Showing papers in "IEEE Transactions on Magnetics in 2005"

Analysis of electromagnetic performance of flux-switching permanent-magnet Machines by nonlinear adaptive lumped parameter magnetic circuit model

Abstract: A nonlinear adaptive lumped parameter magnetic circuit model is developed to predict the electromagnetic performance of a flux-switching permanent-magnet machine. It enables the air-gap field distribution, the back-electromotive force (back-EMF) waveform, the winding inductances, and the electromagnetic torque to be calculated. Results from the model are compared with finite-element predictions and validated experimentally. The influence of end effects is also investigated, and optimal design parameters, such as the rotor pole width, the stator tooth width, and the ratio of the inner to outer diameter of the stator, are discussed.

Composite media for perpendicular magnetic recording

Abstract: A composite perpendicular recording media consisting of magnetically hard and soft regions within each grain is proposed. Application of applied field initially causes the magnetization of the soft region to rotate and, thus, change the angle of the effective field applied to the hard region. This important change in the effective field is enabled by an exchange layer that moderates the interaction between the two regions. Energy arguments show that the resulting performance (as measured by the ratio of energy barrier to switching field) is similar to the previously proposed tilted media, while avoiding some of the difficulties. In particular, fabrication of the proposed composite media appears to be significantly easier than that of tilted media.

A 4-Mb toggle MRAM based on a novel bit and switching method

Abstract: A 4-Mb magnetoresistive random access memory (MRAM) with a novel magnetic bit cell and toggle switching mode is presented. The circuit was designed in a five level metal, 0.18-mum complementary metal-oxide-semiconductor process with a bit cell size of 1.55 mum2. The new bit cell uses a balanced synthetic antiferromagnetic free layer and a phased write pulse sequence to provide robust switching performance with immunity from half-select disturbs. This switching mode greatly improves the operational performance of the MRAM as compared to conventional MRAM. A detailed description of this 4-Mb toggle MRAM is presented

Eddy-current loss in the rotor magnets of permanent-magnet brushless machines having a fractional number of slots per pole

Abstract: We develop an analytical model for predicting the eddy-current loss in the rotor magnets of permanent-magnet brushless machines that have a fractional number of slots per pole, when either all the teeth or only alternate teeth are wound, and in which the unwound teeth may be narrower than the wound teeth The model enables the magnetic field distribution in the air gap and magnet regions to be determined, by neglecting the eddy-current redistribution effect and assuming that the eddy currents are resistance limited It can account for space-harmonic magnetomotive forces (MMFs) resulting from the winding distribution and time-harmonic MMFs due to nonsinusoidal phase currents, as well as for the effect of curvature and circumferential segmentation of the magnets We have validated the model by finite-element analysis, and used it to investigate the eddy-current loss in the magnets of three surface-mounted magnet brushless motors that have similar slot and pole numbers, and employ identical rotors but different stators, when they are operated in brushless ac (BLAC) and dc (BLDC) modes We show that the stator winding configuration, as well as the operational mode, significantly influence the resultant eddy-current loss

Exchange coupled composite media for perpendicular magnetic recording

Abstract: A novel exchange coupled composite (ECC) media was demonstrated and investigated systematically in this work. The writing capability and thermal stability were proved to be engineered separately based on this new media. Proper exchange coupling between [Co-PdSiO]/sub n/ hard layer and FeSiO soft layer was implemented through a PdSi interlayer. Transmission electron microscope plan-view and cross section view observations, macromagnetic, and micromagnetic testing proved vertically grown magnetic grains with soft and hard regions for ECC media. The switching of the soft region of magnetic grains with the external field rotated the magnetization of the hard region of magnetic grains to about 45/spl deg/ with perpendicular direction, which resulted in a similar behavior as a dynamic tilted media. A much lower angle dispersion of the remanent coercivity for the ECC media was found, which is another advantage for such media. ECC media showed better recording performance compared to perpendicular media. Strong exchange coupling between the hard and soft regions of magnetic grains (exchange spring media) was discussed based on the above proposed layer structure too.

Optimal design of a coreless stator axial flux permanent-magnet generator

Abstract: This paper describes a hybrid method for calculating the performance of a coreless stator axial flux permanent-magnet (AFPM) generator. The method uses a combination of finite-element analysis and theoretical analysis. The method is then incorporated into a multidimensional optimization procedure to optimally design a large power coreless stator AFPM generator. The measured performance of the manufactured prototype compares favorably with the predicted results. The design approach can be applied successfully to optimize the design of the coreless stator AFPM machine.

