Cavity Model for the Slot Radiation of an Enclosure Excited by Printed Circuit Board Traces With Different Loads

Traces on a printed circuit board (PCB) couple to the cavity consisting of the PCB ground plane and a metallic enclosure cover. We introduce this common-mode coupling of a PCB trace to the cavity field by an analytical model that is verified with 3-D simulations using HFSS. The cavity field causes radiated emission from the slots of the cavity. For an accurate calculation of the cavity field inside the enclosure and the radiated emission, we consider the radiation loss by a multiport approach. Comparisons of the analytical results for the radiated field to measurements show good agreement. Radiated emission can be calculated for arbitrary geometric enclosure shapes as a function of frequency, position of the trace on the PCB, and trace load/driver impedances.      

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.     

一种基于缝隙天线阻抗的带缝腔体谐振频率计算方法

电磁波经缝隙进入机箱腔体后,会在某些频率点形成驻波而发生电磁谐振,导致腔体屏蔽效能急剧下降.为快速准确预测谐振频率以指导屏蔽腔体设计,本文基于缝隙天线阻抗理论提出一种带缝腔体谐振频率的计算方法.将电磁场用自由空间和腔体格林函数表示,根据缝隙处的边界条件建立等效磁流源的积分方程.通过矩量法求解积分方程,计算出腔体输入阻抗.根据谐振发生时电抗为零或电阻最小,可从频率-阻抗曲线获得谐振频率.本文方法不仅能预测缝隙谐振和低阶模式腔体谐振,还能预测出高阶谐振.与实验和CST仿真结果对比验证了本文方法的准确性及快速性.最后用本文方法分析了腔体和缝隙尺寸以及缝隙位置对谐振频率的影响.     

有孔阵矩形机壳屏蔽效能分析

为了评估矩形金属机壳抗外部电磁干扰的能力,基于传输线矩阵法（TLM）分析加装印刷电路板的有孔阵矩形机壳的屏蔽效能。主要讨论孔间距和孔面积之与不变时增加孔的数量所引起屏效（SE）的变化;孔阵面积和孔径不变时,通过改变孔间距考虑孔的数量变化对屏效的影响;改变孔的数量及介电常数时屏效的变化以及在圆孔阵、圆内接方形孔阵、圆外切方形孔阵3种情况下屏蔽效能的对比;通过仿真结果,验证出最佳方案。     

Shielding Theory of Enclosures with Apertures

This paper develops the theory of EM radiation from metallic enclosures with apertures, excited by an internal source at frequencies below the fundamental resonance of the enclosure. The enclosure with an aperture is analyzed from two different points of view: as a cavity with a small aperture in a wall, and as a waveguide section short-circuited at one end and open at the other. Rectangular geometries are used throughout, since these are by far the most commonly encountered in practical enclosures and cabinets. Using the corresponding dyadic Green's functions, the fields generated inside the enclosure by some simple sources are determined. The fields radiated through small apertures in a cavity are determined using Bethe's theory of diffraction by small holes. The radiation from an open waveguide is calculated with the help of field-equivalence theorems, with assumptions applicable to the case of evanescent waves. The final step is to derive expressions for the " insertion loss" of the shield, defined as the ratio of the field strength at a point external to the shield, before and after the insertion of the enclosure. To do so, the effect of the shield upon the input impedance of the antenna is analyzed, and expressions obtained for the applicable cases. The resulting insertion-loss expressions are numerically evaluated for some representative cases, and graphically compared with a series of measurements performed to obtain experimental confirmation. Very good agreement is obtained in all cases, establishing the validity of the analysis.     

