新型真空灭弧室1/2线圈纵磁结构设计与仿真

为了提高真空断路器的开断性能,本文设计一种新型1/2匝真空灭弧室线圈式纵向磁场触头结构,并对其纵向磁场分布特性进行分析。利用有限元方法建立三维结构模型并仿真,在电流分别处于峰值和电流过零时,得出静触头表面、开距中心平面和动触头表面上的纵向磁场分布以及纵向磁场的滞后时间;纵向磁场在触头表面与开距中间平面比较均匀,纵向磁场在静触头面的最大值为0.782 T,纵向磁场在动触头面的最大值为0.442 T,滞后时间为0.897 ms,导体电阻为28.25μΩ;新型结构新型触头结构具有较强的纵向磁场,电流过零后的剩余磁场小、滞后时间短,且温升较小。     

嵌合型杯状横-纵磁触头结构磁场分析

以高压直流真空断路器(HVDC-VCB)灭弧系统触头结构为研究对象,基于杯状横磁(TMF)与杯状纵磁(AMF)触头结构与磁场特性分析,建立了嵌合型杯状横-纵磁触头模型,并对其稳态磁场与剩余磁场进行有限元仿真模拟。分析表明,在稳态磁场下触头中部区域的横向磁场增强,中心区域纵向磁场提升;而当电流过零时,剩余磁场值远小于传统杯状触头,有利于金属蒸气的扩散以及电弧能量的有效逸散。     

软磁复合材料铁芯电机特性的仿真研究

为了发挥软磁复合材料的高电阻率,低损耗,易于再利用的特点,仿真模拟将其应用在永磁电机的铁芯上.以12槽4极直流电机为仿真对象,把三维计算问题转化成二维模型,用JMAG软件对电机进行建模,阐述SMC与硅钢片铁芯差异,先用两种材料进行仿真,结果说明只靠替换铁芯材料对电机性能改进并不会产生很大改善,改进模型,得出不同延伸高度铁芯延伸长度增加引起的电流和转矩特性与功率变化的关系.利用所建模型将Somaloy500的软磁复合材料与50CS800的硅钢片制备的铁芯进行模拟实验,结果表明:相同条件下软磁复合材料铁芯的效率要更高一些.最低转速时效率增加5%,最高转速时效率增加10%;软磁复合材料铁芯模型抑制电流输出,各向同性的优势明显.结论为SMC材料在低转速电机的开发中依旧能够发挥优势,实现电机性能的提高.     

基于MHD的小间隙真空电弧仿真研究

真空开关电弧电流过零前的电弧等离子体状态对真空开关能否顺利开断具有十分重要的影响。本文在建立小间隙真空电弧磁流体动力学(MHD)模型的基础上,采用通用计算流体力学仿真软件对电弧电流过零前0.5 ms时的电弧等离子体的特性进行数值仿真研究。计算得到了真空电弧等离子体压力、等离子体密度、离子纵向速度、阳极表面纵向电流密度和电弧电压等的空间分布。仿真结果表明:从阴极到阳极,真空电弧等离子体压力和密度逐渐增大,而等离子体速度逐渐减小;阳极表面电流密度存在较大径向梯度,最大值低于形成阳极斑点的极限收缩电流,阳极仍不活跃。仿真得到的等离子体密度分布与高速摄像机拍摄得到的CMOS图像光强基本吻合,计算得到的电弧电压与测得的电弧电压是一致的,从而验证了本模型的可行性。     

微波管永磁聚焦系统三维有限元CAD技术

介绍了微波管永磁聚焦系统三维二阶有限元方法的理论和非线性材料的处理技术,同时这些技术已经应用到三维微波管模拟套装的磁场模拟器(MFS)。通过MFS和商业软件ANSYS-Maxwell分别对单磁环和单周期结构进行仿真,并把MFS计算结果与ANSYS-Maxwell结果进行对比,结果表明:MFS和ANSYS-Maxwell轴线磁场峰值误差小于3%;同时对单磁环结构仿真时,MFS的计算时间只有ANSYS-Maxwell的41%;对单周期结构仿真时,MFS的计算时间占ANSYS-Maxwell的92%。通过这些数值实例说明了本文提出的非线性处理技术是有效的,同时也表明MFS能够用于永磁聚焦结构的工程设计。     

