不同厚度有耗左手材料板中的电磁波研究

 基于有损耗的Lorentz模型的时域有限差分（FDTD）方法,模拟了有耗左手材料（LHM）平板对波源的图像聚焦特性。分别计算了不同宽度的左手材料平板结构。通过比较说明电磁波在不同厚度左手材料板中传播方式相同。材料板越薄,其聚焦点的位置越往板边缘靠近。当左手材料板的厚度不满足聚焦尺寸时,该聚焦点将会消失。     

Generating mechanism of the energy-stream loops for the evanescent waves in a left-handed material slab

The generating mechanism of the energy-stream loops (ESLs) for the evanescent waves around the interfaces of a left-handed material (LHM) slab has been investigated with a finite-difference time-domain (FDTD) method. The simulations have shown that these ESLs originate from standing waves, attributed to the intervention of counter-propagating evanescent waves. Large numbers of ESLs can appear because of the numerous values of wave vectors k_y. The larger ESLs die out more quickly than the smaller ones in time after the source is switched off, the ESLs shrink continuously with increasing delay, and the oscillated distributions of the evanescent waves between the surfaces can also be validated. It is greatly helpful for the further comprehension on energy fluxes of evanescent waves in the LHM slab.     

Numerical analysis of propagation characteristics of electromagnetic wave in lossy left-handed material media

The propagation characteristics of electromagnetic wave in lossy left-handed materials (LHM) are studied using finite-difference time-domain (FDTD) method base on auxiliary differential equation (ADE) technology. The LHM medium is realized with lossy Drude models for both the negative electric permittivity and the negative magnetic permeability. The discretized ADE-FDTD equations are derived in detail. The incident wave used in the simulation is a multiple cycle m-n-m pulses source. The term of Poynting's vector E_xH_y was calculated. These numerical results demonstrate conclusively that the phase velocity direction of electromagnetic wave propagation and the direction of the Poynting vectors are anti-parallel in LHM. The amplitude of electric field is reduced with the enhancive distance of LHM slab. It is also demonstrated that the energy of electromagnetic wave in the LHM slab is obviously attenuated, and the attenuation of energy becomes stronger with the angular plasma frequency ω_p increasing. These results indicate that LHM stealth is effective in theory, and reasonable selection of the large negative index of refraction can greatly enhance its effectiveness.     

非线性左手材料的时域研究

 分析了非线性左手材料模型,推导了非线性左手材料中的时域有限差分法及完美匹配层的计算式。数值模拟了具有Kerr非线性效应的左手材料平板中的电磁波。观察到该材料同样具有电磁聚焦特性。对比线性左手材料,其聚焦点的幅度和位置都会发生偏移。同时改变波源的强度及其到平板边界距离,讨论了不同距离情况下该非线性左手材料平板对电磁波分布的影响。当波源距离材料平板足够远,通过非线性左手材料聚焦的电场强度几乎集中在其外表面。     

A polarization splitter based on slow light effect in a left-handed material waveguide

We propose a polarization splitter (PS) based on the slow light effect in a three-layer waveguide that consists of left-handed material (LHM) and dielectric layers with no birefringence. Transverse electric (TE) and transverse magnetic (TM) waves can be split by the intrinsic configuration of permittivity and permeability of LHM and dielectric layers. Simulation results are given to discuss the influence of electromagnetic parameters on the properties of our PS, and the capture and release of TE or TM waves are also realized in our PS which provides a flexible method to modulate the switching of different polarization waves.     

High-Q microcavities realized in a circular photonic crystal slab

A series of microcavities in circular photonic crystal slabs are studied in this paper. It is shown that high quality factors can be obtained for such microcavities. For a cavity with three inner layers of air holes missing, Q factor larger than 10⁵ can be obtained. It is also worth noting there exists resonant modes with high quality factors, even for the defect-free circular photonic crystal slab, due to gradual change of the average effective index.     

