正方形亥姆霍兹线圈的磁场均匀性

利用三个正方形亥姆霍兹线圈构建三维匀强磁场,并分析其匀强磁场区域特性。将正方形亥姆霍兹线圈视为四段载流导线,采取分段计算然后矢量叠加的方法,分析正方形亥姆霍兹线圈轴线上和空间磁场强度及其均匀性,及其仿真数据结果。最后得到正方形亥姆霍兹线圈三维匀强磁场的结构模型及相关数据分析,证明了三维亥姆霍兹线圈产生的磁场满足匀强磁场要求。     

Uniformity condition for a rectangular field coil with a split winding

A generalized Helmholtz condition for field uniformity is derived from the closed form solution of the magnetic field in a multilayer rectangular coil pair as a function of coil dimensions and pair separation. The relation among the dimensions satisfying this condition is found and plotted in parametric form for single layer coils and for a multilayer coil with a specific winding thickness. For square coils of cross section small compared to their mean radius, the gap separation approaches half the coil radius, analogous to the classical condition for circular coils. Comparison between theoretical and measured values for tolerances within +/-5% of the field at the system center agree within a 6% maximum deviation. For the experimental coil, the area enclosed by the +/-5% contour was 58% of the area of the full coil.     

Note: design of a novel rotating magnetic field device

A novel device to produce a rotating magnetic field was designed, constructed, and tested. The system consists of a Helmholtz coil pair which is mechanically coupled to a dc electric motor whose angular velocity is controlled. The coil pair generates a uniform magnetic field; the whole system is rotated maintaining the coils energized using brushes. The magnetic field strength is uniform (≈5.8 mT) for a workspace of about 100 mm along the rotation axis. The system remains free of undesirable high amplitude mechanical vibrations for rotation frequencies below 10 Hz. We verified the performance of the apparatus by conducting experiments with magnetic swimmers.     

In situ calibration of rotating sensor coils for magnet testing

An in situ procedure for calibrating equivalent magnetic area and rotation radius of rotating coils is proposed for testing accelerator magnets shorter than the measuring coil. The procedure exploits measurements of magnetic field and mechanical displacement inside a reference quadrupole magnet. In a quadrupole field, an offset between the magnet and coil rotation axes gives rise to a dipole component in the field series expansion. The measurements of the focusing strength, the displacement, and the resulting dipole term allow the equivalent area and radius of the coil to be determined analytically. The procedure improves the accuracy of coils with large geometrical irregularities in the winding. This is essential for short magnets where the coil dimensions constrain the measurement accuracy. Experimental results on different coils measuring small-aperture permanent magnets are shown.     

线性测微电感的精化

为提高测微电感传感器的测量精度,提出了基于赫姆霍兹线圈理论设计螺线管线圈的方法,改善了螺线管线圈内轴向上磁场的分布均匀性。首先,分析了螺线管线圈模型,建立了螺线管线圈参数与轴向磁场强度分布相互关系的广义函数模型。然后,通过线圈与磁芯的尺寸确定了系统轴向磁场强度分布函数模型,结合磁芯移动区间范围设置磁场均匀度最小误差目标函数,通过对目标函数寻优得到各螺线管线圈的各项参数。最后,搭建了测微电感传感器的测试系统,测试了传感器性能。实验结果表明:与传统线圈相比,改进型螺线管线圈在100μm测量范围内的线性度由0.46%提高到0.30%。实验显示通过对不同规格的螺线管线圈进行组合,可使得螺线管内轴向上磁场强度分布均匀,从而提高了测量精度。     

微机械电磁阻尼结构分析

提出采用电磁阻尼结构来提高微机械角度调节装置的响应速度.通过建立结构模型和分析结构参数对阻尼效果的影响,给出具体设计实例以及制作工艺,证实该阻尼结构的有效性和可行性.     

卧式柱塞泵曲轴的磁性液体密封设计*

卧式柱塞泵曲轴密封的可靠运行是曲轴轴承实现润滑与液压支架稳定供液的重要基础。基于磁性液体密封理论,设计一种单磁源梯度齿宽磁性液体密封结构,采用数值模拟的方法研究磁性液体密封结构的磁场分布特征,并分析不同密封间隙和转速对密封耐压性能的影响。结果表明：与均匀极齿宽度磁性液体密封结构相比,梯度极齿宽度密封结构平均耐压能力约提高11%;梯度齿宽密封结构中,随着极齿与永磁体距离的增大,各极齿耐压能力逐渐增强;随着密封间隙的增大,离心力引起密封失效的极限转速逐渐减小。     

Optimization of dimensions of a device for circular magnetization of cylindrical components. III. Investigation of circular field component generated by a one-layer toroidal coil

The effect of dimensions of a toroidal coil and the number of turns in the coil on the circular magnetic field component within the region limited by the inside axial sections of the turns has been studied. The configuration of this field has been determined. Optimal dimensions of the coil have been calculated. In order to obtain a higher amplitude of the circular field, one should use coils with smaller numbers of turns. In the inner region of a one-layer toroidal coil close to the turns, the peaks of the circular field diminish with the number of turns, but the number of points where the field intensity is maximal becomes larger, i.e., the field becomes more uniform. Methods of further increase in the circular component of the magnetic field have been suggested.     