Exchange coupled composite media for perpendicular magnetic recording

Abstract: Exchange coupled composite (ECC) media has been shown to possess several major advantages relative to conventional perpendicular media, including a reduction in the switching field of approximately a factor two for the same thermal stability and greater insensitivity to easy axis distribution. In this paper, full magnetostatic interactions are included: this allows comparison between the behavior of multigrain thin films and that of isolated grains as presented earlier. Significant results include hysteresis loops for thin films under various conditions including inadequate and excessive intra granular exchange between the hard and soft materials. An important distinction is made between the coercivity and remnant coercivity as a function of angle between applied field and easy axis. A perpendicular magnetic recording head is used to compare the shape of effective fields for ECC and conventional perpendicular media. Written transitions in the ECC media appear to be similar to those written in perpendicular media at comparable densities.

Tubular modular permanent-magnet machines equipped with quasi-Halbach magnetized magnets-part I: magnetic field distribution, EMF, and thrust force

Abstract: This paper describes the analysis, design, and experimental characterization of three-phase tubular modular permanent-magnet machines equipped with quasi-Halbach magnetized magnets. It identifies feasible slot/pole number combinations and discusses their relative merits. It establishes an analytical expression for the open-circuit magnetic field distribution, formulated in the cylindrical coordinate system. The expression has been verified by finite-element analysis. The analytical solution allows the prediction of the thrust force and electromotive force in closed forms, and provides an effective tool for design optimization, as will be described in Part II of the paper.

Approximate theory of microwave generation in a current-driven magnetic nanocontact magnetized in an arbitrary direction

Abstract: We present an approximate nonlinear theory of microwave generation by spin-polarized direct current in a magnetic nanocontact magnetized in an arbitrary direction. We argue that, when the spin-transfer torque caused by spin-polarized current compensates the natural magnetic dissipation in a "free" layer of the nanocontact, a nonlinear quasi-uniform precession of magnetization about the direction of the internal bias magnetic field is excited. With the increase of the current magnitude the angle of precession increases, making precession strongly nonlinear and reducing the projection M/sub z/ of the precessing magnetization vector on the precession axis (z axis). This reduction of M/sub z/ is responsible for the nonlinear limitation of the precession amplitude and for the nonlinear frequency shifts of the generated microwave oscillations. Because of the influence of demagnetizing fields in the "free" layer, the nonlinear frequency shifts have different magnitudes and signs for different orientations of the external bias field H/sub e/. The theory gives a good qualitative, and even partly quantitative, explanation of the main part of microwave magnetization dynamics experimentally observed in magnetic nanocontacts.

Demagnetizing factors for rectangular prisms

Abstract: For rectangular prisms of dimensions 2a/spl times/2b/spl times/2c with constant material susceptibility /spl chi/, we have calculated and tabulated the fluxmetric and magnetometric demagnetizing factors N/sub f/ and N/sub m/, defined along the 2c dimension as functions of c/(ab)/sup 1/2/(=1/spl sim/500), a/b(=1/spl sim/256), and /spl chi/(=0/spl sim/10/sup 9/). We introduce an interpolation technique for obtaining N/sub f,m/ with arbitrary values of c/(ab)/sup 1/2/, a/b, and /spl chi/.

Flux-linkage calculation in permanent-magnet motors using the frozen permeabilities method

Abstract: Finite-element analysis can be used to determine the magnetization characteristics in terms of curves of flux-linkage against current or rotor position. The "frozen permeabilities" technique is presented as a method of apportioning flux-linkage contributions to the phase currents and permanent magnets, and for inductance calculations. Results from a split-phase interior permanent magnet motor are presented and compared with experimental data. Drawbacks to the method are discussed.

Operational requirements and issues for coilgun electromagnetic launchers

Abstract: Coilgun electromagnetic launchers have capability for low- and high-speed applications. Through the development of four guns having projectiles ranging from 10 g to 5 kg and speeds up to 1 km/s, Sandia National Laboratories has succeeded in coilgun design and operations, validating the computational codes and basis for gun system control. Coilguns developed at Sandia consist of many coils stacked end-to-end forming a barrel, with each coil energized in sequence to create a traveling magnetic wave that accelerates a projectile. Active tracking of the projectile location during launch provides precise feedback to control when the coils are triggered to create this wave. However, optimum performance depends also on selection of coil parameters. This paper discusses issues related to coilgun design and control such as tradeoffs in geometry and circuit parameters to achieve the necessary current risetime to establish the energy in the coils. The impact of switch jitter on gun performance is also assessed for high-speed applications.

