The Response of a Terminated Two-Wire Line Suspended in Air Above a Semi-Infinite Dissipative Medium and Excited by a Plane-Wave RF Field Generated in Free Space

The analysis previously made to determine the response of a two-wire transmission line buried at constant depth near the earth-air interface when excited by a plane-wave electromagnetic field generated in free space is extended to include the case of the line suspended in air at a uniform distance above the earth's surface. The exciting field is the vector sum of the incident and reflected fields at the point midway between the line conductors. The polarization of the electric field is taken to be parallel to the wires, so that there is no pick up by the terminations. The objective of the study is to determine bounds for the current in specified load impedances in terms of the amplitude of the incident electric field evaluated at the surface of the earth.     

Exact surface impedance for a spherical conductor

A spherically concentric model of the earth is employed to obtain expressions for the surface impedance matrix at the surface. It is shown the surface impedance is a function of both the earth's electrical parameter and the source field configuration. In some cases the latter dependence is of minor consequence.     

Research on the Radiation Characteristics of Patched Leaky Coaxial Cable by FDTD Method and Mode Expansion Method

Patched leaky coaxial cable (PLCX) is proposed as an alternative to the conventional leaky cable for wireless links in a complex environment. It is expected to have the capability of adjusting the coupling between the cable and the environment and give smoother electric field coverage. In this paper, the radiation characteristics of the PLCX with general inclined patches are studied by a hybrid method that involves the finite-difference time-domain (FDTD) method for the near-field computation and the mode expansion method for the transformation of near field to far field. In the method, the space around the patched leaky cable is divided into two regions by an artificial closed cylindrical surface that is incorporated with the FDTD lattice surface when implementing the FDTD iteration. The field distribution on the artificial surface is obtained after the implementation of the FDTD method. Meanwhile, the field outside the artificial boundary is expanded in terms of the Floquet modes with coefficients to be determined. By matching the field expressed by modes and the field obtained from the FDTD method at the artificial boundary, a matrix equation with unknown coefficients is obtained. Solving this matrix equation, the expansion coefficients are known, and the field outside the artificial boundary is ready to be obtained.     

分布式光纤测温系统在电缆温度监测中应用

针对目前电力电缆安全中突出的火灾探测问题,提出了一种分布式光纤测温系统,该系统采用光时域反射技术和拉曼散射测温技术,由测温主机、测温光缆及CSM主机构成,具有极高的灵敏度和定位精度。通过光缆获得电缆表面的温度,传递到测温主机中进行数据分析,并在CSM主机上显示电缆温度状态与报警。为了证实分布式光纤测温系统的有效性,在国内某隧道对该系统进行了温度测量试验,试验结果证明,系统能准确地反应现场运行电力电缆的实际运行情况,及时发现和定位温度异常点,当电缆表面温度超过系统设置的预报警温度值时,系统会立刻输出报警信号,为电缆故障提供温度预警功能,避免电力事故发生。     

Electromagnetic fields of a small loop buried in a stratified Earth

The field structure of a buried vertical oscillating magnetic dipole is examined. The earth is represented as a two-layer half-space, and the source is located in the bottom semi-infinite region. Using numerical integration, the magnitude of the ratio of the horizontal to the vertical magnetic field is examined for an observer on the earth's surface. It is shown that at sufficiently low frequencies, the field ratio is not appreciably modified by the finite conductivity and the geometry of the layers.     

A Feasibility Study to Monitor Soil Moisture Content Using Microwave Signals

A buried leaky coaxial cable is used as a sensor to continuously monitor the average moisture content of irrigated soil at a desired depth. The two-phase feasibility study consists of an analytical and an experimental investigation. The modal equation in the cable is expressed in terms of the surface impedance at the inner conductor boundary and an effective surface impedance at the outer leaky conductor boundary. The effective surface impedance is related to the soil moisture content through its measured attenuation. The results of the experimental work condncted in the field are in good agreement with the analytical results. It is shown that the recorded phase difference between the test signal from the buried cable and the reference signal can be used to monitor the soil moisture content.     

