钢轨不平衡电流对应答器电磁特性的影响

为有效评估钢轨沿线电磁环境对应答器电磁特性的影响,以CRH5型电力动车组为例,建立了真实接触网接触线、应答器和钢轨的电磁仿真模型,分析了应答器分别在钢轨三种工况的不平衡电流作用下的空间及内部场分布。仿真结果表明:钢轨不平衡电流越大,空间磁通密度越大,应答器磁通密度峰值越大;应答器内部的磁通密度分布极不均匀;钢轨不平衡电流对x轴、z轴的电场强度分布没有影响。总之,钢轨不平衡电流是影响应答器电磁特性的主要因素,此工作可为提高机车运行的安全性提供技术和理论参考。     

三终端多臂量子环中的持续电流

本文提出了三终端多臂量子环模型,并采用特殊方法来计算持续电流,研究发现：总磁通为零时,持续电流随半导体环增大做非周期和不等幅的振荡.总磁通不为零时,持续电流随AB磁通增强做周期性等幅振荡,Rashba自旋轨道耦合具有改变两种持续电流位相和位相差的效应. 平均持续电流的大小与各臂的臂长和所处的位置以及磁通分布相关.AB磁通对两种持续电流具有不同影响,两种持续电流是可分离的.     

甚低频发信天线电晕电压计算方法研究

文中研究了甚低频发信天线电晕产生的机理,分析了电晕电压发生时伴随的物理现象和化学反应,理论推导了甚低频发射天线电晕电压的计算方法,实例给出了天线导线取值与电晕电压的计算结果,指出电晕电压与天线导线的直径、导线表面的粗糙程度、导线所处位置的大气密度、通过导线的电流频率、淋雨状态及导线的冰渍情况有关。     

名词解释

磁场强度这是一个表示磁场中各点磁力大小和方向的量,它与产生该磁场的电流大小和载流导线的形状有关,它等于磁感应强度与导磁率之比值。磁场强度用表示,单位为安培/米或奥斯特。磁通磁感应强度及与之相垂直面积的乘积叫做该面积的磁通。磁通用Φ表示,单位为韦伯或麦克斯韦。     

真空灭弧室双极和四极从磁场触头设计

纵磁场触头被运用在真空灭弧室中,特别是用来开断大的短路开断电流。本文介绍了双极和四极纵磁场触头的设计,阐述了它们的特性。首先对两种触头结构的原理进行了讨论;接着采用有限元法进行三维场模拟处理,对磁通密度的大小、电流与磁通密度的相位移、燃弧期间固定触头间隙中电流过零后的剩余磁场、触头分闸期间运动对电流参数的影响等进行了研究。在纵磁场电极设计过程中一个重要的参数是电流通过时纵磁场触头产生的电磁吸引力,这个力能够缩减由断路器施加的触头压力。     

以磁通等效实现磁悬浮轴承磁极容错控制

针对8磁极电磁轴承容错控制问题,文中提出了一种基于磁通等效的电磁轴承容错控制方法。该方法首先通过仿真得到磁通的电流-磁通影响系数,利用线性代数理论计算得到电流分配矩阵。当某一个磁极回路发生故障时,利用电流分配矩阵计算重构电流,使8个磁极端面的磁通在故障前后保持不变,即磁通等效,从而实现容错运行。在ANSYS有限元仿真平台进行仿真,用磁通等效方法可以较好地还原故障前的端面磁通和磁力线分布,并计算得到了磁通误差(最大不超过3.2%,绝大部分小于0.5%)和力误差(最大不超过7%,绝大部分小于1.5%),证明了所提出磁通等效容错控制方法的有效性。     

电能表用非接触式U型环短路窃电检测装置设计

提出了一种新的主动式电能表用U型环短路窃电检测技术非接触式短路检测装置。被检测导线穿过由磁环及线圈构成的磁传感器,不需对被检测电路做任何改动。检测信号由自身发出,通过磁感应实现磁信号与电信号的转换,达到检测的目的,与穿过磁环的导线中是否有电流无关。介绍了装置的设计原理、硬件构成、性能分析、实际应用。     

