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Magnetics, IEEE Transactions on

Issue 3 • Date March 2006

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Displaying Results 1 - 25 of 28
  • [Front cover]

    Page(s): c1
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  • IEEE Transactions on Magnetics publication information

    Page(s): c2
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  • Table of contents

    Page(s): 353 - 354
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  • IEEE Magnetics Society Distinguished Lecturers for 2006

    Page(s): 355 - 357
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  • Effects of thickness and heat treatments on giant magnetoimpedance of electrodeposited cobalt on silver wires

    Page(s): 358 - 362
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    We studied the effects of thickness and heat treatments on giant magnetoimpedance (GMI) of cobalt-coated silver wires from 1 kHz to 100 MHz, under axial static magnetic field of 2 kOe. Cobalt, of thickness ranging from 1 to 25 μm, was electro-deposited on 47.7-μm-diameter silver wires. The frequency dependence of GMI varied with cobalt thickness with a maximum of 176% in 10-μm-thick cobalt at the characteristic frequency 2 MHz. The characteristic frequency decreased with increasing thickness of cobalt layer but it was rather insensitive to dc Joule heating and conventional furnace annealing. However, both heat treatments led to magnetic hardening and decrease in GMI ratio. Joule heating also induced anisotropy in wire structures normally dominated by axial anisotropy. View full abstract»

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  • Electromagnetic and absorption properties of carbonyl iron/rubber radar absorbing materials

    Page(s): 363 - 368
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    We measured the effective complex magnetic permeability μeff* and dielectric permittivity εeff* spectra in rubber radar absorbing material (RAM) with various carbonyl iron volume fractions by using the transmission/reflection method with a vector network analyzer. We studied the effects of carbonyl iron content and rubber thickness on the microwave absorption properties in the frequency range of 2.6 to 18 GHz. Our mathematical analysis is based on electromagnetic theory. The results indicate that the effective complex magnetic permeability and dielectric permittivity values of the RAM increase as the carbonyl iron volume fraction increases. For sample thickness of 3.0 mm, an increase in carbonyl iron content reduces the minimum reflection loss from -1.3 to -23.9 dB and shifts the frequency of the minimum reflection loss from 15.5 to 3.5 GHz. For an equal volume fraction of carbonyl iron, the frequency of the minimum reflection loss decreases as the thickness is increased. However, the dip in the reflection loss plot (in decibels) initially decreases to a minimum value before it increases with a further increase in thickness. We determined the value of the reflection loss for the samples by the impedance matching degree (reflection coefficient), which depends on the thickness and composition of the RAM. View full abstract»

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  • Inclusion of temperature effects in a model of magnetoelasticity

    Page(s): 369 - 377
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    In this paper, we report on temperature effects associated with elastic electromagnetic forming by pulsed electromagnetic fields in inhomogeneous, linear, and lossy media. In a previous paper, we discussed the electromagnetic forces associated with these pulsed electromagnetic fields. Here, we calculate the temperature rise from the equation of heat flow in an isolated object to be deformed. The temperature rise is included in the elastodynamic problem to be solved for the presence of electromagnetic forces, and as a consequence the thermoelastic field can be obtained. As an example, we calculate the thermoelastic field in a hollow cylindrical object. View full abstract»

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  • Thermomagnetic fluctuations and hysteresis loops of magnetic cantilevers for magnetic resonance force microscopy

    Page(s): 378 - 381
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    We have used frequency-shift cantilever magnetometry to study individual nickel magnets patterned at the end of ultra-sensitive silicon cantilevers for use in magnetic resonance force microscopy (MRFM). We present a procedure for inferring a magnet's full hysteresis curve from the response of cantilever resonance frequency versus magnetic field. Hysteresis loops and small-angle fluctuations were determined at 4.2 K with an applied magnetic field up to 6 T for magnets covering a range of dimensions and aspect ratios. Compared to magnetic materials with higher anisotropy, we find that nickel is preferable for MRFM experiments on nuclear spins at high magnetic fields. View full abstract»

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  • Effect of oblique light incidence on magnetooptical properties of one-dimensional photonic crystals

