Demagnetization of Layered Ferromagnetic Structures for Magnetically Shielding: Frequency Considerations

This paper provides the background for evaluating the appropriate frequency from measured or manufacturer provided magnetic permeability data. The proper frequency is, among other parameters, a necessary prerequisite for the low residual field demagnetization required for several applications including biomagnetism and particle physics. The paper also presents an interpretation of the material-dependent effects which arise during the demagnetization procedure. The interpretation focuses on magnetic diffusion influenced by magnetic permeability variation accompanying the demagnetization process. Explanations based on energy considerations show how the domain alignment is affected during the demagnetization process. A comparison with the results obtained from an algebraic hysteretic model supports the conclusions.      

导电衬垫材料的屏蔽效能研究

导电衬垫材料是计算机防信息泄漏研究中应用最广泛的一类屏蔽材料，在研制TEMPEST计算机中发挥了重要的作用，本文通过对6种常用的导电衬垫材料的屏蔽效能的测试研究，得出了一些有工程参考价值的结论。     

磁屏蔽效能的有限元分析

提出了磁屏蔽效能问题的三维有限元模型的建立方法,应用ANSYS软件得到磁屏蔽效能为28.78,并将结果绘制成曲线,使结果更加一目了然。为了检验计算结果是否符合实际情况,通过一种间接的方法对磁屏蔽效能进行测试。对比分析以上的计算结果和测试结果,可以得出结论:利用有限元法进行磁屏蔽效能计算,对直流传感器的磁屏蔽效能估算具有一定的指导意义。     

Millimeter-Wave Transmittance Measurements on Ferrites Near Ferromagnetic Resonance

This paper presents complex dielectric permittivity and magnetic permeability measurements of pure and diluted barium ferrites in the millimeter-wave frequency range. A broadband quasi-optical millimeter-wave spectroscopy with backward-wave oscillators as high-power tunable sources of coherent radiation has been utilized. The real and imaginary parts of the dielectric permittivity and magnetic permeability as functions of frequency are computed from the transmittance spectra. A magneto-optical approach in millimeter waves has been successfully employed for the separation of the dielectric and magnetic effects and the simultaneous determination of the magnetic and dielectric parameters of barium ferrite materials near ferromagnetic resonance.     

不同金属填料对电磁屏蔽涂料屏蔽效能的影响

复合电磁屏蔽材料是一类用于防护电磁波干扰的新型功能材料,作为屏蔽组分主体的金属填料的电磁特性及其在涂料中的分布状态对于材料的屏蔽效能具有显著的影响,同时由于复合材料的结构特点使这类复合电磁屏蔽材料的屏蔽效能与传统金属板材的屏蔽效能计算理论有着较大的差异.在实验研究的基础上讨论了几种典型的金属粉末填料构成的复合电磁屏蔽材料的屏蔽效能的特点,并分析了其与传统屏蔽效能计算理论的差异和形成的原因,为设计高效复合电磁屏蔽材料提供必要的参考.     

电流比较仪磁屏蔽效能的计算

大电流比较仪具有高准确度,线性特性好,低漂移等特点,因此被广泛应用于实验室和工业现场。在大电流比较仪的设计中磁屏蔽是非常重要的。长期以来,磁屏蔽效能的计算是依靠解析的方法,误差较大。文章利用目前流行的数值计算方法,对电流比较仪磁屏蔽效能进行了分析。文中提出了电流比较仪磁屏蔽效能问题的数学模型的建立方法,讨论了有限元法在电流比较仪磁屏蔽效能计算中的应用,给出了磁屏蔽体二维和三维模型的计算结果。     

