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Magnetics, IEEE Transactions on

Issue 12 • Date Dec. 2011

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  • [Front cover]

    Page(s): C1
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    Freely Available from IEEE
  • IEEE Transactions on Magnetics publication information

    Page(s): C2
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  • Table of contents

    Page(s): 4669 - 4670
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  • Hard Magnetic Materials: A Perspective

    Page(s): 4671 - 4681
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (674 KB) |  | HTML iconHTML  

    The principles of operation of permanent magnets are summarized, and their development is reviewed. The key figure of merit, the energy product, improved exponentially over much of the 20th century, doubling roughly every 12 years. Yet it has not improved significantly in the last 20 years. Constraints on further development are explained, together with the limits of 1/4 μ0/Ms2 on energy product and 2K10Ms on coercivity, where K1 is the uniaxial anisotropy constant and Ms is the spontaneous magnetization. The challenge of making rare-earth free magnets with a large energy product is discussed, as well as nanocomposite megajoule magnets and the development of new magnetically hard thin-films with perpendicular anisotropy which are potentially interesting for spin electronics or magnetic recording. View full abstract»

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  • Q-Band Ferromagnetic Resonance Study of Fe Thin Films on GaAs(001) Deposited by RF Magnetron Sputtering

    Page(s): 4682 - 4685
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    The magnetic properties of epitaxial Fe(001) films, prepared on GaAs(001) substrates by RF magnetron sputtering, were investigated by ferromagnetic resonance spectroscopy operating at Q-band (35 GHz). The in-plane angle dependence of the resonance fields showed four-fold magnetic anisotropy with an easy (hard) direction along [100] ([110]). The anisotropy constant was slightly smaller than the magnetocrystalline anisotropy constant of bulk Fe. Ferromagnetic resonance linewidths, caused by the magnetic damping of Fe films, were narrow (<;70 Oe) and independent of the in-plane magnetic field directions. It will be shown that the observed linewidth gives good estimate of the upper bound of the Gilbert-type damping in Fe thin films. View full abstract»

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  • Monte Carlo Simulation of Magnetotransport Properties in \hbox {La}_{0.67}\hbox {Ca}_{0.33}\hbox {MnO}_{3} (FM) and \hbox {La}_{0.33}\hbox {Ca}_{0.67}\hbox {MnO}_{3} (AF) Thin Films

    Page(s): 4686 - 4694
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    Manganese perovskites have recently been the focus of renewed interest, due to the "colossal" magnetoresistance (CMR) effect and the coupled metal-insulator and magnetic transitions displayed at the spin-ordering temperature TC by some of these compounds. The essential ingredient of the CMR physics is not only the double-exchange interaction but also other competing interactions, such as ferromagnetic/antiferromagnetic superexchange interactions and charge/orbital ordering instabilities as well as their strong coupling with lattice distortion. In this work, a magnetotransport properties simulation of ferromagnetic (FM) La0.67Ca0.33MnO3 and antiferro magnetic (AF) La0.33Ca0.67MnO3 as a function of the temperature and the magnetic field is presented and discussed. Our study is addressed by using the Monte Carlo method on the basis of a Heisenberg model. Films thickness and external magnetic field influence on the resistivity and magnetoresistance (MR) was analyzed. View full abstract»

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  • Effect of Size and Configuration on the Magnetization of Nickel Dot Arrays

    Page(s): 4695 - 4700
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    We report experimental results on magnetic properties of our fabricated nickel nanodot arrays studied with magnetic force microscopy (MFM) and magneto-optical Kerr effect (MOKE). Arrays of nickel dots with different size and periodicity were fabricated by electron-beam (E-B) lithography and lift-off processes. 50 nm thick arrays (200 nm × 200 nm) of nickel dots exhibit that the magnetization occurs independently in terms of the direction of applied field, while smaller arrays (120 nm × 80 nm) with thicknesses ranging from 12 nm to 35 nm show the effect of size and configuration of arrays whose magnetic responses are different. Thinner dots in such array seem to assume single domain state with a preferential easy and hard axis in the array, but thicker dots show a vortex type remanent magnetization. We ascribe the existence of the preferential magnetization axis to a dipolar-dipolar interaction due to small separation of single domain dots. View full abstract»

