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Magnetics, IEEE Transactions on

Issue 1  Part 2 • Date Jan 2002

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Displaying Results 1 - 17 of 17
  • Turbo-coded optical recording channels with DVD minimum mark size

    Publication Year: 2002 , Page(s): 298 - 302
    Cited by:  Papers (3)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (259 KB) |  | HTML iconHTML  

    Recent work on turbo codes applied to partial response (PR) optical recording channels has focused on unconstrained channels. In this paper, we consider the application of turbo codes to a (1,7) constrained, PR-equalized optical recording channel with digital versatile disc (DVD) parameters. The addition of a (1,7) run-length-limited (RLL) constraint requires the use of a soft RLL decoder to communicate with the turbo code. Although soft RLL decoders were previously developed for use with iterative decoding, application to a practical optical channel has not been addressed until now. Here, results on both correlated noise and media noise optical recording channel models are given for two PR targets, 1+D and 1+D+D2+D 3. We achieved coding gains of 4 to 6.3 dB over a baseline RLL-coded system. We also evaluated system performance at smaller mark sizes, and found that density gains of 17% and 22% are achievable for the two targets, respectively View full abstract»

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  • Improved method of calculating the Fourier coefficients of a magnetic pole head

    Publication Year: 2002
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (166 KB) |  | HTML iconHTML  

    An improved method of calculating the Fourier coefficients for a single unshielded magnetic pole head is presented. The method is based on the knowledge of the exact Fourier coefficients for a magnetic ring head View full abstract»

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  • Pulse shape, resolution, and signal-to-noise ratio in perpendicular recording

    Publication Year: 2002 , Page(s): 288 - 294
    Cited by:  Papers (27)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB) |  | HTML iconHTML  

    The paper theoretically examines playback characteristics of a giant magnetoresistive (GMR) head for perpendicular recorded magnetization transitions with a soft underlayer. The magnetic scalar potential, calculated numerically by the finite-element method, is fitted to a simple formula involving geometry-dependent parameters. The reciprocity principle leads to the shape of the single pulse signal. For high permeability of the underlayer the pulse has an error function-type dependence on distance. Within this approximation, the paper derives simple formulas for the pulsewidth T50, D50, and transition-noise-limited signal-to-noise ratio View full abstract»

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  • Improved analytical model for predicting the magnetic field distribution in brushless permanent-magnet machines

    Publication Year: 2002 , Page(s): 229 - 238
    Cited by:  Papers (141)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (407 KB) |  | HTML iconHTML  

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

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  • Robust adaptive numerical compensation for friction and force ripple in permanent-magnet linear motors

    Publication Year: 2002 , Page(s): 221 - 228
    Cited by:  Papers (86)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (446 KB) |  | HTML iconHTML  

    This paper describes a robust adaptive compensation method for friction and force ripple present in the dynamics of permanent-magnet linear motors. The method is used in ultraprecise positioning applications. The compensation algorithm consists of a PID component and an adaptive component for estimating friction and force ripple. The adaptive component is continuously refined on the basis of just prevailing input and output signals. Computer simulations and real-time experimental results verify the effectiveness of the proposed scheme for high-precision motion trajectory tracking View full abstract»

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  • Generalized formulation for the description of hysteresis in soft magnetic materials

    Publication Year: 2002 , Page(s): 200 - 204
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (250 KB) |  | HTML iconHTML  

    Presents a phenomenological formulation that broadens the range of applicability of the Basso-Bertotti hysteresis model to include soft magnetic materials with very gradual saturation, such as commercial manganese-zinc (MnZn) power ferrites. The formulation also enables the Basso-Bertotti model to better characterize both the major loop and the minor loops of these soft magnetic materials. The formulation introduces a model parameter mt that defines the transition between low fleld/minor loops and high field/major loop. An explicit expression for magnetization in term of domain-wall position was synthesized to make the hysteresis model numerically attractive. The formulation was verified by experimental data of commercial MnZn ferrites View full abstract»

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  • Galerkin's method and the variational procedure

    Publication Year: 2002 , Page(s): 190 - 199
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB) |  | HTML iconHTML  

    Galerkin's method and the variational procedure, when applied to most practical problems in electromagnetics, lead to matrix equations of the same form. Variational procedures for self-adjoint and nonself-adjoint operators also result in the same form of matrix equations for a large subclass of problems. However, the three cases may yield different matrix equations in general. This paper examines the subclass of problems for which these methods result in the same matrix equation and provides systematic ways for classification of problems for which two or all three of the cases lead to the same matrix equation. It also describes properties of the coefficient matrix in the matrix equation View full abstract»