平行激励下脉冲涡流热成像响应规律的研究

为探索脉冲涡流热成像技术中涡流与裂纹平行时的响应规律并分析致热机理,运用有限元仿真软件分析了具有贯穿裂纹缺陷的铁磁、非铁磁材料平行激励时的温度分布;运用MATLAB软件提取仿真及实验数据定量分析磁通密度、电流密度、温度等参数并探究了导致铁磁、非铁磁材料温度分布差异的原因;提出铁磁材料除尖端效应外,裂纹内表面趋肤效应导致裂纹边缘温度升高,非铁磁材料裂纹内表面趋肤效应和裂纹边缘涡流密度增大共同作用导致裂纹边缘温度升高.运用高周波电感应加热器进行了实验验证.实验结果与仿真分析存在较好的一致性.研究成果揭示了非铁磁材料平行激励下的温度响应规律,为工程应用中可能的各方向裂纹定性分析和定量表征奠定基础.     

脉冲放电回路电感的计算

脉冲功率技术广泛用于科学研究、军事、医学及工业等方面。脉冲放电电路为脉冲功率技术的主要研究对象,以高电压、大电流、高功率为特点。电路电感是脉冲放电电路的一个主要关注点,计算机仿真技术(CST)软件为快速计算电路电感提供了一种方法。根据导线间的磁场分布推导了导线电感的理论公式,分析了导线半径及导线间距对电感的影响;分析了基于脉冲放电电路电流波形迭代求解电路电感方法;最后利用CST建模计算了不同电路的电感。将CST计算电感与基于脉冲放电电路电流波形迭代求解的电感做对比,CST可用于辅助分析脉冲放电电路。     

PCB工艺的一些小原则

1：印刷导线宽度选择依据： 印刷导线的最小宽度与流过导线的电流大小有关： 线宽太小，刚印刷导线电阻大，线上的电压降也就大，影响电路的性能，线宽太宽，则布线密度不高，板面积增加，除了增加成本外，也不利于小型化。     

Noninvasive imaging of bioimpedance distribution by means of current reconstruction magnetic resonance electrical impedance tomography

We have developed a novel magnetic resonance electrical impedance tomography (MREIT) algorithm-current reconstruction MREIT algorithm-for noninvasive imaging of electrical impedance distribution of a biological system using only one component of magnetic flux density. The newly proposed algorithm uses the inverse of Biot-Savart Law to reconstruct the current density distribution, and then, uses a modified J-substitution algorithm to reconstruct the conductivity image. A series of computer simulations has been conducted to evaluate the performance of the proposed current reconstruction MREIT algorithm with simulation settings for breast cancer imaging applications, with consideration of measurement noise, current injection strength, size of simulated tumors, spatial resolution, and position dependency. The present simulation results are highly promising, demonstrating the high spatial resolution, high accuracy in conductivity reconstruction, and robustness against noise of the proposed algorithm for imaging electrical impedance of a biological system. The present MREIT method may have potential applications to breast cancer imaging and imaging of other organs.     

Optimization of Permanent Magnet Guideway for HTS Maglev Vehicle With Numerical Methods

Because of the disadvantages of the existing permanent magnetic guideway (PMG) such as low efficiency, a Halbach PMG is proposed to improve the levitation performance of high-temperature superconducting (HTS) magnetic levitation (maglev) vehicle. Magnetic induction of the Halbach PMG is calculated by an analytical method. The screening current density distribution in the superconductor is solved with the flux flow-creep model by the finite-element method, and then the levitation force between the HTS bulk and PMG is calculated by the Lorentz force formula. According to the characteristic of the maglev vehicle, an optimality criterion is proposed to evaluate the levitation performance for the HTS maglev vehicle.      

Self Field Effect Compensation in an HTS Tube

It is well known that the critical current density ${J}_{c}$ of a superconducting material depends on the magnetic flux density $B$ . There exists an electric method to measure the ${J}_{c}({B})$ deduced from the $U(I)$ measurements. The problem with this method is the self field effect because the magnetic flux density is always the sum of the applied magnetic flux density and the self magnetic flux density. This paper presents a special experimental arrangement, compensating fully or partially the self magnetic flux density in an HTS tube. It allows characterizing the true zero magnetic flux density behaviour of the superconducting material. The experimental results of the compensation are discussed. A theoretical analysis based on Bean's model is presented and gives results close to the experimental ones. The proposed compensation is not perfect but the experiments and the theoretical analysis allow validation of the compensation principle.      