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  • Homogenization of Electromagnetic Force Field During Casting of Functionally Graded Composites

    Page(s): 4701 - 4706
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    The paper presents the analysis of the process of casting functionally graded composites under alternating electromagnetic field. The process utilizes the effect of electromagnetic buoyancy on nonconductive particles of the reinforcement in the conducting liquid (melted metal). The authors analyzed the possibilities of homogenizing the distribution of electromagnetic field in such a way as to obtain the desired direction of electromagnetic buoyancy and at the same time minimize the stirring of the molten metal, which makes it difficult to receive the optimal distribution of reinforcement in the casting. The suggested solution was to use the conductive elements of the mold to move the nonuniformity of the electromagnetic field outside the casting and a parabolic inductor to smooth the field distribution in the casting. View full abstract»

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  • Models for Extrapolation of Magnetization Data on Magnetic Cores to High Fields

    Page(s): 4707 - 4711
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (349 KB) |  | HTML iconHTML  

    Reliable representation of magnetization curves at higher magnetic fields is needed to accurately model and design devices in FEM software. Standard closed circuit magnetic induction measurements for ferromagnetic materials in such devices are usually limited to around 2 T for most Epstein frame equipment, above which, measurements become increasingly unreliable, as field generation capacity becomes limited. The popular numerical extrapolation algorithms used by these software packages, though useful, can be misleading due to the lack of magnetic information in the existing algorithms. Hence for better understanding of simulation and modeling of the macroscopic representation of these materials, a critique of various extrapolation procedures has been carried out in this work, along with recommendations for the procedures to use in order improve the accuracy of magnetic material representation in electromagnetic device design at high fields. View full abstract»

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  • Simultaneous Design Optimization of Permanent Magnet, Coils, and Ferromagnetic Material in Actuators

    Page(s): 4712 - 4716
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    This paper presents structural topology optimization of an electro/permanent magnet linear actuator. The optimization goal is to maximize the average magnetic force acting on a plunger that travels over a distance of 20 mm. To achieve this goal, the magnetic field sources (i.e., permanent magnet, positive and negative direction coils), and ferromagnetic material of the yoke are simultaneously co-designed using four design variables for each finite element. The magnetic force is calculated using the Maxwell stress tensor method coupled with finite-element analysis. The optimization sensitivity analysis is performed using the adjoint method, and the optimization problem is solved using a sequential linear programming method. To illustrate the utility of the proposed design approach, linear actuators are designed, and the optimal shapes and locations of the yoke permanent magnet, coils, and ferromagnetic part are provided. In addition, the effects of the PM magnetization direction and the current density strength on design results are described. View full abstract»

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  • Study of EDS & EMS Hybrid Suspension System With Permanent-Magnet Halbach Array

    Page(s): 4717 - 4724
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    In this paper, a permanent magnet (PM) electro-dynamic suspension and electro-magnetic suspension (EDS & EMS) hybrid suspension system is proposed to overcome the shortcomings of the under-damped dynamics in a PM EDS system. The linearized model is established and its stability is also analyzed using the Routh criterion. According to the rational distribution between the repulsive force and the electromagnetic force, a controller is designed to meet the dynamic performance required in practical applications. A novel maglev system using a hybrid suspension scheme is also presented in this paper. Furthermore, a single-degree-of-freedom (SDOF) hybrid suspension experimental mechanism is established, and some experiments have also been undertaken to validate its effectiveness on suppressing the oscillation of the PM EDS system caused by external disturbances. View full abstract»

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  • A Novel Structure for Low-Loss Radial Hybrid Magnetic Bearing

    Page(s): 4725 - 4733
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1054 KB) |  | HTML iconHTML  