Transient plane wave coupling to bare and insulated cables buriedin a lossy half-space

The current induced on an infinite bare or insulated cable buried in a lossy earth medium due to a transient plane wave is presented. An exact solution is formulated in the frequency domain using a spatial transform under the thin-wire approximation. The widely used equivalent circuit transmission line model is derived from the exact solution. Results are presented for typical transmission structures under high frequency transient excitation and the exact solution is compared with the transmission line approximation. The transmission line approach provides good results for a wide range of cases. For accurate results in the high frequency situation it is necessary that the correct incident field expressions be used and that a complete representation of the earth's electrical properties (σ and ϵ) be retained     

新能源充电线缆的高空核电磁脉冲响应

随着新能源技术的不断发展,多频器件和高压线束的大量应用使新能源车辆电磁兼容问题日趋复杂,研究特种车辆新能源充电线缆的复杂电磁环境效应与防护问题具有重要工程价值。文中选择一种新能源充电线缆,利用三维电磁场仿真软件(CST)建立电磁干扰源和充电线缆模型。基于场线耦合原理,仿真分析高空核电磁脉冲照射下的混合动力装甲车内部新能源充电线缆电磁响应。仿真结果表明,同一线束同种线缆横截面积越大,线缆端口耦合电流越大;在同一干扰脉冲照射下,不同线缆端口耦合电流达到峰值的时间以及开始衰减的时间不同;以及线缆布局影响线缆端口耦合电流的大小;线缆阻抗匹配时的耦合电流远远大于阻抗失配时的耦合电流;新能源充电线缆与传统车载SYV-50-3同轴线缆的高空核电磁脉冲响应变化规律吻合良好。     

时变分形曲面的电磁散射

本文提出描述自然地表面的时变分形曲面模型,并采用基尔霍夫解分析时变分形曲面散射场的时域分形特性。理论分析和实验表明散射场的实虚两部在时域上都近似为随机分形函数,其分形特征相同且分维值与分形曲面的分维值一致。     

Compact conical antennas for wide-band coverage

A broadband antenna with a vertically polarized, omnidirectional electric field is studied. The design of the antenna and its feeding system in the wide frequency range from 20 to 1000 MHz is described and the driving-point impedance determined. Also calculated are the voltage standing-wave ratio (VSWR) and the input impedance of a transmission line connected to the antenna. More efficient operation at low frequencies is obtained by adding a length of transmission line to form a resonant section with the antenna. The effect of the different properties of the earth's surface on the field pattern is treated in a companion paper     

Calculating the voltages induced in technological systems during ageomagnetic disturbance

During geomagnetic disturbances voltages are induced in electrically conducting networks such as power systems, pipelines, and phone cables. The voltage produced in a horizontal loop at the Earth's surface can be calculated by considering the changing vertical magnetic field through the loop or by calculating the electric field around the loop from the horizontal magnetic field variations. The two approaches are equivalent, both being a consequence of Maxwell's equations, however, this equivalence is difficult to visualize. By considering the nondivergent nature of the magnetic field, it is shown how the vertical magnetic field through a horizontal loop is related to the horizontal magnetic field at the periphery of the loop. The case of a magnetic disturbance due to a line current above the earth's surface is used to illustrate the equivalence of the two approaches for calculating the voltage induced in a conducting network     

近岸攻击中沿海地表背景温度场建模研究

空舰导弹红外导引头识别近岸攻击舰船目标时,沿海地表复杂的红外辐射对导引头识别舰船目标造成了障碍。根据沿海地表的特点,建立了沿海地表背景温度场计算模型,研究了太阳、大气、海面等对沿海地表红外辐射的影响,选择了3种典型的沿海地表,对其温度日变化情况进行了数值计算,给出了初步的计算结果。经过与实测值的比较表明,所建模型可以较好地模拟沿海地表温度随各气象参数的变化情况。     

双绞线BCI 等效替代强场电磁辐射实验研究

针对低频线缆耦合通道中最常见的双绞线电缆,以比较典型的互连线缆双绞线为研究对象,针对互连系统单端为非线性受试设备的电磁辐射敏感度进行实验研究。对连续波电磁辐射条件下双绞线传输线负载响应进行了理论推导,分析了典型互连系统辐射与注入的等效以及在高场强下的外推条件。对双绞线耦合通道大电流注入法(BCI)等效替代强场连续波电磁辐射的实验结果进行了分析,验证了BCI 等效替代强场连续波电磁辐射实验方法的准确性。     

Some electrical characteristics of the earth's crust

The electrical characteristics of the earth's crust and of the materials forming it are of great interest to those dealing with waves propagated over the earth's surface, particularly at frequencies below 10⁶cps. In addition, recent advances in geophysical prospecting have been made by employing electromagnetic techniques. Both of these facts indicated the importance of knowing the effects of earth's crust materials upon electromagnetic waves. An over-all picture of the earth and its environment is first presented including the types of materials involved. Techniques for measuring electrical properties of materials with emphasis on in situ methods are next given. The conductivity of numerous types of earth materials is considered and results presented in tabular form for ready reference. Finally, the likely variation in conductivity with depth below the surface is considered.     

