The use of a linear Halbach array combined with a step-SPLITT channel for continuous sorting of magnetic species

The Quadrupole Magnetic Sorter (QMS), employing an annular flow channel concentric with the aperture of a quadrupole magnet, is well established for cell and particle separations. Here we propose a magnetic particle separator comprising a linear array of cylindrical magnets, analogous to the array proposed by Klaus Halbach, mated to a substantially improved form of a parallel plate SPLITT channel, known as the step-SPLITT channel. While the magnetic force and throughput are generally lower than for the QMS, the new separator has advantages in ease of fabrication and the ability to vary the magnetic force to suit the separands. Preliminary experiments yield results consistent with prediction and show promise regarding future separations of cells of biomedical interest.     

Analysis of the magnetic field, force, and torque for two-dimensional Halbach cylinders

The Halbach cylinder is a construction of permanent magnets used in applications such as nuclear magnetic resonance apparatus, accelerator magnets and magnetic cooling devices. In this paper the analytical expression for the magnetic vector potential, magnetic flux density and magnetic field for a two dimensional Halbach cylinder are derived. The remanent flux density of a Halbach magnet is characterized by the integer p. For a number of applications the force and torque between two concentric Halbach cylinders are important. These quantities are calculated and the force is shown to be zero except for the case where p for the inner magnet is one minus p for the outer magnet. Also the force is shown never to be balancing. The torque is shown to be zero unless the inner magnet p is equal to minus the outer magnet p. Thus there can never be a force and a torque in the same system.     

Comparison of adjustable permanent magnetic field sources

A permanent magnet assembly in which the flux density can be altered by a mechanical operation is often significantly smaller than comparable electromagnets and also requires no electrical power to operate. In this paper five permanent magnet designs in which the magnetic flux density can be altered are analyzed using numerical simulations, and compared based on the generated magnetic flux density in a sample volume and the amount of magnet material used. The designs are the concentric Halbach cylinder, the two half Halbach cylinders, the two linear Halbach arrays and the four and six rod mangle. The concentric Halbach cylinder design is found to be the best performing design, i.e. the design that provides the most magnetic flux density using the least amount of magnet material. A concentric Halbach cylinder has been constructed and the magnetic flux density, the homogeneity and the direction of the magnetic field are measured and compared with numerical simulation and a good agrement is found.     

Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles

Optimization methods are presented to design Halbach arrays to maximize the forces applied on magnetic nanoparticles at deep tissue locations. In magnetic drug targeting, where magnets are used to focus therapeutic nanoparticles to disease locations, the sharp fall off of magnetic fields and forces with distances from magnets has limited the depth of targeting. Creating stronger forces at a depth by optimally designed Halbach arrays would allow treatment of a wider class of patients, e.g. patients with deeper tumors. The presented optimization methods are based on semi-definite quadratic programming, yield provably globally optimal Halbach designs in 2 and 3-dimensions, for maximal pull or push magnetic forces (stronger pull forces can collect nanoparticles against blood forces in deeper vessels; push forces can be used to inject particles into precise locations, e.g. into the inner ear). These Halbach designs, here tested in simulations of Maxwell's equations, significantly outperform benchmark magnets of the same size and strength. For example, a 3-dimensional 36 element 2000 cm³ volume optimal Halbach design yields a 5× greater force at a 10 cm depth compared to a uniformly magnetized magnet of the same size and strength. The designed arrays should be feasible to construct, as they have a similar strength (≤1 T), size (≤2000 cm³), and number of elements (≤36) as previously demonstrated arrays, and retain good performance for reasonable manufacturing errors (element magnetization direction errors ≤5°), thus yielding practical designs to improve magnetic drug targeting treatment depths.     

An optimized magnet for magnetic refrigeration

A magnet designed for use in a magnetic refrigeration device is presented. The magnet is designed by applying two general schemes for improving a magnet design to a concentric Halbach cylinder magnet design and dimensioning and segmenting this design in an optimum way followed by the construction of the actual magnet. The final design generates a peak value of 1.24 T, an average flux density of 0.9 T in a volume of 2 L using only 7.3 L of magnet, and has an average low flux density of 0.08 T also in a 2 L volume. The working point of all the permanent magnet blocks in the design is very close to the maximum energy density. The final design is characterized in terms of a performance parameter, and it is shown that it is one of the best performing magnet designs published for magnetic refrigeration.     

