Simplified expressions for the near fields of a magnetic frill current

The simplified expressions for the electromagnetic field of the near zone from the magnetic frill are derived. In these formulas,E_{rho}andH_{phi}are expressed as a single integration of the complete elliptical integrals of the first and second kinds. Furthermore the closed form ofE_{z}is obtained approximately. Their accuracy is checked numerically by comparing with Tsai's, and significant improvement in efficiencies is obtained.     

A new method of analysis of the near and far fields of paraboloidal reflectors

An analytical technique for predicting accurately the near (electric and magnetic) fields as well as the far fields of a reflector antenna with a pencil beam is presented. The technique proposed involves the near-field geometrical theory of diffraction (GTD) analysis of reflector antennas developed earlier and spherical vector mode functions. The proposed technique does not place any restriction on the range of polar angles or radial distances of the observation point. It is demonstrated that the technique proposed can predict the fields radiated by the reflector with greater accuracy by comparing the calculated results with the available measured results. A few important applications of the analysis proposed are also highlighted.     

A transform solution for the fields from a current element

A new but general method of solution applicable to any radiation problem which can be reduced to an inhomogeneous wave equation for an arbitrary source in a given medium is used to solve for the vector potential of an infinitesimal dipole radiating in free space. The solution of this simple problem yields insight into the use of this method for the solution of more complicated problems.     

Practicability of determining the modal power distribution by measured near and far fields

Under certain assumptions the modal power distribution in optical multimode fibers can be derived from either the near- or the far-field. We measured both intensities and compared the calculated mode spectra. From these results, it becomes clear which assumptions are necessary and how to control them. The influence on the modal power distribution by leaky modes and some error sources such as the profile exponent, the fiber end quality, and misalignments are shown.     

Comments on "A new method of analysis of the near and far fields of paraboloidal reflectors"

The commenter states that the technique described by M.S. Narasimhan and S. Christopher (ibid., vol.AP-32, no.1, p.13-19, 1984) of combining a spherical near-field (SNF) transformation and a near-field computation based on the geometrical theory of diffraction (GTD) is identical to the SNFGTD method originally used by F. Jensen and F.H. Larsen in 1977. Aside from this, various other criticisms are made on the presentation and on the results, specifically, theH-plane radiation pattern. In their reply, the authors note that the original paper seeks to determine accurately both the near and far fields of a paraboloid. They suggest that the editorial board review the computer programs used by themselves and by the commenter to pass a verdict on this controversy     

Radiation fields of an annular source of radially directed currents

Obtains an expression for the radiation field as a function of the angular current density, the annular radius, and the angular coordinate     

An optically linked electric and magnetic field sensor for Poyntingvector measurements in the near fields of radiating sources

A unique, single-element antenna measurement scheme that can simultaneously measure the electric, magnetic, and time-dependent Poynting vectors of electromagnetic (EM) fields is described. The electric and magnetic responses of the antenna sensor are separated by a O°/180° hybrid junction. The resulting two RF voltages, along with relative phase and frequency information, are transmitted to a remotely located vector analyzer by a pair of well-matched fiber optic downlinks. The remote receiver measures and displays the electric dipole response, the magnetic loop response, and the time phase difference between the two. This information is sufficient to determine the time-dependent Poynting vector. Both a theoretical analysis and a discussion of experimental measurements performed, which describe the capabilities and performance of a working prototype of the antenna measurement scheme, are presented. The results demonstrate that a three-axis (isotropic) version of this system could be used to measure the near fields of EM sources, as well as to completely describe the resultant flow of energy     

A novel expansion of the fields near dipole and helical antennas

An asymptotic analysis is performed to obtain the E- and H-fields in the close vicinity of dipole and helical antennas. Although the mathematical procedure requires some involved algebra, the resulting series representation of the fields lends itself to simple numerical calculations. It is shown that the asymptotic E- and H-field values are in very good agreement with both the experimental results and those obtained via numerical integration. Considerable savings in computer time (a reduction by a factor of 8-10) is achieved when the asymptotic expressions are used instead of the usual integration methods.     

Note on the fields of an upward-traveling current wave pulse

The so-called transmission-line model for an upward-traveling lightning stroke is often employed by the atmospheric and electromagnetic compatibility community. Simple expressions are obtained for the radiation fields of an idealized lightning channel. The model is an attenuated traveling current, which is perpendicular to a perfectly conducting ground plane. The enhancement of the radiation field at higher elevation angles is confirmed following Krider's (1992) prediction     

Amplification of radiation in the far infrared range by hot holes in germanium in crossed electric and magnetic fields

The results of direct gain measurements are reported for the amplification of polarized and unpolarized, long-wavelength, infrared radiation by hot holes in germanium in crossed electric and magnetic fields in the Voigt and Faraday configurations. The experimental data are compared with gain calculations. Fiz. Tekh. Poluprovodn. 31, 1482–1486 (December 1997)     