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  • Axially laminated reluctance motor: analytical and finite-element methods for magnetic analysis

    Publication Year: 2002 , Page(s): 239 - 245
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (369 KB) |  | HTML iconHTML  

    This paper describes two methods - one numerical, the other analytical for analyzing an axially laminated reluctance (ALAREL) motor. The numerical method, finite-element analysis (FEA), is generally used for estimation of the motor magnetic loading and capability for given stator currents. The accuracy of the FEA prediction is confirmed by a comparison between computed and measured magnetic quantities. The analytical model allows a rapid evaluation of the flux density in different parts of the motor, as well as of the capability for given stator current. It uses a distributed parameter network. The paper compares the results obtained from this network with those obtained from FEA. The methods agree well. Finally, the paper uses the two methods to investigate the effect of the quality of the magnetic material as well as the effect on motor performance of a nonuniform distribution of the laminations in the rotor. It shows that, with grain-oriented steel and nonuniformly distributed laminations, a higher flux linkage can be obtained. Consequently, lower current is required to develop the same motor torque View full abstract»

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  • Extending the bandwidth of magnetic tunnel junction sensors by a buffer amplifier

    Publication Year: 2002 , Page(s): 295 - 297
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (217 KB) |  | HTML iconHTML  

    A simple buffer amplifier, consisting of a transistor in an emitter-follower configuration, is proposed to extend the bandwidth of magnetic tunnel junction read sensors. To maximize the bandwidth improvement, the buffer should be used on the slider or on the suspension as near to the slider as possible. The channel front-end (sensor, buffer, interconnect, and preamp) bandwidth is still somewhat limited by the RC product of the sensor resistance and shunt capacitance. However, the buffer can reduce the shunt capacitance to subpicofarad levels, allowing for bandwidths near 1 GHz. Merging the buffer with an interconnect and preamp gives a low-frequency signal-to-noise ratio (SNR) reduction at the preamp input of 0.1 dB and an SNR improvement of 5 to 10 dB over a no-buffer configuration for frequencies between 100 MHz and 1 GHz View full abstract»

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  • Magnetic-field-assisted giant penetration of a radio-frequency electromagnetic field in lanthanum manganites

    Publication Year: 2002 , Page(s): 257 - 259
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (195 KB) |  | HTML iconHTML  

    The penetration of an electromagnetic field in the frequency range of 20 kHz to 30 MHz through the plates of bulk polyerystalline sintered La0.60Pb0.4MnO3 and La0.70Y 0.07Ba0.23MnO3 manganites was studied. A giant increase, up to 10 times, of the transmission coefficient, on application of the magnetic field, was found. Skin depth variations were caused mainly by variation of the dynamical reversible magnetic permeability. The contribution of the magnetic permeability dispersion to the frequency dependence of skin depth was clarified View full abstract»

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  • Evaluation of inductance for various distributions of windings on straight ferromagnetic cores: an unusual approach

    Publication Year: 2002 , Page(s): 246 - 249
    Cited by:  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (235 KB) |  | HTML iconHTML  

    The detailed electromagnetic duality that relates small magnetic structures and small electric structures at ultralow and extremely low frequencies has recently been treated. The strict duality relationship holds provided that the structures possess similar geometry. For example, a short electric dipole antenna gapped in the middle is strongly related to the magnetic structure consisting of a short coil mounted in the middle of a rod of highly permeable material. In particular, the inductance of the latter magnetic structure can be derived directly from the capacitance between the electric dipole arms. The relationship has been thought to hold only for situations where the coil in the center of the core is very short. Here, however, we show that inductance can be evaluated even in cases where the windings are distributed beyond the center and cover relatively long portions of the ferromagnetic core. The extension of the theory described here relies on the fact that the distribution of the flux along the core is triangular-a fact derived from the similarity of the magnetic structure to a short electric dipole antenna, in which the current has a triangular profile. The triangular distribution provides a basis for evaluating the inductance of extended coils by relying on integration of the flux profile through the windings along the core. The results of the evaluation are in good agreement with laboratory measurements. The evaluation method, despite its simplicity, is based on analytical approach, unlike the many empirical methods of inductance evaluation described in the literature View full abstract»

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  • Global linearization and microsynthesis for high-speed grinding spindle with active magnetic bearings

    Publication Year: 2002 , Page(s): 250 - 256
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (335 KB) |  | HTML iconHTML  

