内导体半径对同轴相对论返波振荡器工作频率的影响

利用电磁软件Superfish求解了同轴慢波结构中准TEM模对应的π模的电场矢量分布,分析了内导体半径对谐振频率的影响。采用Karat 2.5维全电磁粒子模拟程序设计了一个L波段相对论返波振荡器,研究了内导体半径参数改变对器件工作频率的影响。通过使用半径为0.50,0.75,1.00 cm的内导体,实验测得微波中心频率分别为1.64,1.63,1.61 GHz,变化趋势与理论分析结果一致。实验测得频率比粒子模拟结果仅高0.01 GHz,两者吻合较好。     

电磁超材料中负磁导率对负介电常数的影响

为深入了解电磁超材料中物质间相互作用关系,理论分析了金属导体线阵列宏结构嵌入单负磁导率媒质中时其等效介电常数的变化特性。数值计算和电磁仿真方法相结合,讨论了单负磁导率媒质和单负介电常数媒质的相互作用关系,提出了减小其相互作用的解决方法。仿真结果显示:将金属线阵列直接嵌入到单负磁导率媒质中时,电磁超材料传输特性在整个频段内为传输禁带;将金属线裹附一层绝缘材料后,传输禁带变为传输通带,这表明金属线阵列和单负磁导率媒质之间必须加入一种绝缘材料才能合成双负的电磁超材料。     

均匀外电场中无限长介质圆柱壳的场分布的计算和讨论

用圆柱坐标系中的分离变量法计算了位于均匀外电场中的无限长介质圆柱壳各区域的电势和电场,由计算结果分析了无限长介质圆柱壳对外电场的屏蔽效果,并指出均匀外电场中的无限长导体圆柱壳、无限长介质圆柱体、无限长导体圆柱及无限大均匀电介质中开有一无限长的圆柱形空腔的电势和电场都可以由均匀电场中的无限长介质圆柱壳电势及电场给出.     

电像法求解线电荷与带有半圆柱凸起的接地平板导体形成的电势和电场

利用电像法求解了线电荷与带有半圆柱凸起的接地导体平板形成的电势、电场分布,讨论了导体表面电荷分布特征,并用Matlab软件绘出了等势图.     

轨道电路系统长钢轨电容补偿电磁脉冲耦合效应

结合时域有限差分(FDTD)方法、传输线方程和长钢轨激励场快速计算方法,研究了一种高效的时域混合算法,实现长钢轨电容补偿电磁脉冲耦合效应的时域快速计算。首先,为避免对钢轨不规则结构的直接建模,根据趋肤效应,将钢轨等效为管状导体模型并提取对应的单位长度分布参数。然后,根据长钢轨激励场快速计算方法,快速计算长钢轨沿线电场分布,并结合传输线方程构建钢轨等效圆柱模型与补偿电容一体化的电磁耦合模型。最后,使用FDTD方法求解传输线方程,获取钢轨沿线各点的电磁脉冲耦合响应。研究结果表明,钢轨耦合电流波形不断展宽,但是峰值随长度增加到一定值后达到饱和状态,此结论可为轨道电路系统电磁防护设计提供重要的数据支撑。     

线电荷与圆柱导体间的相互作用

利用镜像法,在计算线电荷与接地圆柱导体间的相互作用的基础上,通过增加镜像电荷的方法,进一步分析求解得出了线电荷与绝缘圆柱导体、与电源连接的圆柱导体间的相互作用.     