Experimental investigations on a branched tube model in magnetic drug targeting

Magnetic drug targeting (MDT) has been established as a promising technique for tumour treatment. Due to its high targeting efficiency unwanted side effects are considerably reduced, since drug-loaded nanoparticles are concentrated within a target region due to the influence of a magnetic field. This work presents experimental results that are based on systematic quantitative measurements on a branched tube model as a model system for a blood vessel supplying a tumour. The systematic measurements are summarized in novel drug targeting maps, combining e.g. the net amount of targeted nanoparticles, the magnetic volume force and also the position of the magnet. The model, the injection procedure and the ferrofluid are chosen close to the parameters of a medical application. This will allow transfer of the results to future medical investigations. This work will present a targeting map, where the concentration of the injected ferrofluid is in the range of experiments with an ex vivo bovine artery model.     

高功率光隔离器永磁系统的理论研究与优化

基于Halbach阵列永磁体的特点以及光隔离器对磁场的需求,设计了两种适用于高功率隔离器的永磁系统,分析了其磁场分布、磁场非均匀性对隔离度的影响,研究了磁体装配误差对磁场的影响。研究结果表明:通过引入斜向磁化永磁体,选择合适的磁化角度和磁体长度,可以提高永磁体的磁场强度,大幅度减小旋转器所需磁光晶体长度;受磁场非均匀性影响的隔离度与磁光晶体的孔径、长度以及入射激光的光斑半径有关,当晶体长度一定时,减小晶体半径和入射光的半径可以显著提高隔离度。在入射光半径为1.5mm、磁光晶体半径5mm时,对应的隔离度分别为105.8dB和45.4dB。     

Quantitative targeting maps based on experimental investigations for a branched tube model in magnetic drug targeting

Magnetic drug targeting (MDT), because of its high targeting efficiency, is a promising approach for tumour treatment. Unwanted side effects are considerably reduced, since the nanoparticles are concentrated within the target region due to the influence of a magnetic field. Nevertheless, understanding the transport phenomena of nanoparticles in an artery system is still challenging. This work presents experimental results for a branched tube model. Quantitative results describe, for example, the net amount of nanoparticles that are targeted towards the chosen region due to the influence of a magnetic field. As a result of measurements, novel drug targeting maps, combining, e.g. the magnetic volume force, the position of the magnet and the net amount of targeted nanoparticles, are presented. The targeting maps are valuable for evaluation and comparison of setups and are also helpful for the design and the optimisation of a magnet system with an appropriate strength and distribution of the field gradient. The maps indicate the danger of accretion within the tube and also show the promising result of magnetic drug targeting that up to 97% of the nanoparticles were successfully targeted.     

离散式任意充磁角度Halbach永磁电机解析模型研究

Halbach电机因其自身优势在新型船舶推进、海洋洋流发电等方面受到广泛关注. 本文在假设铁磁材料线性和定子内表面光滑的条件下, 通过将任意充磁角度Halbach阵列等效为两组90° Halbach(或180° Halbach)阵列的矢量合成, 提出了一种分析离散式任意充磁角度Halbach永磁电机气隙磁场的解析方法; 通过对电机中磁标量势的傅里叶级数进行计算, 推导出了最简单的90° Halbach永磁电机在极坐标系下的气隙磁密表达式, 并在此基础上, 给出了任意充磁角度Halbach电机永磁体磁化强度在一个极下的表达式, 进而得出任意充磁角度Halbach电机气隙磁密的分布, 并分析了气隙磁密与电机极对数、永磁体厚度和充磁角度间的关系. 最后通过有限元和试验结果验证了本文方法的正确性. 关键词： 离散式Halbach电机 任意充磁角度 矢量等效 解析模型     

