Analytic model for a nonlaminated cylindrical magnetic actuator including eddy currents

The eddy currents induced within a nonlaminated cylindrical magnetic actuator by a changing field have a fundamental influence on the actuator's performance. Understanding of these dynamics is essential in designing high-performance actuators and developing control algorithms for them. This paper presents an analytical approach to modeling the relationship between applied magnetomotive force and mechanical force. The approach is based on dividing the actuator into elements according to the flux distribution inside the actuator and finding the frequency-dependent reluctance of the flux paths of each element. An analytic model and its half-order simplification are derived, both of which are explicitly dependent on actuator material and geometric properties. Performance predictions from both analytic models are compared with finite-element analysis, demonstrating the accuracy of the models.     

Analytical Computation of the Full Load Magnetic Losses in the Soft Magnetic Composite Stator of High-Speed Slotless Permanent Magnet Machines

This paper presents an analytical model for predicting the stator full load magnetic losses in high-speed slotless permanent-magnet machines with surface-mounted magnets on the rotor and a stator core made of isotropic and conductive soft magnetic composite material (SMC). The losses are derived from the computation of the two-dimensional magnetic field distribution created by the rotor magnets, the currents in the stator windings and the eddy currents that circulate in the SMC stator core, according to the time and space harmonics. Both eddy currents and hysteresis losses are computed. The model is cross-validated by 2-D FE analysis in terms of magnetic field distribution and eddy currents losses. 3-D FE simulations are also carried out to quantify the end-effect on the stator no-load eddy current losses. The developed model is an efficient machine design tool, used here to quantify the variations of both the eddy currents and hysteresis losses under full load operation when the control angle is modified.      

A New Approach for Finite-Element Modeling of Hysteresis and Dynamic Effects

Macroscopic behavior of ferromagnetic materials can be considered as the resultant of three phenomena: hysteresis, eddy current, and excess loss. Hysteresis is the behavior of the material under quasi-static variation of magnetic field. Eddy-current and excess losses are dependent on the rate of field variation and are evident in the fast variation of the magnetic field, so they are called dynamic effects. This paper presents a simple and practical technique in field analysis of electromagnetic systems having hysteresis and dynamic effects. Based on the Preisach model for hysteresis and existing formulations for eddy currents and excess loss, an equivalent expression for field intensity has been introduced. A new technique has been presented in order to include this expression in the finite-element code. A typical system has been modeled by this code. Effects of relaxation and time step were examined on the stability and the convergence rate of the method. The validity of the proposed model has been checked by comparing its results with experimental measurements     

Effective magnetization and forces due to eddy currents

A simple method for evaluating the effective magnetization due to eddy currents excited by AC magnetic fields in finite conductive objects is presented. The values of magnetization enable the estimation of the forces exerted on the object by the effect of eddy currents. The method relies on assuming a similarity between eddy current magnetization and the magnetization due to diamagnetic effects, which is easier to evaluate. Its validity is checked by comparing results from the eddy current forces with data obtained from conventional but much more complicated methods or from experimental data. The approach may be useful for evaluating the eddy current losses in finite conductive objects excited by AC magnetic fields or the influence of small conductive objects on AC excitation coils. The method combines techniques related to the conventional evaluation of eddy currents in certain 1-D geometries with techniques that approximate behavior of the AC magnetic field in finite objects in a way similar to that followed when the magnetic forces acting on a diamagnetic object are calculated     

A 3-D Magnetic Charge Finite-Element Model of an Electrodynamic Wheel

When a magnetic rotor is both rotated and translationally moved above a conductive, nonmagnetic, guideway eddy currents are induced that can simultaneously create lift, thrust, and lateral forces. In order to model these forces, a 3D finite-element model with a magnetic charge boundary has been created. The modeling of the rotational motion of magnets by using a fictitious complex magnetic charge boundary enables fast and accurate steady-state techniques to be used. The conductive regions have been modeled using the magnetic vector potential and nonconducting with the magnetic scalar potential. The steady-state model has been validated by comparing it with a Magsoft Flux 3D transient model (without translational velocity) and with experimental results. The 3D model is also compared with a previously presented 2D steady-state complex current sheet model.     

