Implant assisted-magnetic drug targeting: Comparison of in vitro experiments with theory

Implant assisted-magnetic drug targeting (IA-MDT) was studied both in vitro and theoretically, with extensive comparisons made between model and experiment. Magnetic drug carrier particles (MDCPs) comprised of magnetite encased in a polymer were collected magnetically using a ferromagnetic, coiled, wire stent as the implant and a NdFeB permanent magnet for the applied magnetic field. A 2-D mathematical model with no adjustable parameters was developed and compared to the 3-D experimental results. The effects of the fluid velocity, stent and MDCP properties, and magnetic field strength on the performance of the system were evaluated in terms of the capture efficiency (CE) of the MDCPs. In nearly all cases, the parametric trends predicted by the model were in good agreement with the experimental results: the CE always increased with decreasing velocity, increasing magnetic field strength, increasing MDCP size or magnetite content, or increasing wire size. The only exception was when experiments showed an increase in the CE with an increase in the number of loops in the wire, while the model showed no dependence. The discrepancies between experiment and theory were attributed to phenomena not accounted for by the model, such as 3-D to 2-D geometric and magnetic field orientation differences, and interparticle interactions between the MDCPs that lead to magnetic agglomeration and shearing force effects. Overall, this work showed the effectiveness of a stent-based IA-MDT system through both in vitro experimentation and corroborated theory, with the designs of the ferromagnetic wire and the MDCPs both being paramount to the CE.     

永磁体辅助下单畴GdBCO超导体和永磁体之间的磁悬浮力研究

通过对永磁体辅助下单畴GdBCO超导体和圆柱形永磁体在液氮温度、零场冷、轴对称情况下磁悬浮力的测量,研究了两种不同组态下辅助永磁体对超导体磁悬浮力特性的影响.实验结果表明,当长方体辅助永磁体水平磁化、且磁极N指向超导体时,超导体的最大磁悬浮力从没有引入辅助永磁体的29.8 N增加到61.5 N,增加为没有引入辅助永磁体时的206%.当长方体辅助永磁体的N极与圆柱形永磁体的N极反平行时,超导体的最大磁悬浮力从没有引入辅助永磁体的29.8 N减小到19.6 N,减小为无辅助永磁体时的65.8%.这些研究结果说明,通过科学合理地设计超导体和永磁体的组合方式,能有效地提高超导体的磁悬浮力.该研究结果对促进超导体的应用具有重要的指导意义. 关键词： 单畴GdBCO 永磁体 磁悬浮力     

Three dimensional magnetic resonance imaging by magnetic resonance force microscopy with a sharp magnetic needle

An electropolished magnetic needle made of Nd(2)Fe(14)B permanent magnet was used for obtaining better spatial resolution than that achieved in our previous work. We observed the magnetic field gradient |G(Z)|=80.0G/microm and the field strength B=1250G at Z approximately 8.8 microm from the top of the needle. The use of this needle for three dimensional magnetic resonance force microscopy at room temperature allowed us to achieve the voxel resolution to be 0.6 microm x 0.6 microm x 0.7 microm in the reconstructed image of DPPH phantom. The acquisition time spent for the whole data collection over 64 x 64 x 16 points, including an iterative signal average by six times per point, was about 10 days.     

Numerical modeling of magnetic drug targeting

A special focused magnet, designed for the use in the magnetic targeted drug delivery system, was constructed. The theoretical calculation of the adhesion condition for a magnetic fluid drop in magnetic field with obtained design showed that the constructed focused magnet generates a sufficient magnetic force for the capture of a magnetic drop on the vessel wall and can be used 1.5–2 cm deeper in an organism compared with the prism permanent magnet, which can enable non-invasivity of the magnetic drug targeting procedure. The maximal values for magnetic field and gradient of magnetic field are 0.38 T and 101 T/m, respectively.     