基于测录波形的铁芯设备励磁特性转换方法探讨

为获得铁芯设备伏安特性向励磁特性的简便转换方法,该文从励磁特性定义出发,给出基于电流有效值、电压平均值的处理方法和基于电流峰值、电压平均值的处理方法,并针对其处理方法在铁芯饱和下的适用性、电流有效值法带来的误差进行分析。结果表明:随铁芯饱和程度加深,电流谐波含量增加,电流有效值法造成的误差增大。利用对放电线圈放电过程的仿真计算与试验测量,并对比不同方法所测励磁曲线用于计算结果,结果表明利用电流峰值法所得励磁特性比电流有效值法结果更适用于铁芯设备电磁暂态的计算分析。     

斜交简支梁桥纵向地震碰撞反应精细化研究

为精细化分析简支斜交桥地震碰撞反应,首先基于Hertzdamp碰撞理论,采用开放式地震模拟软件OpenSees建立能够考虑碰撞过程中摩擦作用的简支斜交桥精细化计算模型;然后从动力特性、动力反应层面验证模型的可靠性;最后采用三维精细化计算模型分析斜度、摩擦对斜交简支梁桥纵向地震碰撞反应的影响。结果表明：梁体与桥台间最大碰撞力的产生位置随着斜度的变化而改变;最大碰撞力的大小不仅与斜度有关,而且与斜交桥梁端与桥台间摩擦系数也存在一定关系;摩擦作用削弱了斜度对梁端锐角处纵向最大位移的影响,大幅度减少上部结构峰值转角,使峰值转角最大值滞后在较大斜度时出现;不考虑摩擦作用会高估锐角处梁端纵向最大位移反应。     

中低速磁浮列车悬浮电磁铁电磁特性研究与优化

本文针对中低速磁浮列车悬浮电磁铁电磁特性进行研究,建立三维有限元电磁场计算模型,分析了铁芯长度对电磁铁电磁吸力的影响,提出适用于工程设计时电磁铁电磁吸力计算式,并以提升悬浮电磁铁悬浮性能为目标,给出优化后悬浮电磁铁方案,结果表明:优化后悬浮电磁铁有效缓解了铁芯磁饱和现象,当电流大于40A时,优化方案电磁吸力较现有方案提...     

用于偏转线圈三维磁场计算的谐波表面磁荷法

将三维磁场计算的表面磁荷法和空间谐波展开技术相结合 ,提出了一种用于偏转线圈磁场计算的谐波表面磁荷法。利用空间谐波的正交性 ,导出了与铁芯表面感应的磁荷各次谐波一一对应的磁场谐波。根据铁芯表面的法向磁场关系 ,建立各次磁荷谐波的积分方程 ,并进行了离散化。此方法将三维问题简化为一维积分方程问题 ,可以处理铁芯磁导率为有限值及铁芯与线匝间具有任意间隙的情况 ,具有较大的普遍适用性。用此方法计算了一个偏转线圈的例子 ,取得了较好的结果。     

电磁超声钢板测厚装置中脉冲电磁铁的设计

针对传统电磁超声换能器(electromagnetic acoustic transducer,EMAT)在钢板表面移动困难、探头易磨损等问题,提出利用脉冲电磁铁替代永磁铁为换能器提供偏置磁场的方法。该方法通过控制激励电流来控制脉冲电磁铁仅在超声体波发射接收瞬间激发脉冲磁场,提高换能器在试件表面多点测量时的移动性。通过对脉冲电磁铁励磁线圈、铁芯以及驱动电路的设计,使得脉冲磁场满足EMAT对于偏置磁场强度及维持时间的需求。为测试该脉冲电磁铁的性能,搭建电磁超声钢板测厚实验平台。结果表明:激励电流仿真值与实测值相似度达90%,脉冲电磁铁可产生峰值约0.8 T、维持时间120μs的脉冲磁场,以该方法设计的换能器可对50 mm厚钢板进行测厚同时具有良好的移动性。     