不对称左手介质平板波导模式特性分析

对不对称左手介质平板波导的几个低阶的TE模和TM模进行了数值计算,得到了模式特征方程,分析了归一化传播常数β/k_0随平板厚度d变化的色散关系,作出了模式的电场E_y(x)分布．在左手介质平板波导中,每一模式都有截止点, TE_0模和TM_0模不出现,在我们给出的特定的介质参数下,TE_1模和TM_1模不能和其他高阶模式共存,其归一化传播常数β/ k_0随k_0d的增加而减小．给出的结果对左手介质元器件的研究有实际的参考意义．     

水平极化电磁脉冲模拟器空间场的数值模拟

 采用时域有限差分方法，对水平极化电磁脉冲模拟器所产生的电磁场进行数值模拟，在时域中计算了电磁场的时间 空间分布。讨论了电磁脉冲模拟器产生的电磁脉冲波形和场的空间变化、均匀性等重要因素。结果表明，模拟器产生的电磁脉冲前沿为10ns，接近脉冲电压前沿，波形与脉冲电压波形（双指数波）相差较大；峰值场强在对称轴上并非与距离成反比，而是随距离增大而迅速减弱；该模拟器的双锥 笼形天线能在大范围内（大于等于50m,水平方向）产生均匀分布、高峰值场强、快前沿的电磁脉冲。     

不同电磁脉冲作用下地面有限长电缆外导体感应电流的数值计算

 运用时域有限差分法计算了地面有限长电缆在高功率微波、超宽带和核电磁脉冲作用下的外导体感应电流。计算结果表明：场强相同情况下，核电磁脉冲在电缆上感应的电流最大，持续时间最长，高功率微波和超宽带在几m长和几十m长的电缆上感应的电流相差不大；入射角对电缆感应电流也有影响，电场方向与电缆平行时感应最强；地面电缆的感应电流振荡频率比自由空间中电缆的感应电流振荡频率低；随着大地电导率的增大，感应电流反射波衰减加快；电缆任一端接地后，接地端电缆感应电流都会增大。     

左手介质中电磁波的传播速度

在同向介质中,电磁波的群速度一般是能量传播的方向,并且电磁波的相速度和群速度在大部分情况下都满足瑞利关系.为了研究左手介质的电磁特性,本文从理论上导出了左手介质中电磁波的相速度、群速度及其关系,得出左手介质中电磁波的群速度为负,并介绍了左手介质的一些应用前景.     

可多重聚焦电磁能量的左手材料结构

 功分器在微波工程中广泛应用。基于有损耗的Lorentz模型的时域有限差分(FDTD)方法,分析模拟了左手材料(LHM)的平板结构和环状结构对电磁波源的不同聚焦特性。每个左手材料边界均可以对波源发出的波进行聚焦。同时通过比较,在对称结构中,每个聚焦点的电磁场幅度都相同。说明该左手材料结构可以对电磁波源进行多点聚焦。     

Dual bands of negative refractive indexes in the planar left-handed metamaterials

A kind of planar left-handed metamaterial (LHM) with unique configurations is demonstrated, which offers an approach in building dual-band negative-index materials. Simulated and experimental results predict two left-handed transmission bands near 11.1 and 14.6 GHz. Dual bands of negative refractive indexes are verified using the retrieval procedure. Field and current distribution at the dual magnetic resonance are also examined. The effective electromagnetic parameters show that by carefully adjusting dimensions of the unit cell, electric and magnetic resonances can be coexistent at some frequency ranges with both negative permittivity and negative permeability. The idea can help us designing planar negative-index materials with multibands.     

强电磁脉冲信号激励下复杂目标的散射

 用时域有限差分法仿真了某飞行器缩比模型及该模型涂敷雷达吸波材料的散射特性,得到了鼻锥方向、侧向和后向ns级脉冲激励下模型的时域响应和频域雷达散射截面;并在外场用ns级脉冲源进行了该金属模型的探测实验。仿真与外场实验结果均得到了模型的鼻锥方向回波幅度最小,侧向最大;鼻锥方向回波脉宽最宽,侧向最窄的结论。研究结果表明：外形隐身和材料隐身对ns或亚ns级窄脉冲的隐身效果不明显,ns或亚ns级窄脉冲能发现和识别隐身目标。     

左手材料平板对傍轴高斯光束聚焦特性分析

在傍轴近似下,推导出了左手材料平板聚焦系统的传输矩阵,并利用ABCD定律得到了高斯光束在左手材料中和经过平板透镜聚焦后的传输公式。高斯光束在左手材料内部和像空间的传输公式的研究表明:像高斯光束和物高斯光束束腰大小一致,即左手材料平板透镜实际上对高斯光束没有聚焦作用。研究同时表明左手材料平板对高斯光束的聚焦与几何光学成像规律完全一致,而不存在一般透镜聚焦时的焦移效应。     