螺线管结构参数对脉冲磁场的影响

研究了线圈间距、匝数、个数以及不锈钢套筒对脉冲磁体产生磁场的影响规律。在储能电容和电压不变的前提下,研究结果表明：增加线圈间距会导致磁感应强度降低,磁力线包络增大,但总电流达到峰值时刻减小;增加线圈匝数,峰值电流明显减小,会降低磁感应强度,但有利于抑制磁力线包络;增加并联线圈个数,有利于产生较长的均匀区,但是在供能一定的条件下,磁场强度有所降低,同时总电流达到峰值时刻减小。总体来看,在一定均匀区长度的设计要求下,减少单个线圈匝数,增加并联线圈个数,能够得到磁感应强度更大、均匀性更好的磁场,但要考虑线圈承载电流的能力。另外,不对称的阴阳极金属结构会导致磁场不对称分布,且磁感应强度达到峰值时刻要晚于总电流达到峰值的时刻。     

Magnetization Loss in a Striated YBCO Coated Conductor Considering the Intrinsic Critical Current Distribution

In this work we present numerical analysis results of the magnetization loss in a perpendicular AC magnetic field. The numerical analysis is based on the relation of the linkage magnetic flux to current distribution, and takes into account the$J_ c-B$characteristic, and$n$value-$B$characteristic. We discuss the relation between the magnetization losses with striated superconducting tape and the semicylindrical intrinsic critical current density distribution across the width of the superconducting tape. The result shows that the magnetization loss of monocore superconducting tape in a low magnetic field is affected by the intrinsic semicylindrical critical current density distribution. With a striated structure, the influence of the intrinsic critical current density distribution is reduced.     

Biomagnetic Fourier imaging [current density reconstruction

A technique for reconstructing a current density distribution from measurements of its magnetic field is described. The technique assumes that the current distribution is confined to a single plane. The data it requires are measurements of the magnetic flux on a plane. These can be provided by an integrated planar array of superconducting quantum interference device magnetometers. The approach is based on the magnetic lead field which is derived in a simple way based on energy concepts. Using the lead field and conservation of charge conditions provides two linear, spatially invariant imaging equations relating the current density and flux measurements. These equations are solved using Fourier techniques. The validity of the resulting reconstruction technique is shown both analytically and with a computer model. The effects of not satisfying the planar assumption are described for the case where the currents are parallel but not in the same plane.     

多导体传输线的邻近效应和分布参数研究

随着多导体传输线内各导体之间间距的减小, 导体之间的近邻效应对传输线的分布参数和传输特性的影响越来越大.为此, 我们针对三种典型的传输线结构, 分别建立了基于矢势有限元方法分析的多导体传输线的模型, 并分析了近邻效应对磁通密度和分布电感的影响.利用提出的方法计算了同轴传输线的单位长度分布电感, 并将它与采用解析方法得到的结果进行比较来证明该方法的正确性.计算双线传输线在不同间距时的单位长度电感, 与理论分析得到的结果相比较验证了导线间距越小, 近邻效应对单位长度电感的影响越大.最后, 计算考虑了近邻效应的耦合微带线的电感矩阵, 并将它与其他不考虑近邻效应的方法得到的结果相比较, 说明近邻效应对传输线电感矩阵的影响.     

Reconstruction of conductivity and current density images using only one component of magnetic field measurements

Magnetic resonance current density imaging (MRCDI) is to provide current density images of a subject using a magnetic resonance imaging (MRI) scanner with a current injection apparatus. The injection current generates a magnetic field that we can measure from MR phase images. We obtain internal current density images from the measured magnetic flux densities via Ampere's law. However, we must rotate the subject to acquire all of the three components of the induced magnetic flux density. This subject rotation is impractical in clinical MRI scanners when the subject is a human body. In this paper, we propose a way to eliminate the requirement of subject rotation by careful mathematical analysis of the MRCDI problem. In our new MRCDI technique, we need to measure only one component of the induced magnetic flux density and reconstruct both cross-sectional conductivity and current density images without any subject rotation.