气隙对电流比较仪磁屏蔽屏蔽效能影响的研究

电流比较仪的磁屏蔽是减小磁性误差,提高测量精度的重要组成部分,但实际中磁屏蔽往往存在气隙导致屏蔽效能下降,影响比较仪的测量精度。通过建立有限元模型,研究磁屏蔽上引线穿出气隙对屏蔽效能的影响,得到了屏蔽效能随气隙高度变化的规律。对于该模型,气隙高度小于10 mm时,屏蔽效能下降不大;当气隙高度大于10 mm后,屏蔽效能下降明显。最后,搭建实验平台验证气隙对屏蔽效能的影响,实验结果与有限元计算结果相吻合,小气隙对屏蔽效能的影响不大,当气隙超过一定高度后对屏蔽效能影响很大,实际设计中应予以避免。     

发泡金属的电磁屏蔽性能研究

本文对新型材料发泡金属的电磁屏蔽性能进行了研究，并对其屏蔽原理进行了探讨。实验结果表明：该材料具有优异的电磁屏蔽性能，可用作透气的电磁屏蔽材料使用。     

纳米镍粉的制备及其电磁屏蔽效能的研究

采用水合肼为还原剂,氯化镍为原料,在水和乙醇混合介质中,通过化学还原法制备了单分散性的金属镍纳米粉.X射线衍射(XRD)结果表明,所制备的样品是纯镍纳米粉,没有杂相存在.场发射扫描电子显微镜(FE-SEM)的结果表明,所制备样品的粒径均匀.纳米镍粉及纳米镍粉与微米镍粉混合的电磁屏蔽涂料的电磁屏蔽效能测量结果表明,纳米镍粉的加入,虽然会降低电磁屏蔽效能,但却能提高吸收损耗,原因是增大了磁损耗角正切,减少了电磁波对环境、设备造成的破坏及人类健康的危害.     

生物质多孔炭的电磁屏蔽性能研究

以思茅松锯末为原料,固体氯化铵为造孔剂,酚醛树脂为粘结剂,采用现有的固化烧结技术,制备多孔炭材料。利用法兰同轴法测试其电磁屏蔽效能。结果表明,在130～1800MHz内,多孔炭的屏蔽效能在38.8～56.2dB之间,屏蔽效果较好,并优于无孔炭材料。其中,在130～716MHz内,多孔炭的屏蔽效能随着频率的增加而减小;但在716～1800MHz内,多孔炭的屏蔽效能随频率的增加而增加。多孔炭的孔径越大,其电磁屏蔽效能越好,但是随着频率的增加,0.35mm和0.13mm两种孔径的多孔炭屏蔽效能差距越来越小。当孔径和厚度一定时,多孔炭的屏蔽效能随着孔隙率的增加而增大。     

多层金属纤维混纺织物的电磁屏蔽效能

金属纤维混纺织物由于具有较好的电磁屏蔽性能得到了广泛应用,但其屏蔽效能受纺织工艺等诸多因素影响,难以建立精确的计算模型。在分析介质平板屏蔽体屏蔽效能的基础上提出等效算法,将金属纤维混纺织物等效为均匀介质平板,以计算多层织物材料的电磁屏蔽效能。通过测试单、双层金属纤维混纺织物的电磁屏蔽效能,验证了等效方法的正确性和可行性,可用于指导复合材料的设计。     

不锈钢纤维织物电磁屏蔽效能的研究现状

不锈钢纤维织物具有电磁屏蔽效能良好及防辐射效果持久、透气性好、穿着舒适、加工方便等特点,是当今世界上应用最广泛的高效屏蔽织物.简要描述了不锈钢纤维混纺纱线、不锈钢纤维织物的制备方法及其产品开发现状,重点阐述了不锈钢纤维特性、纱线结构、织物结构及电磁波频率等因素对不锈钢纤维织物电磁屏蔽效能的影响规律.此外,还指出对电磁波屏蔽机理的探索和产品的开发是该材料领域今后的研究重点.     

