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。     

孔洞对于机箱屏蔽效能的影响

通风孔是影响机箱电磁屏蔽效能和通风能力的重要因素,在保证通风能力的前提下提高机箱屏蔽效能是结构设计中的关键环节。针对工程实际中通风孔设计不合理导致机箱屏蔽效能不达标,在研究孔洞的形状、尺寸、深度和空占比等因素对机箱屏蔽效能的影响的基础上,提出了通风孔屏蔽设计方法,以提高设备屏蔽效能。在CST软件中建立机箱模型,分析机箱屏蔽效能,并利用CST软件分别分析机箱上有不同形状、不同直径和不同深度的孔洞时机箱的屏蔽效能。在考虑机箱通风性能的基础上,分别仿真孔洞空占比为40%、60%和80%时机箱的屏蔽效能。根据软件的仿真结果确定尺寸和深度为影响机箱屏蔽效能的主要因素,并提出了通风孔屏蔽设计的建议。     

机载设备机箱的电磁屏蔽设计

基于机载设备在复杂电磁环境中实现电磁兼容的目的,利用电磁屏蔽原理提高机载设备抑制电磁干扰的能力,通过分析机载设备对机箱的设计要求,得出了机载设备机箱屏蔽设计包括机箱材料选择和保证屏蔽完整性两方面的结论,并进一步给出了机载设备机箱结构上关于盖板、通风孔、导线穿透和开口、缝隙处理等方面电磁屏蔽设计的方法和技术措施。     

典型机箱的电磁屏蔽效能测试及电磁泄漏分析

测试了机柜中常用的典型机箱的电磁屏蔽效能,得出了该种机箱在频率段30MHz-1CHz时水平极化和垂直极化方式下、有散热孔和无散热孔时的屏蔽效能值,综合分析了影响机箱电磁泄漏的主要因素,为机箱的设计及选用提供了依据。     

一种ATR机箱的电磁屏蔽设计

针对电子设备的结构特点,依据某型(ATR)加固机箱结构设计的电磁兼容性原理和电磁兼容要求,阐述了缝隙、孔、洞在机箱上对电磁屏蔽效果的影响。提出在结构工艺上保证机箱的电磁屏蔽和抑制电磁干扰的具体方法,有效的解决了机箱的电磁兼容超标问题。并由此对机箱电磁兼容特性进行了结果的验证,证明了采用屏蔽措施后对机箱屏蔽效果有了较高的提升。     

金属材料低频磁场屏蔽效能研究

通过分析低频电磁波的屏蔽效能公式,综合考虑材料电磁、物理等特性,选取了五种金属作为屏蔽机箱的材料.分别测试了材料的电导率和相对磁导率,通过屏蔽公式和仿真软件比较了它们的低频磁场屏蔽效能.选用三种金属加工成屏蔽机箱,进行低频磁场屏蔽效能.测试机箱的低频磁场屏蔽效能实测结果与仿真结果基本一致.结果表明:坡莫合金对低频磁场的屏蔽效能最好,0Cr13不锈钢屏蔽效能比坡莫合金稍差,但比其他材料要好,而且其性价比高,可以用于一些需要一定低频磁场屏蔽的场合.     

机箱通风孔屏蔽效能仿真及优化

利用电磁兼容仿真软件,对开有不同形式通风孔的机箱模型,进行了屏蔽效能仿真分析。研究了开孔面积一定时,不同形状、不同数量、不同壁厚、不同孔间距对机箱屏蔽效能的影响,并对通风孔的电磁兼容性设计提出了改进建议。仿真结果表明,优化后的电脑机箱的散热能力基本不变,而屏蔽效能有了较大改善。     

孔缝腔体内传输线负载上最大感应电流的研究

应用多端口网络理论,把孔缝屏蔽腔和腔内传输线一起等效成多天线系统,基于天线的互易定理,提出了快速预测孔缝屏蔽腔内多导体传输线负载上的最大感应电流的方法.由于避免了孔缝屏蔽腔内传输线负载上感应电流的直接全波分析,计算效率显著提高.文中计算了矩形屏蔽机箱上开孔尺寸与形状、机箱大小、传输线在机箱内位置等参数改变下屏蔽机箱内传输线负载上的最大感应电流响应.与直接全波仿真结果比较,验证了方法的有效性.     

导电衬垫转移阻抗法在机箱屏效计算中的应用

介绍了如何用导电衬垫转移阻抗法计算机箱的屏蔽效能,并分析了影响机箱屏蔽效能的因素及改进措施.     