Application of voice coil motors in active dynamic vibration absorbers

Abstract: A dynamic vibration absorber reduces the influence of a force whose excitation frequency nearly coincides with the natural frequency of a rotating machine. However, the performance of this type of passive absorber can be affected by changes in the environment. In this paper, we describe a voice coil motor (VCM) that can serve as the actuator in an active dynamic vibration absorber which can be regulated for different conditions. With a VCM, suitable controllers can be designed for periodic excitation force rejection by using the characteristics of the notch filter in combination with the root-locus theorem. We have evaluated the performance of the active vibration absorber by both simulations and experiments.

Basic characteristics of a consequent-pole-type bearingless motor

Abstract: We describe the basic characteristics of a consequent-pole bearingless motor. The consequent-pole-type rotor has buried permanent magnets (PMs) polarized in the same radial direction. We carried out an analysis to find the optimum pole number for the machine to produce stable magnetic suspension. The results indicate that there is decoupling of the radial suspension forces from the drive torque when eight or more poles are used. Here, we compare the torque and suspension force generation with those of a conventional surface-mount PM rotor. The suspension force is several times higher for the consequent-pole rotor; however, the torque decreases by 12%. We built a test machine and confirmed the torque and suspension characteristics. We also compared the test machine with other conventional bearingless motors.

Application of geometric programming to transformer design

Abstract: This paper considers the transformer design optimization problem. In its most general form, the design problem requires minimizing the total mass (or cost) of the core and wire material while ensuring the satisfaction of the transformer ratings and a number of design constraints. The constraints include appropriate limits on efficiency, voltage regulation, temperature rise, no-load current, and winding fill factor. The design optimization seeks a constrained minimum mass (or cost) solution by optimally setting the transformer geometry parameters and the relevant electrical and magnetic quantities. In cases where the core dimensions are fixed, the optimization problem calls for a constrained maximum volt-ampere or minimum loss solution. This paper shows that the above design problems can be formulated in geometric programming (GP) format. The importance of the GP format stems from two main features. First, GP provides an efficient and reliable solution for the design optimization problem with several variables. Second, it guarantees that the obtained solution is the global optimum. The paper includes a demonstration of the application of the GP technique to transformer design. It also includes a comparative study to emphasize the advantage of including the transformer core dimensions as variables in the design problem.

Use of novel adaptive digital feedback for magnetic measurements under controlled magnetizing conditions

Abstract: There are increasing calls to employ conventional magnetic testers, such as the Epstein frame and single sheet tester, for the accurate measurements of magnetic properties of soft magnetic materials under fully controlled nonsinusoidal flux density waveforms. This paper presents a computerized automated adaptive digital feedback system built for that purpose. We present several examples of the ability of the system to control an arbitrary shape of the flux density waveforms over the frequency range of the data acquisition system (0.5 Hz to 2 kHz) and for peak flux density up to 90% of saturation. The control algorithm is capable of magnetizing magnetic material under controlled sinusoidal, triangular, trapezoidal, and pulsewidth-modulated magnetizing conditions as well as other arbitrary waveforms that do not contain dc components. We provide a full description of the adaptive digital feedback technique together with measurements showing the B-H loops for several magnetic materials under various controlled excitation conditions.

Implementation of a 50-kW four-phase switched reluctance motor drive system for hybrid electric vehicle

Abstract: A high-performance fully digital controller has been designed for the drive of a 50-kW four-phase switched reluctance (SR) motor built for a hybrid electric vehicle (HEV). The SR machine is specifically designed and manufactured to have high power density and low acoustic noise. The controller is based on the advanced digital signal processor (DSP) with internal CAN interface-TMS320F2406 and complex programmable logic device (CPLD)-EPM7128S. The experimental results show that the controller is met with the system specification and requirement, satisfactorily.

Magnetooptic sensor for remote evaluation of surfaces

Abstract: A new magnetooptic (MO) detection method utilizing changes in the optical path through a transparent MO thin film has been developed and studied for evaluation of surface deformation created by subsurface or internal defects in materials. Investigation of defects cannot be performed on nonconducting and nonmagnetic materials using conventional electromagnetic techniques such as eddy-current or magnetic flux leakage. The new method utilizes the controlled periodic displacement of a domain wall in the MO thin film and can be used to measure remotely mechanical deformation of a surface of any type of material by measuring the changes of width of the shoulder in the intensity versus time waveform.

