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Transient Electromagnetic Fields Due to Switching Operations in Electric Power Systems 总被引:3,自引:0,他引:3
Transient electromagnetic fields are produced when breakers, disconnectors, and switches of various types are operated under varying load conditions. For analysis purposes, a discharge current pulse is assumed during switching operations, which can act as a dipole antenna. The transient electromagnetic fields of this antenna can be calculated for near-and far-field conditions. 相似文献
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该文针对现有高功率微波武器辐射天线的不足,提出了将磁化等离子体通道用作电磁脉冲辐射天线的思想磁化等离子体通道天线(MPCA),分析了MPCA周围为有耗气体媒质时MPCA所传播的一般模式。简单阐述了MPCA的具体实现方法,根据MPCA的工作原理,建立了MPCA的几何模型,导出了广义柱坐标系下磁化等离子体中纵向场所满足的波动方程及纵-横的关系,利用边界条件导出了MPCA严格的特征方程。重点讨论了MPCA的传播常数随等离子体通道参数(等离子体频率和通道半径)的变化。结果表明,强磁场时等离子体频率对天线衰减常数影响增大,且有一极值出现。 相似文献
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用于瞬态电磁场测量的宽带脉冲天线 总被引:4,自引:3,他引:1
脉冲天线是脉冲雷达、瞬态电磁场测量等应用的关键设备之一。本文描述了用于瞬态电磁场测量的一种宽带脉冲天线的设计,给出了测量结果,测量结果表明,该天线具有高保真和宽频带特性,有有效地发射或接收毫微秒脉冲信号。实际制作的天线已成功地应用于外场瞬态电磁测试系统。 相似文献
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Exact solutions are given for the transient electromagnetic (EM) fields excited by an electric dipole antenna with an impulsive current in a conducting medium. There exists an optimum waveform for the antenna current which can generate an EM pulse with a maximum intensity at a particular distance from the antenna. It is found that the EM fields of an EM pulse excited by an antenna in a conducting medium can be divided into two parts. The first part is an impulse wave which propagates with the speed of light (1/√(μϵ)) and decays exponentially. The second part builds up gradually and propagates slowly, and more importantly this part attenuates as an inverse power of distance which is a much slower rate than an exponential decay 相似文献
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Approximate solutions for the current of thin circular and elliptical loops have been determined on the basis of an asymptotic antenna theory. The fields at and around the center have been calculated to illustrate the broadband behavior of these structures when used as electromagnetic pulse (EMP) simulators. Fields calculated with this approach and those measured in an actual EMP simulator are compared. The comparison indicates that the model presented might be adequate for describing the salient features of the fields of a real system and could provide an alternative to experimental field mapping efforts 相似文献
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T. N. Ogurtsova 《Radioelectronics and Communications Systems》2016,59(9):402-408
Thetheoretical model of pulse ultrawideband (UWB) receiving antenna consisting of a ferrite element surrounded by a coil of conductor is investigated. The magnetodielectric cylinder of infinite length is selected as the ferrite element. The excitationUWBsignal represents a pulse of electromagnetic field with the envelope in the form of a Gaussian function with high-frequency filling signal. The peculiarities of amplitude-time dependence have been considered for the pulse of induction electromotive force occurring in the closed conducting loop, which surrounds the cylinder, under the assumption of absence of its influence on the scattered fields inside and outside the cylinder. The connection between the electromagnetic parameters of the ferrite element and the frequency-time parameters of the excitation pulse electromagnetic field, which are optimal from the point of view of effective undistorted signal reception, has been determined. 相似文献
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A measure of coupling efficiency for antenna penetrations 总被引:1,自引:0,他引:1
The electromagnetic penetration into a shielded enclosure through an antenna connected to a receiver inside the shield is discussed. Reciprocity is used to relate the far-zone fields to the short circuit current in the transmission line. Using a Norton equivalent circuit, a measure of coupling efficiency is derived, relating the electric field incident on the antenna to the current incident on the receiver. It is shown that the coupling efficiency can be determined from standard electromagnetic measurements. As a first example, an open-ended coaxial waveguide is considered. As a second example, a transmission line connected to a receiver inside the shield and to a center-fed dipole antenna outside the shield is discussed. Numerical results are presented for the dipole for various receiver bandwidths and transmission line characteristics. The results are given both in the frequency domain and in the time domain for a pulse incident field 相似文献