    Page(s): 382 - 388
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    We have investigated the magnetooptical properties of one-dimensional magnetic photonic crystals for the case of oblique light incidence. We developed a theoretical model based on the transfer matrix approach. We found several new effects such as transmittance resonance peak shift versus external magnetic field and the Faraday effect dependence on the incidence angle. We discuss several possible one-dimensional magnetic photonic crystals applications for the optical devices. View full abstract»

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  • Computational aspects of high-speed flows with applied magnetic field

    Page(s): 389 - 397
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB) |  | HTML iconHTML  

    High-speed flows over the surface of hypersonic airfoil subjected to several types of applied magnetic field distributions are numerically simulated. The governing equations are composed of the Euler equation modified to include the effect of magnetic field. In the current applications, the low magnetic Reynolds number approximation is utilized and the Hall effect and ion slip have been neglected. A fourth-order modified Runge-Kutta scheme augmented with the Davis-Yee symmetric Total Variation Diminishing model in post-processing stage is used to solve the magnetogasdynamics equations. The flow simulations are compared to the existing solutions. A good agreement between the present analysis and the available normal shock data is demonstrated. It has been found that the location and distribution of the imposed magnetic field have dominant effects on the flow parameters and the shock standoff distance. View full abstract»

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  • Introducing dynamic behavior of magnetic materials into a model of a switched reluctance motor drive

    Page(s): 398 - 404
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    Dynamic hysteretic effects of magnetic materials are usually neglected in actuators modeling. In order to take into account these effects, we coupled a two-dimensional finite-element (FE) model in an original way with a magnetic equivalent circuit by using dynamic hysteretic flux tubes (DHFT). As an example of an application, we present the model of an ultrafast switched reluctance motor, in which the control of the power converter is of major importance, and where iron losses can reach critical values. View full abstract»

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  • Eddy-current coupling with slotted conductor disk

    Page(s): 405 - 410
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    Eddy-current couplings are becoming popular devices for speed and torque control. Efficiency of these couplings depends on the excitation level; therefore, the routes and density of induced currents affect it significantly. This paper focuses on the design of a squirrel cage-type coupling disk, which forces eddy currents to flow perpendicular to both magnetic field lines and the axis of rotation. Lorentz force and transmitted torque are consequently optimized. The investigation is performed both numerically and experimentally, with results being presented for variable air gaps and speeds. A comparison between plain and slotted disk conductors, tested under identical set-ups, demonstrates the effect of the proposed design on torque throughput and efficiency. In addition to this, the influence of number and size of slots and the effect of filling slots with iron are studied by parametric finite-element modeling verified by experiments. View full abstract»

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  • Design and modeling of shaped-field magnetoquasistatic sensors

    Page(s): 411 - 421
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    The depth of penetration of periodic-field magnetoquasistatic sensors depends on two factors: the skin depth into the material under test and the spatial wavelength of the imposed periodic magnetic field. In applications where high depth of penetration is desirable, the second factor may result in the need for sensors with impractically large dimensions. We describe a way to overcome this problem by generating a field whose effective spatial wavelength is on the order of the sensor length. The magnetic field is shaped by a distributed primary winding that consists of multiple winding segments, with the total current amplitude in each segment following a sinusoidal envelope function. The effective spatial wavelength of the imposed magnetic field may be changed dynamically by changing the excitation current pattern in the primary windings. From a modeling perspective, an advantage of this kind of magnetic field excitation is that the drive current distribution is known from the beginning, since the width of the individual windings is small compared to the wavelength and may be approximated as being infinitely narrow. This greatly simplifies numerical computation, since it makes it possible to apply fast discrete Fourier transform methods directly. We discuss first sensors with Cartesian geometry. We then discuss cylindrical geometry sensors whose models use fast Hankel transforms. View full abstract»

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  • Elastic waves and solid armature contact pressure in electromagnetic launchers

    Page(s): 422 - 429
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    Electromagnetic launchers suffer a phenomenon referred to as armature transitioning: when the armature and rails suddenly lose contact with each other, damage can occur to the armature and the rails of the launcher. In this paper, we explore transient elastic waves as a possible explanation for the transitioning of solid armatures in electromagnetic launchers. We use a finite-element code to model the transient dynamics of a typical electromagnetic launcher guide rail. We found that dynamic rail deflections caused by the movement of the armature are similar in magnitude to those caused by the magnetic field, and that the contact pressure between the armature and the rails changes dramatically when the speed of the armature reaches the critical velocity of the rails. View full abstract»

