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。     

Review of Circuit Approach to Calculate Shielding Effectiveness

The shielding effectiveness of an enclosure at low frequencies can be readily computed using a circuit approach. Not only does this technique include the effects of the properties of the shield material, but it also includes the details of the geometry of the enclosure. Furthermore, this approach allows a nonempirical consideration of mesh enclosures and the effects of resistive seams in enclosure walls. By working with the circuit analogue, penetration by transient fields can also be computed. Essentially the enclosure is viewed as an antenna. In the case of magnetic shielding effectiveness, the enclosure is viewed as a short circuited loop antenna. In the case of electric field penetration, the enclosure is viewed as a fat electric dipole. Using this characterization and exact solutions where available, the current distribution on the outside of the enclosure is first determined. Then, based on the current distribution, the penetrating fields are computed. The equations are developed in such a way as to preserve a lumped circuit analogue for the low-frequency region. The basic circuit equations for magnetic field penetration are rederived from a rigorous solution. Rules to estimate the rise-time, fall-time, and peak magnitudes of transient penetrating fields are developed. The electric shielding effectiveness is developed in a similar manner. In both cases the results of the circuit approach agree well with those based on rigorous solutions of the electromagnetic boundary conditions. The results also agree with published experimental data on both large and small enclosures.     

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。     

Effectiveness of Earphone Shielding for Artifact Control in Auditory Evoked Potentials

Control of the electromagnetic artifact produced by earphones is a major problem in the acquisition of surface-recorded auditory evoked responses, especially short latency responses (0-10 ms). Several investigators have used magnetically shielded earphones to reduce the artifact. In this paper, a method for measuring shielding effectiveness is described, and results obtained with a TDH-39 earphone are presented. Two layers of shielding were found to provide 10-15 dB of shielding effectiveness; the resulting artifact is less than 0.1 ?V for acoustic stimuli below 120 dB sound pressure level (SPL). The shielding also affects the response of the transducer, especially at low frequencies. It is concluded that shielding is effective in controlling artifact for high-frequency transient stimuli. However, for low-frequency stimuli, for which the response begins while the stimulus is present, results obtained with shielded earphones should be interpreted with caution.     

镍基电磁波屏蔽复合涂料制备及在EMC中的工程应用

针对日益严重的电磁环境污染问题,根据电磁波屏蔽材料对电磁波作用原理,用镍粉和金属纤维作为复合填料,以丙烯酸树脂作粘结剂,按照涂料制备的方法,制备了一种能屏蔽电磁波的复合涂料。将其应用在某有线电视网和电子工作间,进行对比法测试,结果表明:在射频段,该材料将有线电视传输网设备中的干扰场强度降低了40%~50%,在电子工作间上的屏蔽效能达到了30~50dB。     

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。     

Analyzing carbon-fiber composite materials with equivalent-Layer models

The purpose of this paper is to investigate the use of equivalent-layer models for the analysis of carbon-fiber composite materials. In this paper, we present three different models for the electromagnetic characterization (effective material properties) of fiber composites that are commonly used in aircraft and EMC/EMI shielding materials. These three models represent various orders (or levels) of detail in the fiber composite structure and, hence, capture various physical aspects of the composite. These models can be used to efficiently calculate the reflection and transmission coefficients, as well as the shielding effectiveness, of these fiber composites. We compare results of the reflection coefficient and shielding effectiveness obtained from these effective-property models to results obtained from a full numerical solution based on the finite-element (FE) method of the actual periodic fiber composite. We show that, as expected, as more of the geometric detail of the fiber composite is captured with the different models, the upper frequency limit of validity increases.     

Transmission Line Mode Response of a Multiconductor Cable in a Transient Electromagnetic Field

This paper describes a technique for obtaining the induced worst case currents on individual wires of a multiconductor cable as a result of a transient electromagnetic radiation field. The technique involved a development of the expression for the induced current in matrix form where the mutual coupling terms and the other cable currents are the pertinent parameters. A worst case solution results from the assumption of maximum coupling orientation of the individual wires. A short example and some test results are presented. The test results show wave shapes for inductive and capacitive coupling. The solution for the individual wire current due to a transient electromagnetic field is important, since it will greatly reduce the required number of cable measurements and will allow the development of improved shielding techniques.     

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...     

