一种解任意横截面柱形薄壳体电磁屏蔽问题的新方法

本文给出了求解任意横截面柱形薄壳体电磁屏蔽问题的一种新方法 .在平均边界条件的基础上 ,利用单层标量波函数法向量导数的间断性定理 ,得到了任意横截面柱形薄壳体电磁屏蔽问题的积分方程组 .利用边界元法对该积分方程组进行了求解 ,通过与精确边界条件下的解比较 ,发现两种结果符合很好 .本文中的方法简便易行 ,足可准确描述柱形薄壳体外两侧电磁场的分布情况     

一种解任意截面柱形薄壳体电磁屏蔽问题的新方法

本文给出了求解任意横截面柱形薄壳体电磁壳体电磁屏蔽问题的一种新方法。在平均边界条件的基础上,利用单层标量波函数法向量导数的间断性定理,得到了任意横截面柱形薄壳体电磁屏蔽问题的积分方程组。利用边界元法对该积分方程组进行了求解,通过与精确边界条件下的解比较,发现两种结果符合很好。本文中的方法简便易行,足可准确描述柱形薄壳体外两侧电磁场的分布情况。     

低频脉冲磁场中磁屏蔽体磁饱和效应的试验研究

针对磁屏蔽体在低频脉冲磁场环境中可能存在的磁饱和问题，利用试验方法开展了磁饱和效应研究，证实了常规工程屏蔽体可在低频脉冲磁场环境中达到磁饱和状态，并通过观测屏蔽效能的变化获得了磁饱和规律，同时分析了磁饱和效应对屏蔽效能的影响及其与屏蔽体的材料磁导率、壳体厚度、外形尺寸等参数的关系. 研究表明:磁屏蔽体屏蔽效能在磁饱和效应影响下，呈现出明显的动态变化特点，具有与屏蔽壳体磁导率类似的变化趋势；壳体厚度2 mm以内、长宽高为2 m×2 m×2 m左右的屏蔽体在上升时间为300 μs、持续时间为1.2 ms的磁场环境中，达到磁饱和状态的磁化场强度约为10 mT，其磁饱和难易程度与磁导率及外形尺寸负相关，与壳体厚度正相关. 试验研究结果与理论分析结论一致，可为磁屏蔽体的科学合理设计提供参考，具有较高的工程应用价值.     

电磁屏蔽中的难题—磁场屏蔽

磁场屏蔽是电磁屏蔽中的难点.本文分析了磁场干扰的产生机理,进而分别对高频磁场屏蔽和低频磁场屏蔽进行了分析并提出了一些抑制磁场干扰的措施.     

混响室法欠模状态屏蔽体屏蔽效能测试技术研究

欠模状态下屏蔽壳体内部场分布不均匀,屏蔽效能测量结果与位置相关,因此需要利用探头或单极子天线进行多位置测量,过程繁琐。文中利用长线天线来测量欠模状态下屏蔽壳体屏蔽效能,并与单极子天线测量结果进行比较。在暗室中测量天线自由空间反射系数S₁₁;在混响室中利用不同天线测量屏蔽壳体的屏蔽效能,并利用S₂₂分析腔体谐振特性。测量结果表明,长线天线宽频带匹配特性优于单极子天线,测量的屏蔽效能能够更好地反映屏蔽体谐振特性,为屏蔽壳体的屏蔽效能测试评估提供了指南,具有工程应用价值。     

某非金属壳体控制设备的电磁屏蔽设计方法与研究

为了解决某非金属壳体控制设备电磁屏蔽效能低,抗外部电磁干扰能力差及对外辐射超标的问题,本文结合工程可行性提出了某非金属壳体控制设备电磁屏蔽改进措施;通过对某非金属壳体控制设备的壳体、开关以及缝隙屏蔽设计,提高该设备电磁屏蔽特性。试验测试证明,改进后控制设备满足GJB 151B-2003中RE102及RS103项目的要求。     

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.     