辅助永磁体厚度对单畴GdBCO超导体捕获磁场分布及其磁悬浮力的影响

研究了两种磁悬浮系统组态中圆台形辅助永磁体厚度对高温超导体捕获磁场和超导磁悬浮力的影响。结果表明,圆台形辅助永磁体的下表面和GdBCO超导体上表面同处在一个水平面上,磁化用圆台形辅助永磁体的厚度H从5 mm增加到45 mm时,超导体捕获磁场和磁悬浮力与圆台形辅助永磁体的厚度直接相关。（1）当圆台形辅助永磁体的北极垂直向上且用液氮冷却后移除辅助永磁体时,最大磁悬浮力从21.8 N增大到26.5 N,再减小到22.9 N;（2）当圆台形辅助永磁体的北极垂直向下且用液氮冷却后移除辅助永磁体时,最大磁悬浮力从20.5 N减小到11.9 N ,再增加到20.4 N;（3）两种磁悬浮系统组态中最大磁悬浮力不一致,与零场冷情况下的最大磁悬浮力14.6 N也不同。在超导磁悬浮应用系统设计中,只有科学选择辅助永磁体形状和尺寸,合理设计组合方式,才能获得较强的磁场强度,提高超导磁悬浮力特性,该结果对促进高温超导体的实际应用具有重要的指导作用。     

NMR永磁体精密温度控制器的设计与实现

低场核磁共振（low-field NMR）谱仪常采用钕铁硼（NdFeB）永磁体提供静磁场.NdFeB对温度非常敏感，磁体温度变化会引起磁场漂移，影响NMR实验的可靠性.为提高低场磁共振谱仪的稳定性，本文提出了一种基于双回路控制算法的磁共振永磁体精密温度控制方案，并在0.06 T磁共振谱仪上进行验证.结果表明：24 h内控温精度达到±0.005℃；相比无温控时，质子共振频率0.5 h内漂移量由255 Hz减小至15 Hz，24 h内漂移量由4 950 Hz减小至145 Hz，有效提高了低场磁共振谱仪永磁体的稳定性.     

永磁体外部磁场的不均匀性研究

从永磁体的分子电流观点、退磁场、工艺等出发, 以矩形永磁体为例, 从理论上分析了影响永磁体外部磁场不均匀性的各种因素.研究结果表明, 永磁体外部磁场宏观不均匀性(好场区均匀度和面积相对大小) 和空间距离及永磁体的外形设计密切相关. 退磁场对永磁体外部磁场微观不均匀性有着复杂影响. 永磁体工艺如粉末颗粒、取向度、烧结凝固、机械加工等将影响永磁体外部磁场的不均匀性, 如磁化偏角、对称性、光滑性等. 关键词： 永磁体 外部磁场 不均匀性 退磁场     

Planar Gradient Coil Design Using L1 and L2 Norms

We present a novel and general formulation for the optimisation of gradient coils, wherein the minimization of the conductor length and the simplicity of construction are two of the main design parameters. The bi-planar gradient coils are intended to be part of a new compact neonatal magnetic resonance imaging (MRI) scanner based on a 0.35 T permanent magnet. It is shown that minimizing the current density vector is equivalent to minimizing the wire length. The gradient coil design involves a convex optimization method where the Euclidian and Manhattan norms of the current density vector are minimized under the field linearity, wire width, force and shielding constraints. The design problem is solved iteratively in order to include the influence of the magnetization of the pole and iron ring over the gradient field linearity. A suite of gradient coils using both norms and resistance minimization are designed and their performances are compared. Gradient coils designed using Euclidian norm show shorter wire length and slightly better performance than that designed using Manhattan norms; however, the presence of straight wires in the current pattern is very convenient for manufacturing purpose.     

质子辐照对永磁合金微观结构演化的研究

钐钴和钕铁硼稀土永磁合金已经广泛应用于粒子加速器的波荡器和其他器件中,作为加速器的重要组成部分,永磁合金在辐照环境中长期服役会出现磁性能损失的现象,这会影响束流的品质.为了探讨产生这个现象的微观机理,采用透射电镜对质子辐照前后的钐钴和钕铁硼稀土永磁合金进行了微观结构演化的表征和分析,统计了由辐照析出的纳米晶体积密度和粒径分布,并讨论了微观结构演化对宏观磁性能损失的影响.结果表明,随着质子辐照损伤程度的增加,永磁合金的微观结构从单晶结构转变为纳米晶多晶结构,且纳米晶和基体的晶体结构相同.钕铁硼的纳米晶体积密度先增大后减小,粒径分布先增大后不变;钐钴的纳米晶体积密度逐渐减小,粒径逐渐增大.在2 dpa的质子辐照损伤程度下,钕铁硼稀土永磁合金比钐钴永磁合金的非晶化趋势更明显.     

