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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Extended multipole image of a nonideal permanent magnet rotor

Alexander V. Kildishev, John A. Nyenhuis, and Yuriy N. Zhilichev

J. Appl. Phys. 93, 8668 (2003); http://dx.doi.org/10.1063/1.1537705 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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Reduction of the external magnetic field (magnetic signature) of large electric motors may be important in military and other applications. This article deals with critical issues in the design and manufacturing of permanent magnet (PM) motors that are responsible for increased magnetic signatures. Emphasis is on analysis of the nonidealities of PM rotors such as imbalances in the permanent magnet excitation system due to manufacturing tolerances and differences in material properties. Spatial harmonic analysis is used to describe the magnetic signature. The rotor simulation considers rectangular PM segments, and uses statistical characterization of possible nonidealities in dimensions, positioning, and magnetization. The approach focuses on lower degree magnetic multipole moments (dipolar, quadrupolar, and octupolar) in spheroidal and spherical domains, and is applied to PM inducing elements. © 2003 American Institute of Physics.
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84.50.+d Electric motors
75.50.Ww Permanent magnets

Crystal orientation control of multipole ring magnets for a surface permanent magnet rotor

M. Komuro, M. Kitamura, Y. Kuriyama, and M. Masuzawa

J. Appl. Phys. 93, 8671 (2003); http://dx.doi.org/10.1063/1.1541655 (3 pages)

Online Publication Date: 9 May 2003

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The effects of the crystal orientation on the surface magnetic flux density and cogging torque were investigated for multipole ring magnets. A high magnetic field was applied to pole positions during the pressing process for the fabrication of ring magnets using anisotropic NdFeB powders. The radial orientation of the c axis of these ring magnets is 10% higher than that of previous ring magnets at pole positions. The ring magnets with a high orientation at the pole positions show a smaller distortion wave form of the surface magnetic flux density and a 20% higher surface magnetic flux density than previous ring magnets. The surface permanent magnet rotors using these ring magnets have a 75% smaller cogging torque with a basic period. © 2003 American Institute of Physics.
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75.50.Ww Permanent magnets
84.50.+d Electric motors
75.70.Rf Surface magnetism
75.50.Bb Fe and its alloys
61.50.-f Structure of bulk crystals

Microscale resin-bonded permanent magnets for magnetic micro-electro-mechanical systems applications

Hyoung J. Cho and Chong H. Ahn

J. Appl. Phys. 93, 8674 (2003); http://dx.doi.org/10.1063/1.1558591 (3 pages) | Cited 9 times

Online Publication Date: 9 May 2003

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A micromachining technique has been developed for the fabrication of microscale resin-bonded permanent magnets. Magnetic paste has been prepared from Sr-ferrite powder and an epoxy resin, filled into lithographically defined molds, and formed into resin-bonded magnets after room temperature curing. Coercivity of 356 kA/m (4480 Oe), retentivity of 33 mT (330 G), and energy density of 2.7 kJ/m3 have been achieved in 65-μm-thick disk arrays with lateral dimensions ranging from 50 to 200 μm. Based on the developed magnet, a magnetic MEMS actuator has been designed, fabricated, and characterized. Actuation current up to ±60 mA operated the actuator up to 70 μm in attractive and repulsive motion. This work can be used for producing thick-film type permanent magnets, which can be scaled from a few tens of micrometers to millimeters on various substrates. © 2003 American Institute of Physics.
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75.50.Ww Permanent magnets
85.70.Ge Ferrite and garnet devices
75.50.Gg Ferrimagnetics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.05.Qk Reinforced polymers and polymer-based composites
07.55.Db Generation of magnetic fields; magnets
07.10.Cm Micromechanical devices and systems
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Microstructure characteristics of hot-pressing Pr–Fe–B–Cu

Jing Pan, Xincai Liu, Changchun Cai, and Zhifeng Xu

J. Appl. Phys. 93, 8677 (2003); http://dx.doi.org/10.1063/1.1544444 (3 pages)

Online Publication Date: 9 May 2003

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In order to research the formation mechanism of [006] texture of cast/hot-pressed magnets, effects of compositions, hot deformation parameters, and thermal annealing on [006] texture and microstructures of hot-pressed magnets of PrxFe93.5−xB5Cu1.5 (x=15–19) have been studied under the conditions of hot-pressing temperature T=973–1273 K, strain rate V=10−6–100/S, and strain E=0%–80%. Higher praseodymium content is detrimental to the formation of the ideal texture [006]. Only at a hot-pressing temperature of 973–1123 K and without fractures during the hot deformation, can [006] texture of PrxFe93.5−xB5Cu1.5 be obtained. Below the critical temperature of the equal strength among Pr2Fe14B and the residual grain-boundary phases, 1173 K, the boundary phases have a higher strength than that of Pr2Fe14B, and most of deformation can be focused within Pr2Fe14B grains and after thermal annealing at 1123 K for 8 h, I006 become more distinguished. The Br of these magnets reach 1320 mT and their magnetic domains, on the longitudinal section, are platelike, with domain walls parallel to the hot deformation direction. The domains on the transverse section are mazelike. © 2003 American Institute of Physics.
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81.05.Bx Metals, semimetals, and alloys
75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
75.50.Ww Permanent magnets
61.72.Mm Grain and twin boundaries
62.20.M- Structural failure of materials

