屏蔽结构完整性及防护措施

本文提出了屏蔽设计中的一个关键问题。即实际的屏蔽壳由于存在不可避免的缝隙孔洞,破坏了屏蔽结构完整性,使屏蔽体实际的屏蔽效能大为降低。文章分析了影响屏蔽完整性的各种因素及其可采用的防护措施,可使屏蔽体的实际效能大为提高。     

金属丝网屏蔽玻璃屏蔽效能的测试研究

文章介绍了金属丝网屏蔽玻璃屏蔽效能的测试方法,以及对屏蔽效能进行的分析.本文选择金属丝网这种常用的屏蔽材料进行测试,得到一些有工程应用价值的数据和结论,并以此来说明屏蔽技术在实际中的应用价值.     

屏蔽室脉冲波屏蔽效能模型估计方法

根据连续波条件下测得的屏蔽室屏蔽效能,采用相位重建、最佳逼近元法参数估计以及迭代修正算法,建立了屏蔽室脉冲波屏蔽效能的时域估计模型.该模型采用系统离散传递函数形式,可通过数字滤波估计出屏蔽室内脉冲波的响应波形和脉冲波峰值屏蔽效能.通过滤波器建模实验和脉冲磁场屏蔽实验,验证了该方法的有效性,为由屏蔽室连续波测量结果评估脉冲波响应提供了可行途径.     

埋地电缆屏蔽体对雷电电磁波屏蔽效能的研究

针对雷电电磁波在埋地电缆线路中的耦合感应电压问题,通过试验研究了埋地电缆屏蔽层接地方式、与雷电波位置关系对于屏蔽效果的影响。结果表明,埋地电缆采用屏蔽层有助于屏蔽部分外界雷电波的干扰;当电缆垂直于雷电波时,其屏蔽层屏蔽效果比电缆平行雷电波时的屏蔽效果差;屏蔽层接地方式对屏蔽层屏蔽效能有影响,屏蔽层接地电阻越小,屏蔽效能越好。     

测量窗口及校准方法对屏蔽材料测量结果的影响

文章分析了在平面屏蔽材料的屏蔽效能测试中,测量窗口和校准条件的不同对测量结果的影响,并通过对实际测试数据的分析,提出了避免这种影响的措施.     

低频电磁屏蔽工程设计研究

在讨论电磁屏蔽原理和屏蔽效能的基础上分析了屏蔽体结构及屏蔽材料对屏蔽效能的影响,给出了低频电磁屏蔽设计内容、设计注意事项和设计流程,并应用于具体工程设计实践,实际屏蔽效能测试验证了设计的有效性.     

电磁屏蔽和吸波材料的研究进展

阐述了研究电磁屏蔽材料和吸波材料的重要性,分析了在不同情况下电磁屏蔽材料和吸波材料的作用机理。综述了常见的电磁屏蔽材料的种类以及各种屏蔽用涂料、填料的特点,同时介绍了吸波材料的种类和研究热点,并着重讨论了导电填料、基体、复合工艺等因素对其屏蔽效能的影响关系。最后对电磁屏蔽材料和吸波材料的研究和发展趋势也作了简要的阐述。     

关于双层带孔缝腔体的屏蔽效能研究

基于现代生活中抗电磁干扰的重要性,给出了完善的求解双层带孔缝矩形腔体在平面电磁波照射下的屏蔽效能的建模过程.在建模中考虑了电磁波的入射角和极化角,并把电磁波作用在腔体外层孔缝上所产生的散射电压作为辐射源.把孔缝建模成不对称的共面带状线,把矩形腔体建模为一端完全开放、另一端完全封闭的矩形波导,并应用传输线理论推导出腔体内任意点的屏蔽效能.相对于以往模型而言,在建模的完整性、计算速度,以及屏蔽效能的提高上均有所改善,为工程实践提供了很好的理论参考.     

