负电磁阻材料在强电磁脉冲防护中的应用展望

介绍了电致电阻效应材料和磁致电阻效应材料等可变阻抗功能材料的最新研究进展,分析了其用于高功率电磁脉冲防护的工作原理,指出变阻抗功能材料用于电磁防护具有电磁能量低通的独特性能,对于低功率的安全电磁波可以高效透射,而对高功率的电磁脉冲则有效屏蔽.最后以变阻抗材料用于雷达天线罩为例展望了此类功能材料在电磁脉冲防护中的独特性能与巨大潜力.     

数控测井地面系统中模拟信号分离单元的设计

在全面、细致地分析了井下仪器回传信号的类型、数据通信的特点基础上,测井仪器的回传的模拟信号均是低频信号,因此模拟信号分离单元电路采用压控电压源二阶低通滤波及电压跟随电路,可将低频模拟信号有效地分离出来。以磁记号信号为例,实验表明,模拟信号经过分离单元,滤除了高频干扰信号,为后期模拟量信号的采集处理提供了可靠保障。     

基于屏蔽暗箱窗口法材料快沿电磁脉冲屏蔽效能测试*

为满足材料强电磁脉冲场屏蔽效能的测试需求,搭建了基于屏蔽暗箱窗口法的材料电磁脉冲屏蔽效能测试系统.首先采用连续波对某种金属织物材料进行了频域测试,通过测试空箱和加载材料内部场强大小,计算了该材料的频域屏蔽效能.然后采用快上升沿电磁脉冲源对该材料进行了时域测试,计算了强场作用下材料的峰值屏蔽效能.对测得的时域信号进行降噪处理和快速傅里叶变换(FFT),得到了该材料频域屏蔽效能曲线,与频域试验所测曲线进行了对比,结果基本一致.实验表明该测试系统能够可靠评价强电磁脉冲作用下材料的屏蔽效能.     

Geometrical aspects of magnetic shielding at extremely lowfrequencies

The magnetic shielding effectiveness for closed and open shield structures is studied at extremely low frequencies. Analytical solutions are used for simple geometries, while more complex structures are evaluated using a finite-element method. Both highly conductive and ferromagnetic materials are studied, and their different shielding behavior is shown. Ferromagnetic shields give good results for small and closed shields and they also give a large field attenuation at close range to the source for open shield geometries. Highly conductive materials, on the other hand, are found to be suitable for large shield sizes. The attenuation is, however, reduced in the close vicinity of the source. Comparisons of numerical results with analytical calculations and measurements confirmed the high accuracy of the finite-element model     

Giant polarization in high polymers

In the course of studying the properties of highly conjugated polymers we found that long range orbital delocalization conferred unexpected properties. The presence of giant electronic orbitals made these materials electroactive yet very stable. A new mode of electronic polarizability resulted, a giant nomadic polarization, making these organic polymers among the most polarizable materials ever encountered. In addition, yet other attributes could be found, such as remanent magnetization, or metallic conductivity, or unusual pressure sensitivity. The giant orbital concept opens up new vistas of materials properties. We note that one can tailor giant orbital polymers to produce pure and highly stable super-dielectrics with high dielectric constants, from 6 to 100,000. Such materials will be useful in the electric power control, as in large motor starting capacitors and in power factor correction. They will doubtless also be useful in low visibility coatings, in obscuration, in EMP shielding, in microcircuitry, in transducers, and in parametric circuits. It remains to be proven if this new molecular mode, nomadic polarization, proves superior in energy storage and loss to that of the conventional “dipole orientation” mode. Preliminary results indicate an advantage for the new giant orbital materials.     

多层平板屏效计算中的等效传输线法

讨论了多层平板屏效计算中的等效传输线法。定义了不同传输线间的反射系数与透射系数,求出了反射系数和透射系数表达式。文中透射系数的定义是对传线基本理论的有益补充。     

Computer Expression for Predicting Shielding Effectiveness for the Low-Frequency Plane Shield Case

A computer expression for predicting the shielding effectiveness of an infinite plane shield has been developed for low frequencies (below 50 kHz). It is shown that this expression, which arises as a special case of the solution of the general wave equation, is a sum of the attenuation term of Schelkunoff's transmission theory and a remainder, which is in integral but calculable form. The computed results are in excellent agreement with values obtained experimentally for aluminum, copper, and steel. Application to cases involving highly ferromagnetic materials is hampered by difficulties in determining permeability and its dependence on frequency and field strength.     