Effects of rotating magnetic field and temperature field on comminution of magnetic particles

Abstract

This study examines the movement patterns and comminution of magnetic Ni particles in pure water in a flask. This flask is on top of an actuator which contains a rotating bar magnet, and is surrounded by circulating water at a constant temperature. A digital camera, a particle size analyzer and a field emission electron microscope were adopted to record the moving patterns, particle size distributions and micrographs of magnetic Ni particles. A thermocouple was employed to measure the temperature of pure water in the flask during Ni particle attrition. The effect of the temperature of the water that circulated around the periphery of the flask and the effect of the shape of the flask were analyzed. This study also investigated the effects of the water‐to‐particulate mass ratio and the placement of a bar magnet with an interface between the positive and negative poles in a bar magnet at an inclination angle on the shrinking and the moving pattern of the Ni particles.     

The Sun's global magnetic field

Our present-day understanding of solar and stellar magnetic fields is discussed from both an observational and theoretical viewpoint. To begin with, observations of the Sun's large-scale magnetic field are described, along with recent advances in measuring the spatial distribution of magnetic fields on other stars. Following this, magnetic flux transport models used to simulate photospheric magnetic fields and the wide variety of techniques used to deduce global coronal magnetic fields are considered. The application and comparison of these models to the Sun's open flux, hemispheric pattern of solar filaments and coronal mass ejections are then discussed. Finally, recent developments in the construction of steady-state global magnetohydrodynamic models are considered, along with key areas of future research.     

Critical magnetic field in layered superconductors

The nature of the dependence H _c2(T) is greatly affected by the presence of magnetic impurities and their ordering at low temperatures. The scattering leads to a change in the sign of the curvature, and consequently to an increase in the value H _c2. The theory allows one to explain recent experimental data with the overdoped cuprates which exhibits behavior that is drastically different from the conventional picture. The calculations are in excellent agreement with the data.The authors are grateful to A. Mackenzie, J. Cooper, and S. Wolf for fruitful discussions. One of us (YNO) wishes to acknowledge the support of the Humboldt Foundation. The research of VZK is supported by the U.S. Office of Naval Research under contract no. N00014-94-F0006.     

Nonlinear magnetic field solutions based on a vector magnetic potential

The earlier successful techniques for numerical solution of magnetic field problems required defining a field quantity and magnetic permeability over the problem grid model. Later improved but limited techniques were introduced whereby it was necessary to define only a field quantity, usually a potentia function, over the grid because the magnetic material characteristics were incorporated directly into the equations. The work presented in this paper represents a culmination of these latter efforts in that technique is presented whereby the general three-dimensional magnetic field boundary value problem with current regions can be solved numerically.     

Cellular uptake of protein-bound magnetic nanoparticles in pulsed magnetic field

A method for fast delivery of proteins conjugated to superparamagnetic iron oxide nanoparticles (SPION) into mammalian cells by applying a strong magnetic field in pulses was proposed. Firstly, SPION were prepared from an alkaline solution of divalent and trivalent iron ions and covalently bound with protein through the activation of N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC). After fluorescently labelling, the protein-nanoparticle conjugate was mixed with mammalian cell line and exposed to a pulsed magnetic field for short durations of few milliseconds. Results suggested that superparamagnetic nanoparticles were able to carry proteins into living cells immediately. Cellular internalization of the fluorescently labelled protein-nanoparticle conjugate was proved by the observation of cell fluorescence in a fluorescent microscopy, as well as cell analysis by a flow cytometer. We found that the cellular uptake was accomplished dominantly by the process of bombardment of magnetic nanoparticles.     