MWECR CVD等离子体系统梯度磁场对沉积a-Si:H薄膜特性研究

分别研究了磁场线圈电流为115.2和137.7A以及137.7A并在加热台下加放SmCo永磁体的方法，来改变单磁场线圈分散场MWECR CVD系统等离子体室及沉积室磁场形貌.用洛伦兹拟合定量地得到了三种磁场形貌的磁场梯度.研究了磁场梯度对沉积a-Si:H薄膜性能的影响.研究表明：在衬底附近，高的磁场梯度可以获得高的沉积速率；在温度不很高时，高的磁场梯度可得到光敏性较好的a-Si:H薄膜. 关键词： 梯度磁场 洛伦兹拟合 a-Si:H薄膜 MWECR CVD系统     

磁体与非磁性运动导体相互作用之讨论

通过分析磁体与非磁性运动导体间的相互作用,发现了一种由非磁性运动导体驱动永磁体转动的非接触驱动方式.从分子环流模型出发,利用毕奥-萨伐尔定律,给出了所用矩形永磁体的磁场分布解析表达式,对运动导体处于永磁体下方5 mm处时永磁体的受力做了定量计算.对相互作用中的磁悬浮效应做了新的解释,澄清了PASCO公司对"磁悬浮实验装置"中由电磁感应产生的物理现象在原理解释上的模糊之处.     

Multi-objective optimization of gradient coil for benchtop magnetic resonance imaging system with high-resolution

Significant high magnetic gradient field strength is essential to obtaining high-resolution images in a benchtop mag- netic resonance imaging （BT-MRI） system with permanent magnet. Extending minimum wire spacing and maximum wire width of gradient coils is one of the key solutions to minimize the maximum current density so as to reduce the local heating and generate higher magnetic field gradient strength. However, maximum current density is hard to optimize together with field linearity, stored magnetic energy, and power dissipation by the traditional target field method. In this paper, a new multi-objective method is proposed to optimize the maximum current density, field linearity, stored magnetic energy, and power dissipation in MRI gradient coils. The simulation and experimental results show that the minimum wire spacings are improved by 159% and 62% for the transverse and longitudinal gradient coil respectively. The maximum wire width increases from 0.5 mm to 1.5 mm. Maximum gradient field strengths of 157 mT/m and 405 mT/m for transverse and lon- gitudinal coil are achieved, respectively. The experimental results in BT-MRI instrument demonstrate that the MRI images with in-plane resolution of 50 ~tm can be obtained by using the designed coils.     

Laser frequency offset-locking using electromagnetically induced transparency spectroscopy of ~(85)Rb in magnetic field

We have experimentally offset-locked the frequencies of two lasers using electromagnetically induced transparency(EIT) spectroscopy of ~(85)Rb vapor with a buffer gas in a magnetic field at room temperature. The magnetic field is generated by a permanent magnet mounted on a translation stage and its field magnitude can be varied by adjusting the distance between the magnet and Rb cell, which maps the laser locking frequency to the space position of the magnet. This frequency-space mapping technique provides an unambiguous daily laser frequency detuning operation with high accuracy.A repeatability of less than 0.5 MHz is achieved with the locking frequency detuned up to 184 MHz when the magnetic field varies from 0 up to 80 G.     

The dynamic behavior of magnetic fluid adsorbed to small permanent magnet in alternating magnetic field

The dynamic behavior of a magnetic fluid adsorbed to a small NdFeB permanent magnet subjected to an alternating magnetic field was studied with a high speed video camera system. The directions of alternating magnetic field are parallel and opposite to that of the permanent magnet. It was found that the surface of magnetic fluid responds to the external alternating magnetic field in elongation and contraction with a lot of spikes. Generation of a capillary magnetic fluid jet was observed in the neighbourhood of a specific frequency of alternating field. The effect of gravitational force on surface phenomena of magnetic fluid adsorbed to the permanent magnet was revealed.     