    This paper proposes a novel radial hybrid magnetic bearing (RHMB), which has integrative magnetic pole boards and continuous working air gaps that reduce the hysteresis and eddy-current losses of the traditional homopolar structure. Its configuration and working principle are introduced. The bias and control magnetic circuits of the RHMB are analyzed with the equivalent magnetic circuit method. Mathematical models, from which the force-displacement and force-current relationships are derived, are built. The method for the rudimentary design of RHMB parameters is illustrated, through which a prototype RHMB for a reaction flywheel system is designed and assembled. Its performance and characteristics are calculated and analyzed with the obtained models and relationships. The results show that in its air gaps, the novel RHMB can generate a continuous and uniform bias magnetic field, which reduces the hysteresis and eddy-current losses and enhances the radial load capacity and axial passive resilience. The bias fluxes of all poles are decoupled from each other at all times. Although the control fluxes of the two channels are slightly coupled when the rotor is not in the central position, the coupling force-current stiffness is very low and can be ignored. These attributes simplify the design of the control system. The novel RHMB is especially suitable for high-speed and low-loss circumstances. A pair of RHMBs are used for the reaction flywheel, and for maintaining suspension of the rotor at the spin speed of 0-6000 rpm. View full abstract»

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  • Structure of One-Axis Controlled Repulsive Type Magnetic Bearing System With Surface Permanent Magnets Installed and Its Levitation and Rotation Tests

    Page(s): 4734 - 4739
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    This paper deals with a new bearing structure of one-axis controlled repulsive type magnetic bearing system that has a motor function of a surface permanent magnet (SPM). We evaluated the magnetic bearing structures by using the 4-pole 4-segment type and 4-pole Halbach array, which were placed around cylindrical permanent magnet sets as field magnets. The comparison of magnetic flux density in the radial direction measured by finite-element analysis indicated that the Halbach array has advantages over the 4-segment type in terms of the total harmonic distortion and internal magnetic influence. Additionally, levitation and rotation tests were performed by implementing each bearing configuration in a newly developed equipment. In both bearing configurations, stable levitation at zero-power position was established and high-speed rotation up to around 16 000 rpm was achieved. As a result, the Halbach array slightly saved electric power. Its total input power to the motor was approximately 1.2 W. View full abstract»

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  • Design of Compact Linear Electromagnetic Actuator for Auto-Focusing in Phone Camera

    Page(s): 4740 - 4744
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (698 KB) |  | HTML iconHTML  

    This paper proposes a novel linear electromagnetic actuator (LEA) for auto-focusing of compact phone cameras. An LEA consists of permanent magnets, iron cores, and coils, which are all magnetic circuit components. When coils are powered, induced magnetic field generates N and S poles around iron cores. Thus, unlike voice coil motors (VCMs) that employ the Lorentz force, the motion of the moving part in this study is arisen from a property-same poles repel each other while opposite poles attract each other. When compared to conventional VCM actuators in simulation results, the proposed LEA generates larger force, whereas using smaller current. View full abstract»

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  • EC-GMR Data Analysis for Inspection of Multilayer Airframe Structures

    Page(s): 4745 - 4752
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1013 KB) |  | HTML iconHTML  

    Eddy-current testing (ECT) is widely used in inspection of multilayer aircraft skin structures for the detection of cracks under fasteners (CUF). Detection of deep hidden CUF poses a major challenge in traditional ECT techniques largely because the weak eddy-current signal due to a subsurface crack is dominated by the strong signal from the aluminum or steel fastener. Giant magnetoresistive (GMR) sensors are finding increasing applications in directly measuring weak magnetic fields associated with induced eddy currents. The measured flux image at a fastener site is in general symmetric and an asymmetry is introduced by the presence of a subsurface crack, which is used for defect detection. This paper presents novel methods that employ the resident phase information, for improving detection probability of GMR signal analysis. Using computational model, the effectiveness of the proposed methods for enhancing detection of CUF is investigated. Results demonstrating the potential of these techniques for detection of second layer CUF are presented. View full abstract»

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  • Reduction of Lift-Off Effects in Pulsed Eddy Current for Defect Classification