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The development of antenna theory for nonsinusoidal electromagnetic waves has been based on the idealized rectangular pulse. In practice, an antenna that is designed to operate in the mode of an electric hertzian dipole would radiate a pulse that best approximates a Gaussian one when the driving current consists of a linear transient. The principle of radiation of nonsinusoidal electromagnetic waves with the time variation of Gaussian pulses is discussed. The properties of the Gaussian pulse are presented, i.e., the autocorrelation function, energy spectral density, and spectrum. Antenna patterns, such as peak-amplitude pattern, peak-power pattern, energy pattern, and slope pattern are derived for a Gaussian pulse received (or radiated) by a linear array antenna. Computer plots of the derived antenna patterns are presented that show a considerable improvement in the angular resolution capability over that of the antenna patterns that have been derived for a rectangular pulse 相似文献
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设计了一种基于吸波材料的屏蔽领结天线, 采用金属腔体提高天线的方向性, 并起到屏蔽作用.通过在腔体内部填充吸波材料, 来降低电磁波在金属腔内部的反射, 并改善天线的频率域特性和时间域信号的拖尾.通过有限元电磁仿真软件HFSS设计天线模型, 优化天线参数.实际天线的各项参数较加吸波材料和金属腔之前得到了有效改善:频率域上, 天线的中心频率有所降低, -10 dB以下带宽从原来的100 MHz提高至200 MHz; 时间域上, 脉冲信号的宽度降低, 信号拖尾得到了明显改善.实际探测证明, 在天线背部加填有吸波材料的金属屏蔽罩, 可以有效降低来自上方的干扰, 分离直达波和有用信号, 提高探测精度. 相似文献
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Chou H.-T. Pathak P.H. Rousseau P.R. 《Antennas and Propagation, IEEE Transactions on》1997,45(5):829-836
A closed-form analytical solution is developed for predicting the early-time transient electromagnetic fields which are generated by a perfectly conducting parabolic reflector antenna when it is illuminated by a transient step spherical wave due to an elemental Huygen's source located at the focus. This closed-form time-domain solution, which is valid both near and far from the reflector (and anywhere in the forward region) can be used via the convolution theorem to efficiently obtain the early-time transient fields generated by the same parabolic reflector antenna when it is illuminated by a realistic finite-energy pulse which emanates as a spherical wave from the focus. The transient solution is developed here by analytically inverting, in closed form, the corresponding frequency-domain solution in terms of a radiation integral that employs an asymptotic high-frequency geometrical optics (GO)-based approximation for the fields in the aperture. Numerical results are presented for the transient fields both near and far from the reflector. The fields on boresight exhibit an impulse-like behavior similar to that of the impulse radiating antenna (IRA) introduced by Baum et al. (1989, 1993) 相似文献
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A broadband receiving antenna was realized using a resistively loaded thin-film V-monopole and a 500-Ω oscilloscope probe. The pulse-receiving performance of the antenna was evaluated in a time-domain antenna range, for various directions of the incident pulse. The antenna is capable of receiving a 520 ps electromagnetic pulse, incident within 45° from the boresite direction, with good fidelity. The antenna was also tested in a transverse electromagnetic cell in the time and frequency domains. The frequency-domain receiving transfer function of the antenna was found to be within -57±3 dB in the 22 MHZ to 1.1 GHz frequency range 相似文献
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电磁脉冲与短波天线耦合特性的研究 总被引:3,自引:0,他引:3
为分析电磁脉冲与短波天线的耦合特性,采用计算电磁学矩量法,提出求解天线问题的一般思路。首先采用分域基函数计算出天线的表面电流与输入阻抗,并与FEKO仿真结果相比较,验证该方法的正确性;再计算了激励为电磁脉冲时,通过天线耦合产生的感应电流的频域及时域响应,对系统的电磁脉冲损伤分析有较好的参考价值。 相似文献
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提出一种电磁脉冲辐射系统设计方案,此系统由Marx发生器、短路-锐化组合开关型脉冲形成线和带低频补偿的高功率超宽带横向电磁波(TEM)喇叭天线组成。Marx发生器产生的单极脉冲经过短路-锐化组合开关型脉冲形成线锐化成双极脉冲,然后馈入天线进行辐射。仿真结果表明,在充电电压为10 kV时,电磁脉冲源可产生脉冲宽度1.41 ns、峰值功率7.69 MW的双极脉冲,此双极脉冲频谱主要分布在0~1.6 GHz频率范围内;高功率超宽带TEM喇叭天线带宽为0.625~2.9 GHz(相对带宽为129%),功率容量可达10 MW,能有效地将电磁脉冲源产生的双极脉冲辐射出去。 相似文献
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为了研究地震产生的机理, 需要分析和研究地基极低频(Extreme-Low Frequency, ELF)电磁波的传播特性.地基任意ELF线天线产生的电磁场可由ELF点源产生的电磁场进行叠加.通过地基ELF点源电磁场的表达式导出了ELF线天线在地-电离层壳体中电磁场的表达式.利用加速收敛算法得到了单条和两条ELF线天线产生电磁场的场强空间分布图, 用色标表示场强值在空间分布的强弱.电场水平分量的场强值要比垂直分量的场强值小, 磁场水平分量的场强值要比垂直分量的场强值大.而且两条线天线产生的场强值要比单条线天线产生的场强值大. 相似文献
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针对平板型表面波放电等离子体源,建立了表面波放电狭缝天线辐射电磁波模型,对狭缝天线辐射电磁场分布进行了三维数值计算,并与表面波电磁场进行对比分析,讨论了平板型表面波放电机理。结果表明:整个狭缝天线阵激发的电磁场是每个狭缝天线激发电磁场的线性叠加;狭缝天线阵直接激发的电磁场强度在临近波导壁面处很大,并且随着空间距离的增大迅速衰减;狭缝天线阵直接激发和表面波的电场均远大于各自的磁场,分析电、磁场对带电粒子的力作用时可以忽略磁场力的作用;表面波电磁场远大于狭缝天线阵直接辐射的电磁场,强电磁场范围也远大于狭缝天线阵直接激发的强电磁场范围,等离子体有增强电磁场强度、扩大强电磁场范围的作用。 相似文献
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