By Topic

Magnetics, IEEE Transactions on

Issue 12 • Date Dec. 2009

Filter Results

Displaying Results 1 - 25 of 31
  • [Front cover]

    Page(s): C1
    Save to Project icon | Request Permissions | PDF file iconPDF (245 KB)  
    Freely Available from IEEE
  • IEEE Transactions on Magnetics publication information

    Page(s): C2
    Save to Project icon | Request Permissions | PDF file iconPDF (39 KB)  
    Freely Available from IEEE
  • Table of contents

    Page(s): 5257 - 5258
    Save to Project icon | Request Permissions | PDF file iconPDF (62 KB)  
    Freely Available from IEEE
  • The Physics of Geomagnetic-Field Transduction in Animals

    Page(s): 5259 - 5265
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (126 KB) |  | HTML iconHTML  

    Birds, fish, sea turtles, and various other animals have been reported to sense the geomagnetic field and to use it for orientation, navigation, and homing. In recent years, exciting progress has been made towards elucidating the physical and structural basis of this remarkable phenomenon. This paper focuses on the two hypotheses that drive current research into magnetoreception. One proposal relies on the presence of molecules that undergo magnetically anisotropic chemical reactions due to transient formation of a radical pair. The proposed mechanism-essentially a chemical compass-is theoretically well-established and specifically designed behavioral experiments may indeed be interpreted that way, which has sparked a hunt for the molecules and structures in question. The ferrimagnetic transduction hypothesis, on the other hand, draws its plausibility from both theoretical considerations and the fact that magnetite has been detected in sensory neurons, with stable single-domain particles in fish and micrometer-scale clusters of superparamagnetic nanocrystals in birds. We discuss the limitations of our current knowledge and suggest future studies. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Saturation Curve for a Synthetic Antiferromagnetic System

    Page(s): 5266 - 5270
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    For toggle magnetic random access memory, the saturation field represents the exterior limit of the work region. Exterior magnetic fields higher than the saturation field lead to an irremediable loss of the stored information because the antiferromagnetic state of the synthetic antiferromagnetic (SAF) structure becomes a ferromagnetic state and data stored in the magnetic memory cell are altered. At the saturation point, the two ferromagnetic-layer magnetizations became parallel oriented, in a direction close to that of the applied field. In this paper, we present a method to find an analytical formula for the magnetic saturation field that depends on the angle between the applied magnetic field related to the easy anisotropy axis, on the amplitude of the antiferromagnetic coupling field between the ferromagnetic layers, on the geometrical characteristics of the SAF structure, and on the second term of the series expansion of the anisotropy energy of the system. This method allows us to obtain an analytical formula for saturation field that depends only on the controllable parameters of the SAF structure. This analytically obtained critical saturation curve perfectly matches with the critical saturation curve reported in previous papers. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Correlation Between the Degradation of Perpendicular Anisotropy and the Double Hysteresis Behavior in [Pd/Co] _{\rm n} /FeMn Exchange Biased Thin Films

    Page(s): 5271 - 5276
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (809 KB) |  | HTML iconHTML  

    We clearly detected double hysteresis by increasing Co layer thickness and decreasing the number of bilayers in perpendicular exchange biased [Pd(0.6)/Co(t)] n/FeMn(11.6 nm) thin films. In-plane tensile stress calculations confirmed that the appearance of double hysteresis is closely related to the degradation of stress-induced perpendicular anisotropy in the [Pd/Co] multilayers. Furthermore, annealing at the magnetic field applied perpendicular to the film plane directly verified that the enhancement of thermally induced perpendicular anisotropy, K eff-induced, in the [Pd/Co] multilayers is the main physical reason for removal of the double hysteresis. All our experimental and theoretical results demonstrated that perpendicular anisotropy is the dominant factor in controlling the double hysteresis behavior of perpendicularly magnetized [Pd/Co]n/FeMn exchange biased thin films. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Temperature Stability and Flux Losses Over Time in Sintered Nd–Fe–B Permanent Magnets

    Page(s): 5277 - 5280
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (231 KB) |  | HTML iconHTML  