    Because of the nonlinear relationship between force and current/displacement, the performance of active magnetic bearing (AMB) systems based on local linearization varies greatly as the operating point of the spindle changes. However, consistent stiffness and displacement tracking performance are demanded for a grinding spindle with AMBs, especially when noncircular workpieces need grinding. Here, we analyze the influence of changing operating point on performance theoretically and present experimental confirmation of the analysis. Three linear compensation methods-minimum flux (MIF), constant flux sum (CFS), and constant flux product (CFP)-are explained and compared in terms of power loss and dynamic performance. In order to design stiffness easily and to guarantee system performance in the presence of model uncertainties and disturbance force, we adopted a microsynthesis controller. We performed some experiments to compare the dynamic performance of the three linear compensation methods. The results show that CFS and CFP have better dynamic performance than MIF. An AMB system based on global linearization yielded almost the same stiffness and displacement tracking performance, despite the change of operating point View full abstract»

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  • Modeling the surface condition of ferromagnetic metal by the swept-frequency eddy current method

    Publication Year: 2002 , Page(s): 205 - 210
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (283 KB) |  | HTML iconHTML  

    Many ferromagnetic metals have, either by design or by happenstance, a very thin surface layer of reduced magnetic permeability. Such a layer might occur intrinsically or it might be induced by surface treatments such as case hardening, shot peening, or surface alloying. We studied the frequency-dependent impedance of a small air-cored coil of wire placed flat upon ferromagnetic metal plates. The impedance changes for nickel and iron could not be fitted to the half-space model for any values of conductivity and permeability. It is likely that the permeability varies continuously with depth in the near-surface region. Hence, it is possible that a multiple-layer model would yield a better representation of the data with a layer depth closer to that observed. In this paper, we illustrate that the multiple-layer model improves the agreement between the measured data and the approximate analytic solution. The results show that the permeability of pure nickel and pure iron decay exponentially from the base to surface View full abstract»

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  • Calculation of the switching constant of magnetic recording media

    Publication Year: 2002 , Page(s): 271 - 278
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    We studied the dynamic switching time in two classes of media by considering two different particle orientation distribution functions. We calculated the switching constant directly from the Landau-Lifshitz-Gilbert equation of motion, which was chosen to simulate the dynamic properties of the media. A strong linear relation between the reciprocal of the switching time and the difference between the applied and anisotropy fields is illustrated. In media for which experimental results are available, the values we obtained here agree within a factor of 2 View full abstract»

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  • Linear density dependence of thermal decay in longitudinal recording

    Publication Year: 2002 , Page(s): 260 - 270
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB) |  | HTML iconHTML  

    We present experimental and theoretical data on the signal decay of recordings measured at various densities. In contrast to expectations, the signal decay does not generally increase with increasing linear density; rather, it peaks at a surprisingly low density. Using a nondestructive spin-stand technique, we determined the energy barrier as well as the anisotropy field distribution. These experimental data are used in a self-consistent recording model that accounts for thermal activation effects at writing as well as at storage. We found that the record process inevitably induces phase shifts in the recorded pattern that lead to the observed decay behavior View full abstract»

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  • Autocorrelation analysis of particle magnetization in erased particulate media

    Publication Year: 2002 , Page(s): 279 - 287
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (371 KB) |  | HTML iconHTML  

    General analytical expressions for the magnetization power spectral densities of particulate media are derived by using the three-dimensional autocorrelation function. Expressions include the effects of AC demagnetized media and any DC components resulting from the presence of particle chains. The replay flux power spectral density is then obtained, assuming a linear replay transducer View full abstract»

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  • Magnetic and eddy current effects in an open-loop pulsed hysteresis graph system for magnetization of rare-earth magnets

    Publication Year: 2002 , Page(s): 211 - 220
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB) |  | HTML iconHTML  

    Describes an open-loop pulsed hysteresis graph system that is capable of magnetizing ceramic and rare-earth permanent magnets such as neodymium, samarium cobalt, and Alnico in cylindrical and rectangular shapes. The prototype system relies on an air-core excitation coil with an inner diameter of 3 cm and a length of 10 cm. A pulsed power supply provides a transient current pulse of up to 9000 A into the air-core coil. The pulse duration is typically about 15-20 ms. In addition, a pair of Helmholtz coils records the applied magnetic field strength, whereas a local coil, tightly wound around the permanent magnet, records the magnetic flux density in the sample. Both fields are electronically acquired, digitized, and processed in a computer to obtain the hysteresis graph response of the sample. The processing allows compensation for the presence of the demagnetization field due to the open-loop system configuration. We present an analytical approach to take into account the effect of permeability in cylindrical samples. We propose a numerical approach that can characterize conductive materials such as Alnico, whose eddy-current influence significantly affects the open-loop recording of the B-H curve 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