基于FEKO仿真评估PCB布局对机箱屏蔽效能的影响

运用仿真软件FEKO对PCB板在机箱的布局进行研究,分析PCB板的安装间距对机箱电场屏蔽效能的影响,并通过仿真的结果对机箱内部PCB板的布局提出合理建议。从两板之间安装间距以及多个板的安装是否等间距这两种情况出发,观察其对机箱屏蔽效能的影响,并总结一些规律。     

Shielding effectiveness of metallic enclosures at oblique and arbitrary polarizations

Shielding effectiveness of metallic enclosures with apertures when illuminated by an oblique incidence arbitrary polarized plane wave has been studied by using an efficient hybrid modal/moment technique. Shielding effectiveness of rectangular enclosures with one, two, and four apertures at multiple points inside the enclosures for various frequencies has been calculated when the illuminating source flies by the front of the enclosure. The work shows that the shielding effectiveness is seriously affected by frequency, angle of incidence and polarization of the illuminating field; the number and orientation of apertures; and the location inside the cavity. It has been shown that the usual assumption about the normal incidence being the worst-case scenario for shielding effectiveness values may not be valid when there is more than one aperture in the cavity. The paper emphasizes the need for the statistical investigation of shielding effectiveness problem of metallic enclosures with apertures.     

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.      

An Efficient MoM Formulation for the Evaluation of the Shielding Effectiveness of Rectangular Enclosures With Thin and Thick Apertures

A detailed analysis of the effects of finite-thickness apertures on the shielding properties of a rectangular metallic box is carried out through an efficient full-wave code based on the method of moments in the spatial domain. An incident plane wave having arbitrary polarization and incidence angle is assumed as a field source. The evaluation of the cavity Green function is accelerated by an application of the Ewald sum technique with a novel Ewald splitting parameter valid for high frequencies, and a recently proposed integral-equation-based approximate model of the aperture thickness is also applied. Numerical results are validated by comparisons with those obtained by means of commercial codes based on different numerical approaches and show rigorously that the effects of a finite thickness can usually be neglected (at least, at sufficiently low frequencies), with the noticeable exception of long slots. The effects of common limiting assumptions adopted in the study of enclosures with zero-thickness apertures are also investigated.     

Prediction of the shielding and resonant behavior of multisectionenclosures based on magnetic current modeling

A new method of moments (MoM) formulation is proposed to evaluate the shielding efficiency of metallic rectangular enclosures. To this end, a mixed potential integral equation (MPIE) is formulated for the magnetic currents in the apertures using the exact Green's function of the enclosure. The accuracy of the method is demonstrated by a number of examples. The method allows the quality factor of the resonances to be predicted. Finally, the effect of partitioning the enclosure by metallic planes is also investigated     

小孔矩形腔体屏蔽特性的研究

本文提出了有孔腔体远、近场电磁屏蔽效能的计算方法，体研究了矩形腔体的屏蔽特性，讨论了各类孔对屏蔽能的影响程度。数值结果表明，理论计算与实验数据吻合较好。     

孔缝结构对电磁屏蔽的影响

介绍屏蔽设计原理和屏蔽效能的计算及测试方法,针对电磁兼容性设计中孔缝结构对电磁屏蔽效能的影响进行分析,在屏蔽效能设计阶段提出了实用的设计方法和建议,指出合理设计对电磁屏蔽具有十分重要的意义。通过仿真和工程实例中线路和结构设计两方面的技术介绍,分析孔缝效应的形成机制和应采取的有效技术手段。     

Coupling studies and shielding techniques for electromagnetic penetration through apertures on complex cavities and vehicular platforms

The multilevel fast multipole moment method is employed to compute the electromagnetic coupling and shielding of various aperture-coupled metallic enclosures. A phenomenological study of electromagnetic coupling, due to various slot shapes and sizes, with or without the presence of wire penetration is conducted. These slots are situated on over-moded cavities and two methods are proposed to mitigate slot coupling into the cavity's interior. As part of this work, we also investigate the coupling through similar slots and apertures within a complex platform such as an automobile. The proposed methods have shown to increase shielding by as much as 5-35 dB within the frequency range of interest.     

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。     

有孔腔体屏蔽效应分析的混合模型

对于带矩形孔缝的矩形腔,利用传输线模型求得孔缝上的近似电场,并以此为等效磁流,利用腔体中的并矢格林函数,估算腔体中的耦合场强与屏蔽效应,并推广到孔缝偏离中心的情形.数值结果与其他方法以及实测值吻合的很好,验证了方法的有效性.分析了孔缝偏离中心、孔缝尺寸变化、平面波斜入射时的屏蔽效应,数值结果表明:孔缝偏离中心使腔体中心...     

Analytical formulation for the shielding effectiveness ofenclosures with apertures

An analytical formulation has been developed for the shielding effectiveness of a rectangular enclosure with an aperture. Both the magnetic and electric shielding may be calculated as a function of frequency, enclosure dimensions, aperture dimensions and position within the enclosure. Theoretical values of shielding effectiveness are in good agreement with measurements. The theory has been extended to account for circular apertures, multiple apertures, and the effect of the enclosure contents