Analytical modeling of rotating eddy-current couplers

Abstract: We present a detailed analytical study of rotational eddy-current couplers. We provide a field solution by the variable separation method, and we analyze radial geometry structures. The couplers consist of a permanent-magnet stator and a multilayer conductive rotor. We present different analytical solutions in order to study single- and double-sided permanent-magnet frames. We validate the models by two-dimensional and three-dimensional (3-D) finite-element studies, and we perform an exhaustive parametric analysis to estimate the influence of the dimension parameters of the two structures. Finally, we present an analytical approach to a 3-D correction.

Hysteresis model for finite-element analysis of permanent-magnet demagnetization in a large synchronous motor under a fault condition

Abstract: This paper describes a rare-earth-transition metal alloy permanent-magnet (Nd/sub 2/Fe/sub 14/B) hysteretic behavior model within finite-element analysis. The present work analyzes the demagnetization states of permanent magnets during fault conditions in a permanent-magnet synchronous motor and characterizes the ability of the motor to sustain the designed rated outputs after the fault conditions occur.

Simple resistance calculation in litz-wire planar windings for induction cooking appliances

Abstract: We present a simple method to calculate the winding resistance of a litz-wire inductor in an induction cooking appliance, taking into account eddy-current losses, including conduction losses and proximity-effect losses. The method, which uses numerical calculation of the magnetic field, can be used to determine the optimum number of strands in the litz wire. The effects of the temperature on the winding total resistance are included in the calculation. We have built a prototype to verify the calculation method and its limitations. We consider the accuracy limits of the method.

New procedures for minimizing the torque ripple in switched reluctance motors by optimizing the phase-current profile

Abstract: This paper introduces five new optimization procedures for the minimization of the torque ripple in the switched reluctance motor (SRM). These new procedures are based on the optimization of the phase-current profile. Two optimization techniques, the simplex method and the genetic algorithm, are adapted to these optimization procedures. The paper compares an older optimization procedure, the optimum harmonic current injection procedure, and the new optimization procedure, and presents conclusions.

State-periodic adaptive compensation of cogging and Coulomb friction in permanent-magnet linear motors

Abstract: This paper focuses on the state-periodic adaptive compensation of cogging and Coulomb friction for permanent-magnet linear motors (PMLMs) executing a task repeatedly. The cogging force is considered as a position-dependent disturbance and the Coulomb friction is non-Lipschitz at zero velocity. The key idea of our disturbance compensation method is to use past information for one trajectory period along the state axis to update the current adaptation law. The new method consists of three different steps: 1) in the first repetitive trajectory, an adaptive compensator is designed to guarantee the l/sub 2/-stability of the overall system; 2) from the second repetitive trajectory and onward, a trajectory-periodic adaptive compensator stabilizes the system; and 3) to make use of the stored past state-dependent cogging information, a search process is utilized for adapting the current cogging coefficient. We illustrate the validity of our state-periodic adaptive cogging and friction compensator by actual PMLM-model-based simulation.

A novel switched reluctance motor with C-core stators

Abstract: This paper presents a novel switched reluctance motor (SRM) design in which the stator is simply formed from C-cores. Unlike conventional SRMs, the windings of the new motor can be individually wound into the stator cores without complex winding equipment. Because of the inherent axial field distribution, this type of SRM requires a three-dimensional (3-D) finite-element analysis (FEA) model for detailed flux analysis. This paper proposes an approximated two-dimensional FEA model to speed up computational time. In addition, since the proper current that ensures operation in the saturated region (to maximize torque and efficiency) is often hard to determine systemically, the paper proposes a simple method to determine the optimum operating current so that one can easily decide the rated current and also obtain the maximum motor efficiency. Finally, the paper compares some characteristics of a traditional SRM with those of the proposed SRM. The comparison shows that the proposed SRM performs well in terms of torque and efficiency, and provides a higher degree of flexibility in winding design.