室温磁制冷高场强永磁磁路

在中空圆柱型磁场源(hollow cylindrical flux source)的基础上,设计并制作出用于室温磁制冷机(往复式和旋转式)的高场强永磁磁路,在磁路工作气隙为20mm时,工作气隙中心的场强的计算值及实测值均高于1.5T.     

Monosize magnetic hydrophobic beads for lysozyme purification under magnetic field

Monosize and magnetic poly(glycidyl methacrylate-N-methacryloyl-(l)-tryptophan) [mPGMATrp] beads (1.6 µm in diameter) were used for hydrophobic affinity capture of lysozyme from chicken egg-white. N-methacryloyl-(l)-tryptophan (MATrp), which gives hydrophobicity to the resulting polymer, was synthesized by reacting methacryloyl chloride and l-tryptophan methyl ester then characterized by Nuclear Magnetic Resonance (NMR). mPGMATrp beads were produced by dispersion polymerization in the presence of magnetite nano-powder. mPGMATrp beads were characterized by means of swelling studies, elemental analysis, Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope (SEM). Lysozyme adsorption experiments were performed under different experimental conditions (i.e., lysozyme concentration, temperature, and ionic strength) in magnetically stabilized fluidized bed system, (MSFB). Maximum adsorption capacity was 263.9 mg/g. It was observed that mPGMATrp beads can be used without significant loss in lysozyme adsorption capacity after 25 adsorption-elution cycle.     

Capillary magnetic field flow fractionation and analysis of magnetic nanoparticles

This paper reports the purification and analysis of magnetic nanoparticles using capillary magnetic field flow fractionation, which utilizes an applied magnetic field oriented orthogonal to the capillary flow. To validate this approach as a separation method for nanometer-scale particles, samples of magnetic nanoparticles composed of either gamma-Fe2O3 (maghemite) or CoFe2O4 with average diameters ranging from 4 to 13 nm were prepared and characterized by transmission electron microscopy and SQUID magnetometry. Retention of the samples on the capillary was investigated as a function of solvent flow rate and the nanoparticle size and composition; the elution times of the nanoparticles are strongly dependent on their magnetic moments. We demonstrate the use of this method to separate a mixture of nanoparticles into size-monodisperse fractions. The magnetic moments of the particles are calculated based on analysis of the retention parameters and correlate with values obtained in separate SQUID magnetometry measurements.     

Induction magnetic field transducers stability limits

The contradiction between widening the frequency range (FR) and rising the flat part of transfer function (TF) of an induction magnetic field transducers (IT) device while maintaining steady operation is solved by deducing the stability conditions and, finally, the informational and metrological characteristics are stated. Such stability limits are proposed as the relationship of IT circuit values with positive and negative magnetic flux feedback loops. The basic metrological characteristics for five wide-band IT modes are formulated. The steady function of these modes is ensured by satisfying simultaneous inequalities. Such characteristics are in a state of flux in the FR from <0.1 Hz to >10 MHz and the TF up to 500 Vm/A. In addition, we propose the informational capability index of ITs as FR and TF generalization and also the establishment of a precise upper frequency limit.     

CMOS magnetic field to frequency converter

In this paper, a CMOS magnetic field to frequency converter with high resolution is presented. It is composed of two voltage-controlled ring oscillators whose output frequency differences linearly vary with the magnetic field perpendicular to the chip surface. The prototype circuit has been fabricated in a 0.5-/spl mu/m CMOS process and operated at a 5-V supply voltage. The measured sensitivity is 24 kHz/mT and the power consumption is 5.1 mW. The small equivalent resolution of at least 20 /spl mu/T can be achieved. The frequency offset is 42 kHz when no magnetic field applied. Its nonlinearity within /spl plusmn/120 mT is smaller than 0.56%.