Optimization of multilayer cylindrical coils in a wireless localization system to track a capsule-shaped micro-device

A wireless electromagnetic localization method has been presented to track capsule-shaped micro-devices in the gastrointestinal tract. And a prototype for the novel localization system has been developed. In the localization method, cylindrical coils placed on the patient’s abdomen generate alternating electromagnetic fields one by one. The system of equations from the localization model has been established and then transformed into a nonlinear optimization problem. The localization method presents excellent anti-interference ability and high stability. In order to solve the magnetic inverse problem in the localization model, an analytical expression between the magnetic flux density and the position & orientation should be derived by superposition of the fields generated by the coil turns, which causes systematic errors. As a result, the geometry of the cylindrical coils is optimized to reduce the errors. A full factorial experiment with two factors has been carried out. The experiment shows that the optimal L/Dout ratio and Din/Dout ratio are 0.4 and 0.8, respectively. In this case, the mean error and the standard deviation are reduced to 0.89% and 0.77%, respectively, where the distance along the axis of the cylindrical coil from the coil’s center to a measured point is 30 mm. Furthermore, the experimental results also show that the imitation error decreases significantly with increased distance from the coil. The accuracy of the localization model can be further improved using the optimized coil.     

一种任意正交折线线圈阻抗的解析建模新方法

提出了一种位于导体上方正交折线线圈的阻抗解析建模方法。首先,在前人研究的基础上,定义了外形位置因子,得出了单矩形线圈的入射场感应电压及散射场电压简化计算方法;其次,将多个矩形线圈自感电压及两两之间的互感电压叠加,建立了串联等效电感模型;再次,根据任意正交折线线圈的几何原理,将该线圈拆解为有限个相同截面的矩形线圈并进行重构,得出入射场阻抗及散射场阻抗的广义二重积分表达式。最后,利用Mathematica对回折线圈实例进行了计算与实验比较,并根据影响阻抗的各个变量绘制阻抗平面图。拆解重构方法可用于不同形状、不同激励频率、不同提离高度的正交折线线圈平行置于任意电导率导体上方的阻抗解析计算。     

基于Maxwell的磁场发生装置设计及分析

为了实现混有钕铁硼粉末的水凝胶磁化,设计了一种基于亥姆霍兹线圈的新式磁场发生装置。利用Maxwell软件3D模块绘制出磁场系统的三维模型,采用Magnetostatic静磁场求解器分析了增设的辅助线圈距离变化对场强的影响,得到了磁场发生装置的优化结构;再对比磁场发生装置和亥姆霍兹线圈的中心磁场强度和磁感线分布密度,验证结构优化的可靠性。结果表明:当辅助线圈距离为70 mm时,中心磁场强度最大;安匝数相同时,磁场发生装置的中心磁场强度要明显高于亥姆霍兹线圈,最终优化后的磁场发生装置中心磁场强度可达到1.37 T,磁感线分布更加均匀、密集。该仿真结果能够对磁场发生装置结构设计与工作特性分析提供参考,缩短了磁场发生装置设计成本与开发周期。     

电磁驱动薄壁铝合金柱壳的动态膨胀变形特征

采用ANSYS多物理耦合场有限元模拟分析了电磁线圈驱动不同轴向高度铝合金柱壳动态膨胀变形过程的磁压力分布及变形特征,并与试验结果进行对比.结果表明:有限元模型能较准确地模拟电磁线圈驱动柱壳膨胀的径向磁压力分布和变形情况;柱壳高度为20 mm时,端部的径向磁压力大于中部的,发生外凹形不均匀膨胀;柱壳高度为30,40 mm...     

基于迭代补偿的纳米粒子磁化信号检测方法研究

磁粒子成像是一种无创成像技术,通过检测磁粒子示踪剂磁化信号,表征其浓度分布图像。在实际检测中,检测线圈的感应信号包含激励磁场信号与磁性纳米粒子磁化信号。将激励信号从感应电压中去除,获取粒子信号是磁性粒子成像信号检测需要解决的关键问题。针对磁性纳米粒子成像信号检测中激励磁场耦合消除方法进行研究,设计平面梯度检测线圈,并提出迭代补偿控制方法,消除激励磁场耦合,实现磁性纳米粒子磁化信号检测。仿真计算与实验测量的结果表明,对于不同检测模型,所提出的检测方法均可以完成粒子信号检测。该方法获得的粒子信号的信噪比是原有信号消去检测方法的2.2倍,与滤波方法相比信噪比提高到1.3倍,激励磁场耦合衰减可达到34 dB。     

