方形亥姆霍兹线圈磁场系统均匀性分析

方形亥姆霍兹线圈用于模拟零磁场或量程范围内的任意大小和方向的磁场,其磁场均匀区与线圈结构尺寸有关。为了得到其磁场均匀区与结构尺寸的关系,构建了方形亥姆霍兹线圈的数学模型,导出了线圈内部任意点的磁感应强度矢量表达式,得出了输出电流与产生磁场大小的对应关系,利用程控恒流源和磁强计跟踪补偿动态地模拟出稳恒磁场,对系统产生的磁场的均匀区进行了测定,分析表明,理论计算与实验结果有较好的一致性。     

引信电磁保险机构降低功耗影响因素分析

针对引信电磁保险机构功耗较高,在引信应用中受到限制的问题,通过对电磁保险机构降低功耗影响因素分析,得出电磁保险机构功耗对工作性能的影响规律：降低工作电压、减小线圈线径、弹簧的预抗力、弹簧刚度或增加线圈匝数有利于降低功耗,但会使电磁保险机构工作性能下降。仿真研究表明：功耗减小45%,电磁保险机构响应时间增加49%。     

基于通电空心线圈的脉冲磁场分析

基于通电空心线圈,运用有限元分析软件以及自行搭建的磁场测量装置研究了激励信号频率、线圈外径对线圈中轴线中点处的磁感应强度的影响,以及在频率时变脉冲信号激励下,线圈中轴线中点处磁感应强度的实时变化。结果表明,线圈中轴线中点处的任意周期内的磁感应强度的均方根值随激励信号频率和线圈外径的增加而减小,仿真分析结果与实测结果的变化规律一致,且与理论分析的结果相同,相对误差在3%以内。在频率时变脉冲信号激励下,仿真与实测的线圈中轴线中点处的磁感应强度变化趋势一致,相对误差在5%以内。     

太赫兹波在均匀磁化等离子体中的传播特性

研究了太赫兹波通过均匀磁化等离子体的传播特性,给出了太赫兹波衰减和相移随等离子体密度、碰撞频率、太赫兹波频率和磁感应强度的变化规律。等离子体电子密度越大,衰减和相移越大;随着碰撞频率的增大,电磁波的衰减先增加到峰值后逐渐减小,且随着磁感应强度的增加,衰减的峰值变大,峰值向碰撞频率减小的方向移动;当电子碰撞频率接近电磁波频率时等离子体对右旋极化波的衰减达到极大值。太赫兹波频率增大,衰减逐渐减小,而相移先增加后逐渐减小。     

一种非高压条件下的对称脉冲磁场对撞试验研究

本文介绍了激磁波的产生机理，并利用麦克斯韦方程对偶极子磁场传播特性进行了理论分析；设计实现了一种基于对称线圈的脉冲磁场对撞试验装置，对比分析了线圈匝数、作用距离等因素对激励脉冲信号的影响。结果表明，试验条件下对称磁场激励信号幅值近似呈 1/R 规律传播衰减，且在穿透特性上与激磁脉冲波差异较为明显。本文对开展激磁脉冲波的试验研究具有一定借鉴意义。     

MRI平面梯度磁场模型的研究

建立了MRI(磁共振成像)平面梯度磁场的纵向和横向梯度模型,并对其进行分析计算,得到均匀的MRI平面梯度磁场.重点分析了由两组不同线圈匝数的"麦克斯韦对"绕组组成的最高到7阶的纵向梯度模型和相距2z0的12个串联供电K匝线圈的矩形绕组组成的横向梯度模型,在此基础上对模型的基本参数进一步优化,得到了更大线性偏差＜1 %的高线性度梯度场.分析表明:模型中的3、5、7阶对磁场梯度的线性均有影响,弱化高阶奇数导数对磁感应强度的影响可以得到更加均匀的线性梯度场.结果表明:应用相同的优化方法,纵向梯度模型的优化效果优于横向梯度模型.     

