Accurate Characterization of Shielding Effectiveness of Metallic Enclosures With Thin Wires and Thin Slots

In many electrical and electronic systems, metallic enclosures are used to provide electromagnetic shielding. These enclosures normally contain thin wires, thin slots, and frequency-selective slots (FSS) that degrade the shielding effects. In this paper, integrated FDTD formulations are developed that can model both subcellular thin slots and thin wires simultaneously. The formulations are shown to be capable of accurately predicting shielding effectiveness and inner field distributions of a metallic enclosure in both the frequency- and time-domains when subject to a high-power electromagnetic pulse.      

结构/屏蔽一体化复合材料研究现状及发展趋势

面对电子设备和系统的综合性迫切需求,现有电磁屏蔽材料在屏蔽效能、带宽、密度、强度以及极端环境适应性等方面各有优缺点,结构/屏蔽一体化复合材料已成为近几年电磁防护材料技术领域的研究重点和热点。重点介绍了国内外在结构/屏蔽一体化复合材料方面的研究情况,并对铝镁合金、树脂基电磁屏蔽复合材料等典型结构/屏蔽一体化复合材料的发展趋势进行展望。     

Corrosion of a zinc-coated steel enclosure at the contactinterfaces of gasket joints

A typical enclosure for information technology (IT) equipment is made of various sub-assemblies such as enclosure cases, gaskets and I/O connectors, and the shielding effectiveness of the enclosure is largely determined by junctions in the enclosure for electrically connecting different shielding panels or components. Inter-metallic junctions may get corroded and the shielding effectiveness of the enclosure may deteriorate. The identification of the corrosion mechanisms responsible for the shielding degradation of zinc-coated steel enclosures is the primary focus of this study. A series of preliminary experimental investigations were conducted to help in identifying the corrosion mechanisms. Factors contributing to the corrosion process are discussed. This work provides a basis for on-going effort in experimentally quantifying and modeling the corrosion and corrosion-induced shielding-degradation behavior of electromagnetic shielding enclosures     

Ansoft HFSS在电磁屏蔽设计中的应用

随着电磁环境的日渐复杂,电子设备的电磁屏蔽设计显得愈加重要。在阐述电磁屏蔽原理和屏蔽效能计算方法的同时,简要介绍了有限元法的基本原理。利用Ansoft HFSS软件对某电子设备机壳进行了屏蔽效能分析,计算出了机壳内场的分布和机壳的屏蔽效能。通过比较不同尺寸缝隙对机壳屏蔽效能和谐振频率的影响,提出了提高屏蔽效能的改进措施。通过算例也显示了HFSS软件在电磁屏蔽设计中的优越性。     

Wideband Pulse Responses of Metallic Rectangular Multistage Cascaded Enclosures Illuminated by an EMP

A generalized mathematical procedure is developed for investigating shielding performance and inner wideband pulse responses of metallic rectangular multistage cascaded enclosures with multiple rectangular apertures, which is illuminated by an electromagnetic pulse (EMP). The mathematical methodology is based on the integral equation technique combined with the method of moments, by which all unknown aperture fields are solved according to a set of linear algebraic equations of infinite order. Numerical computations are performed to show frequency- and geometry-dependent shielding effectiveness and inner pulse waveforms of single- and double-stage cascaded enclosures, respectively, with computational accuracy and convergence rate also checked. It is found that using appropriate metallic multistage cascaded enclosures, high shielding performance can be achieved, which can provide an effective protection for certain electronic and communication systems from the interference of an EMP.      

电磁屏蔽室屏蔽等级和测量方法研究

电磁屏蔽室的屏蔽效能检测是衡量和判定屏蔽室等级的主要手段,因此正确选定其依据的屏蔽等级和测量方法的标准非常重要。文中对现行电磁屏蔽室屏蔽效能等级和测量方法的相关标准进行了梳理和对比,为在实际测量和确定屏蔽室等级时正确选定恰当的标准提出了可供参考的意见。另外结合工程实际,对屏蔽室单点与多点接地、绝缘、屏蔽门的设置等问题进行了讨论。     

双层加载电路板屏蔽腔屏蔽效能研究

为了提高设备中电子元件抵御来自外界和内部其他元件的电磁干扰,根据传输线理论,将双层加载电路板屏蔽腔体模型转换为电路图,利用电路图推导出腔体中心屏蔽效能的等效公式。利用Matlab生成传输线法屏蔽效能曲线,并通过仿真软件CST建模仿真,仿真结果与Matlab输出曲线良好吻合,验证了公式的正确性。运用CST研究了一些因素如电路板大小、数量、放置方式以及距孔缝的距离对屏蔽效能的影响。为了更加贴合实际,采用加载集成运算放大电路的印制电路板来研究腔体屏蔽效能以及腔体对电路板功能的影响,最后提出了一些提高屏蔽效能的方法。     