    Demagnetization occurring with time in a constant temperature is often assumed to be negligible, provided that the operating point of the magnet is above the knee of the B-H curve. However, because it is important to ensure that no permanent flux losses occur in permanent magnets during their use in industrial applications, there is a clear need to quantify these time-dependent losses. We measured losses over time for four commercial sintered Nd-Fe-B magnet grades at five different temperatures (23degC-150degC). We tested samples with three different permeance coefficient (Pc) values for each material. The time-dependent losses measured fitted the logarithmic law of magnetic viscosity well. We demonstrated that the total flux loss in a lifetime of 30 years can be estimated according to the temperature, coercivity of the material, and the permeance coefficient of the magnet. With proper selection of the magnet material, in accordance with the designed Pc of the application, the total flux loss in 30 years can be minimized almost to zero even at 150degC. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effect of Factors on Coercivity in Sr–La–Co Sintered Ferrite Magnets

    Page(s): 5281 - 5288
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1662 KB) |  | HTML iconHTML  

    We varied the composition and sintering temperature of Sr-La-Co ferrite magnets to analyze the effects of various important factors on coercivity (H cJ). We examined the effects of crystal grain size and distribution, the mechanism of magnetization reversal, the degree of crystal grain orientation (OD), and the anisotropy field (H A) on H cJ. We proposed an equation based on the experimental results that expresses the measured H cJ and considers these effects as H cJ = C t(0.4/R h) OD (H A - H d - H in), where C t, R h, H d, and H in are the crystal grain size effects on H cJ of sintered magnet, rotational hysteresis integral corresponding to the mechanism of magnetization reversal, demagnetizing field of shape anisotropy, and interaction field between crystal grains, respectively. We found that apart from the volume ratio for single-domain crystal grains and H A, the mechanism of magnetization reversal had significant effects on H cJ for Sr-La-Co sintered ferrite magnets. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Magnetometric Demagnetizing Factors for Various Shapes of Rotational Symmetry

    Page(s): 5289 - 5295
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (399 KB) |  | HTML iconHTML  

    We have investigated the magnetometric demagnetizing factors of rotation-symmetrical magnetic bodies of relative permeability mu placed in a uniform magnetic field parallel to the axis of rotation. The bodies we considered include a cylinder, a sphere, a bicone, and a rotating astroid. We numerically calculated the magnetometric demagnetizing factors from the surface magnetic charge densities sigma obtained by the surface magnetic charge simulation method. We show that the magnetometric demagnetizing factors for various shapes of rotation-symmetrical bodies are significantly different from those of a sphere. We have determined the shape producing the largest demagnetizing field in ferromagnetic bodies with sufficiently large relative permeability mu . We report the magnetometric demagnetizing factors for uniformly magnetized bodies (mu = 1 , i.e., susceptibility chi = 0 ) of various shapes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Direct Current Effects on High-Frequency Properties of Patterned Permalloy Thin Films

    Page(s): 5296 - 5300
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (506 KB) |  | HTML iconHTML  

    We have investigated experimentally direct current (dc) effects on high-frequency properties of two different permalloy (Py) submicrometer patterns of 0.24 mum and 0.55 mum width, 10 mum length, and 100 nm thickness. The natural ferromagnetic resonance (FMR) frequencies for the two samples are about 8.5 and 11.5 GHz. A 50 mA dc produces a FMR frequency reduction of about 1 GHz in both samples. We extracted susceptibility spectra for the samples from the measurement data. We studied inductance variations of Py embedded transmission lines for different dc levels. With 50 mA dc, the operational frequencies of the inductances decreased by 9% and 12.5%. We also tested effects of magnetic fields generated by external magnets on the submicrometer patterns for comparison. To obtain the same magnetization rotation angle, the external magnetic field needs to be about five times larger than the Ampere field created by the direct current. This behavior is unique and may be associated with the increased thermal energy from the Joule heating effects. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • B-Scalar Measurements by CMR-Based Sensors of Highly Inhomogeneous Transient Magnetic Fields

    Page(s): 5301 - 5306
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (958 KB) |  | HTML iconHTML  