小型化宽带磁场探头仿真与设计

提出了一种近场磁场探头,可用于集成电路电磁辐射发射测量,对电子设备中的辐射源定位。探头采用四层印刷电路板设计,介质材料采用高性能、低损耗的Rogers 4350B 材料,确保结构简单和小型化。多层板结构可以有效屏蔽外部空间中的电场耦合。通过使用过孔栅栏和同轴过孔结构实现良好的阻抗匹配,并且提高工作频率。同时,屏蔽过孔能够形成屏蔽腔,有效抑制谐振,提高电场抑制性能。采用HFSS 仿真软件得到磁场探头的性能参数,并进行实物加工。实验结果表明,探头工作频带可达到12 GHz,空间分辨率为2 mm,有良好的电场抑制度,仿真与实测结果吻合良好。     

低频脉冲磁场中磁屏蔽体磁饱和效应的试验研究

针对磁屏蔽体在低频脉冲磁场环境中可能存在的磁饱和问题,利用试验方法开展了磁饱和效应研究,证实了常规工程屏蔽体可在低频脉冲磁场环境中达到磁饱和状态,并通过观测屏蔽效能的变化获得了磁饱和规律,同时分析了磁饱和效应对屏蔽效能的影响及其与屏蔽体的材料磁导率、壳体厚度、外形尺寸等参数的关系.研究表明：磁屏蔽体屏蔽效能在磁饱和效应影响下,呈现出明显的动态变化特点,具有与屏蔽壳体磁导率类似的变化趋势;壳体厚度2 mm以内、长宽高为2 m×2 m×2 m左右的屏蔽体在上升时间为300μs、持续时间为1.2 ms的磁场环境中,达到磁饱和状态的磁化场强度约为10 mT,其磁饱和难易程度与磁导率及外形尺寸负相关,与壳体厚度正相关.试验研究结果与理论分析结论一致,可为磁屏蔽体的科学合理设计提供参考,具有较高的工程应用价值.     

PCB电路电磁脉冲效应混合仿真方法

电磁脉冲作用于屏蔽腔内的微带线电路的过程十分复杂。目前已有的研究存在局限,缺少将场分析与电路分析结合起来的研究方法。通过一个混合模拟方法计算了电磁脉冲辐照下的含屏蔽腔的微带线电路上的耦合电压。该方法通过建立腔体与微带线的电磁拓扑模型,利用BLT方程计算得到电磁脉冲在微带线上的耦合电压,结果表明电场强度为1 000 V/m的电磁脉冲会在微带线终端产生1.5 V左右的耦合电压。通过电路仿真软件仿真计算了外辐射场对电路工作状态造成的影响,外辐射场在300 V/m时会影响信号放大电路的正常工作。     

钢筋网及钢筋混凝土电磁脉冲屏蔽效能研究

采用ＦＤＴＤ法和ＭＰＭＬ吸收处界条件,对无限大钢筋网、钢筋混凝土层和素混送终凝土层的电磁脉冲屏蔽效能进行了时域全波分析。得出了典型结构尺寸钢筋网的电磁脉冲屏蔽效能及其随测点位置变化的规律,并对混凝土层的屏蔽效能以及钢筋交叉点焊接与否对钢筋网电磁脉冲屏蔽效能的影响进行了讨论。通过不同规格钢筋网屏蔽室模型和钢筋混凝土屏蔽室模型的电磁脉冲模拟试验,研究了钢筋粗细、间隔、钢筋交叉点焊接还是绑扎,有否浇筑混     

Some Electromagnetic Compatibility Grounding and Shielding Considerations in Titanium Aircraft Structures

High resistivity of titanium alloys (in the vicinity of 200 microohm-cm) requires special consideration of the role of airplane structure as a current return and as an electromagnetic shield. Experimental data and supporting analysis are presented. Voltage drops due to structure currents are larger in titanium than in aluminum airplanes. Return currents in structure are distributed widely instead of being relatively concentrated. For representative skin thicknesses, magnetic field shielding effectiveness is rather insignificant even at frequencies in the ADF range. Achieving electromagnetic compatibility in titanium airplanes will require greater than previous use of wire rather than of structure returns for susceptible circuits. To obtain a given magnetic field, isolation between a source and a receptor will require greater reliance on physical separation than on intrinsic magnetic field shielding of the structural material.     

Low-Frequency Shielding of a Circular Loop Electromagnetic Field Source

The problem of low-frequency shielding of a loop axially perpendicular to a plane shield of infinite extent is analyzed by 1) the thin shield work of S. Levy, 2) solution of the vector wave equation, and 3) application of the transmission theory of shielding of Schelkunoff. Experimental data are obtained and compared with results of parts 1) and 3) in the frequency range 100 Hz to 50 kHz. The first analytical technique is not general, and the limits of applicability of the results are discussed. In the second solution, which is general, expressions are derived for the total electric and magnetic fields on both sides of and within the shield. The resulting expression for shielding effectiveness is not solved because of its complexity. The results of the third theory are adapted to the problem. The shielding effectiveness expression S = R + A + B is computer evaluated for the six shields considered (1/16-inch and 1/8-inch thick aluminum, copper, and steel). Although some approximations are made, this analytical method is the most useful in predicting the insertion loss of the shield, since the theory includes those parameters neglected in the first analytical technique.     