辅助永磁体的引入方式对单畴GdBCO超导块材磁场分布及其磁悬浮力的影响

通过对永磁体辅助下单畴GdBCO超导体和方形永磁体在液氮温度、 零场冷、 轴对称情况下磁悬浮力的测量, 研究了三种不同组态中辅助永磁体的引入方式对单畴GdBCO超导块材磁场分布及其磁悬浮力的影响. 实验结果表明, 如果处在超导体上方的测量用方形永磁体N极向下, 则在轴对称情况下, 当方形辅助永磁体N极向上与超导体下表面贴在一起时, 超导体的最大磁悬浮力从没有引入辅助永磁体磁化的14.3 N增加到31.8 N, 提高到222%; 当方形辅助永磁体放置在超导体上表面、 N极垂直向上且场冷后去掉辅助永磁体时, 超导体的最大磁悬浮力从没有引入辅助永磁体磁化的14.3 N增加到21.6 N, 增加到151%; 当方形辅助永磁体放置在超导体上表面、 N极垂直向下且场冷后去掉方形辅助永磁体时, 超导体的最大磁悬浮力从没有引入辅助永磁体磁化的14.3 N减小到8.6 N, 减小为无辅助永磁体时的60%.这些结果说明, 只有通过科学合理地设计超导体和永磁体的组合方式, 才能获得较高的磁场强度, 有效地提高超导体的磁悬浮力特性, 该结果对促进超导体的应用具有重要的指导意义.     

振动线准直技术的原理和研究概述

振动线准直技术是一种通过直接测量空间磁场分布情况来进行磁铁设备准直的方法,其原理完全不同于目前国内正在使用的基于磁铁机械结构进行准直的方法。振动线方法具有很高的准直精度和灵敏性,可以用于单个磁铁磁中心测量、磁铁准直标定和多块磁铁磁中心准直等。主要介绍了振动线准直技术的原理、起源和国际上的应用研究概况。     

复合磁场引导的小型化二极管初步设计

设计了一种非浸没式小型化轴向无箔二极管,其阴极发射区位于螺线管中心孔以外,采用螺线管、永磁体和软磁体构成的复合引导磁场系统。采用CST优化设计二极管结构,使其满足800 kV电压下绝缘要求; 优化设计磁场系统结构及物理参数,使其满足引导强流相对论电子束高效率传输的要求。采用粒子模拟(PIC)软件仿真电子束产生及传输过程,验证其高传输效率。设计的阳极筒直径比原结构缩小约40%,在产生同样均匀区轴向磁场强度情况下,引导磁场重量和功耗比原结构降低约40%,仿真结果显示主引导磁场0.85 T下,8 kA电流能够实现100%传输效率。     

永磁体空间磁场的分析计算及其在永磁磁力轴承中的应用

在介绍三种永磁体空间磁场计算模型的基础上,利用泛函理论分别推导出等效磁荷模型和等效电流模型对应的变分形式,并就等效磁荷模型详细地介绍了有限元法．由于等效磁荷模型使用仅有一个自由度的标量磁位,因而计算起来比具有三个自由度的矢量磁位的等效电流法更简便．从永磁磁力轴承磁场的计算算例中可以看出,用等效磁荷模型的有限元法计算永磁体空间磁场是非常简便和有效的．     

Theoretical and Experimental Investigation of the Magnetic Field of a Strongly Magnetized Permanent Magnet

An analytical expression is obtained for the magnetic strength of a permanent magnet in the form of a rectangular parallelepiped uniformly magnetized at an angle to its lateral faces. The results from experimental measurements of the magnetic field strength of a permanent magnet in the form of a rectangular parallelepiped using a Hall sensor are presented and compared to those from analytical calculations.     

周期永磁环爆磁压缩发生器

 首次提出了利用周期永磁环做初始能源的螺旋型爆磁压缩发生器，该结构由4节永磁环正反排到组成。阐述了这种周期永磁环爆磁压缩发生器的结构及其特点，并利用等效电路模型分析了轴线起爆周期永磁环爆磁压缩发生器的磁通变化规律和爆磁压缩过程，得到了基本的电流变化关系。 分析及数值计算结果表明：这种周期永磁环爆磁压缩发生器能够实现电流放大，在磁化电流为0.13 MA，磁化回路负载电感为1.0 μH条件下，最终输出电流可达0.16 MA。周期永磁环可以作为爆磁压缩发生器的初始能源，这种概念设计值得进行进一步的实验探索。