    We present local measurements of absolute values of pulsed magnetic fields in a typical electromagnetic launching system-a small coilgun. For this purpose, we designed magnetic field sensors based on thin polycrystalline La0.83Sr0.17MnO3 films exhibiting a colossal magnetoresistance (CMR) effect. We measured the magnetic field distribution inside the bore of a coilgun consisting of a multilayer coil and inserted a copper projectile in the shape of a hollow cylinder using an array of CMR-based sensors. In order to identify places with highly inhomogeneous magnetic field changes in direction and value, we simulated a pulsed magnetic field inside the coilgun. The measurements of magnetic induction compared well with simulations. CMR-based sensors are able to measure highly inhomogeneous magnetic fields in very small areas independently of the magnetic field direction with respect to the orientation of the sensor. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Demagnetization of Layered Ferromagnetic Structures for Magnetically Shielding: Frequency Considerations

    Page(s): 5307 - 5314
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (453 KB) |  | HTML iconHTML  

    This paper provides the background for evaluating the appropriate frequency from measured or manufacturer provided magnetic permeability data. The proper frequency is, among other parameters, a necessary prerequisite for the low residual field demagnetization required for several applications including biomagnetism and particle physics. The paper also presents an interpretation of the material-dependent effects which arise during the demagnetization procedure. The interpretation focuses on magnetic diffusion influenced by magnetic permeability variation accompanying the demagnetization process. Explanations based on energy considerations show how the domain alignment is affected during the demagnetization process. A comparison with the results obtained from an algebraic hysteretic model supports the conclusions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Field-Circuit Hybrid Method for Magnetic Actuator Using a Laminate Composite

    Page(s): 5315 - 5318
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (295 KB) |  | HTML iconHTML  

    The magnetic actuator using a laminate composite of piezoelectric (PZT) and magnetostrictive materials (MM) achieves active control of magnetic force without Joule heat loss. To study its characteristics, the field-circuit hybrid method is proposed based on the equivalent magnetic circuit and the finite element analysis (FEA) of piezoelectric and magnetic fields. The strain of laminate composite under different voltage is obtained through the piezoelectric FEA. On the basis of magnetostrictive equation, the MM branch in the magnetic circuit of the actuator is transformed equivalently, the work point of the actuator is determined, and the corresponding FEA model of magnetic analysis is then set up. The relationships between magnetic force, gap, and voltage are discussed by the hybrid method, which can be expanded into the design and analysis of the magnetostrictive actuator and sensor to improve simulation efficiency and precision. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A New Structure for Permanent-Magnet-Biased Axial Hybrid Magnetic Bearings

    Page(s): 5319 - 5325
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (509 KB) |  | HTML iconHTML  

    We propose a new structure for a permanent-magnet-biased axial hybrid magnetic bearing. Starting with the inner air gap and the outer air gap of conventional axial magnetic bearings, we first construct a novel air gap between the permanent magnet and the outer housing, which we call the second air gap, separating the bias flux paths from the control flux paths. As a result, the control flux paths will have lower reluctance, and the power loss of the axial magnetic bearing will be lower. Next, we modeled this axial hybrid magnetic bearing and analyzed it using the equivalent magnetic circuit method, 2-D finite element method (FEM), and 3-D FEM. We have designed and assembled an axial hybrid magnetic bearing prototype for a reaction flywheel system with angular momentum of 15 Nmiddotmmiddots at a speed of 5000 r/min. The theoretical analysis and the prototype experiments show such advantages as simple structure, good force current and force displacement, and high operating reliability. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical Characterization of All-Magnetic NOT Gate Operation in Vortex Rings

    Page(s): 5326 - 5332
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1566 KB) |  | HTML iconHTML  

    We have demonstrated deterministic operation of inverters (NOT gates) using vortex magnetization states in pairs of linked 5 mum diameter permalloy rings with a small region of overlap. The input ring is clipped so that the state can be controlled by global fields, and is designed to switch at lower fields than the unclipped output ring, which then inverts the logical state of the input. Optical coatings over half of each ring provide distinct magnetooptic Kerr effect (MOKE) signatures for saturation, clockwise, and counterclockwise states in our focused beam system. We demonstrate that excessive overlap between the rings leads to overall shape anisotropy dominating the behavior of the structure. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Embedded Ring-Type Inductors Modeling With Application to Induction Heating Systems

    Page(s): 5333 - 5343
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1077 KB) |  | HTML iconHTML  