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  • Computation of force density inside the channel of an electromagnetic pump by Hermite projection

    Page(s): 430 - 433
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    This paper presents a coupled model of linear induction pump for liquid metal. The model computes the magnetic field in the motionless domains by a finite-element method and calculates the field inside the moving parts by Fourier transform and spectral projection on a Hermite basis. The paper focuses on the analysis of the force density according to the current supply and speed variations. View full abstract»

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  • Investigation of very fast transient overvoltage distribution in taper winding of tesla transformer

    Page(s): 434 - 441
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    In order to study the very fast transient overvoltage (VFTO) distribution in the taper winding of a tesla transformer under high-frequency steep-fronted voltage surge, we built a distributed line model based on multiconductor transmission line (MTL) theory. We used a new hybrid algorithm combining finite-element-method (FEM) and interpolation formulas to quickly evaluate the induction coefficient matrix K by utilizing some characteristics of the taper structure. The turn-to-ground and interturn voltage distributions can be obtained by solving the telegraphist's equations in the frequency domain. We measured the voltage distribution inside the taper winding to find some ways to weaken the voltage oscillations. Here, we compare the results with numerical values. View full abstract»

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  • Effect of magnet segmentation on the cogging torque in surface-mounted permanent-magnet motors

    Page(s): 442 - 445
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    We present a method that minimizes the cogging torque in rotor surface mounted permanent-magnet motors. The key idea is to set the distribution of the air-gap flux density by segmenting the magnet pole into several elementary magnet blocks. By choosing either the appropriate elementary magnet block span or the relative position of the magnet blocks, the cogging torque may be significantly reduced. Our analytical approach uses Fourier series to predict the cogging torque harmonics, and finite-element computations. Our numerical results confirm the analytical conclusions. View full abstract»

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  • Multiobjective design optimization of air-core linear permanent-magnet synchronous motors for improved thrust and low magnet consumption

    Page(s): 446 - 452
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    Although air-core linear permanent-magnet (PM) synchronous motors are widely used in precision applications because of their advantages such as fast dynamics, lack of detent force, and negligible iron loss, they basically suffer from low developed thrust, thrust ripple, and excessive use of permanent-magnet materials, all of which lead to undesirable performance and high production cost. In this paper, we analyze performance characteristics of an air-core linear PM synchronous motor by varying motor design parameters in a layer model and a d-q model of the machine. We propose a multiobjective design optimization to improve thrust, thrust ripple, and consumed magnet volume independently and simultaneously by defining a flexible objective function. A genetic algorithm is employed to search for optimal designs. The results confirm that desirable thrust mean and substantial reduction in magnet volume and thrust ripple can be achieved. We draw several design conclusions from the motor analysis and design optimization. Finally, we carry out a time-stepping finite-element analysis to evaluate the effectiveness of the machine models and the optimization method. View full abstract»

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  • Stator design consideration of a brushless DC motor for robust rotor position detection in inductive sense start-up

    Page(s): 453 - 459
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    This paper presents a method to improve three-phase brushless DC (BLDC) motor design for easier application of inductive sense start-up algorithms. Using the experimental results of motor start-up, a failure analysis of the successful and unsuccessful motors identifies the root cause of failure. The unsuccessful motors had smaller inductance difference when energized by a positive test current than when energized by a negative test current. Finite-element method (FEM) analysis then is used to examine the effect of the stator geometry on the sensitivity of the inductance to the permanent magnet polarity. A modified stator design is obtained through FEM study. The performance improvement is verified by current rise simulation. View full abstract»

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  • Novel high-response electromagnetic actuator for electronic engraving system

    Page(s): 460 - 464
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB) |  | HTML iconHTML  

    We describe a new moving-iron electromagnetic actuator that utilizes cantilever-beam-type springs, π type armature, full-bridge magnetic circuits, and a single driving coil. The actuator is suitable for electromechanical converters with high response and minor displacement for use in electronic engraving systems. We analyzed its static and dynamic characteristics by using a three-dimensional finite-element method. We used a simple and practical measuring method based on light reflection to detect the actuator's real hysteresis loop and amplitude frequency response characteristics. The results show that the actuator has a displacement of ±65 μm, hysteresis of less than 5.5%, and amplitude cutoff frequency of 3.1 kHz. We tested the actuator on a real engraving system and confirmed its characteristics by the engraving results. View full abstract»

