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。     

一种三维磁场电能表关键元器件磁屏蔽测量方法

电能表关键元器件磁屏蔽效果测量是电能表形式试验中的一个重要项目,传统二维磁场测量测量磁泄露的方法存在测量的盲区。对此该文提出一种利用三维磁场测量磁屏蔽的理论方法。首先从理论上证明只有在球面三维磁场下才能找到磁屏蔽泄露的薄弱点,通过电磁场理论给出三维条件下感应电流与电磁强度的公式。其次在此基础上搭建自动检测装置,针对该装置设计一套评估磁屏蔽效能的试验方法。最后利用该方法对多种屏蔽材料构成的屏蔽壳进行磁泄露测试,试验结果验证该方法的有效性,表明该方法可以用于对电能表关键元器件屏蔽材料的选取及其内部结构设计。     

复合材料地雷壳体X波段HPM辐照效应实验研究

采用不锈钢纤维填充工程塑料制备复合材料地雷壳体,内部放置磁引信并连接电引火头,在微波暗室中进行X波段HPM辐射下毁伤效应实验。数值计算屏蔽效能>20dB,实验结果验证计算。当壳体存在半径5mm以下圆孔时,实验结果与数值计算均表明其对屏蔽效能影响较小;当壳体存在矩形孔缝时,其长度l、孔缝与极化方向之间角度为最大影响因素。复合材料壳体有助于提高磁引信地雷在战场高功率电磁环境下的生存能力。     

浅谈屏蔽盒校准问题

自从无线电通信和电报通信问世以来,电磁环境已成为人类生存环境中不可或缺的组成部分。一些有意的和非有意的源所产生的电磁能量会对它们周围很多电气与电子设备产生干扰,影响它们正常工作。在手机进行研发、生产、维修的过程中,需要对手机进行功率准确度及灵敏度方面进行测试,如果受到外界其他干扰源的干扰,很容易导致手机性能测试的不准确。为了保证手机测试的过程中不受其他外界干扰,普遍使用屏蔽盒来有效地屏蔽外界电磁辐射对手机测试过程中产生的种种影响。屏蔽效能是屏蔽盒性能好坏的一项重要指标参数,如何去测量屏蔽盒的屏蔽效能就显得尤为重要。本文通过研究屏蔽效能测量的方法和原理,提出合理的测量方法。     

基于超导磁场环境真空测量电离规磁屏蔽结构仿真研究

聚变装置超导磁场环境下真空测量电离规因灯丝变形、带电粒子轨迹变化等物理机制导致真空测量精度不高,不能满足工程精确测量的需求.基于磁屏蔽的理论,构建了半封闭式和开放式的两种多层磁屏蔽结构模型,利用Maxwell有限元软件,仿真研究了结构材料层不同厚度和不同磁场方向等条件下磁屏蔽效能的变化规律.结果 表明,屏蔽效能随铁层材...     

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。     

磁控溅射抗EMI金属膜的研究

首先对金属屏蔽的机理以及Schelkunoff电磁屏蔽理论进行了分析,然后采用磁控溅射的方法在PET塑料上沉积了Cu/1Cr18Ni9Ti,并采用波导的方法对样品的屏蔽效能进行了测试.研究表明单次反射损耗对屏蔽效能的贡献最大,双面金属膜层比单面金属膜层具有更高的屏蔽效果.     

二维高频磁特性测量中关键性问题研究

为准确测量磁性材料的磁特性,提出二维磁特性测试方法,使用新型激磁装置及传感结构,针对二维磁特性激磁装置的电磁干扰及屏蔽结构进行深入研究,设计屏蔽结构,屏蔽效能可以达到61.699d B。讨论测试过程环境中的直流干扰和工频及低频杂波对实验结果的影响等关键性问题,并提出解决方案。实验证明:所提出的解决方法是实用有效的,具有可行性。     

多层复合材料屏蔽电磁波的理论模型

本文从基本的电磁波传播理论出发，考虑了电磁波在屏蔽层中的反射、衰减及多次反射，提出了多怪复合材料屏蔽效能的理论模型和计算公式。公式的应用简便，快捷，适用范围广，可用于不同入射方向的电磁波入射多层复合材料的屏蔽效能计算预测。最后对公式进行验证，计算结果与实验数据基本吻合。     

An accurate method of calculating multilayer, multimaterial cylindrical magnetic shields

The basic concepts of shielding theory have existed since the last century [1,2]. There have been many publications on the subject of magnetic shielding, treating the case of shielding apparatus from static fields by means of multiple concentric shields and deriving several principles of fundamental importance. Unfortunately, however, theory has been applied to only the most ideal shield configurations, for the case of constant permeability [3-5]. This paper covers the analysis of shielding effectiveness of variable Permeability cylindrical shielded enclosures for the DC magnetic field case. When the permeability is a function of magnetic induction, the simple boundary solution for spherical or cylindrical shields can no longer be applied since the induction, through the permeability, is caused to vary as much as two orders of magnitude, causing nonuniformity in the field in the cavity and inside the shield. Thus, the permeability of the shielding material is considered as a function of the induction, and a significantly improved method of estimating the induction and permeability of the shield is presented. The effects of a multiple-shell geometry are treated in the equations of this analysis. This method gives fast, accurate results and can be run on a small computer for shielding optimization. Results of these magnetic field calculations allowed the selection of optimization criteria and showed how system requirements could be met by choosing a suitable shell structure arrangement. Experimental measurements on real materials for various shell structures confirmed the accuracy of this method.     

