1,721,018 research outputs found
Characterization of noise and vibration sources in interior permanent-magnet brushless DC motors
No full textThis paper characterizes electromagnetic excitation forces in interior permanent-magnet (IPM) brushless direct cur, rent (BLDC) motors and investigates their effects on noise and vibration. First, the electromagnetic excitations are classified into three sources: 1) so-called cogging torque, for which we propose an efficient technique of computation that takes into account saturation effects as a function of rotor position; 2) ripples of mutual and reluctance torque, for which we develop an equation to characterize the combination of space harmonics of inductances and flux linkages related to permanent magnets and time harmonics of current; and 3) fluctuation of attractive forces in the radial direction between the stator and rotor, for which we analyze contributions of electric currents as well as permanent magnets by the finite-element method. Then, the paper reports on an experimental investigation of influences of structural dynamic characteristics such as natural frequencies and mode shapes, as well as electromagnetic excitation forces, on noise and vibration in an IPM motor used in washing machines
Analysis of Electromagnetic Excitation Sources of Noise and Vibration in Interior Permanent Magnet Motor
Full text linkLow temperature noncollinear behavior in FePt nanogranular thin film system
No full textWe report the low temperature noncollinear magnetic behavior of direct current (DC) sputtered FePt thin films investigated by performing DC magnetization, thermoremanence, magnetic relaxation, and electrical transport measurements down to 1.8 K. The obtained results, interestingly, indicate a transition from ferromagnetic state to a low temperature disordered state where a collective frozen magnetic state with grain moments oriented randomly occurs. The magnetic relaxation and electrical resistivity measurements at low temperature support the spin-glass like phase, which diminishes and finally disappears with an applied field of moderate strength. We interpret the observed low temperature noncollinear magnetic behavior to be due to random freezing of grain moments. (c) 2005 Elsevier B.V. All rights reserved.This research work was supported by the Korean Ministry
of Science and Technology through the Creative Research
Initiatives Project
Fine control of L1(0) ordering and grain growth kinetics by C doping in FePt films
No full textWe present the results on highly anisotropic oriented face-centered-tetragonal ordered equiatomic FePt thin films embedded in a C matrix prepared by cosputtering technique on MgO (100) substrates at 400 degreesC. We have found that doping of C in FePt alloy films is an effective and appropriate way to control the L1(0) ordering and growth of grain size down to 4 nm. Room-temperature magnetic measurements reveal that perpendicular magnetic anisotropy exists for these films with C concentration up to 25 vol %. These films are very promising and the results are of relevance for ultrahigh-density magnetic recording media. (C) 2003 American Institute of Physics.This research work was supported by the Korean Ministry
of Science and Technology through the Creative Research
Initiatives Project
A study on the adhesion enhancement of polyetherimide to Si wafer using an Al-chelate treatment during multichip module fabrication
No full textAl-chelate coupling agent was successfully applied to improve the adhesion strength of a thermoplastic polyetherimide resin, Ultem 1000 (R) to a silicon wafer during the fabrication of multichip module (MCM) substrates, The origin of the enhanced adhesion strength achieved by applying Al chelate was also investigated using a surface characterization experiment and a theoretical approach. The peel strength of as-laminated Ultem film on an untreated Si wafer was the same as that on a coupler-treated one right after lamination. However, the Ultem layer laminated on an untreated Si wafer lost its adhesion strength to zero within 24 h of 85 degrees /85% relative humidity (RH) aging. In contrast, the Ultem film laminated on the coupler-treated Si wafer maintained its adhesion strength even after 30 days of 85 degreesC/85% RH treatment. Atomic force microscopy (AFM), surface energy calculation using contact angle measurement, and high-resolution X-ray photoelectron spectroscopy (XPS) analysis were conducted to characterize the surface conditions of a bare Si wafer and a coupler-treated Si wafer. It was revealed by the AFM experiment that the surface roughening caused by Al-chelate treatment was negligible, meaning that the enhanced adhesion stability during 85 degreesC/85% RH aging is mainly attributed to the surface characteristic change of Si substrate. Based on the results of XPS analysis and contact angle measurement, a model of surface bonding structure of an Al-chelate treated Si wafer was suggested and compared with that of a bare Si wafer. Finally, peel strength variation of Si wafers with and without the coupling agent as a function of 85 degreesC/85% RH aging times can be explained by the zero point of charge consideration. Stable lamination based MCMs and micro-via build-up processes can also be obtained using these results. (C) 2001 Elsevier Science B.V. All rights reserved
Perpendicudar thin films of carbon-doped FePt for ultrahigh-density magnetic recording media
No full textThe microstructural and magnetic properties of the carbon-doped equiatmoic (Fe50Pt50)(1-x)C-x thin films, prepared by,de magnetron cosputtering on MgO (100) substrates held at 400 degreesC, were investigated. Particles consisting of the highly anisotropic tetragonal L1(0) FePt phase and embedded in a C matrix were obtained. By controlling the added C content, the samples with average grain size of 5 nm were obtained with perpendicular coercivity of about 5 kOe. The. remanence ratio kept high values of about 1 when x less than or equal to 25 vol%, and it decreased abruptly as x > 25 vol%. The room temperature magnetic measurements suggest that the perpendicular magnetic anisotropy exists for these films with C concentration up to 25 vol%. The obtained results suggest that this system might be applicable to ultrahigh-density magnetic recording media
Magnetic properties of carbon-doped FePt nanogranular films
No full textThe room-temperature magnetic properties and magnetization reversal process of ordered (FePt)(1-x)C-x thin films, prepared by a cosputtering technique on MgO (100) substrates held at 400 degreesC substrate temperature, have been studied. Perpendicular magnetic anisotropy was obtained for the films with carbon concentrations up to 25 vol % and coercivity enhancement was observed with small carbon-doped FePt thin films. A clear spin-reorientation transition from perpendicular to the in-plane direction was observed with an increase in carbon concentration. The observed magnetic properties are intercorrelated to microstructural changes that occur as a function of the carbon doping. (C) 2003 American Institute of Physics.This research was supported by the Korean Ministry of
Science and Technology through the Creative Research Initiatives
Project
Effects of the polymer residues on via contact resistance after reactive ion etching
No full textThe effects of CF4 addition to O-2 reactive ion etching (RIE) of a polyetherimide (Ultem(R)) surface and resultant via contact resistance were investigated using scanning electron microscopy (SEM), x-ray electron spectroscopy (XPS), and cross bridge Kelvin resistor (CBKR). In pure O-2 RIE, the SEM micrograph showed that the originally smooth Ultem surface became rough and the rough features coarsened with increasing RIE time, resulting in residual particles on the metal pads. However, in the case of O-2 + CF4 RIE, the Ultem surface remained smooth throughout the etching process, and residue free metal pads were obtained, The XPS experiments identified that the origin of the Ultem surface roughening was organo-Si compound, which is easily converted to silicon oxide during O-2 RIE. In contrast, the atomic fluorine in O-2 + CF4 RIE process etched out the silicon and the silicon oxide, resulting in smooth film surface and residue free metal pads. The metal to metal via contact resistance was measured by CBKR, and the pattern fabricated by O-2 + CF4 RIE showed lower contact resistance than those by O-2 RIE. These results are discussed in the criterion of contact area and contact conformality differences. (C) 2002 American Vacuum Society
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