低频高性能屏蔽装置的设计

为了合理评估磁屏蔽体对低频磁场的屏蔽效果,设计了一种磁屏蔽体并提出一种屏蔽方案,计算静磁场与交变磁场共同影响下,其屏蔽装置对其屏蔽性能的影响,并通过实验来论证该屏蔽体和设计方案在实践中的应用可行性。实验结果表明,设计的电磁屏蔽室,室内静磁场B≤200 n T,50 Hz交流磁场干扰<0.10μT;大于100 k Hz交流磁场屏蔽系数S≥1 000;满足磁传感器系统等相关仪器的实用要求,为实践屏蔽室屏效验收提供理论依据。     

某雷达接收系统的电磁兼容设计

本文介绍了某3公分雷达中频接收系统的电磁兼容设计,屏蔽壳体的厚度、孔洞及缝隙的能量泄露、实际屏蔽效果的计算方法,并指出只有合理地选取结构参数,才能设计出满足电磁屏蔽要求的屏蔽壳体。     

某雷达接收系统的电磁兼容设计

本文介绍了３公分雷达中频接收系统的电磁兼容设计，计算屏蔽壳体的厚度，孔洞及缝隙的能量泄漏，实际屏蔽效果。通过合理选取结构参数，所设计屏蔽壳体能满足电磁屏蔽的要求。     

Resonance suppression of a spherical electromagnetic shieldingenclosure by using conductive dielectrics

The resonance suppression for the electromagnetic shielding enclosure is theoretically investigated. A simple model of a double-layered spherical shell with a plane-wave illumination is assumed. When a spherical shell made of conductive dielectrics is covered with a thin metal layer, the conductivity of the dielectrics has an optimum value which minimizes the Q-factor at the fundamental resonant frequency. The optimum conductivity is shown to be a function of the resonant frequency and the thickness of the dielectric layer. The improvement of the shielding effectiveness by introducing the optimum conductivity is shown     

Low-Frequency Shielding Effectiveness of Nonuniform Enclosures

This paper presents a quasi-static approximate solution to the magnetic shielding of several nonuniform enclosures using the integral form of Maxwell's equations and insight gained from other approaches. The solution is called quasi-static as the assumptions made are from physical arguments based on low-frequency cases where the enclosure size is much less than a wavelength. The integral form of Maxwell's equations is used to obtain a first order correction to the static solution to obtain induced currents in the time-varying case. A cylindrical shell immersed in an axial magnetic field is used to illustrate the method, which is then extended to derive a formula for a similarly excited rectangular enclosure. These shields are seen to behave like a low-pass filter. Although the enclosure dimensions are small compared to the wavelength, the skin depth effects in the walls cannot be neglected even for relatively thin material as usually encountered in an enclosure. These skin effects are included in the analysis and experimental checks performed on a variety of enclosure sizes and materials, excited by a Helmholtz coil show agreement within two decibels over the 4-octave frequency range examined. No one can say whether this method offers a better solution to the shielding problem, as all solutions are approximate, but the author attempts to present an alternative formulation that aids in understanding the physical processes involved in the shielding effectiveness of an enclosure and fills some of the gaps between the plane-wave analysis and circuit approaches presently used.     

A new model for the FDTD analysis of the shielding performances ofthin composite structures

A new model is proposed for the transient analysis of the electromagnetic field penetration through air-embedded conductive structures realized by thin multilayered composite panels. A magnetic field controlled formulation is developed in the frequency-domain to express the tangential components of the electric field on the external faces of the composite slab as a function of the tangential components of the magnetic field by means of the surface and transfer impedances of the thin panel coated on a perfect magnetic medium. The corresponding time-domain model is obtained by applying the inverse Fourier transform to the field quantities; an efficient piecewise linear convolution procedure is developed for the numerical calculation of the resulting convolution integrals. The model is implemented in one-dimensional (1-D) and two-dimensional (2-D) FDTD codes and applied to the analysis of different shielding configurations, both in the frequency and in the time domain     

A simple hybrid method for ELF shielding by imperfect finite planar shields

A simple method is described for calculating the shielding performance of a two-dimensional (2-D) thin finite-width shield made of imperfect material in the presence of the magnetic field from line source conductors. First, solutions to two canonical problems with closed-form simple analytic formulas are presented; shielding by reflection from and absorption in thin planar shields of infinite extent and shielding by perfect conductor shields of finite width. Then the method for calculation of magnetic-field shielding by perfect conductor finite-width shields is extended using the simple interpolation method, to thick shields made of imperfect material. Finally, the hybrid solution is developed by adding the two results in quadrature. The result is a simple theory for shielding by finite-width shields made of any real shielding material of arbitrary thickness. Its accuracy has been validated by comparison to finite-element method solutions and existing measurements.     