高功率光隔离器永磁系统的理论研究与优化

基于阵列永磁体的特点以及光隔离器对磁场的需求设计了两种适用于高功率隔离器的永磁系统,分析了其磁场分布、磁场非均匀性对隔离度的影响,研究了磁体装配误差对磁场的影响。研究结果表明：通过引入斜向磁化永磁体,选择合适的磁化角度和磁体长度,可以提高永磁体的磁场强度,大幅度减小旋转器所需磁光晶体长度;受磁场非均匀性影响的隔离度与磁光晶体的孔径、长度以及入射激光的光斑半径有关,当晶体长度一定时,减小晶体半径和入射光的半径可以显著提高隔离度。在入射光半径为1.5 mm、磁光晶体半径5 mm时,对应的隔离度分别为105.8 dB和45.4 dB。     

Enhancement of the efficiency of magnetic targeting for drug delivery: Development and evaluation of magnet system

Deep magnetic capture and clinical application are the current trends for magnetic targeted drug delivery system. More promising and possible strategies are needed to overcome the current limitations and further improve the magnetic targeting technique. Recent advances in the development of targeting magnet system show promise in progressing this technology from the laboratory to the clinic. Starting from well-known basic concepts, current limitations of magnetic targeted drug delivery system are analyzed. Meanwhile, the design concepts and evaluations of some effective improvements in magnet system are discussed and reviewed with reference to (i) reasonable design of magnet system; (ii) control modes of magnet system used to generate dynamical magnetic fields; and (iii) magnetic field driving types.     

In vitro investigation of the behaviour of magnetic particles by a circulating artery model

Magnetic drug targeting is the use of coated magnetic nanoparticles as carriers for cytostatic drugs. After intraarterial application of these carriers, they are attracted with an external magnetic field to, for example, an experimental VX2 tumour. The biological compatibility of this system depends on several physiological and physical parameters. We established an in vitro model to simulate in vivo conditions in a circulating system consisting of a circuit with an intact bovine femoral artery close to an external magnetic field. Nanoparticle suspensions were applied by a side inlet. After the magnetisation procedure particle size, concentration and distribution was examined.     

An adjustable linear Halbach array

The linear Halbach array is a well-known planar magnetic structure capable, in the idealized case, of generating a one-sided magnetic field. We show that such a field can be created from an array of uniformly magnetized rods, and rotating these rods in an alternating fashion can smoothly transfer the resultant magnetic field through the plane of the device. We examine an idealized model composed of infinite line dipoles and carry out computational simulations on a realizable device using a magnetic boundary element method. Such an arrangement can be used for an efficient latching device, or to produce a highly tunable field in the space above the device.     

Synthesis and characterization of magnetic poly(glycidyl methacrylate) microspheres

Magnetic nanoparticles encapsulated in poly(glycidyl methacrylate) microspheres were prepared and their detailed structural and magnetic characteristics given. Iron oxide nanoparticles were obtained by chemical coprecipitation of Fe(II) and Fe(III) salts and stabilized with dextran, (carboxymethyl)dextran or tetramethylammonium hydroxide. The microspheres were prepared by emulsion or dispersion polymerization of glycidyl methacrylate in the presence of ferrofluid. The microspheres were uniform both in shape and usually also in size; their size distribution was narrow. All the magnetic parameters confirm superparamagnetic nature of the microspheres. Blocking temperature was not observed, suggesting the absence of magnetic interactions at low temperatures. This is most probably caused by complete encapsulation and the absence of agglomeration. Such microspheres can be used in biomedical applications.     