Electromagnetic coupling between wires inside a rectangular cavityusing multiple-mode-analogous-transmission-line circuit theory

This paper examines the coupling between two arbitrarily positioned wire segments inside a rectangular enclosure. The enclosure is treated as a superposition of analogous transmission lines which have been short circuited at two positions on the propagation axis. Each analogous transmission line is associated with a particular waveguide mode in the cavity. Previous work has used this analogy to predict the coupling between two monopoles inside a small box using the dominant TE ₁₀ mode. This paper considers the general case of high-frequency coupling between two wire monopoles in a large rectangular cavity, where several higher order modes are active. By taking into account higher order modes, and the mutual coupling between the modes, a simple equivalent circuit is presented which can give a prediction for the coupling between the monopoles. Experimental results for various monopole pair positions are shown, which indicate the success of the multimode theory. The technique requires far less computer resources than traditional methods for solving such a problem (e.g., MoM, TLM or FDTD), with solution times of less than a second on an average PC. In addition, considerable insight into the coupling process can be gained by including or excluding particular waveguide modes. This is not possible with numerical methods     

Composite Hole Conditions on Complex Permittivity Measurements Using Microwave Cavity Perturbation Techniques

This paper examines the edge effects of introducing a dielectric test cylinder with a test material into a cavity via a metallic support tube extending outside the cavity. A first-order perturbation theory is used for this metallic hole containing two different concentric dielectric materials. The Galerkin method is used to determine the amplitudes of numerous evanescent modes which exist in such composite hole geometries. Comparisons are made with the effects produced by a simple hole in which a single dielectric is postulated inside the metallic support tribe. The effects of the composite hole on the measurement of the dielectric properties of materials are given.     

Influence of a metallic enclosure on the S-parameters of microstripphotonic bandgap structures

Planar microstrip photonic bandgap (PBG) structures are periodic arrays of holes etched in the ground plane of a conventional microstrip line. Most of the published studies considered the PBG as an unshielded structure. However, to fabricate a circuit with a PBG structure, a metallic enclosure is often needed. Thus, the S-parameters of the PBG structure will be altered correspondingly. In this paper, the influence of the metallic enclosure on a shielded PBG structure as well as the finite ground plane on an unshielded PBG structure on the S-parameters are analyzed using the finite-difference time-domain (FDTD) method. Conditions for which the influence can be neglected are obtained. The results are useful for the applications of PBG structures     

Numerical and experimental analysis of the field to enclosure coupling in reverberation chamber and comparison with anechoic chamber

This paper presents a study of coupling between an external field and a metallic enclosure with a long aperture in the frequency range which includes several box resonances. A reverberation chamber (RC) and an anechoic chamber (AC) are considered as a field generation structure. In both cases, a customized FDTD code is used to calculate the current induced by the external field in a loop placed inside the enclosure. In order to simulate the AC facility, a single plane wave is used to represent the test field, whereas for the RC, the field is represented by a proper superposition of random plane waves. Numerical results are experimentally validated. The proposed method is useful to investigate the performance of the enclosure during its early design stage before the realization of a prototype.     

Diffusive electromagnetic penetration into metallic-enclosures

The physics of shielding by a metallic enclosure is discussed. Simple engineering formulas in the frequency and time domains are deduced from a rigorous formulation to calculate the cavity fields for certain canonical enclosure shapes. These simple formulas are generalized so as to be applicable to enclosures of arbitrary shape. The great difference in shielding effectiveness between enclosures and planar slabs is pointed out.     

An Experimental Study for Determining Optimum Antenna Placement Within a Metallic Enclosure

The problem of placing an antenna inside a metallic room in order to receive a signal originating outside the room is studied. The limitations of a theoretical analysis of the problem are noted. Some general conclusions are drawn from the experiments performed in a shielded enclosure.     

带孔缝矩形金属腔体屏蔽效能研究

针对带孔缝矩形金属腔体在电磁辐射下的屏蔽效能问题,利用基于时域有限积分法的电磁仿真软件CST,建立了平面波辐照条件下含孔缝金属腔体的耦合模型,重点研究了电场极化方向,腔体材料,矩形孔缝的长度、宽度和深度,孔缝填充介质介电常数及其厚度等参数对屏蔽效能的影响规律.研究结果表明:典型金属材料对屏蔽效能的影响差别不大,垂直于电场极化方向的孔缝边长更能影响腔体的屏蔽效能,孔缝尺寸会影响矩形金属腔体的谐振点,孔缝深度能够通过衰减入射波在一定程度上影响屏蔽效能,孔缝填充介质会降低屏蔽效能,介质厚度及其介电常数会影响屏蔽效能峰值点.研究结果对金属腔体的电磁兼容设计有一定的指导意义.     