三维远场涡流探头的设计与应用研究

设计了一种新型三维远场涡流探头，通过其远场耦合特性确定了合适的屏蔽结构。以油田采油钢管为检测对象，对管壁的对称缺损和不对称缺损进行了对比检测实验，结果表明：新型探头可确定缺损的三维位置，既适用于大管径管道测量，又适用于小管径管道测量，适用性较高。     

新型磁性液体微压差传感器的设计及耐压分析

传感器是磁性液体的重要应用领域之一。为弥补现有磁性液体微压差传感器的不足,设计了一种新型的磁性液体微压差传感器,该传感器的复合磁芯由磁导率高的1Cr13和永久磁铁构成,磁性液体被吸附在永久磁铁的端部形成环状起到润滑和密封的作用,敏感元件采用1Cr13,转换元件采用对称线圈。当磁芯进入线圈后,使得线圈电感发生变化,电桥电路输出明显的电压信号。在此基础上,提出了回复力的线性程度和磁性液体环的耐压能力决定了磁性液体微压差传感器的量程范围,并通过理论推导、仿真分析和实验研究的手段证明了磁性液体环的密封耐压能力能够满足磁性液体微压差传感器的测量要求。该传感器体积小、成本低、便于安装,具有很强的实用价值。     

一种复合式磁场空间装置的探讨

探讨了一种在磁屏蔽室内套装三轴亥姆霍兹线圈系统的复合装置。该装置可以在周边磁场较乱、磁场梯度较大的环境中构建一个大区域、高均匀度的弱磁场空间，拓宽了弱磁空间的应用领域，降低了构建成本和构建难度。给出了该装置构建的5个技术环节要点。     

Research on magnetic pulse sizing of aluminum tube

We investigated the effects of primary system parameters on the magnetic pulse sizing of aluminum tubes. Furthermore, we present the applicable design method of the sizing coils required for tube sizing. For the AA5056-O tube, we utilized the method of three-section sizing, with one coil for the corresponding position and three times discharge. The research results indicate that the length of the solenoid coil is inversely proportional to the nominal peak value of magnetic pressure; the appropriate combination of the discharge voltage and the gap between the tube and die dictates the sizing; the sizing precision can be improved greatly by iterative sizing, and three times is optimal. The experimental results of magnetic pulse tube sizing meet the technical requirements.     

基于MRI导航的血管内磁性药物颗粒驱动研究

为了解决化疗方法治疗肿瘤存在的毒副作用、药剂效率低等问题,研究一种基于核磁共振成像技术（Mag-netic Resonance Imaging,MRI）导航的血管内磁性药物颗粒投送系统.介绍了外磁场驱动磁性药物颗粒向血管内病变区集中的作用机理,采用数值计算的方法对空间磁场强度和磁场梯度分布进行了分析,从而界定了有效工作空间,在此基础上探讨了多颗磁性颗粒的驱动方案与线圈设计,为磁性药物靶向治疗的临床应用提供参考.     

Rapid rise time pulsed magnetic field circuit for pump-probe field effect studies

Here we describe an electronic circuit capable of producing rapidly switched dc magnetic fields of up to 20 mT with a rise time of 10 ns and a pulse length variable from 50 ns to more than 10 micros, suitable for use in the study of magnetic field effects on radical pair (RP) reactions. This corresponds to switching the field on a time scale short relative to the lifetime of typical RPs and maintaining it well beyond their lifetimes. Previous experiments have involved discharging a capacitor through a low inductance coil for a limited time using a switching circuit. These suffer from decaying field strength over the duration of the pulse given primarily by the ratio of the pulse width to the RC constant of the circuit. We describe here a simple yet elegant solution that completely eliminates this difficulty by employing a feedback loop. This allows a constant field to be maintained over the entire length of the pulse.     

High-temperature superconducting quantum interference device with cooled LC resonant circuit for measuring alternating magnetic fields with improved signal-to-noise ratio

Certain applications of superconducting quantum interference devices (SQUIDs) require a magnetic field measurement only in a very narrow frequency range. In order to selectively improve the alternating-current (ac) magnetic field sensitivity of a high-temperature superconductor SQUID for a distinct frequency, a single-coil LC resonant circuit has been used. Within the liquid nitrogen bath, the coil surrounds the SQUID and couples to it inductively. Copper coils with different numbers of windings were used to cover the frequency range from <1 to nearly 100 kHz. A superconducting coil made of YBa(2)Cu(3)O(7-delta) tape conductor was also tested. With the LC circuit, the signal-to-noise ratio of measurements could be improved typically by one order of magnitude or more in a narrow frequency band around the resonance frequency exceeding a few kilohertz. The best attained equivalent magnetic field resolution was 2.5 fT/radicalHz at 88 kHz. The experimental findings are in good agreement with mathematical analysis of the circuit with copper coil.