厚膜永磁阵列微致动器的磁路研究

研究了厚膜永磁阵列微致动器中的磁场分布，并研究了永磁阵列单元几何尺寸对微致动器电磁力的影响。结果表明，厚膜永磁阵列单元高宽比和磁体单元间隔对微致动器电磁力影响较大磁徕单元高宽比为0．7是一个比较合适的尺寸。     

电动车用永磁同步电机非线性扭转振动模型

针对电动车车身阶次振动和车内噪声的主要振源—永磁同步电机的扭转振动问题,首先,利用集中参数法建立了永磁同步电机扭转振动的非线性动力学模型,解析求解了考虑非正弦分布的永磁磁场、定子开槽、时间谐波电流的永磁同步电机电磁转矩,获取了定子铁芯、机壳的刚度和阻尼参数,指出了电磁转矩波动是引起永磁同步电机非线性振动的主要原因。然后,采用状态变量法求得了非线性方程组的解。最后,通过永磁同步电机扭转振动实验验证了本模型的有效性。     

Permanent Magnet Couplings: Field and Torque Three-Dimensional Expressions Based on the Coulombian Model

This paper presents three-dimensional expressions for the optimization of permanent-magnet couplings. First, we give a fully analytical expression of the azimuthal field created by one arc-shaped permanent magnet radially polarized which takes into account its magnetic pole volume density. Such an expression has a very low computational cost and is exact for all points in space. Then, we propose two semianalytical expressions of the azimuthal force and the torque exerted between two arc-shaped permanent magnets. These expressions are valid for thick or thin arc-shaped permanent magnets. Furthermore, this approach allows us to realize easily parametric studies and optimizations. The analytical approach taken in this paper, based on the Coulombian model, is a good alternative compared to the finite element method generally used to study such configurations.      

Computation of the Three-Dimensional Magnetic Field From Solid Permanent-Magnet Bipolar Cylinders By Employing Toroidal Harmonics

We present an analytical method, employing toroidal harmonics, for computing the three-dimensional (3-D) magnetic field from a circular cylindrical bipolar permanent magnet. Bipolar magnets are those which are polarized perpendicular to the axis of the cylinder. We take a completely analytical approach in order to facilitate parametric studies of the external 3-D magnetic field produced by bipolar magnets. The results of our analysis are verified by comparing them to previously published results. The application of toroidal harmonics are ultimately shown to be well-suited for both parametric studies as well as numerical computation.     

振动驱动的电磁－永磁复合驱动建模

对一种新的电磁-永磁复合激励永磁体偏转驱动的机理进行振动应用理论分析和实验验证研究。对于这种电磁－永磁复合激励方式,提出一种基于面磁荷计算电磁扭矩的数值方法,建立电磁扭矩随电流和永磁体偏摆角度变化的数学模型,并将理论建模进行对比试验研究,验证所提出理论分析方法的正确性和基于永磁体偏摆驱动在振动驱动领域应用的可行性。     

Magnetic Field Created by Tile Permanent Magnets

This paper presents an analytical calculation of the three components of the magnetic field created by tile permanent magnets whose magnetization is either radial or axial. The calculations are based on the Coulombian model of permanent magnets. The magnetic field is directly calculated, without the magnetic potential. Both axial and radial magnetization of the tiles are considered. The expressions obtained give the magnetic field in all the space. Such analytical expressions are very useful for the design and optimization of many industrial applications.      

Empirical expression for the axial field of cylindrical bar magnets

Theoretical values of the magnetic field intensity outside a permanent magnet usually agree with experiment only at distance greater than the length of the magnet. This theoretical formula is modified to fit experimental results at shorter distances as well so that it can serve as a convenient analytical approximation for practical problems involving cylindrical bar magnets. Measurements are reported for the field of five Alnico V magnets whose diameters are roughly 1/8,3/16,1/4,1/2, and 1 inch, and whose lengths range from 4 to 6 inches. For all these, the modified formula describes the axial field in a distance range of 9 to 81 mm from the nearest face of the magnet to within a few percent from the measured values.     

