行波磁场摆动器产生自由电子激光的初步研究

在一定放置的线圈中通以正弦交流电时,其附近空间就会产生一个正弦行波磁场,磁场的极距和行波的速度都可以通过输入的频率加以调节。相对论性电子在这种摆动器中的散射波长比较短,而能量因子值可以变,这既有利于向短波长方向发展,又有助于自由电子激光器的小型化。     

支柱瓷绝缘子的爬波检测方法研究

在检测方法研究中针对绝缘子及瓷套缺陷产生的特点设计多种探伤方式,国内外现有的检测方法使用超声波检测未得到推广.而其他检测方法因为检测环境的限制,对在役使用的绝缘子检测结果偏差较大.结果表明,支柱瓷绝缘子在超声波探伤时选择爬波探头对法兰口裂纹的检测非常有效.     

Uniform asymptotic solution for the diffraction by a discontinuity in curvature

An asymptotic solution for the electromagnetic diffraction by a discontinuity in curvature in a perfectly conducting surface or in an impedance surface is developed. The solution is uniform through the reflection transition region. It is of the uat type and gives the field in the transition region up to the order k^-3/2 included where k is the wave number. It is continuous and all its derivatives in the direction normal to the transition direction are continuous. The solution is established for a curvature discontinuity along a generatrix of a two dimensional surface illuminated by a plane wave. Its efficiency is illustrated by numerical examples.     

三维机翼前缘影区爬行波RCS研究

分析了三维机翼前缘影区的爬行波散射机理,建立了前缘影区爬行波的雷达散射截面(RCS)计算模型.根据光滑凸曲面的一致性绕射理论(UTD)给出爬行波的后向散射远区电磁场计算公式,按RCS定义计算爬行波散射贡献.采用微分几何原理分析任意凸曲面上的爬行波短程线特性,根据爬行波在光滑凸曲面上的短程线测地曲率为零的条件,给出一种三维机翼表面短程线计算方法.对三维机翼前缘爬行波进行计算和测试,并计算分析不同机翼参数对前缘影区爬行波的影响.计算结果和测试结果吻合良好,表明该方法计算爬行波RCS快捷有效,可应用于工程分析.     

干扰弹壳体的超声爬波及横波无损检测研究

干扰弹壳体材料要求高,壳体坯料的缺陷检测是非常必要的。针对某型干扰弹壳体坯料可能存在缺陷的特征,结合不同检测区域的检测方法及厂家的检测需求,提出一种基于超声波横波和爬波同时对工件缺陷进行检测的方法,并根据检测需要设计了检测系统,该系统可满足此类坯料缺陷的快速精确检测。通过实验和实际使用证明该方法可行,系统运行可靠,并可有效提高检测效率。     

Spherical wave operators and the translation formulas

Translational formulas for both scalar and vector spherical wave solutions of the Helmholtz equation are developed in a straightforward manner using differential operator representations for the modal functions and well-known expressions for the scalar and dyadic free-space Green's functions. The expansion coefficients are given in compact integral or differential operator forms useful for analytic investigation     

Exact formulas for wave impedance and propagation constants ofhomogeneous, lossy dielectric and/or magnetic materials

Calculations of propagation constants for lossy materials are performed under the approximations of low loss (or high conductivity). To improve the understanding and better predict the analysis of such materials, exact formulation for wave impedance and propagation constants of homogeneous, lossy, dielectric/magnetic materials are proposed. Formulation is based on dielectric and/or magnetic loss tangent of the material     

Diffraction by a discontinuity in curvature including the effect ofthe creeping wave

The existing geometrical theory of diffraction (GTD) solution for the diffraction by a discontinuity in curvature on a perfectly conducting cylindrical surface is uniformly extended in the region where the surface diffraction of the creeping wave launched by the discontinuity is involved     

Approximate formulas for the far field and gain of open-ended rectangular waveguide