A new algorithm for coupled solutions of electric, magnetic andmechanical systems in dynamic simulation of solenoid actuators

An algorithm is presented for the simultaneous solutions of the coupled electric, magnetic, and mechanical problems in the dynamic simulation of a solenoid actuator. The transient nonlinear field in the coupled problem is analyzed using the finite-element (FE) method, which considers the effects of saturation, eddy current, and armature movement in the actuator. The nonlinear electronic circuit is represented by equivalent circuit equations that are coupled to the FE equations and are solved simultaneously with them in an iterative manner. Dynamic responses of the solenoid actuator predicted by using this algorithm agree closely with experimental results. The advantage of this method is that its principle is applicable to general types of power electronic devices. With suitable modifications, it can be used to simulate the dynamic responses of power-electronic-controlled electric machines     

Analysis of a novel laminated coil using eddy currents for AC highmagnetic field

The analysis and performance of an eddy current type laminated coil for a high AC magnetic fields are described. It is usually difficult to obtain a high AC magnetic field using an air-gap coil because of eddy currents. The present coil circumvents this limitation by making use of the magnetic shielding effect of eddy currents. Two different realizations of the coil are proposed to provide design flexibility. The field distributions are analyzed by the two-dimensional finite-element method. The coils can also be applied to an induction electromagnetic pump     

Numerical simulations of an electromagnetic acoustictransducer-receiver system for NDT applications

The development of a multistage numerical model of an electromagnetic acoustic transducer (EMAT), with particular emphasis on an EMAT receiver, is presented. The model includes five separate modeling states: static magnetic field simulation of an electromagnet; pulsed eddy current distribution of a generic meander-line coil suspended over a conducting specimen; Lorentz force distribution due to the interaction of the static magnetic field with the eddy current distributions; acoustic wave generation and propagation based on the dynamic Lorentz forces; and acoustic wave detection by an EMAT receiver. In particular, it is shown how the transient particle displacement fields are converted into an induced voltage response as part of the EMAT receiver system. Numerical simulations show that the voltage response is dependent on the wire spacing of the receiver coil     

冲击载荷下永磁式电涡流减振器设计及动态特性分析

为研究轮式车辆的电涡流减振器在行进间冲击载荷下的动态特性,结合电涡流理论设计了一种永磁式电涡流减振器,并基于等效磁路模型和麦克斯韦方程分析了其导体筒表面空气间隙处磁感应强度与阻尼力之间的关系;同时,利用有限元法对永磁式电涡流减振器的静、动态磁场分布进行了研究,并分析了不同结构参数对其阻尼特性的影响及不同运动速度下的示功特性曲线。通过建立1/4车辆悬架动力学模型和基于高斯滤波白噪声的随机路面激励模型,对车辆行进间冲击载荷下永磁式电涡流减振器的动态特性进行了分析。结果表明：永磁式电涡流减振器的磁场在动态条件下会发生退磁以及磁感线趋速聚集现象,各结构参数对其阻尼特性的影响较大;永磁式电涡流减振器的响应速度快,压缩、复原阻尼力恒定且平稳,可以高效、快速地消除轮式车辆越野时受到的路面激励和车载武器射击时的冲击载荷,能够有效抑制车体振动。研究结果对提高轮式车辆的越野机动性以及车载武器的射击精度具有重要意义。     

新型竖向电涡流-磁力混合阻尼装置试验研究

针对大跨轻质结构的减振需要,研制了一种新型竖向电涡流-磁力混合阻尼器样机.介绍混合阻尼器的减振原理及振动方程;接着介绍了3种不同的磁路设计和制作过程;随后对样机进行试验,测量其动力参数和减振性能.结果 表明:在铜板后方和底板上方安装磁铁均能改变阻尼器的附加刚度;特定磁路设计减少电涡流阻尼系数,增大等效磁力阻尼系数和负刚...     