    We derive integral expressions of the equivalent impedance of ring-type coils for induction heating systems. These expressions are obtained by integrating the analytical solution of the field generated by a circular filamentary current placed between two linear and homogeneous semi-infinite media. Constant current density is assumed for the coils, since they are wound with an appropriate Litz wire. The model also gives the magnetic field in the cross section of the windings, which is necessary to calculate the proximity losses in the cables. The solution is given in terms of Bessel function integrals, showing an improvement of the convergence with respect to the filamentary model solution. We constructed several prototypes having different turns and layers and tested them with different substrates. Our measurements confirm the validity of the analytical models. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Investigation of Fluid Structure Interaction of a Head Stack Assembly in a Hard Disk Drive

    Page(s): 5344 - 5351
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1871 KB) |  | HTML iconHTML  

    An analysis of three-dimensional, unsteady flow field is conducted in a 3.5-in, 7200 rpm hard disk drive (HDD) using FLUENT software. The analysis is carried out for the head stack assembly (HSA) positioned at the outer diameter (OD). A finite element model (FEM) of the HSA, built in ANSYS, is used for the forced vibration analysis. The flow field analysis yields the aerodynamic forces and moments which are applied to the HSA FEM. The effects of a damper plate and arm holes introduced to the HSA design are investigated. The analysis shows that a damper plate attenuates the root mean square (RMS) of aerodynamic loads acting on the HSA, resulting in a significant reduction of off-track displacement of the heads. It also shows that a weight-saving hole in the arm causes a complex vortex structure inside the hole. The vortex structure exhibits a forming/collapsing frequency of 7 to 9 kHz, which resonates with the structural modes of the HSA, causing additional off-track vibration of the heads. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Evaluating Track-Following Servo Performance of High-Density Hard Disk Drives Using Patterned Media

    Page(s): 5352 - 5359
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1022 KB) |  | HTML iconHTML  

    In recent years, track densities of magnetic hard disks have continued to grow. A promising approach to continuing the trend to ultrahigh density is using bit-patterned media (BPM). However, the implementation of BPM in hard disk drives (HDDs) to achieve high recording density is challenging and requires various new techniques, such as new servo pattern designs and position error signal (PES) decoding schemes. In applying BPM in HDDs, it is important to select a servo pattern providing sufficient PES quality for head positioning. In this paper, we discuss evaluation of PES quality and servo pattern performance from a closed-loop (servo) point of view in order to evaluate the quality of several servo patterns. We consider three servo patterns (the amplitude pattern, chevron pattern, and differential frequency pattern) as case studies. We developed a PES simulation tool to provide a realistic HDD track-following simulation. Because of PES nonlinearity in the amplitude servo pattern, we considered time-based servo patterns as alternatives. For time-based servo patterns, we found that readback signal sampling and transition jitter greatly affect PES quality. Therefore, we conclude that the differential frequency servo pattern is superior to other patterns, since it is less sensitive to transition jitter and readback signal sampling. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Validation of a Time-Harmonic Numerical Model for Solving Magnetic Field in End Region of a Radial-Flux Machine

    Page(s): 5360 - 5367
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (764 KB) |  | HTML iconHTML  

    We present an analysis of the magnetic field in the end region of a radial-flux rotating machine. In numerical simulations, we used three familiar boundary conditions to replace the modeling of the end shields and frame. We made measurements for comparison, and the simulation results were quite consistent with the measurements. Our analysis shows that the eddy current in the end shields and frame influences the magnetic field in the end region slightly and that the use of a homogeneous Neumann boundary condition or a standard impedance boundary condition (SIBC) to replace the end shields and frame can solve the magnetic field in the end region more accurately than a homogeneous Dirichlet boundary condition. Validation by the measurements demonstrates that 3-D current-driven time-harmonic model with suitable boundary conditions can be used to solve the magnetic field in the end region quite accurately. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An Analytical Circuit Model of Switched Reluctance Motors

    Page(s): 5368 - 5375
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (605 KB) |  | HTML iconHTML  

    We have developed a dynamic analytical circuit model to simulate the performance of switched reluctance motors (SRMs). Our model expresses flux linkages as multiple decoupled one-argument functions, either current dependent or rotor position dependent, instead of one two-argument function dependent on both current and rotor position. We propose a novel approach for the computation of the air gap permeance at various rotor positions. By using this analytical model, the performance of a SRM can be simulated very efficiently and with improved accuracy. As an application example, we present a simulation of an 8/6 pole SRM in the system domain, and compare the results with transient finite element analysis (FEA) solutions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measurement and Real-Time Modeling of Inductance and Flux Linkage in Switched Reluctance Motors