Improving sintered NdFeB permanent magnets by powder compaction in a 9 T superconducting solenoid

T. M. Mulcahy, J. R. Hull, E. Rozendaal, J. H. Wise, and L. R. Turner

J. Appl. Phys. 93, 8680 (2003); http://dx.doi.org/10.1063/1.1544525 (3 pages)

Online Publication Date: 9 May 2003

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Commercial-grade magnet powder (Magnequench UG) was axial die pressed in the 76.2 mm warm bore of a 9 T superconducting solenoid. Otherwise, processing was performed as part of normal factory operations. This pressing was done to improve the alignment of the anisotropic single-crystal particles of the compact and, thus, the remanent magnetization of the sintered cylindrical permanent magnets (12.7 mm diameter). Although the press was operated in batch mode for this proof-of-concept study, its design enables automated production. Improvements of up to 8% in magnetization and 16% in energy products were obtained, as the alignment field H was increased above the 2 T maximum field of electromagnets used in industry. The greatest improvements were obtained for magnets with the smallest length-to-diameter ratios, L/D<0.5. The production of quality magnets in this near-final-shape size range is currently being pursued by industry to eliminate expensive machining steps. To understand the potential for 2–8 T alignment fields to overcome the distortions created in the otherwise uniform field by the self-field of short compacts, electromagnetic code (Opera) calculations were made. A simple material model was used to predict the distortions. The trends in the predicted field-line inclinations, with L/D and H, compare to trends in the improvement of the magnetic properties. © 2003 American Institute of Physics.
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75.50.Ww Permanent magnets
75.50.Bb Fe and its alloys
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Bx Metals, semimetals, and alloys
07.55.Db Generation of magnetic fields; magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effect of ZrB2 addition on SmCo-1:7 high temperature magnets

Fernando M. F. Rhen, M. Venkatesan, I. R. Harris, and J. M. D. Coey

J. Appl. Phys. 93, 8683 (2003); http://dx.doi.org/10.1063/1.1558593 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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This work focuses on a search for magnets that can be used at elevated temperature. We have studied the effect of ZrB2 addition on the magnetic properties and stability of nanocrystalline 1:7 type Sm(Co,Ti,Zr) magnets up to 500 °C. Amorphous ball milled powder was annealed to develop the TbCu7 type structure. The room temperature coercivity of SmCo6.5(ZrB2)0.033Ti0.4 is 2.1 T. The microstructure is stable at 400 °C, where the coercivity is 0.5 T. © 2003 American Institute of Physics.
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75.50.Ww Permanent magnets
75.50.Cc Other ferromagnetic metals and alloys
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.30.Bx Phase diagrams of metals, alloys, and oxides

Magnetic properties of Mn–Al system alloys produced by mechanical alloying

Tetsuji Saito

J. Appl. Phys. 93, 8686 (2003); http://dx.doi.org/10.1063/1.1544526 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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Mechanical alloying of Mn-Al and Mn-Al-C powder mixtures resulted in the formation of α-Mn solid solution. Heat treatment of these mechanically alloyed powders resulted in the formation of the metastable τ phase. The mechanically alloyed powders annealed at relatively low temperatures (500–700 °C) showed small saturation magnetization of less than 1 emu/g in both Mn–Al and Mn–Al–C powders. On the other hand, the Mn–Al powders showed saturation magnetization of 8 emu/g and their Mn–Al–C counterparts exhibited large saturation magnetization of more than 20 emu/g when annealed at relatively high temperature (800–1100 °C). Although the annealed Mn–Al powders showed small coercivity, the Mn–Al–C powders exhibited large coercivity, up to 3.3 kOe, after selected heat treatment. © 2003 American Institute of Physics.
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75.50.Ww Permanent magnets
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
07.55.Db Generation of magnetic fields; magnets
85.70.-w Magnetic devices
81.40.Gh Other heat and thermomechanical treatments
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Bx Metals, semimetals, and alloys

Computer aided design of an axial-field permanent magnet brushless dc motor for an electric vehicle