不同表面结构特征圆柱导体的太赫兹散射特性

太赫兹频段下导体表面的细微结构、粗糙度等细节将对目标电磁散射行为产生影响。为衡量这一影响程度,以圆柱导体为例研究了太赫兹频段下目标表面不同结构特征的电磁散射现象及其在图像域的表现规律。利用高频电磁计算方法获得了表面分别为理想光滑、带刻痕和周期粗糙的三种圆柱多姿态角、多频点单站散射场;基于转台成像算法重建了小转角下目标的二维图像。从仿真结果可以看出:m量级的细节特征在太赫兹雷达图像上有着显著的表现,表明太赫兹雷达能够获取更加丰富和精细的目标信息,从而为目标探测识别提供新的特征和技术手段。     

复合结构偏心对同轴波导电磁特性的影响

采用三维电磁仿真软件CST Microwave Studio,数值模拟了内外导体轴线复合结构偏心对同轴波导电磁特性的影响。结果表明:当内外导体的轴线同时存在平行偏心和倾斜偏心时,改变了波导的边界条件,从而导致同轴波导的S21参数和电场幅值实质性下降。随着复合结构偏心程度的加剧,同轴波导的S21参数和电场幅值减小越大。同时,复合结构偏心比平行偏心或倾斜偏心单独存在时对同轴波导电磁性能的影响更大。因此,在同轴波导的实际制作过程中,应尽力避免发生复合结构偏心。     

等效电路模型在漂移管直线加速器场稳定性调制中的应用

漂移管直线加速器(DTL)通过采用杆耦合器加速结构,实现加速电场的稳定性。为了分析电场稳定性的调制机理,简要说明DTL的腔体结构,并对其进行集总参数的等效模拟,给出等效电路分布。最后着重对耦合杆与漂移管之间相互作用的等效电容进行了仿真研究。针对上述电路分布,采用电路理论分析了高频场扰动及稳定性的实现机理。通过将稳定结构下的等效电容求解结果与该电容的模拟仿真值进行比较,得出稳定状态下的耦合杆与漂移管之间间隙取值的合理区间。最后通过对不同调节条件下的扰动电场进行仿真分析,一定程度上验证了结论的正确性。     

两平行相交带电圆柱导体的空间电场

用镜象法求解由两平行相交带电圆柱导体所组成的柱形导体边界静电场边值问题,通过简单的数学分析,获得两类平行相交带电圆柱导体问题的空间电场分布．     

Switchable directional scattering based on spoof core—shell plasmonic structures

Manipulating directional electromagnetic scattering plays a crucial role in the realization of exotic optical phenomenon. Here, we show that the spoof plasmonic structure is able to achieve the switching of directional scattering direction on a subwavelength scale by inserting a perfect electric conductor (PEC) cylinder into the hollow of the spoof plasmonic structure. Based on the modal analysis, it is found that the electromagnetic response of the core-shell structure not only is well excited, but also exhibits the directional scattering by interference between the electric and magnetic dipolar resonances. We also discuss the influence of PEC cylinder radius on the performance of the directional scattering. Finally, the active tunable directional scattering is realized by switching between the two states. This work provides a feasible pathway to the subwavelength manipulation of electromagnetic wave. Moreover, it offers a simple method to switch the directional scattering direction. The proposed design approach can be easily applied to digital electromagnetic wave communication and associated applications.     

外开槽同轴波导传播特性

 根据满足边界条件的一系列电磁场方程,采用场匹配法,详细推导了外开槽同轴波导的特征方程。在外开槽同轴波导光滑内同轴半径等于零的情形下,即变成外开槽圆波导,得到其特征方程。数值模拟了外开槽同轴波导及外开槽圆波导中TE₀₁模式的传播特性,得到了不同尺寸外开槽同轴波导开槽间隙半张角和槽深与特征根的变化关系。结果表明:开槽越深,间隙半张角越小,特征根值越小。     

Confined and interface polarons in cylindrical nanowires in an electric field

The effect of an electric field on the basic parameters of confined and interfacepolarons in cylindrical nanowires embedded in a non-polar matrix are studied theoreticallyfor the first time. By using the Lee, Low, and Pines variational method, the analyticalexpressions for the quasi-one-dimensional Fröhlich polaron self-energy and effective massare obtained as functions of the wire radius and the strength of the electric fieldapplied perpendicular to the wire axis. We have shown that the polaron self-energy as wellas effective mass strongly depents on both the strengths of the electric field and on thewire radius. This will be taken into account in the interpretation of optical phenomenarelated to polaron motion in cylindrical nanowire, when the effect of an applied electricfield competes with the spatial quantum confinement.     