    Page(s): 5376 - 5382
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1114 KB) |  | HTML iconHTML  

    This paper presents a real-time model to identify the inductance and the flux linkage of switched reluctance motors (SRMs). A dynamic measurement method is used for the real-time modeling. An artificial neural network (ANN), designed in accordance with the inductance and the flux linkage data obtained from the dynamic measurement method, is used to make the real-time model. Experimental studies are realized to prove the applicability of the dynamic measurement method and the ANN-based model. The experiments are performed by using a TMS320F2812 digital signal processor (DSP). The results show that the dynamic measurement method and the ANN-based model ensure real values in all the positions and load conditions of the motor. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • In-Depth Study of the Torque Constant for Permanent-Magnet Machines

    Page(s): 5383 - 5387
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB) |  | HTML iconHTML  

    The torque constant, together with the back-EMF constant, was originally used in permanent-magnet DC commutator (PMDC) motors to couple electric circuit equations with mechanical equations. It is still an open question how these two constants should be defined in brushless DC (BLDC) motors and permanent-magnet (PM) AC motors. We present an in-depth study of these two constants, and conclude that the definition based on the dq axes is applicable for the dynamic motion control of not only PM AC motors, but also BLDC motors. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Attenuation of Harmonic Rotor Vibration in a Cage Rotor Induction Machine by a Self-Bearing Force Actuator

    Page(s): 5388 - 5398
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1575 KB) |  | HTML iconHTML  

    In this paper, attenuation of flexural rotor vibration in electrical machines is considered. In order to generate force on the machine rotor, an electromagnetic actuator based on self-bearing machine working principle is examined. A control method for attenuating harmonic rotor vibration components is applied in a 30 kW two-pole cage induction machine. The machine is equipped with a four-pole supplementary winding for generation of lateral force on the rotor. Experimental results for the two-pole induction motor are presented. The main contribution of this paper is to apply a control method, specially designed for compensating harmonic excitations, by using a built-in electromagnetic actuator in an induction machine. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Modeling of the Starting Performance of Large Solid-Pole Synchronous Motors Using Equivalent Circuit Approach

    Page(s): 5399 - 5404
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (813 KB) |  | HTML iconHTML  

    We present a method of modeling the starting performance of large solid pole synchronous motors based on an equivalent circuit approach. In this approach, the solid rotor body is assumed to have two sets of separate virtual windings. Therefore, the two-axis theory can be used for the solid pole synchronous motor. We derived parameters associated with the solid-pole, together with their transformation coefficients. We simulated the starting performance and validated the results by testing a 15 000 hp, 13.2 kV, four-pole solid-pole synchronous motor. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Design, Prototyping, and Analysis of a Novel Tubular Permanent-Magnet Linear Machine

    Page(s): 5405 - 5413
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (992 KB) |  | HTML iconHTML  

    In this paper, we present a new tubular permanent-magnet linear machine with square-shaped cross section and derive its corresponding analytical model by solving Maxwell equations and applying the superposition theorem. The analytical field solution is necessary for obtaining an analytic form of the machine parameters and variables such as the self- and mutual inductances of the windings, the thrust force, and the windings electromotive force (EMF). These provide a valuable tool for tubular machine analysis, design, and optimization. In order to achieve maximum force density, we optimized the design parameters of the proposed machine using the analytical model. We used finite-element analysis and experimental results to demonstrate the validity of the developed analytical model. Again using the Fourier series of the cogging force and its harmonic analysis, in this paper, we introduce two techniques for cogging force reduction in the new tubular linear permanent-magnet machine. The first technique reduces the cogging force due to interaction between the permanent magnets and the stator teeth, and the other reduces the cogging force due to finite length of the armature. These techniques are straightforward, and their implementations in the tubular linear permanent magnet machine with square cross section are easy. We investigated the effectiveness of the proposed techniques in cogging force reduction by 3-D finite-element analysis and experimental measurements. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

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.

Full Aims & Scope

Meet Our Editors

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