    Page(s): 4753 - 4760
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    Pulsed eddy-current (PEC) testing is an electromagnetic nondestructive testing & evaluation (NDT&E) technique and defect classification is one of the most important steps in PEC defect characterization. With pulse excitation, the PEC response signals contain more features in time domain and rich information in frequency domain. This paper investigates feature extraction techniques for PEC defect classification including rising time, differential time to peak and differential time to zero, spectrum amplitude, and differential spectrum amplitude. Experimental study has been undertaken on Al-Mn 3003 alloy samples with artificial surface defects, sub-surface defects, and defects in two-layer structures under different lift-off. Experimental results show that methods are effective to classify the defects both in single-layer structures and two-layer structures. Comparing the results of different methods, it is found that differential process can eliminate the lift-off in defect classification in both time domain and frequency domain. The study can be extended to defect classification in complex structures, where lift-off effects are significant. View full abstract»

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  • Design of Gradient Coil for Magnetic Resonance Imaging Applying Particle-Swarm Optimization

    Page(s): 4761 - 4768
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    Designing a gradient coil for magnetic resonance imaging (MRI) is an electromagnetic inverse problem often formulated as a constrained optimization, which has been successfully solved by inverse boundary element methods. The constant search for new coil features and improved performance has highlighted the need of employing more versatile optimization techniques capable of dealing with the new requirements. In this paper, the solution of linear and nonlinear optimization problems using particle-swarm optimization (PSO) algorithms is presented. Examples of coil designed using this heuristic method are shown, including a comparison to solutions provided by conventional optimization approaches. Numerical experiments reveal that the application of PSO for the solution of inverse boundary element problems for coil design is a computationally efficient algorithm that is capable of handling nonlinear problems and that offers fast convergence, especially for those symmetric coil geometries where the computational effort can be drastically reduced by using suitable dimensionality-reduction techniques. View full abstract»

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  • Recording Behavior of Exchange Coupled Composite Media

    Page(s): 4769 - 4774
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (486 KB) |  | HTML iconHTML  

    The recording behavior of exchange coupled composite (ECC) media is investigated. It is found experimentally that the change of the written track width is less pronounced as a function of linear density when the write-ability is controlled by varying the vertical exchange coupling between the various layers in the medium stack as opposed to varying the lateral exchange coupling between the grains. The results are explained using a simple three-spin model which captures the essential physics. It is pointed out that the traditional concept of an effective field that separates out the field angle effect does not apply to the recording process of ECC media. View full abstract»

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  • Investigation of Two-Dimensional Magnetic Recording (TDMR) With Position and Timing Uncertainty at 4 Tb/in ^{2}

    Page(s): 4775 - 4780
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    The feasibility of two-dimensional magnetic recording (TDMR) at 4 Tb/in2 customer areal-density is investigated via numerical simulations. In addition to the coding overhead needed to correct possible errors in a TDMR channel, the overhead required to obtain accurate position and timing estimates is taken into account in determining achievable customer density. The TDMR channel model used for this investigation is based on a random Voronoi granular medium, a two-dimensional (2-D) Gaussian read sensitivity function with random position and timing offsets and additive white Gaussian noise (AWGN). Read channel signal processing consists of a 2-D linear minimum mean square error (LMMSE) equalizer, a Gaussian mixture model (GMM) based log likelihood ratio (LLR) extractor and a low-density parity-check (LDPC) decoder. This work suggests that reliable performance may be achieved on media with 14 × 1012 grains/in2 by TDMR at a net customer areal-density of 0.29 bits per grain, including the overhead required for the LDPC code and the position and the timing fields. View full abstract»

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  • Influence of the Electrical Steel Grade on the Performance of the Direct-Drive and Single Stage Gearbox Permanent-Magnet Machine for Wind Energy Generation, Based on an Analytical Model

    Page(s): 4781 - 4790
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (613 KB) |  | HTML iconHTML  