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  • Playback performance of ultrahigh-capacity tape media with nanosized composite advanced particle (NanoCAP)

    Page(s): 465 - 467
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    We have developed nanosized composite advanced particles (NanoCAP) with spherical shape and high coercivity, and fabricated dual coated tape to evaluate playback performance. The spherical shape contributes to smooth surfaces and reduced boundary variation between the magnetic layer and underlayer. The fine particle size, 17 nm, yields low media noise and high signal-to-noise ratio. The high coercivity, compared to metal particulate media, contributes to high amplitude resolution (D50=170 kfci). We confirmed that write demagnetization is well restrained and that NanoCAP tape should show very good playback performance with a superior writer. View full abstract»

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  • A novel damping scheduling scheme for proximate time optimal servomechanisms in hard disk drives

    Page(s): 468 - 472
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    The proximate time-optimal servomechanism (PTOS) is widely used in hard disk drives because of its simplicity and good performance. There have been many studies to improve PTOSs, though they are complex or need a time-consuming tuning process. Here, we propose a novel damping scheduling PTOS (DSPTOS) for hard disk drives. The proposed algorithm keeps the closed-loop damping coefficient at a predetermined value. Compared to the original PTOS, smaller damping in deceleration will boost the rising speed, and larger damping in the settling phase reduces the overshoot and residual vibrations. Moreover, the DSPTOS maintains the simplicity of the PTOS by introducing just a predetermined damping coefficient. We applied the proposed DSPTOS algorithm to a voice coil motor in a hard disk drive. Through simulations and real-time experiments, we verified the effectiveness of the DSPTOS. In particular, with respect to long stroke seeks, the DSPTOS performs better than the PTOS. View full abstract»

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  • Writer pole tip remanence in perpendicular recording

    Page(s): 473 - 480
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    We studied the remanent field from perpendicular writer pole tips by micromagnetic modeling. The pole tip remanence has two causes: 1) the residual flux from the yoke due to undesirable material properties and/or yoke design and 2) the geometry of the pole tip. An optimal yoke design for low remanence includes a wide and short yoke with relatively shallow yoke flare angle around 30° that favors transverse major domains. Horizontal anisotropy in the yoke and the pole tip also helps suppress the vertical magnetization, mainly in the yoke, which yields less residual flux into the pole tip, hence lower remanence. The remanent field is also a strong function of the throat height, i.e., the pole tip length, due to the shape anisotropy effect. Micromagnetic modeling shows that multilayer lamination, both in the yoke and in the pole tip, is an effective way to achieve low remanence. It also eliminates the sensitivity of remanence to the throat height. To improve the robustness of the remanence against the stray field, an antiferromagnetic coupling (AFC) between the lamination layers may also be necessary. Our results apply to both single pole heads and shielded pole heads. View full abstract»

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  • Comments on "Improving accuracy of intrinsic coercivity measurement for magnetically soft materials"

    Page(s): 481
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    The authors of the paper by Hilton et al. (see ibid., vol. 41. no. 8, P.2322-7, Aug. 2005) conclude among other things that "the commercial imperative is to obtain accurate coercivity results. How slow does the magnetizing field decay have to be in order to achieve this? There is no universal answer; it depends on the material and on the dimensions. For routine coercivity measurement of soft iron bars, a 60-s linear ramp time is advised. This protocol allows accurate coercivity measurement within an acceptable amount of laboratory time." The present author would like to mention that years ago a number of experiments were carried out indicating that coercivity of magnetically soft materials depends strongly on the rate of rise of the driving field. In the case of a linear ramp driving held, the coercivity, depends linearly on the square root of this rate of rise, k/sub i/. It was shown experimentally that the above dependence holds also for soft ferrites and Permalloy cores as well as for magnetic thin films. View full abstract»

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  • Reply to comments on "Improving accuracy of intrinsic coercivity measurement for magnetically soft materials"

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    For original article by G. Hilton et al. see ibid., vol.41, no.8, p.2322-7, Aug. 2005. For comments by H.K. Lachowicz see ibid., vol.42, no.3, p.481, March 2006. 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