Shielding Performance of Metallic Cylinders

Electrical and electronic equipment must often be protected against external interference. Accordingly, metal shields are used against microwave radiation, electromagnetic effects, etc. Conducting materials, impregnated with elastic substances, are also used in many cases. The present paper deals with the performance of such a cylindrical shield, including a reference to shielding effectiveness. It is shown that with the assumed model the shield is pervious along its axis over a spectrum of frequencies.     

Proposed Recommended Practices for the Measurement of Shielding Effectiveness of High-Performance Shielding Enclosures

Uniform measurement procedures are proposed for determining the relative effectiveness of room-size high-performance shielding enclosures. Test procedures are designated to measure the effectiveness of a rectangular parallelepiped with edge dimensions ranging from 1.5 to 15 meters. They are formulated to enable use of commercially available equipment for conducting tests under nonideal conditions. The standard does not, however, specify construction details for shielding enclosures nor does it suggest methods for calculating their effectiveness.     

导电衬垫材料的研究与发展

导电衬垫材料是电子设备中应用最为广泛的一类屏蔽材料，在抑制电子设备缝隙电磁泄漏方面发挥了重要作用。文章结合作者的科研工作，对于衬垫材料的抑制机理、材料类型、屏蔽特性、屏效计算、应用技术、测试方法等关键技术进行了综述，并提出了将来研究发展的方向。     

某收发系统的电磁屏蔽设计

分析并确定了电子设备的内外部电磁环境电平,确定了屏蔽设计模型;利用转移阻抗概念,对使用导电衬垫机箱的电磁屏蔽效能进行了定量计算,从而指导结构设计。     

军用电子设备常用电磁屏蔽材料及其应用

军电子设备的电磁兼容性设计是关键,基于此从材料角度阐述电磁屏蔽理论,介绍了军用电子设备常用的电磁屏蔽材料及其具体应用,总结了一些常用屏蔽材料的特性及优缺点。     

HIRF penetration through apertures: FDTD versus measurements

The penetration of high-intensity radiated fields (HIRF) into conducting enclosures via apertures is an EMI issue that is relevant to all aviation. The stories are numerous, of disrupted communications, disabled navigation equipment, etc., due to the effects of EM sources external to the aircraft. Here, the FDTD method is used to predict the shielding effectiveness of conducting enclosures with apertures, and the numerical results are compared with measurements. Several issues related to the FDTD analysis of highly resonant and high-quality factor (high-Q) structures, such as windowing and acceleration techniques, are examined and discussed     

New figures of merit for the characterization of the performance of shielding enclosures

Evaluation and measurement of shielding performance of enclosures and protection structures in general are based on the comparison between the local field values with and without the shield. Apart from some practical problems arising in specific, but relevant, situations like enclosures of small dimensions, such an approach appears rather incomplete and sometime deceitful. Despite this, shielding effectiveness (SE) is a well-established parameter, and it seems that for decades, the attention has been focussed more on how to evaluate and measure the so-called SE, rather on what the goal of any shielding structure is and why each evaluation and measurement should be performed. The main drawback is that SE is a local quantity and its knowledge does not help in the prediction of the real mitigation of undesired effects achieved by means of any shielding structure; undesired effects are mainly due to an integral of an electric or magnetic field, and/or to spatial variations of electric and magnetic field components. In the past, proposals were advanced toward an improved definition and measurement of electromagnetic SE; the proposed new figures of merit were based on the energy (power) penetrating the enclosure, perceived as the key factor for the shielding problem. However, it seems more adequate and correct the direct reference to the mechanism of birth of induced effects, as stemming from Maxwell equations. For these reasons, two new figures of merit are proposed for the comparison of enclosures and shields performance.     

