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。     

应用于铯喷泉钟的磁屏蔽系统的设计

高质量磁屏蔽系统是铯喷泉钟的重要部件之一。首先给出评定磁屏蔽效果的3个指标,即磁场均匀区长度、磁场均匀区起点位置和磁屏蔽效率。在此基础上,讨论了利用有限元计算3层磁屏蔽系统的层间径向间距、轴向间距、端盖孔套管长度和端盖连接方式对磁屏蔽的影响,给出了相应的优化参数,并对比了按优化参数设计的3层磁屏蔽与原有4层磁屏蔽系统用有限元计算的磁屏蔽效果。有限元计算结果为中国计量科学研究院新铯喷泉钟磁屏蔽系统的技术设计提供了理论指导。     

复合材料屏蔽效能测试方法的研究

对平板型复合材料屏蔽效能的测量概括起来可以分为两大类：“近场法”和“远场法”、“近场法”主要用来测量材料对电磁波近场（磁场为主）的屏蔽效能,“远场法”主要用来测量材料对电磁波远场平面波的屏蔽效能。本文对上述两类方法的原理,适用范围等作了详细阐述。     

塑料表面溅射电磁屏蔽膜的研究

电磁干扰(EMI)日益严重,在产品表面镀覆电磁屏蔽膜成为抗EMI主要措施之一.本文采用磁控溅射技术在聚酯塑料(PET)上制备出附着力大于5 MPa、2 GHz～4 GHz频率范围内屏蔽效能大于60 dB的复合结构的电磁屏蔽膜,并研究了导电膜、导磁膜及其复合膜层的电磁屏蔽特性.有关数据表明:镀覆500 nm Cu+300 nm 1Cr18Ni9Ti的复合屏蔽膜可以获得屏蔽效果、成膜速率和结合力的综合好效果.溅射功率、膜层厚度对电磁屏蔽特性和结合力有一定影响.     

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。     

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。     

电磁屏蔽层设计及其磁控溅射制备的研究

通过传输线模型推导出多层无限大平板的屏蔽效能的计算公式,并根据公式设计了双层屏蔽层,通过多靶直流溅射制备了多种金属屏蔽膜.研究结果表明衰减损耗是各层屏蔽效果线性相加的结果,反射损耗与各层相对位置关系无关,层数多或各屏蔽层的反射越大,则屏蔽效果越好.采用Cu/1Cr18Ni9Ti的金属屏蔽层结构,可获得良好的屏蔽效能及耐候性,单纯用表面阻抗来评估多层金属膜的电磁屏蔽效果并不合适.     

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。     

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。     

合成纤维复合夹层屏蔽结构改性及其电磁特性研究

提出具有复合介质夹层屏蔽结构模型的设想,利用铜箔-聚四氟乙烯为原材料,设计了单层屏蔽结构与复合夹层屏蔽结构的对比实验,测试了复合夹层屏蔽结构的电磁屏蔽效能增量,并用Ватолцн多层电磁屏蔽理论公式进行了验证。具有复合夹层屏蔽结构材料的电磁屏蔽效能明显优于单层屏蔽结构材料的电磁屏蔽效能。继而以涤纶无纺布、锦纶合成纤维为研究对象,采用电化学改性的方法,制备了具有复合夹层屏蔽结构的柔性电磁屏蔽材料。结果表明,通过对研究对象的选择和优化电化学改性的工艺,可以制备出1 MHz~1000 MHz入射电磁波频段范围内,满足不同要求的合成纤维复合夹层屏蔽结构改性材料,其SE值最高可达98 dB。     

Magnetic Shielding Properties of MgB2Fe Superimposed Systems

We studied the magnetic shielding properties of a MgB₂/Fe hybrid structure consisting of two coaxial cups subjected to a magnetic field applied parallel to their axis. This study was performed to analyze the magnetic shield properties of a system contemporary exploiting the opposite magnetic properties of superconducting/ferromagnetic materials. The MgB₂ cup was grown by a microwave-assisted Mg-infiltration technique that allows obtaining samples with different shapes and easily scalable sizes, meeting the requirements of different shielding applications. Measurements of mitigation of the magnetic induction were performed in applied magnetic field up to 1.5 T and in different positions along the cup axis at temperature T=20 K. A decrease of the shielding factor (SF) of the hybrid system with respect to the MgB₂ cup alone turns out at low magnetic field. On the contrary, at higher magnetic field the superposition of the two cups increases the SF of the hybrid system up to 3 times over that one of the single MgB₂ cup.     