    The performance of a variable speed wind turbine using a direct-drive permanent-magnet synchronous generator (PMSG) as well as a PMSG with single stage planetary gearbox is compared for two grades of electric steel applied for the generator stator core lamination. A ring type, radial flux PMSG is modeled. For a fixed mechanical power input, the geometry of the generator is optimized for each turbine systems and two materials to maximize the annual efficiency of the generator. The annual efficiency is calculated based on the power curve of the generator and the probability density function of the wind speed. This function is approximated by the Weibull distribution function for a site with average wind speed of 7 m/s. For both generator systems, the annual efficiency of two optimized generators using different steel grades differs around 1%. The difference depends on a mass of active material of the generator. View full abstract»

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  • Analytical Open-Circuit Magnetic Field Distribution of Slotless Brushless Permanent-Magnet Machines With Rotor Eccentricity

    Page(s): 4791 - 4808
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1419 KB) |  | HTML iconHTML  

    Analytical expressions for the no-load magnetic field distribution of slotless brushless permanent-magnet (PM) machines with static, dynamic, and mixed rotor eccentricities are presented. The proposed analytical expressions can be used for slotless brushless PM machines with any radius-independent magnetization pattern. The analytical expressions and the results for six different magnetization patterns are presented. Based on the analytical magnetic field distribution, the line and phase back-electromotive force waveforms, local traction components and unbalanced magnetic forces are obtained. The analytical results are compared with those from finite-element analyses to validate the derived expressions. View full abstract»

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  • A Linear Doubly Salient Permanent-Magnet Motor With Modular and Complementary Structure

    Page(s): 4809 - 4821
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    A linear doubly salient permanent magnet (LDSPM) motor is particularly suitable for long stator applications due to its simple and low cost stator, which consists of only iron. This paper proposes a new LDSPM motor design with complementary and modular structure. The key of this structure is that the primary mover is composed of two modules whose positions are mutually four and one half of the stator pole pitch apart and there is a flux barrier between them. Hence, the back electromotive force (EMF) waveform and cogging force of the two modules have 180 electrical degree differences. This design results in the total cogging force being significantly reduced and the back-EMF of each phase becoming symmetrical because the even harmonics are canceled. For fair comparison, an existing linear LDSPM motor is designed based on the same electromagnetic parameters and compared by the means of finite element analysis (FEA). The results reveal that the proposed LDSPM motor can offer symmetrical back-EMF waveforms, smaller cogging force, lower force ripple, and higher magnet utilization factor than the existing one. View full abstract»

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  • Thermal Model With Winding Homogenization and FIT Discretization for Stator Slot

    Page(s): 4822 - 4826
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    The aim of the method detailed in this paper is to get an equivalent thermal model of a stator slot, in order to simplify the calculation of desired temperatures in an electrical machine winding. This study is divided in two steps: First, the equivalent thermal conductivity is deduced from a homogenization of the winding, and next, a discretization is achieved using the finite integration technique considering transient analysis. In order to evaluate the method, results from the equivalent model are compared with finite element simulations considering two slot geometries. View full abstract»

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  • Reduction of Unbalanced Magnetic Pull in Synchronous Machines due to Parallel Circuits

    Page(s): 4827 - 4833
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (294 KB) |  | HTML iconHTML  

    This paper describes an analysis of the damping of unbalanced magnetic pull (UMP) in salient pole synchronous machines due to parallel stator circuits. Measurements of the UMP and currents in the parallel circuits have been performed on a 12-pole generator with the stator displaced relative to the rotor, creating a static eccentricity, and the stator winding connected as one circuit or two parallel circuits. Experiments were done at no-load conditions. Two numerical studies of the force reduction are also presented, one using a finite-element code and one using a permeance model. A good correspondence between measured and simulated forces is obtained. Results indicate that the reduction of UMP is strongly dependent on the direction of unbalance relative to the line of separation of the stator circuits. Eddy currents induced in the rotor during operation were found to reduce the standstill UMP with more than 20%. View full abstract»

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  • Correction to “Estimation of Fichera-Type Eigenvalues Using Standard Functions” [Aug 09 3046-3054]

    Page(s): 4834
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    In the above titled paper (ibid., vol. 45, no. 8, pp. 3046-3054, Aug. 2009), Equation (10) was presented incorrectly. The correction is presented here. View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology