Properties of Near and Far Fields for the Electric Line Source Illumination of a Lossy Metamaterial Covered Dielectric Cylinder

The electric field properties of the electric line source radiation in the presence of a lossy metamaterial covered dielectric cylinder are investigated. Firstly, the electromagnetic model configuration is given. The exact solution of the electromagnetic is presented. Secondly, the near field and the far field properties are investigated according to the electromagnetic and geometrical parameters. The different “focus” phenomenon, the directivities and the normalized radiation resistance are discussed and important conclusions are obtained. During all the numerical computation, the lossy conventional material covered dielectric cylinder is utilized as the reference.     

不同渐变方式的喇叭结构对电-磁振子组合型超宽带天线特性的影响

 电-磁振子组合型超宽带（UWB）天线的物理结构包括3部分：天线的馈电系统、TEM喇叭辐射单元和电流环辐射单元。采用CST MICROWAVE STUDIO电磁场数值计算软件,对该组合型天线的结构与端口S参数和时域辐射特性的关系进行了分析。仿真结果表明：当TEM喇叭辐射单元和电流环辐射单元由3段金属板构成时，天线的端口S参数较小，主轴辐射功率较大，方向性较好。     

Properties of near and far fields for the electric line source illumination of a lossless metamaterial covered conductor cylinder

This work concentrated on an ELS (electric line source) radiating parallel to a lossless metamaterial covered infinitely long conductor cylinder. First, the exact analytical solution of the electromagnetic model is derived. Second, the numerical results based on the solution are given. Under different geometric and electromagnetic parameters, the patterns of the near field are obtained; the directivity and normalized radiation resistance are presented to discuss the properties of the far field. Because of the negative refraction of the metamaterial, it can be seen that there is a distinct “focus” in the metamaterial layer from the near field pattern, which does not exist in conventional material layer. The presented electromagnetic model is compared with the former, simpler model through the directivity and its validity is proven. PACS 78.70.Gq; 81.05.Zx; 84.40.Ba     

线电流源激励下无耗异向介质层覆盖导体圆柱电磁特性的研究

研究了线电流源平行放置在无耗异向介质层覆盖的无限长导体圆柱附近模型的电磁特性.首先，给出了电磁模型描述，求出此电磁模型的精确解.其次，利用精确解进行数值计算，得到几何参数和电磁参数不同情况下电磁模型的近场图形，并通过方向性系数和归一化辐射阻抗研究其远场特性.利用异向介质的负折射特性，在异向介质层的近场图形内得到明显的“焦点”，这个焦点在普通介质层中是不存在的.该电磁模型同前人方法进行了比较，验证了本电磁模型的有效性. 关键词： 线电流源 异向介质 方向性系数 辐射阻抗     

有耗异向介质层覆盖普通介质圆柱电磁特性的研究

研究了线电流源平行放置在有耗异向介质层覆盖的无限长介质圆柱附近模型的电磁特性.首先,提出电磁模型并给出此电磁模型的精确解.其次,利用精确解进行数值计算,得到不同电磁参数情况下该电磁模型的近场分布图形,并通过方向性系数和归一化辐射阻抗研究其远场特性.由于有耗异向介质的负折射特性和损耗的同时作用,相比于无耗异向介质层以及有耗普通介质层,得到了有耗异向介质层覆盖普通介质圆柱模型在近场和远场特性上极为不同的电磁特性. 关键词： 线电流源 异向介质 方向性系数 辐射阻抗     

Generation of Ultrawideband Electromagnetic Radiation by a Vacuum Photodiode with Anode with a Sapphire Input Window

Technical Physics - Generation of ultrawideband electromagnetic radiation by a vacuum photodiode with a plane cesium antimonide photocathode is studied. Thin aluminum plates deposited on a sapphire...     

海洋波导中目标声辐射场的计算方法

针对海洋波导中目标声辐射场的计算问题,提出了一种基于波叠加法并在近、远场采用不同水声传播模型的建模方法,可以将近、远场作为一个统一的系统进行高效地分析。该方法通过给定的已知表面振动速度的结构计算出目标内部虚拟点声源的源强,再配合在相应的水声环境中点声源传播模型的Green函数计算出结构外的声辐射场。以Green函数为纽带,在求源强和计算近场声辐射场时采用镜像虚源法,而在计算远场声辐射场时采用简正波法。通过该方法得到的有限水深波导中声速剖面为正梯度、负梯度、负跃层的3种情况下的脉动球、刚体摆动球的声辐射场计算结果与COMSOL的有限元计算结果进行对比,结果表明了该方法在提高计算效率的同时保证了计算精度。      

THE QUANTUM CORRECTIONS ON THE THEORY OF TRANSITION RADIATION

A Scheme of quantum treatment for transition radiation is proposed. The Fresnel coefficients are adopted to describe the stationary states of electromagnetic fields near the interface between two mediums before a canonical field quantization procedure can be performed. Then an usual perturbation approach in field theory leads to the general expressions of radiation intensity in two different polarizations. The second order quantum corrections are ascribed to the existence of electron spin. Some concrete formulas for the cases of electron or monopole acrossing a metal surface are presented as well.

     

Probe field spectroscopy in three-level Λ systems under arbitrary collisional relaxation of low-frequency coherence

We investigate theoretically the spectrum of weak probe field absorption by three-level atoms with the Λ configuration of levels in the field of a strong electromagnetic wave acting on an adjacent transition and colliding with buffer gas atoms. Analysis is carried out for the general case of arbitrary collisional relaxation of low-frequency coherence at a transition between two lower levels. It is shown that, in the absence of collisional relaxation of low-frequency coherence, the probe field spectrum always exhibits clearly manifested anisotropy with respect to mutual orientation of wavevectors of the strong and probe radiation (even under small Doppler broadening). It is found that the probe field spectrum may acquire under certain conditions supernarrow resonances with a width proportional to the diffusion coefficient for atoms interacting with radiation. This fact may form the basis for a spectroscopic method for measuring transport frequencies of collisions between absorbing and buffer particles. A large-amplitude supernarrow resonance (with an amplitude much larger than the amplitude of the resonance near the line center), which is observed in the far wing of the absorption line, exhibits collisional narrowing (a nonlinear spectroscopic analog of the Dicke effect) at collision frequencies several orders of magnitude lower that the Doppler linewidth. Simple working equations proposed for describing the probe field spectrum are convenient for experimental data processing.     

Interaction of directive electromagnetic radiation with isotropic plasma-coated PEMC cylinder

ABSTRACT

In this study, we analyzed the influence of isotropic plasma on far field scattering radiation of perfect electromagnetic conductor (PEMC) cylinder in the presence of directive electromagnetic radiation excited from an electric line source. Two cases regarding electric line source have been considered to gain more graphical variation corresponding to plasma parameters. In the first case, electric line source is placed outside the coating layer while in second case electric line source placed inside the coating. It has been demonstrated that the far field scattering patterns of PEMC, PEC, and PMC are strongly dependent on plasma parameters; however, their importance to control scattering pattern slightly changed/reversed corresponding to electric line source placement (inside the coating and outside the coating).     

光子晶体发光二极管光抽取效率及远场辐射特性的数值研究

运用三维时域有限差分法,研究了完美/缺陷光子晶体特定参量的改变对发光二极管光抽取效率影响,得出优化参量.基于近场远场转换,进一步分析了两种不同类型的缺陷引入及其周边空气孔半径的改变对光子晶体发光二极管远场辐射特性的影响.数值研究的结果表明,通过引入缺陷以及减小缺陷周围空气孔半径能够同时提高光子晶体发光二极管的光抽取效率和远场辐射方向性.     

电力线谐波辐射在分层各向异性电离层中的传播特点

电力线谐波辐射特指在电离层或磁层中观测到的来源于地面电力系统输电线的电磁波辐射, 其在电磁场时频功率谱中表现为400 Hz至5 kHz范围内, 频率间隔为50/100 Hz或60/120 Hz 的平行谱线, 已成为近地空间环境的一种人为污染源. 对于该现象的形成机理尚缺乏定量研究. 本文研究了非理想导电大地上方由电偶极子源产生的电磁场在分层各向异性电离层中的传播模型, 提出了一种新的求解方法, 有效解决了编程计算中的数值溢出问题, 并利用已有解析解对所提方法进行了验证. 在此基础上, 利用实际电力线、大地、电离层的相关参数, 研究了偶极子源频率、电离层下边界高度、大地电导率、地磁场方向等对电力线谐波辐射在电离层中的传播的影响. 结果表明, 频率等于地-电离层波导导波模截止频率时透入电离层的电力线谐波辐射强度更大; 谐波电流一定时, 大地电导率小的地区, 电力线谐波辐射的功率更大; 电力线谐波辐射在电离层中沿地磁场方向传播. 本文所得结果有益于阐释电力线谐波辐射现象的形成机理.     