Improved analytical model for predicting the magnetic fielddistribution in brushless permanent-magnet machines

A general analytical technique predicts the magnetic field distribution in brushless permanent magnet machines equipped with surface-mounted magnets. It accounts for the effects of both the magnets and the stator windings. The technique is based on two-dimensional models in polar coordinates and solves the governing Laplacian/quasi-Poissonian field equations in the airgap/magnet regions without any assumption regarding the relative recoil permeability of the magnets. The analysis works for both internal and external rotor motor topologies, and either radial or parallel magnetized magnets, as well as for overlapping and nonoverlapping stator windings. The paper validates results of the analytical models by finite-element analyses, for both slotless and slotted motors     

新型永磁隔振器的隔振性能分析与实验研究

在超精密加工、IC制造、光学、高端的物理及化学试验中,隔振器已经成了许多设备的一个关键部件,隔离来自地面和设备内部的振动。随着稀土永磁材料的迅速发展,永磁隔振器已成为国内外研究的热点之一。本文将采用环形永磁体提出了一种新构型的永磁隔振器;根据环形永磁体的磁力和刚度的解析模型对隔振器的隔振性能进行参数化分析,确定了该隔振器磁环的结构参数。作为新型永磁隔振器的试验研究,搭建了永磁隔振试验台,通过理论计算和试验证实了该磁浮隔振器在其最大承载能力时具有良好的低频隔振性能。     

Fields, forces, and performance equations of air-core linerself-synchronous motor with rectangular current control

An analytical field approach to determine the permanent magnetic field distribution in a flat air-core self-synchronous linear motor with a permanent magnet mover is reported. Thrust and normal forces are calculated for idealized rectangular-current inverter control. Notable thrust and normal force time pulsations are shown through a numerical example. The performance equations with an on-off current controller are developed with the motor fed from a voltage source transistor inverter. The analysis represents a reliable tool for refined design and control of permanent magnet air-core linear self-synchronous motors     

Analysis of fields and forces in a permanent magnet linearsynchronous machine based on the concept of magnetic charge

Two-dimensional and three-dimensional field distributions produced by permanent magnets (PMs) of a permanent-magnet linear synchronous motor (PMLSM) are obtained in analytical forms, based on the concept of magnetic charge and the method of images. The determination of electromagnetic forces and parameters of this type of a motor is examined. The proposed method and the resulting simplified formulas are useful for the design and analysis of PMLSMs as well as for other types of PM motors. Calculated results compare favorably with the experimental results, and thus validate the assumptions and the analysis     

Designing Static Fields for Unilateral Magnetic Resonance by a Scalar Potential Approach

We present a method for designing single-sided magnets suitable for unilateral magnetic resonance (UMR) measurements. The method uses metal pole pieces to shape the field from permanent magnets in a target region. The pole pieces are shaped according to solutions to Laplace's equation, and can be designed using a combination of analytical methods and numerical optimization. The design leads to analytical expressions for the pole piece shapes and magnetic field. Here, we develop the method in Cartesian, polar, and spherical coordinates, and discuss the merits of each system. Finite magnet size has a substantial effect on the field quality in many cases, according to our simulations. We found that in order to achieve a compact magnet in which the static field closely matches that specified, a full 3-D design approach is necessary. A magnet designed by our method produces a static field with a constant gradient over a region 2 cm in diameter and 2 mm thick. This leads to a compact cylindrical magnet just over 11 cm in diameter, topped with a single metal pole piece. The design is validated through simulation. The simulated field is found to agree closely with that specified analytically through the design procedure     