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.     

Microstructure and magnetic properties of plasma-sprayed Fe73.5Cu1Nb3Si13.5B9 coatings

Amorphous and nanocrystalline Fe_73.5Cu₁Nb₃Si_13.5B₉ coatings were formed by plasma-spraying micron-sized powders onto H62 brass substrates and aluminum pipes. The coatings are about 0.2-0.3 mm in thickness with fully dense and low porosity. The microstructure of the coatings is classified into two regions, namely, a full amorphous phase region and homogeneous dispersion of α-Fe nanoscale particles with a scale of 30-70 nm. The hardness of the amorphous and nanocrystalline coatings is about 960 HV_100g. Coercivity (Hc), saturation induction (B₈₀₀), and initial relative permeability (μ_i) of the coatings are 144 A/m, 0.27 T, 249, respectively, under 800 A/m direct current (DC) magnetic field. The magnetic shielding performance is good under DC magnetic field and its magnetic shielding effectiveness (SE) is 10-12 dB at coating thickness of 0.45 mm under static magnetic field of 2-40 Oe. The SE increases by increasing the coating thickness when the magnetic field frequencies are 50, 100 and 200 Hz with an intensity of 0.85 Oe. The results indicate that the amorphous and nanocrystalline alloy coatings can be good for some magnetic shielding applications.     

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。     

DC sensor based on magnetic potential self-balance and feedback compensation

A new type of DC current sensor for 10 000 A, which integrates the advantages of DC measurement devices based on the open-loop and closed-loop principle, is presented. One magnetic core carrying two windings is designed as a magnetic potential self-balance loop. In order to detect and compensate the remaining ampere-turns except magnetic potential self-balanced, two feedback compensation detection magnetic cores are designed as a feedback compensation loop. Its operation principle and characteristics, including stability, error analysis and dynamic response, are analysed in detail. Finally, its validity is verified by experiment and the results show that the measuring accuracy of the proposed DC sensor can be enhanced up to 0.13% whereas the accuracy of a conventional DC sensor is only 0.5%.     

Graphene oxide/ferrofluid/cement composites for electromagnetic interference shielding application

This paper deals with the preparation of graphene oxide-ferrofluid-cement nanocomposites to evaluate the electromagnetic interference (EMI) shielding effectiveness (SE) in the 8.2-12.4 GHz frequency range. It has been observed that incorporation of graphene oxide (30 wt%) along with an appropriate amount of ferrofluid in the cement matrix leads to a shielding effectiveness of 46 dB (>99% attenuation).The presence of graphene oxide and ferrofluid in the cement leads to strong polarizations and magnetic losses that consequently result in higher shielding effectiveness compared to pristine cement. The resulting nanocomposites have shown Shore hardness of 54 and dc conductivity of 10.40 S cm( - 1). SEM reveals the homogeneous dispersion of graphene oxide and ferrofluid in the cement matrix.     

非接触搭接结构电磁屏蔽特性的数值分析

非接触搭接是电子设备箱体常见的连接形式,搭接处会不可避免地存在缝隙,而缝隙是电磁泄漏的主要途径,将致使箱体屏蔽效能降低,故有必要探索增强腔体屏蔽效能的方法．以几种典型非接触搭接金属箱体为研究对象,在平面波激励下,利用传输线矩阵法（TLM）和波导理论,对搭接长度、缝隙宽度、缝隙长度等参数对箱体屏效的影响进行了定量的数值计算和定性的理论分析,结论表明通过减小缝隙宽度、增加搭接长度和螺钉分段均可提高箱体屏效．同时计算分析了不同搭接形式对箱体屏效的影响,提出了能够实现高屏效的搭接结构途径,并结合矩形波导理论得到采用弯折搭接结构也能够显著提高箱体屏效的结论．研究结果可为电子设备的电磁屏蔽设计提供依据．     

三明治型电磁屏蔽材料的制备与性能

根据Schelkunoff的多层电磁屏蔽理论，分析了双层和3层屏蔽材料的综合屏蔽特征，提出了一种简单有效的三明治型夹层结构材料设计方案，制备出金属箔、涂料两种三明治型层状电磁屏蔽材料，通过理论计算、样品的综合屏蔽性能测试和SEM微观组织观察，讨论了三明治型材料设计方案的正确性与材料的性能。结果表明，三明治型电磁屏蔽材料的屏蔽效能增量（△SE）随电磁波频率的增加而增大，可以实现结构优化；金属箔三明治型电磁屏蔽材料的屏蔽效能增量与理论计算结果相符合；涂料三明治型电磁屏蔽材料的SE值比普通型高，当入射电磁波的频率为1GHz时，三明治型比普通型高18dB。