Numerical Comparisons of Terahertz Radiation from GaAs and GaAs: As+ Substrates

In this paper, we have numerically analyzed the ultrafast change of local fields on the surfaces of a large-aperture photoconducting (LA-PC) antenna with GaAs and GaAs: As+ substrates. We find that the ultrafast screening of photogenerated carriers to the externally applied electric field has different effects on the saturation of THz radiation as the function of the laser fluence in the near and far field, respectively. Both screening effect of photocarriers and radiation effect are important in forming the saturation phenomena in the case of near field. But in far field, only the radiation effect is important.     

电磁脉冲对金属板搭接缝隙耦合效应分析

 针对在缝隙耦合研究中,对金属板接合处搭接缝隙电磁特性的讨论相对较少的情况,应用时域有限差分方法模拟了强电磁脉冲对搭接缝隙的耦合穿透过程,计算了缝隙口径面等效面磁流和进入另一空间的透射场。为便于由等效磁流外推透射场,应用等效原理将电磁流在1/4空间的辐射等效为电磁流及其镜像在自由空间的辐射,避免了计算搭接缝隙边界情形下空间格林函数的困难。外推时采用分区外推法节省了计算时间。最后通过分析耦合场的变化曲线,总结了耦合共振规律。     

Radiation from a short vertical dipole in a metal-backed rod array

Based on an effective medium approach, we investigate the problem of radiation of a short vertical electric dipole embedded in a metal-backed dielectric rod array. We obtain the radiated electromagnetic field in the form of a Sommerfeld integral, and calculate the near and far electric fields for both lossless and lossy rod arrays. The characteristic equation for the guided modes is derived and solved. The guided modes are found to be slow waves and their propagation constants and modal distributions are extracted. All theoretical results are compared with full-wave simulations.     

Scattering of a Generic Two-Dimensional Field by Cylindrical Structures in the Presence of a Plane Interface

A new method for treating the scattering of a two-dimensional electromagnetic field, expressed by means of its plane-wave spectrum, by an arbitrary configuration of circular cylinders in the presence of a plane interface between two different media, is presented. The proposed method allows us to solve the problem for both polarizations and to calculate the scattered field both in the near and in the far zone. Numerical results relevant to vacuum-dielectric interfaces are presented and compared with previous known results.     

STUDY ON THE RADIATION ACOUSTIC FIELD OF RECTANGULAR RADIATORS IN FLEXURAL VIBRATION

In this paper, the radiation acoustic field of a rectangular radiator in flexural vibration is studied. The radiator is a rectangular thin plate in flexural vibration with simply supported boundary conditions. Based on the theory of Rayleigh integral, the acoustic pressure distribution of the radiator in its far field is obtained analytically and the near acoustic field of the radiator is also computed numerically. In the near field, the three-dimensional acoustic pressure distribution is obtained. In the far field, the two- and three-dimensional acoustic pressure distribution patterns are calculated. The dependence of the radiation acoustic pressure of the radiator on the vibrational order of the plate in flexural vibration is analyzed. It is demonstrated that the radiation acoustic pressure along the central axis of the radiator is always zero in the near and far acoustic fields, and the radiation near acoustic field and the far acoustic field are both directional. This is different from the acoustic field generated by an oscillating piston. On the other hand, when the vibrational order is increased, the acoustic pressure distribution of the radiator becomes complex.     

Far-field detection of the dipole vortex

The energy flow lines (field lines of the Poynting vector) of electric dipole radiation exhibit a vortex structure in the near field when the dipole moment of the source is in circular rotation. The spatial extend of this vortex is smaller than a wavelength and may not be observable by a measurement in the near field. We show that the rotation of the field lines close to the source affects the image of the dipole in the far field, and this opens the possibility for observation of this vortex by a measurement in the far field.     

无线电波发射设施周边环境电磁波检测技术

电磁波检测技术的应用,可以防止对人体的辐射。当今无线通讯技术迅猛发展,如何对变电所及输电线与移动电话基地台所产生的电磁场强度进行评估,便成为一个重要的工作。通过分析电磁波特征,提出了对这些电磁波辐射设施所产生的电磁场强度检测的方法。     

基于积分方法的二维平行剪切层声远场预测

本文采用二维Ffowcs Williams＆Hawkings(FW-H)方程对平行剪切层远声场辐射特性进行了研究。近流场时间精确数据通过计算气动声学(Computational Aeroacoustics,CAA)技术数值模拟获得,声远场信息则通过FW-H方程对近流场内的可穿透积分面进行积分获得。该方法首先采用具有解析解的涡/尾缘干涉问题进行了校核,进一步采用CAA/FW-H匹配技术对二维平行剪切层声辐射问题进行了预测,计算结果表明,积分解与计算域内的CAA数值解吻合较好。