Experimental Investigation of the Magnetic Shielding Effect of Mineral Powders in a Drilling Fluid

Magnetic contamination of the drilling fluid shields the Earth's magnetic field measured by the magnetic sensors, and may contribute significantly to errors in directional surveying of a wellbore. A series of laboratory measurements were performed to investigate such magnetic shielding effects. In the measurement, a single axis fluxgate magnetometer was immersed in model drilling fluids prepared by mixing powders of known magnetic properties (magnetite and pure iron) into a solution of xanthan gum in fresh water, whereafter the vertical component of the Earth's field inside the fluid was measured. It was found that the strong shielding effect of dry iron powder essentially vanished when was suspended in the drilling fluid. The magnetic shielding caused by magnetite, however, remained significant also in solution, showing a complex dynamical behaviour. Initially the magnetic field was significantly damped, and this shielding was found to increase further for the next hour or so, reaching a fairly sharp maximum. The shielding then started to decay slowly and irregularly again over the next few days.     

Smoothing of Magnetic Fields for Superconducting Bearings by Multilayers

Losses in magnetic bearings, whether conventional or superconducting, are caused by any magnetic inhomogeneities in the direction of motion. These can be smoothed by inserting a permeable sheet between the magnet and superconductor. However, this will also have the effect of reducing the field of the main magnet, which supplies the levitating force. Drawing on the parallel with shielding, where shields with air-gaps are more effective than solid shields of the same thickness (Rucker in Philos. Mag. 37:95, 1894), the same principle can be applied to smoothing layers. Analytic solutions are easy to obtain by using an anisotropic permeability in the smoothing layer. An air gap makes the normal permeability about unity while maintaining the parallel smoothing permeability which shorts out small wavelength inhomogeneities. For inhomogeneities which are mainly in the direction of motion we can striate the layer so that the in plane permeability is also inhomogeneous. The results are applied to a magnet track made of permanent magnets joined together with an effective gap of 0.1 mm. A suitable ferromagnetic layer can reduce the dip in field by a factor of 53 while only reducing the main field by 3 %.     

Magnetic Characterization of MgB2 Bulk Superconductor for Magnetic Field Mitigation Solutions

Magnetic shielding properties of MgB₂ bulk samples synthesized by the SPS (Spark?CPlasma?CSintering) technique were characterized in low applied magnetic fields at temperatures ranging from 20 to 37 K. The used growth technique allows one to produce this compound in different shapes and sizes required for shielding applications. In this framework, shielding magnetic-induction field profiles generated by MgB₂-based shield components, shaped as planar thick disks, were measured by means of a suitable Hall probe in-plane array. The magnetic field distribution at different vertical distances above the sample was also obtained by a micrometric motion of the probe ensemble. Magnetic field profiles were then analyzed in the framework of the critical state model and the critical current density, J _c , was evaluated. The J _c magnitude indicates that the material under test is a good candidate for passive magnetic shield manufacturing up to temperatures close to the transition one.     

计算机信息防泄复合薄膜屏蔽材料设计─Ⅰ．理论部分

本文在计算机信息防泄复合薄膜屏蔽材料研究中，引入材料设计的思想，运用传输线的理论模型，借助于计算机，对不同材料进行多层屏蔽设计。计算结果表明，非磁性导体间的多层复合，屏蔽效果随分层数的增加而趋于一极大值，但变化值很小；磁性导体的多层复合，屏蔽效果与分层数存在着最佳的匹配关系，并随频率、膜厚、成分变化而变化；金属与铁氧体的复合，仅当屏蔽衰减较大时（膜较厚），铁氧体对屏蔽才起明显作用，分层才有意义。     

Calculation of AC Magnetizing Loss of ReBCO Superconducting Tapes Subjected to Applied Distorted Magnetic Fields

In recent years, there are fast-increasing concerns on the utilizations of superconducting rotating electrical machines in different application areas, such as ship propulsion systems, aircraft drivers, and wind turbine generators, since these machines exhibit the merits of high current density, compact design, high power density, light weight, high torque density as well as high efficiency. One of the main limitations in front of the vast use of superconducting tapes in the fabrication of electrical machineries is AC magnetizing loss when tapes are exposed to an external magnetic field, which can decrease the critical current density of wires, as well. In the literature, most of the research works have been done on calculation of the AC magnetizing loss under a pure external magnetic field, while in reality, magnetic flux lines in AC electrical machines are usually distorted with harmonics because of different reasons such as distorted leakage flux, distributed coils of a winding in several slots, cogging fields, mechanical faults, etc. Since these distorted fields contain harmonics, then in this paper, the AC magnetizing loss of superconducting tapes has been electromagnetically modeled and calculated when they are subjected to nonsinusoidally distorted external magnetic fields. The magnetic field dependency of critical current density has been considered in a proposed finite element model. The results have shown that the AC magnetizing loss increases significantly under a distorted applied field compared with a sinusoidal one. In addition, the loss increase depends on the harmonic content which would increases drastically with total harmonic distortion of the applied magnetic field.     

Magnetic field dependence of shielding current density in Y-Ba-Cu-O rings at 77 K

A method for contactless measurement of the shielding critical current density and its dependence on the external magnetic field is described and analyzed. The obtained values are compared with those measured resistively on two different samples. It is shown that the shielding critical current densityJ _cs and the intergranular transport current densityJ _cr are identical if the measurement conditions are similar. A degradation ofJ _cs measured in the external field with AC ripple has been observed.