Highly Stretchable Polymer Composite with Strain-Enhanced Electromagnetic Interference Shielding Effectiveness

Polymer composites with electrically conductive fillers have been developed as mechanically flexible, easily processable electromagnetic interference (EMI) shielding materials. Although there are a few elastomeric composites with nanostructured silvers and carbon nanotubes showing moderate stretchability, their EMI shielding effectiveness (SE) deteriorates consistently with stretching. Here, a highly stretchable polymer composite embedded with a three-dimensional (3D) liquid-metal (LM) network exhibiting substantial increases of EMI SE when stretched is reported, which matches the EMI SE of metallic plates over an exceptionally broad frequency range of 2.65–40 GHz. The electrical conductivities achieved in the 3D LM composite are among the state-of-the-art in stretchable conductors under large mechanical deformations. With skin-like elastic compliance and toughness, the material provides a route to meet the demands for emerging soft and human-friendly electronics.     

弹体磁屏蔽效能的计算与仿真

根据弹体形状的特点,引入近似法计算其横截面和纵向截面的磁屏蔽效能,并用有限元软件ANSYS进行了仿真验证.结果表明符合程度较好,在钢质弹体材料相对磁导率取其最大值时,弹体对地磁场的屏蔽系数可达99%以上.该结果为地磁探测硬件电路设计和姿态角算法设计提供了重要参考.     

层压包装材料电磁屏蔽度模型研究

根据平面波屏蔽理论,从单层介质电磁屏蔽度模型出发,分析了多层层压包装材料的屏蔽特性,导出了其电磁屏蔽度模型。     

电磁搅拌法制备导电聚苯胺纳米线的电磁屏蔽性能研究

针对低频频段(<1.5GHz)的电磁屏蔽涂层,采用快速混合法制备出导电聚苯胺纳米线,使用透射电镜(TEM)对其形貌和尺度进行表征,研究了搅拌方式对聚苯胺/聚氨酯涂层的导电性能和电磁屏蔽性能的影响。研究表明,由于磁场的作用,采用电磁搅拌法可以缩短聚苯胺聚合反应时间,合成均一的导电聚苯胺纳米线,其渗滤阈值为33.3%,含量为33.3%的聚苯胺纳米线的聚苯胺/聚氨酯涂层的电磁屏蔽性能为32.2dB,优于含量为45%的机械搅拌法制备的聚苯胺粉体,这可能是由于线性结构的导电聚苯胺在基体中能够较容易形成三维导电网络结构所致。     

A Computational Approach to Investigate Electromagnetic Shielding Effectiveness of Steel Fiber-Reinforced Mortar

The electromagnetic shielding effectiveness of steel fiber-reinforced mortar was numerically examined in this study. A series of numerical analysis on twenty-seven types of specimens of different diameters, lengths, and volume fractions of fibers were conducted using the FE program HFSS to investigate the effect of the dimensions of steel fibers and the amount of fibers added to the mortar on the shielding effectiveness. S-parameters of some specimens were experimentally measured by the free space method and the experimentally measured S-parameters were compared with those computed in order to verify the present numerical analysis method. It was found that smaller diameters and larger volume fractions provided better shielding effectiveness. Fiber length did not strongly influence the shielding effectiveness. The number of fibers was found to strongly influence the shielding of electromagnetic waves, and the optimal number of fibers in the mortar was found.     

金属纤维填充聚合物复合材料的导电性能和电磁屏蔽性能

以不锈钢纤维作为填料,分别与ＡＢＳ和ＰＰ两种聚合物复合制得了电磁屏蔽用导电性高分子复合材料。通过研究复合材料导电性能和电磁屏蔽性能与纤维含量的关系,发现结晶性的ＰＰ基体比无定形ＡＢＳ基体所需的纤维临界填充量低,同时ＳＳＦ／ＰＰ的屏蔽效果高于ＳＳＦ／ＡＢＳ复合材料;此外,结果还表明这类复合材料对电磁波的屏蔽效果以吸收损耗为主,反射损耗量较小。     

Metrological Assurance of Measurements of the Electromagnetic Parameters of Ferromagnetic Film Materials at High Frequencies

A version of the VÉT 122-1-92 working standard, with extended functional and technical capabilities, for providing metrological backup for measurements of the electromagnetic parameters of ferromagnetic film materials at high frequencies is presented.