的双入射超宽带复合媒质材料设计与分析

通过设计一定的单元结构, 可以实现超宽带人工电磁材料. 基于蘑菇型金属结构, 提出了一种同时具有左右手通带无缝结合的超宽带双入射型复合媒质材料结构单元. 该结构由嵌入到介质板的两个反向对称的蘑菇型金属结构组成, 能够同时引发电谐振和磁谐振而得到左手通带. 通过利用CST软件仿真、等效电磁参数提取、折射率计算以及建立等效磁谐振电路模型等方法, 分析验证了该结构的双入射特性和左手特性. 仿真结果表明, 在电磁波垂直于介质板和平行于介质板入射两种情况下, 在X波段均表现出左手通带特性, 并具有1 GHz以上的左手带宽. 当电磁波垂直于介质板入射时, 在7.2 GHz-9.3 GHz频段为右手通带, 在9.3 GHz-11 GHz频段为左手通带; 当电磁波平行于介质板入射时, 在7.0 GHz-9.0 GHz频段为右手通带, 在9.0 GHz-10 GHz频段为左手通带. 在两种情况下分别于9.3 GHz与9.0 GHz处得到了零折射率, 从而构造了一种正-零-负复合媒质材料, 实现了具有3 GHz带宽的双入射超宽带平衡结构.     

基于传输线原理的混响室散射场场线耦合模型

基于传输线原理,构建了均匀分布在单位球表面的入射波用于模拟混响室内"全向辐照"的电磁辐照模型,并利用Agrawal散射电压公式计算双导线传输线模型的终端负载响应电流。研究了均匀分布在球面入射波的入射方向、极化方向以及入射波数量对传输线终端响应的影响,并将数值计算结果与蒙特卡罗方法的计算结果进行对比。结果表明:分布在球面上的电磁波入射角为0~π、极化角度为0~π时,即可满足响应信号的数值完整性;入射电磁波数量达到100时,能够满足混响室内"全向辐照"的要求;理论模型计算结果与蒙特卡罗方法的计算结果吻合较好,该模型可以用于混响室内散射场场线耦合规律计算。     

一种计算HEMP环境下电缆感应电流的混合算法北大核心CSCD

对高空核爆电磁脉冲(HEMP)环境下、地面上方电缆的感应电流进行了研究。考虑有耗地面的影响,提出了一种将时域积分方程(TDIE)和时域传输模式法结合求解有耗半空间上方电缆瞬态电流的时域方法。通过电磁波本征模的关联性得到斜入射有耗半空间平面波的时域反射系数,不需计算贝塞尔函数的无穷项和便可以得到时域反射系数的精确解。最后给出了核爆脉冲照射下地面上方电缆感应的电流的仿真结果。结果表明:对于水平放置的电缆,当反射脉冲到达电缆后,反射场总是试图抵消入射场,使得电缆上感应电流小于只考虑入射脉冲时的感应电流;电缆的耦合电流会随架设的高度发生显著变化,相对于铺地的电缆,架空的电缆有更大的感应电流。     

微带线电路板端口对入射电磁波的电压响应

 在考虑电磁波与电子设备的耦合时,屏蔽腔中电路板端口对入射电磁波的电压响应是一个重要的参数。分别计算了微带线电路板端口在自由空间和在屏蔽腔内这两种不同情况下的电压响应,以及屏蔽腔内耦合系数的变化。对所得结果进行了比较分析,结果表明,在自由空间时,响应电压频谱为连续的变化,而在屏蔽腔内时,只有在本征模的频率处才会激励起端口电压,频谱分布变为分立的。当屏蔽腔上开有窄缝时,窄缝方向和入射场极化方向对激励起来的端口电压都有影响,而电场极化方向和微带线方向之间的关系,是决定端口激励电压大小的关键因素。     

磁化等离子体对平面电磁波吸收特性的数值研究与全波仿真

研究了平面电磁波在磁化、稳定、二维、非均匀等离子体中的传播特性;采用等效输入阻抗方法计算非均匀磁化等离子体层对不同模式入射电磁波的功率吸收情况。结果表明,电子数密度、碰撞频率和外磁场大小是等离子体对电磁波功率吸收的主要影响因素。采用等效介电常数的方法模拟等离子体特性,代入有限元软件进行平面电磁波入射等离子体仿真,得到了非寻常波与右旋极化波的吸收特性。根据数值计算和全波仿真结果可知,当等离子体密度为1017 m-3、碰撞频率2.5 GHz、外加磁场的磁感应强度为0.15 T时,磁化等离子体对电磁波有强烈的吸收特性。     

金属导线偶合THz表面等离子体波

利用THz时域光谱技术,研究了具有不同排列参数的金属导线阵列的透射特性,分析了金属导线半径,排列间隔以及入射电场的偏振方向对表面等离子体波产生和传播的影响.在具有等间隔缝隙的金属导线中,当电场偏振方向垂直金属导线时,透射信号受等离子模式和谐振腔模式的共振效应的影响;而当电场偏振平行金属导线时,只存在谐振腔模式的共振. 关键词： THz 时域光谱 铜导线 表面等离子体     