超精密大行程麦克斯韦磁阻驱动器磁场建模与推力分析

为了克服大行程麦克斯韦磁阻驱动器在大气隙下漏磁大幅增加、气隙区磁场分布不均匀且非线性强烈等现象导致的磁场和推力解析模型精度较低等问题,利用考虑综合高斯函数的加权漏磁系数的磁路建模方法,改进了磁阻驱动器的三维漏磁分布计算方式,并得到了可准确描述其推力与输入电流函数关系的解析模型,从而为该类驱动器的设计及控制提供重要依据。首先,建立了大行程麦克斯韦磁阻驱动器考虑漏磁前后的工作磁路,分析了永磁偏置磁路的作用及使用永磁偏置结构后仍具有非线性的原因,并利用安培环路定律和磁路的欧姆定律以及磁场的可叠加性,建立了该磁阻驱动器的推力解析模型。然后,为了优化解析模型,提出了基于高斯曲线的加权漏磁系数计算方法,同时利用有限元仿真软件对大行程麦克斯韦磁阻驱动器的三维磁场分布及漏磁系数进行了分析计算,得到了考虑加权漏磁系数的推力解析模型。最后,搭建了大行程麦克斯韦磁阻驱动器推力测试系统,并通过对比优化前后解析模型计算推力与仿真推力和实测推力,验证了解析模型的准确性。结果表明,优化后解析模型的均方根误差仅为优化前的11.1%,其精度得到有效提升;同时,优化后解析模型计算推力与实测推力之间的均方根误差小于0.6 N,精度较高。研究结果对高端微纳制造装备与测量仪器中新型超精密驱动部件的设计有一定意义和参考价值。     

Numerical Studies of Axial and Radial Magnetic Forces Between High Temperature Superconductors and a Magnetic Rotor

The magnetic bearing is considered as one of the most prospective applications of high temperature superconductors (HTSs) which can realize stable levitation in a magnetic field generated by permanent magnet devices or coils. The exploration of this kind of HTS bearing through numerical investigation is usually made by assuming the induced current circulates only within the ab-plane and thus simplifying the actual three-dimensional problem to a two-dimensional one. In this paper, on the basis of the three-dimensional model of the HTS bulk established before, we further introduce the developed finite-element software to calculate the magnetic field generated by a magnetic rotor which is composed of permanent magnet (PM) rings and ferromagnet (FM) shims, and in this way, we can investigate the magnetic forces (radial force and axial force) of a simplified HTS bearing model, i.e., two symmetric HTS bulks and a magnetic rotor, at a three-dimensional level. The investigations performed in this paper lead to the observations: the favorable configuration to construct the HTS bearing is that the axial height of each HTS element should be equivalent to the axial heights of PM ring plus FM shim; the increase of the radial thickness of PM ring will improve both the radial force and the axial force considerably, but its margin decreases; the enhancement of critical current density of HTSs due to the decrease of operating temperature can result in a higher increase of both the radial and axial force with a lower nominal gap between the HTSs and the magnetic rotor.     

Use of paired, bonded NdFeB magnets in redox magnetohydrodynamics

Bonded neodymium-iron-boron (NdFeB) permanent magnets in a paired configuration were successfully used to control mass transport in redox-based, magnetohydrodynamics (MHD). Control of fluid flow based on magnetic fields has potential for use in portable lab-on-a-chip (LOAC) and analytical devices. Bonded magnets, composed of magnetic powder and organic binder materials, are less expensive and easier to fabricate and pattern than electromagnets and sintered permanent magnets, which have been previously used in MHD studies on electrochemical systems. The ability to pattern bonded magnets near and around the electrodes is expected to allow for better control over the magnetic field distribution and solution flow. Current was generated at an 800-microm-radius platinum disk electrode in a solution of 0.06 M nitrobenzene and 0.5 M tetra-n-butylammonium hexafluorophosphate in acetonitrile. Increases in limiting current in the presence of the magnetic field, which indicate enhancement in mass transport, for sintered (210+/-14%, N = 4, where B(r) = 1.23 T and magnetic field strength is 0.55 T) and bonded (94+/-8%, N = 4, where B(r) = 0.41 T and magnetic field strength is 0.20 T) magnets, were similar to those obtained using an electromagnet with the same magnetic flux densities. The magnetic field strength and not the magnet type is important in controlling fluid flow, which is encouraging for integration of bonded permanent magnets into LOAC devices.     

Modulating thickness multipole permanent magnets

The magnetic field distributions of modulating thickness permanent magnets [1,2] are discussed in this paper. The field distributions are calculated by using the program POISCR and the actual demagnetization curve of the REC permanent magnet material. The results show that the performance of the MT type magnets is about the same as or even better than that of the modulating magnetization direction type (MMD) [3] and that the MT type magnet with soft iron shield requires less REC material than MMD type magnets.     