电流密度高的超导线圈

日立电缆公司和日立公司合作,应用铌-钛三锡多芯细线绕制成的超导线圈,在4.3K温度下产生的磁感应强度高达17.2T. 此磁场线圈的内直径为42mm,外直径为114mm,高为150mm.线圈缠在不锈钢框架上,能承受铌-钛三锡放出的热量.将线圈放在15.1T偏转磁场线圈里,在4.2K温度下,通过155A电流产生的最大     

瞬变电磁测井同轴多匝线圈误差校正模型

受井眼尺寸限制,井下瞬变电磁系统通常采用同轴多匝接收线圈来改善探测性能.但是,线圈匝数的增加在提高信号强度的同时,也引入了模型失配误差.针对该问题,本文在柱状多层非均匀结构基础上,分析了接收与发射线圈间距对感应电动势的影响,并提出了一种瞬变电磁测井同轴多匝线圈误差校正模型.最后,不同收发间距的仿真结果表明,该模型可以有效校正多匝线圈模型失配误差,提高瞬变电磁测井反演精度.     

浅海底瞬变电磁探测系统关断沿影响因素研究

运用电路理论对发射线圈进行了建模分析;讨论了采用多匝小线圈进行浅海底瞬变电磁探测时,发射电流关断沿时间与电流幅值和发射线圈匝数之间的关系;给出了在保证发射磁矩的前提下,合理确定发射电流幅值与发射线圈匝数以缩短发射电流关断沿的原则,并通过实验进行了验证.     

基于线性霍尔传感器的角度测量的非线性校正方法研究

本文提出了一种基于线性霍尔传感器的角度测量的非线性校正方法,在固定磁铁上绕制一定匝数的线圈,线圈产生的磁场与磁铁产生的磁场垂直,空间磁场为上述两个磁场的叠加,固定霍尔传感器的位置,同时保持控制电流不变,让磁铁绕霍尔传感器旋转产生角度的变换,霍尔传感器输出电压也将产生变化。对增加线圈和不增加线圈两种结构进行理论分析和仿真,从仿真结果看,霍尔电压与夹角的关系曲线明显线性增加,测量范围扩大,在角度测量中具有独特的优点。同时设计了传感器硬件电路,进行了实验测量,仿真和实测结果表明：该方法具有电路简单、实时性好、频率相应快、抗干扰能力强、安装调试方便等特点。     

A system for the exposure of small laboratory animals to a 25-mT60-Hz alternating or traveling magnetic field

A versatile exposure system which can be used to investigate the effects of a 60-Hz alternating magnetic field or traveling magnetic field on small laboratory animals is described. Special attention was given to the design of the electric circuit to simplify the supply requirements and to keep the overall current to a minimum. A magnetic field having a flux density up to 30 mT (300 G) can be generated, and a traveling magnetic field is obtained by reconnecting the coils to a three-phase supply. The total magnetic field due to the currents in the three coils used in the exposure system is analyzed. A computer program was written to evaluate the magnetic field in the region where the animals are located. The difference observed between measured and computed values is attributed to the representation of the multiturn, multilayer coils by equivalent single-turn coils     

Magnetic coil design considerations for functional magnetic stimulation

Our studies have demonstrated effective stimulation of the bladder, bowel, and expiratory muscles in patients with spinal cord injury using functional magnetic stimulation. However, one limitation of the magnetic coils (MC) is related to their inability to specifically stimulate the target tissue without activation of surrounding tissue. The primary goal of this study was to determine the governing parameters in the MC design, such as coil configuration, diameter, and number of turns in one loop of the coil. By varying these parameters, our approach was to design, construct, and evaluate the induced electric field distributions of two sets of novel MC's. Based on the slinky coil design, the first set of coils was constructed to compare their abilities in generating induced electric fields for focal nerve excitation. The second set of coils was built to determine the effect that changes in two parameters, coil diameter and number of turns in one loop, had on field penetration. The results showed that the slinky coil design produced more focalized stimulation when compared to the planar round coils. The primary-to-secondary peak ratios of the induced electric field from slinky 1 to 5 were 1.00, 2.20, 2.85, 2.62, and 3.54. We also determined that coils with larger diameters had better penetration than those with smaller diameters. Coils with less number of turns in one loop had higher initial field strengths; when compared to coils that had more turns per loop, initial field strengths remained higher as distance from the coil increased. In our attempt to customize MC design according to each functional magnetic stimulation application and patients of different sizes, the parameters of MC explored in this study may facilitate designing an optimal MC for a certain clinical application.     