Visualization and size estimation of fiber waviness in multidirectional CFRP laminates using eddy current imaging

This paper presents an eddy current method to visualize fiber waviness in multidirectional carbon fiber reinforced plastics. Since eddy currents induced by a driver coil flow along carbon fibers, waviness can be visualized if the eddy current path is visualized. We proposed a new complex plane analysis method to visualize an eddy current path from magnetic field measurements. The validity of the method was verified by finite element method analyses. Experiments were performed for multidirectional carbon fiber reinforced plastic specimens. In-plane waviness with misalignment angle from 6.9° to 24.9° were artificially induced in the specimens. An eddy current path was visualized from magnetic field data and it corresponded to the shape of induced waviness. The sizes of the wavy eddy current path were compared with waviness sizes measured by X-ray computed tomography and from optical images. Experimental results indicate that the surface waviness size can be estimated accurately, whereas the subsurface waviness size is underestimated.     

剪切型磁流变流体阻尼器--柔性转子系统动力特性的理论和试验研究

首先给出了剪切型磁流变流体阻尼器--柔性转子系统不平衡响应的试验结果,然后提出了磁流变流体阻尼器动力特性的一般模型,在基于Bingham流体模型的基础上从理论上研究了剪切型磁流变流体阻尼器--柔性转子系统的不平衡响应.理论结果虽与试验结果在定性上较为一致,但磁流变流体阻尼器的动力模型仍需改进.     

A Miniature Short Stroke Linear Actuator—Design and Analysis

We report a newly developed miniature short stroke tubular linear permanent-magnet actuator for robotic applications. Compared to a rotary-to-linear mechanism, the linear actuator has the advantages of efficiency, thrust control, and compact size in generating linear motion. We optimized the electromagnetic force of the actuator analytically by selecting appropriate dimensions and then predicted the force produced by the winding currents by the finite-element method under the brushless dc excitation scheme. We analyzed the actuation performance by dynamic modeling of the actuator. We constructed and tested a prototype on a specially designed test bench to verify the design. Finally, we analyzed and measured the end effect on the magnetic force due to the limited length of the stator core and translator.     

Electromagneto-thermo-mechanical behaviors of conductive circular plate subject to time-dependent magnetic fields

This paper presents an analysis on electromagneto-thermo-mechanical behaviors of conductive plates, an analytical solution is given for a conductive circular plate in a time-dependent magnetic field by using a T-method of the eddy current which is widely used in the eddy current analysis of conductive and superconductive structures. The solution is expressed in an analytical series form and it is suitable for a circular plate under any arbitrary axisymmetric magnetic fields changing in time. Some interesting results including the eddy current, the increment of temperature, and the electromagneto-thermal stresses are investigated, respectively, in this paper. Some characteristics such as the distribution of temperatures, the in-plane electromagnetic stresses and the dynamic response of the conductive plate are first studied and displayed. This study not only reveals some characteristics on the eddy current, the temperature of the plate, the in-plane electromagnetic thermal stresses and the dynamic responses of the conductive plate which is in a time-dependent magnetic field, but presents a new possible way to simplify the analysis of the electromagnetic coupling problem for conductive structures.     

Calculation of eddy-current-induced magnetic fields in vacuuminterrupters with axial magnetic field contacts

The variation of the nonsteady magnetic-induction field of axially symmetric contact arrangements in space and time is calculated by using a finite-element program system. The influence of individual design elements on the induction field is analyzed and the effectiveness of measures for suppressing eddy current is represented. The delaying and damping effect of the eddy currents on the magnetic field increases from the outside towards the axis of symmetry. This changes the radial field distribution for the duration of the arc and the zone of maximum induction travels towards the inside. When the contacts are open, the radial component predominates over the axial induction field in the vicinity of the contact edge. The azimuthal inherent magnetic field of the arc is free of eddy currents and dominates in the outer arc region, particularly in the phase of current increase     