FDTD Study on Back Scattering of Conducting Sphere Coated with Double-Negatibe Metamaterials

The shift operator method in finite-difference time-domain method for anisotropic double-negative (DNG) metamaterials is derived. The problem which incorporates both anisotropy and frequency dispersion at the same time is solved for the electromagnetic wave propagation in DNG media. By comparing with the mie series solution, the numerical verification of the method and program are confirmed by computing the back scattering of isotropic unmagnetized plasma sphere. The back scattering of conducting sphere coated with DNG media with different parameters is computed by using the shift operator method. One finds that the degree of DNG media’s match and isotropy plays important parts in the decrease of the back scattering of the conducting sphere. This work was supported by National Key Laboratory of Electromagnetic Environment fund (51486030305HT0101). An erratum to this article can be found at     

Guided surface modes in a hollow slab waveguide with a left-handed material substrate or cover

The structural dispersion characteristics of guided surface modes in a hollow slab waveguide with a left-handed material substrate or cover are investigated. Dispersion relation is derived by using normalized parameters, and universal dispersion curves have been obtained analytically, by solving transcendental dispersion equations in a reverse way. Existence condition, mode degeneracy and other dispersion properties of guided surface modes have been discussed for different ? or μ of three layers for this substrate or cover layer.     

Goos-Hänchen shift of the uniaxially anisotropic left-handed material film with an arbitrary angle between the optical axis and the interface

The Goos-Hänchen shift at the surface of a uniaxially anisotropic left-handed material film is investigated, for the situation of that there is an arbitrary angle between the optical axis and the interface of the material. The analytical expressions of the Goos-Hänchen shifts are derived, for both cases of that the total reflection occurs and does not occur at the first interface. The sign of the Goos-Hänchen shifts in the two situations is analysed. The results show that the Goos-Hänchen shift of the reflected wave is the same as that of the transmitted one for the case that the total reflection does not occur at the first interface; the Goos-Hänchen shift of the transmitted wave oscillates as the thickness of the film is increased, and its overall tendency is increased; the Goos-Hänchen shift of the transmitted wave realizes its absolute maximum when the transmitted wave resonances, the absolute maximum is almost several 10 times of the wavelength of the incident wave; the Goos-Hänchen shift of the transmitted wave is significantly influenced by the incident angle and the angle between the optical axis and the interface.     

高功率电磁波脉冲在电离层中的传播

 用时域伪谱(PSTD)算法数值模拟了高功率电磁波脉冲在整个电离层中的传播。利用缩减的电离层模型并忽略非线性过程,脉冲在电离层中的传播可用脉冲在冷等离子体中的传播方程来描述。时域有限差分(FDTD)法解决这个问题将耗费大量的时间和内存,因此,使用PSTD方法来解决冷等离子体中的方程,并采用完全匹配层边界条件截断求解空间。所得脉冲在整个电离层传播的数据显示,在265 km附近有一个分界点,其以下是反射波,以上既有反射波又有前向波。这与用高阶(FD)2TD方法数值模拟结果一致,表明时域伪谱算法模拟电磁波在电离层中长距离传播的有效性。     

光学元件表面微结构的局域场分布特性研究

在强激光系统中光学元件表面的微结构会引起局域场强增强,进而会影响元件抗激光损伤能力。采用时域有限差分方法对波长量级的表面微结构进行了电磁场分布的数值模拟,一方面为损伤模型的建立奠定了基础,另一方面也为光学元件的设计制作提供了理论指导。     

电磁波在负折射材料填充的3层平板波导中的传播特性

从电磁场理论出发对负折射材料填充的3层平板波导的传播特性进行研究,并进行了数值计算,分析TE和TM波在平板中传播的性质,得到了电磁波的模式方程,与电磁波在右手材料填充的平板波导中的传播特性做了对比,考察了TE模式的能流密度,进行了归一化计算。结果分析表明：基模、一阶模不存在,且任何模式都存在一个截止厚度,随着厚度的增大,模式数量也增多;在一定的入射频率下,平板薄膜厚度趋向一定数值时,可以同时传播多种模式的波,并且入射波频率越高,波导同时存在多种模式的可能性越大;与右手材料相比,左手材料填充相同尺寸的3层平板波导可以传播更高能量的电磁波,导波效果更好。