Minimum Stored Energy High-Field MRI Superconducting Magnets

A globally optimum minimum stored energy optimization strategy is implemented to design actively shielded superconducting magnet configurations used in high-field applications. The current density map is first obtained and used as a foundation for the magnet configurations by placing coils at current density local extremities. Optimized current density maps based on the stored energy formulation along with final magnet arrangements are provided to illustrate the findings. In this work, the focus was on compact superconducting magnets as measured by physical size and system footprint for given magnetic field properties inside the imaging region. The process of obtaining the current density maps proposed here over the given magnet domain, where superconducting coils are laid out, suggests that peak current densities occur around the perimeter of the domain, where in the most compact designs, with the domain length less than 1 m, the current direction alternates amongst adjacent coils. To reduce the peak magnetic field to acceptable levels on the superconductors in high-field designs, the size of the magnet domain is made larger, to the extent that the current densities no longer alternate between coils.      

光纤陀螺在直流及交变磁场中的磁敏感性研究

介绍了光纤陀螺的磁敏感性机理并进行了实验研究。利用亥姆霍兹线圈装置和光纤陀螺测试平台,研究了光纤陀螺在直流磁场中的磁敏感性,得到光纤陀螺数据输出与磁感应强度基本呈线性关系,以及轴向磁场和径向磁场影响系数的大小和光纤陀螺磁敏感轴的方向。主要针对50Hz的交流磁场研究交流磁场对光纤陀螺零偏和零漂的影响及其交流磁敏感性,得到交流磁场对零偏的影响可以忽略,但磁感应强度与陀螺零漂值的大小基本呈线性关系。研究了不同频率交流磁场对光纤陀螺输出的影响,说明了光纤陀螺数据输出主要与瞬态的磁感应强度成正比,不同频率交流磁场对光纤陀螺零漂值的影响不同,存在一个频率(或频率范围)对光纤陀螺零漂的影响较大,其频率范围与光纤陀螺输出带宽有关。     

Electromagnetic field near rail guns

The field in the neighborhood of an electromagnetic rail gun is computed for the case of constant current. The analysis centers on the Westinghouse EMACK launcher in which two rails of 2-m length carry a peak current of 2.1 MA, while a peak power of over 10 GW is delivered to the rails. Expressions are derived for electric field strength and magnetic flux density as functions of gun parameters. These formulas can be used to compute the electromagnetic pulse produced by a rail gun of any given characteristics     

Flux trapping in a ring-shaped YBCO bulk by pulsed fieldmagnetization

A pulsed magnetic field can be applied using small coils to generate a strong magnetic field for the magnetization of the high-Tc superconductors (HTS) to be used as quasi-permanent magnets in flywheels and motors. The dynamic electromagnetic behavior of two melt-processed ring-shaped Y-Ba-Cu-O bulks using the pulsed field magnetization (PFM) process has been experimentally investigated and analyzed. The flux trapped in the bulk by PFM process was compared to the flux trapped by field cooling process. Both cases then have been analyzed with a numerical model based on the finite-element method (FEM). The power-law model was utilized to relate the electric field to the current density inside the superconductor. The dependence of the critical current density on the magnetic field density was taken into account. Measured and calculated results are compared and discussed     

一种可调的新型永磁迴路

本文设计了一种可调的叠式钐钴永磁迥路。用三层径向磁化的钐钴磁体和软铁类磁导材料,借助于计算机,设计了沿轴向长2.0mm,磁场强度1.2kGs,波动0.7％的均匀磁场,为高功率微波管的永磁聚焦系统提供了一种优良的永磁迴路。     

三网孔介观电容耦合电路的量子效应

本文将三网孔介观电容耦合电路系统看作一个正则系综，通过计算正则系综的密度矩阵方程得出有限温度下耦合电路中电荷和磁通量的量子涨落．高频下，电路中电荷的量子涨落类似于低温下的情形，表现为典型的量子噪音；磁通量的量子涨落则不单是零点的量子涨落，总是和温度有关；绝对零度下，输入、输出网孔中电荷和磁通量不确定度的乘积保持相等．