用于高功率微波器件的永磁体的设计和测试

报道了用于高功率相对论返波管振荡器的永磁体的设计和试制。以Halbach阵列结构为基础, 通过选择高性能的永磁材料, 调整磁钢的充磁方向、排列方式和尺寸, 优化设计了可用于某相对论返波管振荡器的永磁体结构, 其均匀区磁场强度0.98 T。采用粒子模拟方法, 进行了永磁体与返波管振荡器的一体化设计, 设计结果表明:器件输出功率超过1 GW, 设计的永磁体能够满足器件对磁场强度和位形的要求。对永磁体进行了试制和测试, 测试结果为:均匀区磁场0.88 T, 均匀区长110 mm, 磁体重量约306 kg。     

用于高功率微波器件的永磁体的设计和测试

报道了用于高功率相对论返波管振荡器的永磁体的设计和试制。以Halbach阵列结构为基础, 通过选择高性能的永磁材料, 调整磁钢的充磁方向、排列方式和尺寸, 优化设计了可用于某相对论返波管振荡器的永磁体结构, 其均匀区磁场强度0.98 T。采用粒子模拟方法, 进行了永磁体与返波管振荡器的一体化设计, 设计结果表明：器件输出功率超过1 GW, 设计的永磁体能够满足器件对磁场强度和位形的要求。对永磁体进行了试制和测试, 测试结果为：均匀区磁场0.88 T, 均匀区长110 mm, 磁体重量约306 kg。     

HL-2A装置ECRH超导磁体磁场分布测量

测量了HL-2A装置ECRH超导磁体的磁场分布。测量结果析表明,其归一化纵向磁场在磁场中心20mm区域内大于0.992,径向分布在磁场中心平面上浮动小于1.48%,杂散场在贴近超导磁体表面时的最大分量小于50mT,满足实验要求。     

Overhauser DNP and EPR in a Mobile Setup: Influence of Magnetic Field Inhomogeneity

Power-dependent Overhauser dynamic nuclear polarization (DNP) enhancements and continuous-wave electron paramagnetic resonance (EPR) spectra of nitroxide radicals were measured in the magnetic field of a mobile Halbach-array permanent magnet and compared with results from a commercially available electromagnet. DNP saturation factors for varying microwave power were obtained from both measurement series and used to investigate how the increased magnetic field inhomogeneity present in the Halbach magnet affects the saturation efficiency. An EPR detection system was designed to allow continuous-wave EPR measurements at microwave power up to 20?W. Our results show that despite the lower magnetic field homogeneity, a Halbach-array magnet can be used for EPR and DNP-enhanced nuclear magnetic resonance of high quality providing almost the same performance as a more homogeneous electromagnet.     

A model for predicting magnetic targeting of multifunctional particles in the microvasculature

A mathematical model is presented for predicting magnetic targeting of multifunctional carrier particles that are designed to deliver therapeutic agents to malignant tissue in vivo. These particles consist of a nonmagnetic core material that contains embedded magnetic nanoparticles and therapeutic agents such as photodynamic sensitizers. For in vivo therapy, the particles are injected into the vascular system upstream from malignant tissue, and captured at the tumor using an applied magnetic field. The applied field couples to the magnetic nanoparticles inside the carrier particle and produces a force that attracts the particle to the tumor. In noninvasive therapy, the applied field is produced by a permanent magnet positioned outside the body. In this paper, a mathematical model is developed for predicting noninvasive magnetic targeting of therapeutic carrier particles in the microvasculature. The model takes into account the dominant magnetic and fluidic forces on the particles and leads to an analytical expression for predicting their trajectory. An analytical expression is also derived for predicting the volume fraction of embedded magnetic nanoparticles required to ensure capture of the carrier particle at the tumor. The model enables rapid parametric analysis of magnetic targeting as a function of key variables including the size of the carrier particle, the properties and volume fraction of the embedded magnetic nanoparticles, the properties of the magnet, the microvessel, the hematocrit of the blood and its flow rate.     

A novel approach to preparing magnetic protein microspheres with core-shell structure

Magnetic protein microspheres with core-shell structure were prepared through a novel approach based on the sonochemical method and the emulsion solvent evaporation method. The microspheres are composed of the oleic acid and undecylenic acid modified Fe₃O₄ cores and coated with globular bovine serum albumin (BSA). Under an optimized condition, up to 57.8 wt% of approximately 10 nm superparamagnetic Fe₃O₄ nanoparticles could be uniformly encapsulated into the BSA microspheres with the diameter of approximately 160 nm and the high saturation magnetization of 38.5 emu/g, besides of the abundant functional groups. The possible formation mechanism of magnetic microspheres was discussed in detail.