Complex modes in open and shielded lossless planar transmissionlines and their correspondence with leaky modes

The wavenumber of complex modes in lossless planar transmission lines inside a metallic box, with or without top cover, are computed using the transverse resonance method. Without the top cover, some leaky modes can be observed. When these open guiding structures are covered, it is shown that these previous modes generate either evanescent or complex modes, depending on the metallic enclosure position     

A 3D numerical study of humidity evolution and condensation risk on a printed circuit board (PCB) exposed to harsh ambient conditions

In many applications, electronics enclosures are exposed to harsh environmental conditions. For a reliable design, it is crucially important to understand the effects of such conditions on the local climate inside the enclosures. In this study, the relative humidity (RH) and temperature inside an electronic enclosure exposed to harsh ambient conditions (relative humidity of 100% and cyclic temperature changes from 10 to 50 (°C)) are studied by developing a full 3D finite element based CFD model. The RH evolution is studied in three stages: first, in an empty enclosure, then in an enclosure with a PCB, heatsink and a heater, and finally in the case of an internal cyclic heat load. In all three parts, the effect of the opening size of the enclosure is also studied. The numerical simulation results are compared with corresponding experimental results from the literature, and a good agreement is found.The presence of components inside the enclosure damps the response of the internal climate to the ambient changes and this is especially the case for the aluminum heatsink. In case of exposure to RH of 100%, controlling the moisture concentration appears to be more effective than controlling temperature with the aim of reducing the condensation risk on the PCB.     

平面波照射下贯通导线电磁干扰快速算法

提出了一种基于BLT（Baum-Liu-Tesche）方程的平面波辐照下金属腔贯通导线电磁干扰分析的快速计算方法.首先采用电磁拓扑理论将整个问题进行拓扑分解,根据场线耦合理论获得场线耦合节点的传输函数,进而采用广义BLT方程获得外界电磁波与贯通导线相互作用时金属腔内终端负载上的干扰电流.将该算法用于贯通单导线、贯通双导线和贯通传输线网络电磁干扰问题分析,计算获得的终端负载上感应电流结果与全波分析方法结果吻合较好,证明了该快速算法的有效性.该快速算法计算时间仅为全波分析法的万分之一,且所占内存相比全波分析法缩小了几十倍.     

ESD indirect coupling modeling

Electrostatic discharge (ESD) indirect coupling on electronic equipment is theoretically and experimentally investigated considering the effects for three typical structures: a coaxial cable, a multilayer PCB, and a metallic enclosure. The analytical approach is based on classical electromagnetic theory and is developed in a simple way that is easy to apply and accurate enough to give the designer a reliable estimation of the interference produced by an ESD event     

Suspended Slot Line Using Double Layer Dielectric

This paper presents a rigorous analysis of a) slot line on a double layer dielectric substrate, and b) slot line sandwiched between two dielectric substrates. The structure is assumed to be suspended inside a conducting enclosure of arbitrary dimensions. The dielectric substrates are assumed to be isotropic and homogeneous and are of arbitrary thickness and relative permittivity. The conducting enclosure and the zero thickness metallization on the substrate, are assumed to have infinite conductivity. The effect of shielding on the dispersion, characteristic impedance, and the effective dielectric constant are illustrated. These results should find application in the design and fabrication of MIC components and subsystems.     

Experimental Measurement of Fields Excited Inside the Fuselage of an Aircraft

In computing the fields excited inside the fuselage of an aircraft [1] when subjected to external electromagnetic (EM) radiation, the results of [2]-[4] have been used and the fields were assumed to propagate in free space instead of inside a cavity. This measurement program shows that it is improper to do so since the presence of metallic structures and the cavity resonances may account for deviations ofover 20 dB in relation to the free-space field.     

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。     

Per unit length parameters of a multiconductor line with earthreturn inside a tunnel

This paper describes an algorithm for the calculation of the per unit length parameters of a multiconductor line with earth return inside a tunnel in the quasi-static range. The main application of this work is the characterization of an electrified railway line, located inside a generic tunnel, as a source of electromagnetic interference on structures like telecommunication cables, metallic pipes and ducts