复合结构丝中的电流密度分布和巨磁阻抗效应

提出了由中间为高电导率的非铁磁性金属丝外面包裹一层铁磁材料组成的复合结构丝的电流 密度分布和巨磁阻抗(GMI)效应模型，并对Cu/FeCoNi复合丝进行了数值模拟. 结果表明：在 相同的磁性材料几何尺寸和磁特性时，Cu/FeCoNi复合丝铁磁层内的电流随频率的升高比匀 质FeCoNi铁磁丝内的电流更趋于表面分布，而且开始出现趋肤效应时对应的频率明显降低. 当在比较低的频率下就可以观察到明显的MI变化时，复合结构丝中的电阻和电抗变化主要是 由趋肤效应引起，趋肤效应仍然是引起复合结构材料(包括多层薄膜结构) 关键词： 电流密度 巨磁阻抗效应 趋肤效应     

Magnetic levitation: The track currents

An infinitely long wire carrying a direct currentI moves parallel with a conducting plate of thicknessd. The motion is at right angles to the current. A relativistic formulation is used to obtain the lift and drag forces on the primary currentI, and the distribution of currents induced in the track. Extensive numerical data are provided, especially on the track currents.     

Conduction noise absorption by fiber-reinforced epoxy composites with carbon nanotubes

Nearly all electronic equipment is susceptible to malfunction as a result of electromagnetic interference. In this study, glass fiber, and carbon fiber as a type reinforcement and epoxy as a matrix material were used to fabricate composite materials. In an attempt to increase the conduction noise absorption, carbon nanotubes were grown on the surface of glass fibers and carbon fibers. A microstrip line with characteristic impedance of 50 Ω in connection with network analyzer was used to measure the conduction noise absorption. In comparing a glass fiber/epoxy composite with a GF-CNT/Ep composite, it was demonstrated that the CNTs significantly influence the noise absorption property mainly due to increase in electric conductivity. In the carbon fiber composites, however, the effectiveness of CNTs on the degree of electric conductivity is negligible, resulting in a small change in reflection and transmission of an electromagnetic wave.     

200-m optical fiber with an integrated electrode and its poling

More than 200 m of germanosilica optical fiber is manufactured with an internal wire electrode running parallel to the core. In this new fabrication method the wire is integrated into the fiber during the draw process. This length of fiber is an order of magnitude longer than other previously reported fibers with internal electrodes. The optical loss is less than our measurement floor of 0.5 dB/m at 1550 nm. A 0.9-m section of the fiber is thermally poled, inducing a permanent second-order nonlinearity of 0.0125 pm/V. Methods to increase the induced nonlinearity are discussed. Integrating the wire into the fiber during the draw allows lengths of fiber with internal electrodes greater than 1 km to be manufactured and subsequently poled.     

碳碳复合阴极在相对论速调管放大器中的应用北大核心CSCD

研制了一种碳纤维分布具有高取向性的碳碳复合材料,并采用该材料制作的阴极开展了相对论速调管放大器的实验研究。实验结果表明:碳碳复合阴极爆炸发射的点火机制以尖端场增强为主,运行1000发后碳纤维结构稳定,重复频率25Hz运行时输出微波功率大于1GW,脉冲宽度大于100ns,阴极发射电流密度约3.82kA/cm2。碳碳复合阴极在启动速度、电流延迟时间及阻抗特性等方面性能还有待进一步的研究。     

Composited BCN/carbon fibers prepared by hot-filament chemical vapor deposition

The combined BCN/carbon fibers with porous configuration have been successfully prepared by hot-filament chemical vapor deposition (HF-CVD). The composited materials consist of carbon fiber inside covered by the cylindrical BCN films. The differences in the surface morphology and the diameter of the composite fibers are related to the different reactant gases. It is demonstrated that the elements of B, C, and N are chemically bonded with atomic-level BCN hybrid in the composite fibers. The resistance of the composite fibers is about 300 Ω which is 10 times higher than that of the isolated carbon fibers (27.5 Ω). When the applying voltage increases up to 8-15 V, the BCN films have been broken down and the resistance of composite fibers decreases to the typical value of the carbon fibers. The composite fibers with porous configuration have the strongly capacity to adsorb oxygen. The findings suggest that the combined BCN/carbon fibers are favorable for achieving high performance nano-optoelectronic and sensor devices.     

Microwave excitation of ultrasound in graphite-fiber reinforced composite plates

In this paper is demonstrated the effect of microwave beam polarization on the thermal generation of acoustic waves in continuous fiber-reinforced composite laminates. It is found that beam polarization strongly influences the dielectric interaction that leads to thermal losses, bulk expansion, and acoustic wave generation. The oriented graphite fibers in the composite laminate effectively short the microwave fields and reduce the generation efficiency nearly to zero. Ultrasonic waves at several hundred kHz generated in the composite are detected by air-coupled acoustic transducers located on the opposite side of the plate specimen from the 9.41 GHz incident microwave beam. With some averaging signal-to-noise ratios of better than 26 dB are obtained. Applying a conventional model of electromagnetic wave scattering in anisotropic media to this experiment yields good agreement between calculations and measured data. Implications for microwave-acoustic testing of graphite-reinforced composites are also discussed.     

Electromagnetic field perturbation by an internal void in a conducting cylinder excited by a wire loop

A thin prolate spheroidal void in an infinite conducting circular cylinder is used to model an internal flaw in a wire rope. The rope is excited by an electric ring current which is a model for a thin solenoid or multi-turn wire loop. The anomalous external fields are computed from the induced electric and magnetic dipole moments of the void. For this type of excitation, the induced axial magnetic dipole moment is the dominant contributor to the scattered field. The results have application to nondestructive testing of wire ropes.