Approximate formulas are derived for the far field and gain of standard, open-ended, rectangular waveguide probes operating within their recommended usable bandwidth. (Such probes are commonly used in making near-field antenna measurements.) The derivation assumes first-order azimuthal dependence for the fields, and anE-plan pattern given by the traditional Stratton-Chu integration of the transverse electric (TE_{10}) mode. TheH-plane pattern is estimated by two different methods. The first method uses a purelyE-field integration across the end of the waveguide. The second, more accurate method approximates the fringe currents at the shorter edges of the guide by isotropically radiating line sources. The amplitude of the line sources is determined by equating the total power radiated into free space to the net input power to the waveguide. Comparisons with measurements indicate that forX-band and larger waveguide probes, both methods predict on-axis gain to about 0.2 dB accuracy. The second method predicts far-field power patterns to about 2 dB accuracy in the region90degoff boresight and with rapidly increasing accuracy toward boresight.     

Comparison of asymptotic solutions for the surface field excited by a magnetic dipole on a cylinder

In the analysis of mutual coupling in apertures on a convex surface, the surface field due to a magnetic dipole on a large conducting cylinder is an important canonical problem. Over the years a number of approximate asymptotic solutions have been described in the literature. In this paper the accuracy of five of the best solutions currently available is tested by comparing them with the exact modal solution. This comparison is accomplished by placing the modal solution in a more efficient form for numerical evaluation. From a study of four ray trajectories on cylinders of radius 1.5171 and four wavelengths it is concluded that two complementing solutions due to Boersma and Lee and the author have best overall accuracy. The former solution is most accurate near the source and in the paraxial region while the Latter is best far from the source and off axis. The worst case errors observed for the test trajectories on the four wavelength cylinder were approximately 1 dB in magnitude and3degin phase for the Boersma-Lee solution and 0.5 dB and4deg, respectively, for the author's solution. Generally the errors arc considerably less than these values.     

基于均匀同心圆阵列的近场宽带波束形成

该文提出了一种频率不变近场宽带波束形成的方法。该方法将均匀同心圆阵列的输出经傅里叶逆变换转换成相位模式信号,并经过近场矫正和频率补偿网络,可达到频率响应不变的远场阵列响应效果。在此基础上,该文将传统远场窄带波束形成法推广到近场宽带阵列中。仿真结果表明,该文提出的近场宽带阵列响应具有近似频率响应不变的效果,其波束图也接近远场窄带阵列波束图。另外,与其他几种波束形成方法相比,基于该文提出的频率不变近场宽带阵列提升了波束形成性能,且具有较低的计算复杂度。     

Accurate asymptotic solution for the surface field due to apertures in a conducting cylinder

Asymptotic solutions for the surface field due to a magnetic point source on a cylinder can simplify the computational task in the analysis of mutual coupling-e.g. in conformal arrays. Although several asymptotic solutions are at present available, their accuracy is limited. The aim here is to obtain a new approximate solution with improved accuracy. An asymptotic solution of the exact modal solution for the field on a cylinder which contains terms up to(k_{0}t)^{-2}, wheretis the distance from the source, is derived. Approximate terms up to(k_{0}t)^{-3}are included from the solution for a source on a plane conductor and an earlier asymptotic solution. The new approximate solution consists of the exact solution for a plane conductor, modulated by a Fock function, plus a contribution associated with the cylinder which vanishes in the limit of infinite radius. Typically for cylinders of radius greater than one and half wavelengths it agrees to within 0.5 dB in magnitude and1degin phase of the modal solution. Results for dominant mode mutual and self-admittances of rectangular apertures on a cylinder obtained from this solution are presented. A formula is also given for calculating self-admittances from an asymptotic solution. There is excellent agreement between admittances computed from the asymptotic solution and the modal solution. One exception is the self-susceptance of an axial slot where the error is larger than expected, although the error is low enough to be acceptable in most practical cases.     