P. R. Upadhyay, K. R. Rajagopal, and B. P. Singh

J. Appl. Phys. 93, 8689 (2003); http://dx.doi.org/10.1063/1.1558595 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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This article presents the computer-aided design and analysis of a pancake-type three-phase axial-field permanent magnet brushless dc motor meant for the direct drive of an electric two-wheeler. The motor has been designed for accommodating inside the rim of the wheel. Initially, the motor design was carried out using the conventional procedure. Then three-dimensional finite element analysis was carried out to arrive at the optimum design by tuning the geometry to achieve the best utilization of all materials used. The effects of all machine parameters on performance of the motor have been studied in detail and the results of this parametric study are provided. The entire design procedure is explained with the help of a flow chart. All steps involved in the design of the motor such as selection of the configuration, design of the magnetic circuit, selection of materials, calculation of machine parameters, and calculation of performance are discussed. © 2003 American Institute of Physics.
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89.40.-a Transportation
84.50.+d Electric motors
02.70.Dh Finite-element and Galerkin methods

Comparison of Halbach magnetized brushless motors equipped with air-cored and iron-cored rotors

Z. P. Xia, Z. Q. Zhu, G. W. Jewell, and D. Howe

J. Appl. Phys. 93, 8692 (2003); http://dx.doi.org/10.1063/1.1537706 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The performance of Halbach magnetized brushless motors equipped with air-cored and iron-cored rotors is investigated theoretically and experimentally. It is shown that an optimal combination of magnet thickness and pole number exists for maximum air-gap flux density. By employing a rotor back iron, the air-gap field and hence the output torque can be enhanced significantly if the ratio of the radial thickness of the magnet to the pole pitch is small. © 2003 American Institute of Physics.
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84.50.+d Electric motors
85.70.Rp Magnetic levitation, propulsion and control devices

Magnet shape optimization for high performance single-phase line start synchronous motor

Sol Kim, Jae-Hak Choi, and Ju Lee

J. Appl. Phys. 93, 8695 (2003); http://dx.doi.org/10.1063/1.1558599 (3 pages)

Online Publication Date: 9 May 2003

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This article presents an optimal design for a single-phase line start synchronous motor according to permanent magnet and flux barrier geometries. To explore the improved torque and efficiency over that of conventional single-phase induction motors for compressors, three types of magnet shape and flux barrier are introduced. A time-stepped two-dimensional finite-element method that considers the external running capacitor is used for analysis of the steady state characteristics. Counter electromotive force at the rated speed, Ld and Lq inductances, torque, and efficiency are calculated to optimize the shape of the magnet and the flux barrier. From the torque and efficiency characteristics taking variation of the load angle into consideration in the steady state, we can determine an optimal design for the permanent magnet and the flux barrier. © 2003 American Institute of Physics.
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84.50.+d Electric motors
85.70.-w Magnetic devices
75.50.Ww Permanent magnets

Effect of maximum torque according to the permanent magnet configuration of a brushless dc motor with concentrated winding

Kab-Jae Lee, Sol Kim, Ju Lee, and Jae-Eung Oh

J. Appl. Phys. 93, 8698 (2003); http://dx.doi.org/10.1063/1.1558601 (3 pages)

Online Publication Date: 9 May 2003

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A brushless dc (BLDC) motor, which has a permanent magnet (PM) component, is a potential candidate for hybrid or electric vehicle applications. Minimizing the BLDC motor size is an important requirement for application. This requirement is usually satisfied by adopting a high performance permanent magnet or improved winding methods. The PM configuration is also a critical point in design. This article presents the effect of the PM configuration on motor performance, especially the maximum torque. Four representative BLDC motor types are analytically investigated under the condition that the volume of the PM and magnetic material is constant. An embedded interior permanent magnet motor has the best torque performance the maximum torque of which is more than 1.5 times larger than that of the surface mounted permanent magnet motor. The performance of back electromotive force, instantaneous torques is also investigated. © 2003 American Institute of Physics.
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84.50.+d Electric motors
85.70.-w Magnetic devices
75.50.Ww Permanent magnets

Static torque profiles of a hybrid stepper motor having relative eccentricity between stator and rotor axes

K. R. Rajagopal, Bhim Singh, and B. P. Singh

J. Appl. Phys. 93, 8701 (2003); http://dx.doi.org/10.1063/1.1558596 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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A smooth and controlled driving load for a hybrid stepper motor requires detailed knowledge of the motor’s static and detent torque profiles. Uncertainties to measured torque profiles may be due to rotor/stator concentric misalignment as one possible factor. This article presents the results of a detailed experimental analysis on a stepper motor’s relative eccentricity between the rotor and stator axes. The nonuniform airgap not only introduces a position-dependent fundamental detent torque along with the conventional fourth harmonic detent torque, but also changes the static torque profile. The sum effect on static torque is a changed torque equilibrium point, dependent both on rotor position and motor phase. Detent torque harmonic component analysis of a set of 0.5° hybrid stepper motors, with rotor-to-stator eccentricity as the control variable, showed how increased eccentricity exceeding a given limit will cause a loss of stable equilibrium of the detent torque at each step position. © 2003 American Institute of Physics.
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84.50.+d Electric motors
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