地下工程中金属门非核电磁脉冲屏蔽效能研究

以圆形截面坑道为简化模型,运用旋转对称体时域有限差分法将三维问题转化为二维问题处理,计算了地下防护工程口部金属门对高功率微波、超宽带电磁脉冲的屏蔽效能,分析了门缝大小、门框嵌入岩土介质深度对屏蔽效能的影响,确定了场泄漏的主要途径.计算结果表明,门对坑道中不同的传输波模具有不同的屏蔽效能;泄漏场主要是通过门框的绕射进入工程内部,门缝的泄漏较小,门缝大小以及门框嵌入岩土介质的深度对屏蔽效能的影响是次要的;另外,通过门的泄漏场在工程内部迅速衰减;HPM的载频越高,UWB的脉宽越窄,门的屏蔽效能越好.最后对数值计算结果和实验测得数据进行了比较,二者吻合较好,证实了数值计算的有效性.     

等效传输线法在求解金属接缝屏效中的研究与应用

介绍了用等效传输线法解析求解孔缝屏蔽效能的原理,在此基础上提出了求解金属接缝屏蔽效能的方法,然后通过算例验证了该方法的有效性,最后给出了该方法在实际中的应用.     

Experiment on the shielding by hollow conducting tubes

This paper describes several practical aspects of shielding provided by openings such as ventilation vents acting as waveguides. Fundamental properties of electromagnetic waves in the interior of a hollow conducting cylindrical tube are presented. Then the guidelines for oscillator's design and harmonic generation by nonlinearities are presented. A consequent wideband setup having low cost and common devices as well as high dynamic range is proposed to perform reliable measurements from 50 MHz to 1.5 GHz. Measurements of circular cylindrical waveguide effectiveness point out the simplicity of the systematic procedure and illustrate the effects of apertures on shielding walls. Shielding loss achieved by these apertures at frequencies below cutoff allows engineers to gain more insight into analysis and design of shields with intentional discontinuities used to exclude and to confine electromagnetic interference.     

屏蔽对电子设备EMC性能影响分析

针对电磁兼容(Electromagnetic Compatibility,EMC)测试标准对电子设备机箱屏蔽效能的需求,首先从屏蔽机箱的反射损耗与吸收损耗等方面入手,分析了屏蔽机箱的屏蔽效能,描述了如何根据实际使用情况对屏蔽机箱的材料及其厚度进行选择。根据屏蔽机箱实际使用情况,分析了孔洞和缝隙对其屏蔽效能的影响。结合2个电子设备的EMC测试实例,分别描述了如何对屏蔽机箱上的孔洞和缝隙进行处理,从而提高设备的EMC性能。分析并讨论了如何在设计阶段采取措施,通过加强屏蔽,改善设备的EMC性能。     

垂直入射均匀平面波的多层平板屏蔽效能分析

本文基于电磁场方法,详细导出多层平板屏蔽体对垂直入射均匀平面波的屏蔽效能计算公式。此外,提出计算屏蔽效能时,集肤深度和屏蔽体厚度的约束关系,给出用作计算机机箱的几种常用材料的屏蔽效能计算实例。     

基于正交振幅调制的压电声透通信系统设计

在有金属障碍物遮挡的环境中,传统无线通信技术由于电磁屏蔽效应而无法有效完成信息传输。压电声透通信通过声波穿透障碍物以克服这一缺陷,在实现通信的同时无需破坏金属原有结构,因此具有独特的优势和应用价值。设计并实现了一种压电声透通信系统,采用数字通信和信号处理手段生成调制信号,利用波形发生器和高速数据采集卡发送和接收信号。实验表明,该系统能有效地实现金属板两侧的声透通信。     