A computational methodology and results for quasistaticmultilayered magnetic shielding

A methodology for accurate calculations of shielding factors for quasistatic multilayered magnetic shields is described. “Transfer relations” for individual layers with specified magnetic permeabilities and electrical conductivities are spliced together. Specific transfer relations for four layer geometries (planar, cylindrical with transverse fields, cylindrical with axial fields, and spherical) and constraints at source and shielded surfaces for six source-shield configurations involving both externally applied fields and enclosed sources are developed. Limiting cases are extracted for magnetically permeable, nonconducting layers, and for thin, magnetically nonpermeable, conducting layers. Reciprocity conditions are identified for interchanged source and shielded regions in planar, transverse field cylindrical, and spherical geometries. Variations of magnetic field and flux density with position are shown for a specific planar example involving alternating layers of aluminum and steel, with the same total shield thickness occupied by either one or five layer pairs. Simulations with alternating layers of aluminum and steel for the four layer geometries are used to study the effects of material composition, number of layer pairs, and air gaps. An optimal number of layer pairs for a given total shield thickness is identified. Results from simulations where induced currents in the steel layers are neglected are compared with those for simulations with a realistic conductivity value for steel to assess the relative effects of flux shunting and induced current shielding     

手征球壳的低频电磁屏蔽效应分析

分析了手征介质球壳的低频电磁屏蔽效应，给出了一组手征电磁屏蔽球壳的设计曲线。比较了手征材料的一般电、磁屏蔽材料的不同之处，重点说明了该材料的特殊性。理论计算表明，这种新型材料是一种非常有前途的电磁屏蔽材料。     

Thermoelectric Properties of Polycrystalline Thin Films Under an External Magnetic Field

A theoretical model is proposed to predict the Seebeck coefficient and the electrical conductivity for a polycrystalline thermoelectric (TE) thin film under an external magnetic field. The model considers the distribution of electrons in the microstructure of TE thin-film materials, taking the scattering effect of electrons at the grain boundary as the boundary condition for electron transport in the grain. The transmission coefficient is introduced to describe the probability of electrons passing through the grain boundary potential barrier, while the relationships between the Seebeck coefficient, the electrical conductivity, and the transmission coefficient are studied. Furthermore, the results from the calculations of the Seebeck coefficient, the electric conductivity, and the power factor of TE materials under various applied magnetic fields, transmission coefficients, and grain sizes indicate that the applied external magnetic field has a very significant influence on the TE properties of polycrystalline thin films.     

Scattering from a finite length rod with endpoint contribution

A uniform, high frequency analysis for calculating scattering from thin, finite length cylinders is presented. The cylinder diameter is assumed to be small (on the order of a wavelength or less) so that the modal solution is valid. The total field consists of the incident field, the scattered field from the specular point, and two endpoint contributions. A thin wire tip diffraction coefficient (TDC) is developed for calculating the end point contributions. The incident fields are those of a spherical source radiating throughout space. While the specularly scattered field and end point contributions are discontinuous, these discontinuities cancel each other, resulting in a uniformly continuous total field. Good agreement is obtained between measured and calculated results.     

Shielding effectiveness of rectangular cavity made of a new shielding material and resonance suppression

New shielding material has become an alternative to traditional metal to shield boxes from electromagnetic interferences. This article introduces the theory of transmission line method to study the shield boxes made of a new sort of material, and then expands the fundamental formulas to deal with the cases of multiple holes and polarization with arbitrary angle. By means of genetic algorithms with the aid of a three dimensional simulation tool, the damping of electromagnetic resonances in enclosures is researched. The computation indicates that under resonant frequency, electromagnetic resonance results in low, even negative shielding coefficient; whereas, for the same areas, shielding effectiveness of a single hole is worse than that of multiple holes. Shielding coefficient varies when polarization angle increases, and the coupled field through the rectangular aperture with the long side parallel to the thin wire is much weaker than that with the long side vertical to the thin wire. By using the metallic-loss dielectric layer of optimized calculation on the internal surface of the cavity, the best result of resonance suppression has been realized with the same thickness of coating. Finally, according to the calculation result, suggestions for shielding are proposed.