Analysis and characterization of switched reluctance motors: Part II. Flow, thermal, and vibration analyses

Abstract: This paper presents new approaches for certain mechanical characterizations, such as thermal and vibration analyses, of switched reluctance motors (SRMs). The paper presents, in three parts, the modeling and simulation procedure for three-dimensional (3-D) finite-element analysis (FEA)-based flow analysis, flow-analysis-based thermal analysis, and a realistic vibration analysis. Section I documents a computational fluid dynamics (CFD) flow analysis procedure for the evaluation of the air velocity distribution inside the SRM at any speed. Section II presents a prediction method for steady-state and transient thermal characteristics of an SRM, using 3-D FEA. The convection coefficient at various heat-dissipating surfaces inside SRM, which is not a material property, but a quantity that solely depends on the air velocity at the respective surfaces, is the major parameter to be evaluated for an accurate simulation of heat distribution. The results of CFD analysis are used, for the first time on SRM, for this purpose. Windage loss calculation, one of the other applications of CFD, is introduced. Vibration in electric motors is an inevitable, at the same time undesirable, property that originates from four major sources: mechanical, magnetic, applied loads and, to a smaller extent, the associated electronic devices. Section III presents: 1) a thorough numerical study of vibration analysis in SRMs, using 3-D FEA methodology, covering all the above vibration sources except the electronics; 2) a 3-D modal analysis of SRMs including stator and rotor structures, shaft, end shields, bearings, and housing; 3) an unbalanced rotor dynamics analysis; 4) associated harmonic analysis; and 5) a stress analysis under various loading conditions. The 3-D vibration analyses presented in this paper to examine the vibration in SRM as a whole are new additions to SRM vibration analysis. Section IV concludes the paper. Future work in every section is highlighted.

B-concentration dependence on anisotropy field of CoFeB thin film for gigahertz frequency use

Abstract: B was added to the high moment CoFe thin films (Co/sub 35/Fe/sub 65/, Co/sub 25/Fe/sub 75/, and Co/sub 15/Fe/sub 85/) using synchronous triple-RF magnetron sputtering to obtain the films with large anisotropy fields greater than 500 Oe. These films required inductor core materials operating at the frequencies of several gigahertz. Magnetic properties and the crystalline structure of the CoFeB films were investigated. It was found that the B addition increased the anisotropy field to 400-700 Oe and that the increase in anisotropy field was associated with changes in the crystalline structure, crystallite sizes, and crystallite orientation. The results indicated that CoFeB films have potential for use in magnetic cores and inductors operating at gigahertz frequencies.

Effect of island distribution on error rate performance in patterned media

Abstract: The size, shape, and distribution of islands in a patterned medium depends on the patterning process adopted. The off-track performance in this case is mainly dominated by inter-track interference due to the neighboring islands. In this paper, the effect that the island distribution has on the off-track performance is investigated with respect to read channel bit-error-rate performance.

Bridge configured winding for polyphase self-bearing machines

Abstract: The self-bearing or bearingless machine is an electromagnetic device that supports its own rotor by way of magnetic forces generated by windings on its stator. Various winding configurations have been used to accomplish the task of force production. This paper proposes a winding based on a bridge connection for polyphase self-bearing rotating electrical machines with advantages such as: 1) requiring only one power supply for torque production; 2) lateral forces are produced using auxiliary power supplies of relatively low current and voltage ratings; 3) relatively low power loss; and 4) preserving the flexibility for extensions to other polyphase machines. The bridge connection has been verified to exhibit the characteristics of a self-bearing motor via an electrically coupled finite-element analysis. A comparison of power loss with conventional winding schemes and general applications of such a proposed scheme are also presented.

Effects of magnetically induced vibration force in brushless permanent-magnet motors

Abstract: This paper discusses magnetic force imbalance and cogging torque in permanent-magnet motors under both static and dynamic rotor eccentricity. The characteristic frequencies of magnetic force imbalance and cogging torque due to rotor eccentricity can be used for fault diagnostics and quality control of permanent-magnet motors. The paper derives analytical expressions for their characteristic frequencies. The validity of the expressions has been confirmed by finite-element analyses.

A new wideband common-mode noise filter consisting of Mn-Zn ferrite core and copper/polyimide tape wound coil

Abstract: A new wideband common-mode noise filter for switching power supplies has been developed. The filter consisted of an Mn-Zn ferrite core and a copper/polyimide tape wound coil. The tape wound coil had two signal lines, two ground lines, and a polyimide dielectric film. The filter exhibited a common-mode rejection of over 30 dB in the wide frequency range of 100 kHz to 100 MHz. The wideband common-mode filtering was due to the high-frequency magnetic loss of the Mn-Zn ferrite core and the optimum ground point selection for the ground lines.