金属网栅电磁屏蔽窗口薄膜的设计与制备

通过光刻掩膜技术、电阻热蒸发沉积技术制备电磁屏蔽窗口金属网栅薄膜,研究金属网栅的红外透射率和电磁屏蔽效能。为了能有效地屏蔽电磁波,使用CST Studio Suite电磁仿真软件设计不同周期、线宽的金属网栅,采用光刻掩膜技术、电阻热蒸发技术在双面抛光单晶硅基片上完成线宽为30μm,周期分别为350μm、450μm、550μm、650μm、750μm的金属网栅薄膜的制备。采用真空型傅立叶红外光谱仪和矢量网络分析仪分别对不同结构参数金属网栅薄膜的光谱特性和电磁屏蔽效能进行测试。结果:实现在双面抛光单晶硅基底上制备的网栅在12~18 GHz频段内,网栅的电磁屏蔽效能均达到12 dB以上。在3~5μm波段的透射率损失仅为8%。为了得到既具有高透光率,又具有强电磁屏蔽效能金属网栅薄膜需要合理设计金属网栅的线宽和周期。制备过程中网栅的光学-电学特性不仅受周期和线宽影响,掩膜板的加工精度、金属网栅的加工缺陷等也会造成不同程度的影响。     

平面波斜入射到有孔腔体的屏蔽效能分析

使用解析方法研究了缝隙偏离中心的有孔屏蔽腔屏蔽效能。将有孔腔体的屏蔽和传输特性用等效传输线的高次模进行分析,推导了平面波以任意角度和极化方向入射时,有孔腔体屏蔽效能的解析计算表达式。分析了入射角度、极化方向、孔缝尺寸、测试点位置、腔体壁损耗、工作频率等参量与腔体屏蔽效能的关系。经与腔体谐振频率比对,表明该解析方法得到的结果可信,而且解析公式计算速度快,利于参量分析,能为屏蔽腔体设计提供依据。     

Structured Reduced Graphene Oxide/Polymer Composites for Ultra‐Efficient Electromagnetic Interference Shielding

A high‐performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via high‐pressure solid‐phase compression molding. Superior shielding effectiveness of 45.1 dB, the highest value among rGO based polymer composite, is achieved with only 3.47 vol% rGO loading owning to multi‐facet segregated architecture with rGO selectively located on the boundaries among PS multi‐facets. This special architecture not only provides many interfaces to absorb the electromagnetic waves, but also dramatically reduces the loading of rGO by confining the rGO at the interfaces. Moreover, the mechanical strength of the segregated composite is dramatically enhanced using high pressure at 350 MPa, overcoming the major disadvantage of the composite made by conventional‐pressure (5 MPa). The composite prepared by the higher pressure shows 94% and 40% increment in compressive strength and compressive modulus, respectively. These results demonstrate a promising method to fabricate an economical, robust, and highly efficient EMI shielding material.     

基于有限元方法的波导管结构电磁屏蔽屏蔽效能分析

提出一种在屏蔽箱体孔缝结构的外部增加截止波导管结构的方法,利用截止波导管对高频电磁波的衰减作用来提高屏蔽箱体屏蔽效能。基于有限元法分别对截止波导管的长度、厚度及其形状进行仿真,仿真结果表明:在0.1 GHz~1 GHz频率范围内,随着截止波导管长度及厚度的增加屏蔽箱体屏蔽效能提高15d B以上,圆形和矩形截止波导管对屏蔽效能影响不大。根据实际情况合理选择截止波导管的长度及厚度可以提高微弱信号处理电路的电磁抗干扰能力。     

NEMP fields inside a metallic container with an aperture in onewall

The finite-difference time-domain (FDTD) method was used to study the nuclear electromagnetic pulse (NEMP) waves coupling into one metallic container through a small aperture in one face of the container. The incident electric fields of NEMP waves were expressed by double exponential forms with two different decay constants. The time-domain behavior of the electric field inside the metallic container excited by the waves was obtained by the FDTD method. The electric field distributions on various layers for the area of the aperture of 10×10 cm² were also calculated. It was found that the shielding effectiveness is greatly improved by a factor of 255 by reducing the area of the aperture from 10×10 to 1×1 cm² . The aperture filled with dielectric materials was also studied for shielding effectiveness. The coupled electric field inside the metallic container was round to be a nonlinear function of the relative dielectric constant of insulators filled in the aperture     

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.