The penetration of EM waves through loaded apertures

In many cases, the effectiveness of an electromagnetic shield is determined by apertures that exist in the shield. To minimize the penetration of EM fields through a large aperture, the aperture is sometimes loaded with conductive material. The solution of the loaded aperture problem can be reduced to the calculation of equivalent magnetic surface currents, M&oarr;_s, that exist over the surface of the aperture. In the paper, the relevant integro-differential equations have been solved using the method of moments to determine M&oarr;_s for a small, square aperture loaded with a number of impedance sheets of practical interest. These values of M&oarr;_s have been used to calculate the magnetic and electric insertion losses of these impedance sheets. The numerical results are compared with shielding measurements that have been made on carbon composite materials and wire meshes and grids     

基于直接数字频率合成的可编程遥测信号源

针对传统的遥测信号源缺乏灵活可配置性、通用性差的问题,提出采用FPGA和DDS技术为核心设计灵活可配置的可编程遥测信号源。该信号源的硬件电路主要由低成本FPGA芯片和DDS芯片组成,采用Verilog语言进行编程,使FPGA控制核心输出不同的相位、频率、波形等控制字信息给DDS芯片,经DDS芯片后输出所需波形。仿真表明,该信号源能够输出频率范围在0～12.5MHz的频率、相位可调的正弦波、三角波、方波等波形信号,具有一定的通用性。     

小信号低频放大器的调整与测试

针对新安装完成的小信号低频放大器，通过对电路的测试和调整，可发现和纠正设计方案的不足，并查出电路安装中的错误，然后采取措施加以改进，使之达到预定的技术要求。本文就小信号低频放大器给出了完整的调整与测试步骤，具有很高的理论参考意义和实际使用价值。     

Design Theory of Up-Converters for Use as Electronically-Tunable Filters (Sep. 1961 [T-MTT])

The up-converters discussed use a single diode, a wide-band impedance matching filter at their signal input, a moderately wide-band impedance matching filter at their pump input, and a narrow-band filter at their sideband output. With a narrow-band filter at the sideband output, the frequency which will be accepted by the amplifier can be controlled by varying the pump frequency. Analysis of the impedance matching problem involved shows that tuning ranges of the order of a half-octave to an octave are possible. Theory is presented for both the lower-sideband and upper-sideband types of tunable up-converters and for the design of the required impedance matching networks. It is shown that, because of the pump input bandwidth required, it will generally be necessary to accept some mismatch at the pump input. But, by use of a properly designed impedance matching filter, the reflection loss can be kept nearly constant across the pump band, and the incident pump power required is not unreasonable. It is seen that properly designed devices of this type using voltage-tunable pump oscillators should have wide tuning range, fast tuning capability a useful amount of gain, no image response, and a low noise figure.     

The fields due to a small loaded loop in free space

A theoretical analysis of a resistively loaded, electrically small loop is presented which shows the variations of the transverse-wave impedance close to the loop as the resistive loading is altered. The theoretical results are compared with those obtained from a numerical simulation using Numerical Electromagnetics Code (NEC). Depending upon the loading, the loop exhibits electric (high wave impedance) or magnetic (low wave impedance) dipole properties, or intermediate wave impedances. These changes in wave impedance are closely related to variations in the far-field radiation pattern, and simulations are used to demonstrate this. Measured results are used to demonstrate that the variations predicted in wave impedance actually occur in practice. These results have bearing on the interpretation of emission measurements and on the design of circuits to minimize interference to other neighboring circuits     

T/R组件阻抗失配对相控阵天线性能的影响

T/R 组件为满足低剖面的设计要求,收发开关一般采用集成度较高的单刀双掷(SPDT)开关设计方案,然而有源相控阵天线大角度扫描时随着有源电压驻波比的增大,会导致T/R 组件与天线辐射单元阻抗失配。文中分析了该阻抗失配问题,并对采用SPDT 开关的T/R 组件进行了阻抗失配实验,从发射输出峰值功率、组件发射效率、发射通道相位三个方面定量分析了T/R 组件输出端口阻抗失配对发射性能的影响,并将该T/R 组件应用于有源相控阵天线,通过测试等效全向辐射功率(EIRP)进一步讨论其影响。     

Radiation properties of a pigtail-terminated coaxial transmissionline

The method of moments is used to study the shielding effectiveness of a pigtail-terminated shielded wire (coaxial line) above a perfectly conducting ground plane. Numerical computations are performed in the RF frequency range, i.e. 25-1000 MHz. Pigtail wires on either or both ends of the shield are considered. Results are compared to those from the ungrounded case (floating shield). Results show that the presence of pigtail wires as ground connections at RF frequencies is undesirable and may further enhance radiation. The impedance terminations have a small effect on the shielding effectiveness of the antenna structure