适用于5G电磁屏蔽的介质开孔型频率选择表面设计

5G通信技术的迅速发展和产业化进程给电子设备的电磁屏蔽设计带来了严峻挑战。5G通信中24 GHz以上的电磁波极易通过电子设备屏蔽外壳上的各种孔缝耦合进入电子设备内部,影响设备的正常工作。针对常规散热孔设计难于适应5G通信发展需求,提出了一种介质开孔型频率选择表面(FSS)结构。该结构在不影响设备通风散热的条件下,实现对28 GHz频段信号的电磁屏蔽。经过全波分析方法仿真,所设计的FSS结构在28 GHz频段电磁屏蔽效能(SE)达30 dB以上,带宽大于2 GHz。无论是TE还是TM极化电磁波,在0°~60°入射范围内具有良好的电磁屏蔽稳定性。     

Electromagnetic Shielding Effectiveness of Steel Sheets with Partly Welded Seams

The effect of single welding flaws on the electromagnetic (EM) effectiveness of welded steel enclosures has been assessed. The possibility of resonant reradiation by these flaws has been examined, using resonance calculations and direct EM measurements. Using these results, a method was developed for assessing shielding quality of hardened military structures, such as SAFEGUARD sites, and EM shielded enclosures. The effect of four formns of incomplete welds on the shielding effectiveness of welded steel enclosures was determined for single flaws. Electromagnetic shielding effectiveness tests (from 10 kHz to 10 GHz) were made on various test specimens of 11-gauge steel plate. These test specimens included butted plates with incomplete welds and plates with single holes and slots cut into them. Tests simulated the worst cases of cracks, lack of fusion, and porosity. Shielding effectiveness as a function of flaw size was determined for each defect, and a critical or transition flaw size was determined for each of three frequency bands and at the 100-dB shielding level for each type defect. The measured results were compared to a calculated resonance response by modeling the flaws as slot antennas.     

机柜布局对方舱屏蔽效能影响的研究

电磁屏蔽方舱作为机动式指挥系统的车载运行环境,内有多种电子设备。为了保障舱内的电磁环境满足电子设备正常工作的需要,方舱必须具有良好的电磁屏蔽性能。方舱内的机柜布局是影响电磁屏蔽方舱屏蔽效能的一个重要因素。通过对电磁屏蔽方舱屏蔽效能的测试分析和CST仿真分析,定量分析了机柜布局对电磁屏蔽方舱屏蔽效能的影响,并对机柜的布局...     

Electromagnetic shielding characteristics of optical-fiberfeedthroughs

A number of commercially available optical-fiber connector styles ST, SC, and FC were tested to determine the extent to which their use in bulkhead adapter feedthroughs would compromise the shielding of electromagnetic interference for electronic enclosures. Connectors and adapter barrels made from metal, ceramic, and polymer materials were included in the tests. The tests were carried out using a nested reverberation cell and covered a frequency range from 1 to 16 GHz. Although we rely on data acquired by making shielding effectiveness (SE) measurements, we report the results in terms of a transmission cross-section which is the ratio of the power coupled into an enclosure through an aperture to the power per unit area incident on the aperture. The amount of coupling through the feedthroughs we tested varied over 70 dB. The shielding of an all-metal FC connector system was nearly equal to that of a blank reference plate. In some cases, a feedthrough coupled more energy into the enclosure than was coupled through the empty hole required to mount the adapter barrel. Unlike SE, the transmission cross sections do not depend on the volume, shape, or construction materials of the enclosure and can be used to estimate the degradation in the SE for enclosures other than our reference cell. The uncertainties in the reported transmission cross sections are calculated to be ±3 dB and are small compared to the differences between the measured cross sections     

武器装备中电子插件板的环境适应性设计研究

军用电子设备的使用范围广泛,面临的环境条件复杂多样,设备的环境适应性问题比较突出。介绍了武器装备中电子插件板的环境适应性设计,包括热设计,电磁兼容设计,抗干扰设计,耐振动、抗冲击设计以及＂三防＂设计等,通过提高电子设备基本组成单元的耐气候、机械、电磁以及生物、化学环境能力,从而增强整个设备的环境适应性。     

超轻多孔金属材料在军事上的应用

开孔型多孔隙泡沫金属材料以其高度均匀的孔结构、连续规则重叠的孔分布、极好的通透性及良好的导电性等优点,广泛应用于各类电子设备通风散热装置的电磁加固.文中采用沉积法制备高通透多孔隙泡沫镍,通过对样品的导电率及屏蔽效能进行测试,结果表明多孔隙泡沫镍在孔隙率大于95%时,导电率仍达到10⁵ S/m,导电性良好;屏蔽效能达到25 dB（10 kHz）、87 dB（15 MHz）、46 dB（18 GHz）等,在很宽的频率范围均有很好的屏蔽效能.进一步采用三维模型法,基于多孔隙泡沫镍大多数相同孔的立体网状骨架结构特性,建立电磁传输十二面体基本结构单元模型,探讨了多孔隙泡沫镍的屏蔽机理,为高通透多孔隙泡沫金属材料的电磁防护应用提供有益指导.