Design and test of a 700 mm long hexapole composed of rectangular rare earth cobalt permanent magnets

A hexapolar magnet with inner diameter of 80 mm and an air gap inductance of > 400 mT on the pole faces is described. This magnet consists of six parallelepiped rare earth cobalt permanent magnet bars, 17 × 700 mm²in cross section and 42.1 mm in height. The whole device, which is used as part of an ECR-Heavy Ion Source, is placed into a magnetic mirror field with strong axial field strength. To assure a proper superposition of the hexapole field and mirror field, no iron Circuit could be used. The radial and axial field distribution inside the hexa-pole magnet was measured, and compared with calculated data. The variation of field strength, especially the variation of lines with constant field strength as a function of both the height and width of the magnets is discussed.     

Magnetizing of permanent magnets using HTS bulk magnets

A demagnetized Nd–Fe–B permanent magnet was scanned just above the magnetic pole which contains the HTS bulk magnet generating a magnetic field of 3.27 T. The magnet sample was subsequently found to be fully magnetized in the open space of the static magnetic fields. We examined the magnetic field distributions when the magnetic poles were scanned twice to activate the magnet plate inversely with various overlap distances between the tracks of the bulk magnet. The magnetic field of the “rewritten” magnet reached the values of the magnetically saturated region of the material, showing steep gradients at the border of each magnetic pole. As a replacement for conventional pulse field magnetizing methods, this technique is proposed to expand the degree of freedom in the design of electromagnetic devices, and is proposed as a novel practical method for magnetizing rare-earth magnets, which have excellent magnetic performance and require intense fields of more than 3 T to be activated.     

Permanent Magnet Enhancement of Fully Superconducting MgB2-YBa2Cu3O7−x Bearing

This paper reports the experimental verification and improved concept of the previously reported fully superconducting magnetic bearing using bulks on both the rotor and the stator in a cylindrical geometry. Experimental measurements on pulsed magnetisation and levitation force between a magnetised 25.5 mm diameter YBCO bulk inside an MgB₂ hollow cylinder are reported proving the concept of a bulk–bulk bearing. The maximum force achieved after field cooling of the MgB₂ bulk in the field of a 1.68 T magnetised YBCO bulk was 501 N. The improved concept relies on additional ring shaped permanent magnets placed on the bottom of the MgB₂ cylinder. These rings create additional axial force in the bearing system. Permanent magnet rings can boost the force for the existing bearing design by enhancing the field trapped in the MgB₂ tube and providing a ‘cushion’ of magnetic field for the bottom YBCO bulk by exploiting zero field cooling. In particular the enhancement of the force is largely due to the favourable distortion of the trapped field in the MgB₂ cylinder and is much greater than the direct repulsive force between a magnetised YBCO bulk and permanent magnet only. Various permanent magnet configurations are evaluated by modelling of levitation force using the perfectly trapped flux model. The high force densities of bulk–bulk bearings allow them to support large loads useful for application such as flywheel energy storage.     

阵列永磁体产生旋转磁场的机理及实验

 诊疗微机器人外磁主动驱动是一种重要的可行的驱动方式,而如何产生合适的外部磁场是一个比较复杂的问题．相对于目前常用的通过电磁线圈组合产生驱动磁场方式,提出一种新的简单可行的永磁体组合产生旋转磁场方法,即圆周阵列永磁体并将其调整到对应的初始方位角后,同步转动在阵列中心区域产生旋转磁场,作为微机器人的主动驱动场．对于阵列中心区域的磁感应强度分布,作了理论分析和数值计算,并搭建了实验台．实验表明,采用边长为50 mm、高为18 mm的钕铁硼永磁体阵列,阵列数为6,阵列直径为275 mm时,可以在±50 mm×±50 mm×±20 mm阵列中心区域产生一个大小为0.012 T的均匀磁场,该磁场与永磁体同步旋转但是方向相反．这种新的磁场产生方法可以用于微机器人特别是诊疗微机器人的驱动,具有广阔的应用前景．