高频状态下的圆孔屏蔽效能经验公式

电子设备电磁屏蔽效能的好坏直接影响着屏蔽体内电子器件工作的稳定性,而电磁屏蔽体上的孔洞造成的电磁泄漏是一个不容忽视的问题。针对这个问题,对有孔洞的屏蔽体的电磁泄漏进行了仿真计算,定量分析孔洞大小对屏蔽外壳的屏蔽性能的影响。分析结果表明在屏蔽体壁厚保证的情况下,孔洞的直径越小,屏蔽效能越高。当孔洞的半径在10mm以下时,屏蔽效能在30dB以上,满足实际工程要求的屏蔽效能要求。并由此得到屏蔽效能经验公式。     

箱式屏蔽效能测试方法设计

从屏蔽效能的原理出发,通过分析影响屏蔽效能的关键因素,提出箱式屏蔽效能测试方法,并对影响测试结果的因素进行优化。测试方法简便可行、数据可靠有效,为屏蔽材料的选型提供技术依据,为工程技术人员进行产品设计提供参考。     

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。     

含短贯通导体金属腔体电磁耦合规律研究*

为研究平面波辐照下含短贯通导体金属腔体电磁耦合规律,利用电磁仿真软件CST 搭建仿真耦合模型,从频域角度进行了仿真研究,并利用矢量网络分析仪、功率放大器、GTEM 室和电场测试探头搭建实验系统进行了验证。通过仿真研究了贯通导体长度、贯通孔尺寸和腔体内屏蔽效能监测点位置等因素对屏蔽效能的影响。结果表明:仿真和实验的结果具有一致性;贯通导体腔体外长度越长,屏蔽效能越低,腔体内长度越长,腔体谐振频点越低;贯通孔尺寸越大,腔体屏蔽效能越低;监测点位置离贯通导体越近,屏蔽效能越低。同时研究了吸波材料和开口金属环对含短贯通导体金属腔体的防护效果。此研究具有实用意义,能够指导电子设备的设计和安装。     

电磁防护用品的屏蔽效能测试分析

设计了人体电磁防护用品屏蔽效能的测试方法和测试步骤,明确人体模型重要的测试部位.分析了电磁防护用品不同缝制方式对屏蔽效能的影响及简化的电磁防护用品模型的测试结果,认为不同的极化方式和照射方向对屏蔽服的防护效果都有影响.     

钢筋混凝土层对高功率电磁环境的屏蔽效能研究

本文采用时域有限差分 (FDTD)法 ,分析了常用地下建筑工程钢筋混凝土层对高功率电磁环境的屏蔽效能 ,研究了钢筋网交叉点焊接、拉筋连接方式、自然防护层等因素对屏蔽效能的影响。     

黄铜和不锈钢丝网电磁屏蔽效能的研究

金属网由于具有通风、采光等明显优势而在电磁屏蔽工程中得到广泛利用.本文对不锈钢丝网和黄铜丝网在远场时的电磁屏蔽效能进行理论计算,并进行了实际测试,通过计算和实测数据对黄铜和不锈钢丝网的电磁屏效进行了分析和比较.     

非互联状态多层电磁屏蔽体屏效研究与分析

大型射电望远镜建设加速,迫切需要研究超高电磁屏蔽技术并将其应用于工程实践。文中从理论层 面推导和分析了非互联状态多层屏蔽壳体屏蔽效能与层数之间的关系,并依据GB/ T 12190 电磁屏蔽室屏蔽效能的 测量方法,建立了单层、双层、三层预测分析模型,采用优势主路径法预测分析了不同层数屏蔽体的屏蔽效能,通过 与理论计算结果进行对比,验证了非互联状态多层屏蔽层数与屏蔽效能之间的关系,为大型射电望远镜超高屏蔽环 境构建提供技术和理论支撑。     

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。     

屏蔽门金属弹簧片的屏蔽效能分析

采用时域有限差分法(FDTD)对屏蔽门上的金属弹簧片进行建模分析，研究了其屏蔽效能特性。由于弹簧片上的缝隙是造成电磁泄漏的主要通道，因此首先对弹簧片的近似结构——薄金属板上的缝隙在不同形状下的屏蔽特性进行了研究，其次对弹簧片、安装槽和刀口组成的屏蔽组件进行了整体建模和仿真，得出弹簧片的屏蔽效能与缝隙长度、宽度、深度以及安装槽结构问的关系。结果表明该弹簧片结构无论对电场还是磁场都有非常高的屏蔽效能，这也为屏蔽门的优化设计提供了理论参考。     

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.