基于单片机的汽车前照灯远近光自动切换系统

考虑到汽车的安全性能,设计了一款采用STC89C52单片机为电子控制单元核心的汽车前照灯远近光自动切换系统。该系统主要由光强检测系统和单片机系统组成。详细介绍了系统的基本原理、理论分析及硬件设计,并提出了软件的实现方法。其中,硬件系统模块包括处理器模块、通信模块、传感器模块、显示模块和电源模块。该前照灯系统较智能化,确保了汽车夜间行车的安全性。     

Surface fields and near fields of a linear antenna

In a variational impedance formulation, antenna trial functions are modified to satisfy the edge conditions of diffraction theory. For a half-wave antenna, this provides a charge distribution with experimentally verified linear portions. The linearity of the charge distribution appears to be correlated with near-field fluctuations of the antenna.     

A numerical solution to the Zakharov-Shabat inverse scatteringproblem

A novel numerical method to solve the inverse scattering problem associated with the Zakharov-Shabat coupled mode equations is developed. In this problem the coupling coefficient for two propagating modes is determined from reflection data. Both codirectional and contradirectional coupling can be accommodated as well as the presence of bound states. Analytical results based on an independent analytical method are derived in order to demonstrate the accuracy of the proposed method, which is applicable to a broad class of reflection data     

一种局域化协同增强太赫兹波电磁场的超材料

设计了一种太赫兹(THz)波段的超材料,可以实现 对垂直入射THz波的电、磁场局域化协同增强。数 值仿真表明,在线偏振的THz脉冲垂直辐照下,利用本文超材料的结构能得到强显著增强且 高度局域化的电、磁场 分布,入射THz波的电、磁场分量可以分别增强20倍;被增强的电、磁场局域化 在μm²尺度范 围内,且在空间上不重叠。基于等离激元理论分析了超材料内部的面电流分布以及超材料内 部电 荷的积累,给出了电磁场协同增强及局域化的理论解释,即超材料的特殊结构产生的 电容效应及面 电流的汇聚作用分别是导致电、磁场协同局域化增强的原因。最后,具体分析了超材料关键 的几何参数对 于场增强效果的影响。本文提出的超材料方案,有望应用于THz波段近场光学、非线性光 学及THz波与磁有序介质相互作用等领域。     

A new transform relationship for interpreting axial fields near a focus

A new Fourier transform relationship is shown to apply between the axial distribution of a field near a focus and the field, averaged around the axis, in the aperture of the focussing device. If phase and amplitude are measured along the axis the transform gives the radial distribution in the aperture, averaged around the axis, of the field amplitude and of any deviations in phase from an ideally focussed wavefront. The transform is, therefore, useful in diagnosing surface errors in reflector antennas. It may also be of use in determining errors in optical aspheric lenses and mirrors where radial errors are more prevalent in manufacture than are azimuthal errors. If only axial power is measured, a Wiener-Khinchine relationship gives the autocorrelation of the averaged radial field distribution in the aperture. The autocorrelation by itself contains useful phase information and, in some instances, the averaged aperture field can be recovered from the autocorrelation through a process of modeling. Symmetry relationships are discussed together with a practical example where phase and amplitude in a radio telescope aperture are estimated by modeling from the autocorrelation function.     

Enhanced localized near field and scattered far field for surface nanophotonics applications

The scattering physics of photons is traced back to Rayleigh scattering theory in 1871 and Mie scattering theory in 1908. However, the scattering near field and far field have recently emerged again as a new fundamental physics and innovative nanoprocessing technology in quantum electronics and photonic devices. An enhanced near field generated by plasmonic particles can concentrate optical energy into a nanoscale space as a nanolens even with near infrared laser pumping. This plasmonic nanophotonics extends the existing optical science to a new class of photonics inclusive of surface enhanced Raman scattering, nanoprocessing of advanced electronic and photonic materials, etc. The Mie scattering near field also opens up new fields. The Anderson localization of light in a planar random photonic crystal laser is also a new class of quantum electronics devices, where Slow Bloch Mode is scattered by artificial structural randomness in a photonic crystal. In this contribution we will review the recent efforts of our scattering photonics research, which have resulted in significant advances in the plasmonic surface photonics of near-field and far-field nano/micro photonics and the Anderson localization in random lasing.     

汽车远近光灯智能切换系统设计

夜间行驶的车辆相会时,很多驾驶员由于疏忽或者缺乏会车常识而不进行远近光灯的切换,带来了很大的安全隐患。结合光电检测技术、坡路检测技术、路况智能检测技术,设计实现了汽车远近光灯智能切换系统。试验表明,该系统可以灵敏地实现夜间行驶在坡路、拱桥、人行横道等路段时的自动远近光交替闪烁功能,在会车时也可以准确地实现远近光灯的切换。