An effect of excitation of a transverse magnetic creeping wave when a transverse electric wave crosses the line of the coincidence of propagation constants

Transverse electromagnetic electric (TE) and transverse magnetic (TM) creeping waves on a surface with an anisotropic impedance boundary condition are considered. An asymptotic theory is developed for creeping waves. The theory is valid near the line where the attenuation parameters of two different types of waves coincide and, therefore, standard asymptotics are inapplicable. Asymptotic formulas describing physical effects that occur when a creeping wave propagates across the degeneracy line are derived. It is found that, behind the degeneracy line, a propagating TE wave excites a TM wave with a small amplitude (of order O(k ^−1/6)) and a propagating TM wave excites a TE wave.     

Comment on “The minimization of the back scattering of acylinder by central loading”

K.M. Chen and V. Liepa (IEEE Trans. Antennas Propag., p.576-82, September 1964) described the broadside backscatter of a thin dipole. The model is summarized by various. These work very well at all frequencies specified by those authors, except for one-physical resonance. This is the wavelength at which the antenna's total length is half a wavelength. The present author develops an alternate set of equations which are valid at resonance     

用微控制器或DSP电路控制开机／关机功能

在许多设备中,一个开/关按键可开启或关断电源.一般情况下,不管微控制器或DSP电路正在处理的是处理功能还是负载,在按下按键时,系统都会关断.图1所示的小型电路可用来使微控制器或DSP电路控制这一开/关功能.这样,系统就可先完成各种必需完成的作业,如数据处理、数据存储等,然后再发出指令关断电源.图2示出了它的定时图.虽然最终的设备是与电源断开的,但开关直接与直流电源或电池连接.因此,所有的电容器都会放电.最困难的工作就是使图1中的两个D触发器都进入所需的"关"状态.     

电磁场与电磁波教学思考

“电磁场与电磁波”课程是电子科学与技术、通信工程、电子信息等专业的一门重要的专业基础课程。该课程具有内容多、涉及面广、理论性强、概念抽象、涉及数学概念多等特点,是有一定教学难度的课程。本文针对这些特点,从内容安排、形式设计多个角度展开探讨,认为通过细致的课堂教学安排,充分利用各类资源可以达到更好的教学效果。     

General nonasymptotic and asymptotic formulas in channel resolvability and identification capacity and their application to the wiretap channel

Several nonasymptotic formulas are established in channel resolvability and identification capacity, and they are applied to the wiretap channel. By using these formulas, the epsi capacities of the above three problems are considered in the most general setting, where no structural assumptions such as the stationary memoryless property are made on a channel. As a result, we solve an open problem proposed by Han and Verduacute. Moreover, we obtain lower bounds of the exponents of error probability and the wiretapper's information in the wiretap channel     

A uniform asymptotic evaluation of the field radiated from collinear array antennas

A uniform asymptotic representation of the electromagnetic field radiated from arbitrary collinear array antennas is presented. The asymptotic field is obtained applying the saddle-point technique to the radiation integrals after expressing the current excited along the array axis by means of a Fourier spectral representation. The resulting electromagnetic field is expressed in terms of propagating and evanescent truncated Floquet waves (FWs). The leading asymptotic term of the FWs exhibits an optical behavior and is responsible for the slow decay of the array near-field, which can be described as cylindrical in character. The transition toward the spherical wave propagation regime is due to the interference of the cylindrical field with the relevant scattered field from the array truncations, while the reactive energy storage is due to the evanescent FWs, as well as to the progressive inductive and progressive electrostatic FWs excited close the antenna axis. Using the asymptotic field representation, prediction formulas for the spatial locations where the array near-field exhibits peak deviation from the cylindrical decay, and where the transition from cylindrical to spherical wave propagation regime takes place, have been derived. The proposed analytical technique can be adopted to analyze the spatial field distributions and the radiation mechanisms of periodic and nonperiodic linear arrays.