Leaky coaxial cable with adjustable coupling loss for mobilecommunications in complex environments

A new kind of leaky coaxial cable composed of an axially-slotted line covered with periodic metallic patches is proposed. The basic cable sets up a surface wave and does not radiate itself, but excites the patch apertures into radiation. The direction of the radiation field can be changed by adjusting the size and period of the patches according to the environmental application. A combined method that involves FDTD iteration and integration of the equivalent surface magnetic current is introduced in order to determine the radiation field accurately     

Resistivity Response of a Homogeneous Earth with a Finite-Length Contained Vertical Conductor

The effect of embedded conductors such as well casings on apparent resistivity measurements on the earth's surface is of interest in geophysical exploration. A relatively simple and computationally efficient method of analysis is presented to determine the apparent resistivity error that is caused by the presence of long slender cylindrical conductors embedded vertically into the earth. The conductors may be of arbitrary length, with arbitrary longitudinal resistance and interface resistance. The potential at the well casing surface is found by modeling the casing as a set of finite-length line current sources and obtaining their values by a matrix inversion. The currents thus found are equivalent to the current that actually flows into the different sections of the well casing, and the potential at a field point due to the finite line current sources and the point current source can then be readily found and can be compared to the undisturbed field point voltage. Apparent resistivity profiles calculated for pole-pole, Schlumberger, and dipole-dipole arrays with adjacent well casings are presented.     

Couplage entre le champ électromagnétique rayonné par un coup de foudre et une ligne de télécommunication aérienne ou enterrée

This paper describes the determination of the current induced by a lightning discharge on a telecommunications cable using a transmission line theory. The electromagnetic field due to the return stroke is calculated by modeling the channel by a vertical antenna situated above a perfectly conducting ground. The electromagnetic coupling to a telecommunications line is then determined by introducing the finite conductivity of the ground into the transmission line model. Examples are given for various positions of the lightning discharge with respect to telecommunications cable. A comparison with results obtained during the last experiment at Saint-Privat-d’Allier is also presented. To get the response of a buried cable the authors first determine the propagation constant and the primary parameters of the line. The reference for the voltage is also analysed. The authors show that the choice of the origin at the infinity allows to take into account the energy propagating in the ground parallel to the cable.     

基于FDTD/MTL 混合算法求解飞行器线束电磁敏感度

结合GJB151A 中的测试标准,求解平面波照射下飞行器线束电磁敏感度（electromagnetic susceptibility ,EMS） 问题。采用时域有限差分法（Finite-Difference Time-Domain ,FDTD）求解空间电磁场在线束屏蔽层上产生的感应电流, 并将其作为多导体传输线（multi-transmission line ,MTL）方程中的激励源[6],计算线缆电磁脉冲响应。该算法可减少 网格剖分数目,节省计算资源,适合电大尺寸目标中线束问题的求解。最后,利用该方法分析了飞行器屏蔽效能和电 磁脉冲极化方式对线束EMS 的影响,得到了电缆设备端感应电压的频率响应特性。计算结果验证了该方法的高效性和 可行性。     

The Magnetic Field in the Vicinity of Parallel and Twisted Three-Wire Cable Carrying Balanced Three-Phased Current

An analysis of the low-frequency magnetic field in the vicinity of three-wire cable carrying three-phase current is presented. Parallel wire systems and twisted wire systems are considered. Radial and tangential components for the parallel wire system are obtained as a function of the position of the observation point in a polar coordinate system. The magnitude of both components approach equality at large distances and at these distances become invariant with angle around the cable. At positions close to the cable the tangential component is maximum opposite to each wire but the radial component has a mimum at different angular positions at different distances. The twisted cable analysis extends earlier work with two-wire single-phase systems. The results show that the behavior at large distance is very similar for the two- and three-wire systems, the only difference being that the latter has a constant multiplier of 0.75. Detailed curves of fields for the parallel wire case are presented. A combined curve for tangential field for parallel wire cable at small distances and the asymptotic field for twisted wire cable at large distances is also presented.     

电磁随钻测量的电激励模式的分析

本文提出一种电磁随钻测量的电激励模式的分析方法。这一方法可计算电磁随钻测量研究中的重要参数,如地面信号场强分布规律及其与工作频率的依赖关系,发射机构的输入阻抗等,从而为随钻测量系统的总体设计提供基本的依据。用这一方法对试验模型和现场试验进行的计算与试验结果很好符合。