磁流变液阻尼器响应时间的试验研究及其动态磁场有限元分析

摘 要：首先,试验测试了不同速度和电流变化下,大吨位磁流变液阻尼器的响应时间;然后,对激励电流变化时阻尼器的磁场变化进行了有限元模拟,基于阻尼器间隙内磁流变液剪切屈服强度的变化考察了阻尼器的响应时间,并与试验数据做了比较。最后,研究了涡流和阻尼器电磁回路中电流响应时间对阻尼力响应时间的影响。结果表明,可以用有限元模拟得到的间隙内磁流变液的平均有效剪切屈服强度的时程曲线来研究磁流变液阻尼器的响应时间;电磁响应时间是阻尼力响应时间的决定因素,减小阻尼器中的涡流是缩短磁流变液阻尼器响应时间的重要途径;电流下降时涡流对阻尼器磁路的影响要大于电流上升的情况;无论是上升还是下降,电流初值越小,涡流对阻尼器磁路的影响越大,阻尼力响应时间也越长。研究还表明,缩短电流的响应时间,会带来更大的涡流,并不一定能缩短阻尼力的响应时间。     

Magneto-thermo-elastic problem of a conducting rectangular cylinder subjected to sinusoidal change in time of magnetic field

This study is concerned with a magneto-thermo-elastic problem of a conducting rectangular cylinder in an external magnetic field which varies sinusoidally in time. Analytical solutions of eddy currents induced in the cylinder are derived on the basis of a theory of the quasi-stationary current. Two-dimensional transient temperature change produced by the eddy current loss is derived by means of the Green’s function method. The stresses in the infinitely long cylinder in a plane state are derived by making use of the Airy’s stress function. The effect of a frequency in a sinusoidal change in time of the external magnetic field on behaviors of eddy current loss, temperature change and stresses in the cylinder is examined by numerical calculation. The skin effect with an increase in a frequency of the external magnetic field on the transient response of temperature change and stresses in the cylinder is discussed.     

Feasibility of noncontacting electromagnetic despinning of asatellite by inducing eddy currents in its skin. I. Analyticalconsiderations

The servicing of disabled satellites requires that the units be despun before any repair can be done. This paper embarks on the feasibility study of an electromagnetically coupled despinning system based on inducing eddy currents in the satellite skin by an external dc magnetic field. The eddy current power input would act in such a way as to reduce the rotational energy of the satellite. The system does not contact the disabled satellite, and therefore, eliminates the hazards associated with physically attaching equipment, or astronauts with equipment, to the satellite. Two methods are investigated for inducing the eddy currents: (1) a large-diameter current loop positioned around the satellite such that the axis of the satellite rotation is in the plane of the loop, and (2) a magnet, either bar or U-shaped, positioned close to or surrounding the satellite. Closed-form solution for-the interacting magnetic flux, in terms of which the eddy current power input may be derived, is given for the two cases. Design parameters are evaluated for the two despinning systems in terms of input power and weight requirements     

Eddy current analysis of a conductor with a groove by surface integral equation with one unknown

In this paper, we study how to solve eddy currents induced in a conductor with a narrow groove in the case of thick skin depth by using surface integral equations, of which unknowns are the surface electric and magnetic currents. When the skin depth is small, the surface integral equations give accurate solutions except around the sharp edge and corner. Some edges and corners of the groove are so close that it is difficult to get accurate solutions; moreover, as the width of the groove becomes narrower, the surface integral equations become ill conditioned. In order to solve these problems, we propose a method to analyze the eddy currents induced in a conductor with a groove by introducing a lumped loop magnetic current, which is formulated by a surface integral equation derived from the normal component of the electric field.     

Considerations for high data rate recording with thin-film heads

The significance of head inductance and eddy currents in limiting field rise times is discussed. Poor rise times can cause severe distortion and loss of performance at high data rates. A simple reluctance model is developed to explore the relationship between the geometry of a head and its inductance. The model is extended to include the effects of eddy currents, and to allow the frequency-dependent efficiency (hence the field rise time) to be calculated. Based on this rise time, a geometric model is used to calculate the positions of the recorded transitions and the resulting transition-shift distortion. Experimental results at transition separations down to 6 ns reveal a strong write current dependency which is not seen in the model. This dependence is, however, clearly seen in a simple domain wall model which implicitly includes magnetic saturation. Transition shift distortion can be mitigated by the use of precompensation. It is found that it is possible to successfully recover data at 180 Mbit/s using a conventional thin-film head