ELECTRIC FIELD EFFECTS ON FILM BOILING ON A WIRE

Experimental results concerning pool film boiling on a wire under the action of an externally imposed electric field are reported. The working fluid was saturated R113 at atmospheric pressure, the heaters were platinum wires of 0.2, 0.3, and 0.6 mm diameter. An electrostatic field of cylindrical geometry was created around the wire by means of a 60-mm-diameter cylindrical cage in order to assess electrohydrodynamic (EHD) effects on boiling. Voltages up to 15 kV d.c. were applied. The results showed that two different film boiling regimes, separated by an additional boiling crisis, can exist in the presence of an electric field. The first regime, at low wire superheat, is strongly influenced by the electric field, showing a remarkable heat transfer enhancement with increasing voltage. The second one, at higher superheat, is weakly dependent on the field strength and almost coincident with the zero field one. The two film boiling regimes are separated by a transition characterized by a hysteresis cycle, similar to the one between nucleate boiling and first film boiling regime.     

Wilson chains are not thermal reservoirs

The effects of transverse electric field on the electronic structures, exciton states and excitonic absorption spectra in a cylindrical quantum wire are theoretically investigated in detail. The quantum wire is assumed to GaAs material surrounded by the infinite potential barrier. The results show that the external electric field removes the degeneracy of the electron or hole states. The energy levels of electron and hole, exciton binding energy, excitonic absorption coefficient and absorption energy decrease with increasing the strength of the electric field or the wire radius. The effects of the electric field become more significant for wide wires. The phenomena can be explained by the reduced spatial overlap of ground electron and hole states.     

Binding energy and photoionization cross section of hydrogen-like donor impurity in quantum well-wire in electric and magnetic fields

The effect of uniform electric and magnetic fields on binding energy and photoionization cross-section of an off-axis hydrogen-like donor impurity in a QWW, approximated by a cylindrical well of finite depth, is investigated within the framework of variational approach. The dependencies of the binding energy and photoionization cross-section on electric field strength, magnetic field induction, wire radius and impurity position are obtained. The cases when the polarization vector of incident radiation is parallel and perpendicular to the wire axis are both discussed.     

均匀带电圆环片的空间静电场分布

利用1/︱r-r′︱的柱函数展开式及贝塞尔函数的性质,计算出均匀带电圆环片在空间产生的电势及场强,并对结果进行讨论;指出当所研究的问题具有轴对称性时,利用柱函数展开式能更方便地分析其形成的空间静电场,其求法对柱体、螺线管等形成的电磁场同样适用.     

Electrical conduction of a thin cylindrical wire in a longitudinal magnetic field

The electric conductivity of a metallic cylindrical wire in a longitudinal magnetic field is calculated. The case when the radius of the wire is much smaller than its length is considered. As the boundary condition of the problem, the condition of diffuse reflection of electrons from the inner surface of the wire is adopted. Limiting cases are considered and the results are discussed.     

柱面非线性麦克斯韦方程组的行波解

柱面电磁波在各种非均匀非线性介质中的传播问题具有非常重要的研究价值.对描述该问题的柱面非线性麦克斯韦方程组进行精确求解,则是最近几年新兴的研究热点.但由于非线性偏微分方程组的极端复杂性,针对任意初边值条件的精确求解在客观上具有极高的难度,已有工作仅解决了柱面电磁波在指数非线性因子的非色散介质中的传播情况.因此,针对更为确定的物理场景,寻求能够精确描述其中更为广泛的物理性质的解,是一种更为有效的处理方法.本文讨论了具有任意非线性因子与幂律非均匀因子的非色散介质中柱面麦克斯韦方程组的行波精确解,理论分析表明这种情况下柱面电磁波的电场分量E已不存在通常形如E=g(r-kt)的平面行波解;继而通过适当的变量替换与求解相应的非线性常微分方程,给出电场分量E=g(lnr-kt)形式的广义行波解,并以例子展示所得到的解中蕴含的类似于自陡效应的物理现象.