• Journal of the Korean Magnetics Society
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• v.7 no.6
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• pp.321-326
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• 1997

We analyzed an important part of control valve, magnet unit, which is used to control the fluid. Magnetic circuit which is composed of magnet and yoke is analyzed using finite element method. Then, flux density and coil force were calculated and compared with those of measured. According to the simulation results, the gap field, force constant, and permeance coefficient were 3~5 kG, 27.5 N/A, 22.1, respectively, which corresponded reasonably well with the measured values. We also obtained reluctance factor of 1.1 and fringing factor of 1.4 by simulation.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.1
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• pp.48-55
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• 2003

The design and analysis of a three-phase 6/8 structure SRM(switched reluctance motor) art described. The range of the stator ole arc and the rotor pole arc of the motor we analyzed in the linear region. The optimum range of the stator pole arc and the turn-off angle of the main switches in the power converter are given with the 2-D finite element electro-magnetic field calculation of the motor and the nonlinear simulation. Test results of the prototype are discussed. This type is good for high efficiency drive because the drive circuit is simple and current density and copper loss of the winding are law.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.80-82
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• 1995

This paper describes a computer model of the secondary arc associated with single pole switching scheme to use in system simulation studies. The computer model is based on the mathematical model described by A.T.Johns, et.al[3], and is implemented by the EMTDC which is similar to the Electro Magnetic Transient Program(EMTP). Simulation results using the computer model compare with a previous simulation and field test results.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.2
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• pp.82-90
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• 2011

The small precision spindle motors in the high value-added products including the visible home appliances such as DLP projector require not only the energy conversion devices but also high efficiency, low vibration and sound operation. However, the spindle motors using the conventional ball bearing and sintered porous metal bearing have following problems, respectively: the vibration by the irregularity of balls and the short motor life cycle by the ball's abrasion and higher sound noises by dry contact between shaft and sleeve. In this paper, it is proposed that the spindle motor with a fluid dynamic bearing is suitable for the motor to drive the color wheel of the DLP(digital lightening processor) in the visible home appliances. The proposed spindle motor is composed of the fluid dynamic bearing with both the radial force and the thrust force. The fluid dynamic bearing is solved by the finite element analysis of the mechanical field with the Reynolds equations. The magnetic part of spindle motor, which is a type of Brushless DC Motor, is designed by the electro-magnetic field analysis coupled with the Maxwell equation. And the load capacity and the friction loss of fluid dynamic bearing are analyzed to bearing clearance variation by the fabrication error in designed motor. The design of the proposed motor is implemented by the load torque caused by the eccentricity and the unbalance of the fluid dynamic bearing when the motors are fabricated in error. The prototype of the motor with the fluid dynamic bearing is manufactured, and experiment results show the vibration, sound, and phase current at no load and color wheel load of the motors in comparison. The high performance characteristics with the low vibration, the low acoustic noise and the optimal mechanical structure are verified by the experimental results.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.5
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• pp.955-964
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• 2011

In renewable energy system such as flywheel energy storage system, wind power and solar power, the motor/generator is the important key for offering the electric energy to the electric loads. For example, the heavy and large flywheel is rotated by electromagnetic torque of pemanent magnet synchronous motor (PMSM) and, in case of a breakdown of electric current, the PMSM used as generator supplies electric energy for the various electric utilities using mechanical rotation energy of the flywheel. Thus, design of a motor/generator should be performed in effort to reduce cogging torque and electromagnetic loss for high efficiency. In our paper, a slotless permanent magnet synchronous motor/generator (SPMSM/G) with output power 15kW at the rotor speed 18000rpm is designed from electromagnetic analysis and dynamic performance analysis. In analytical approach, design parameters such as back electro-motive force (back EMF), inductance and electromagnetic torque are derived from analytical method which is one of the electromagnetic analysis method. And using the design parameters, this paper deal with system design considering the driving characteristics and electric load in required power. Finally, the analytical results are verified by the experiment and finite element method (FEM).

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.6
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• pp.2961-2966
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• 2012

Extremely low frequency electro magnetic fields (EMFs) have been classified as possibly carcinogenic to humans by the International Agency for Research on Cancer. An increased number of chromosomal alterations in peripheral lymphocytes are correlated with elevated incidence of cancer. The aim of the present study was to assess occupationally induced chromosomal damage in EMF workers exposed to low levels of radiation. We used conventional metaphase chromosome aberration (CA) analysis and the micronucleus (MN) assay as biological indicators of non ionizing radiation exposure. In the present study totally 70 subjects were selected including 50 exposed and 20 controls. Informed written consent was obtained from all participants and the study was performed in accordance with the Declaration of Helsinki and the approval of the local ethical committee. A higher degree of CA and MN was observed in exposed subjects compared to controls, the frequency of CA being significantly enhanced with long years of exposure (P<0.05). Moreover increase in CA and MN with age was noted in both exposed subjects and controls, but was significantly greater in the former. The results of this study demonstrated that a significant induction of cytogenetic damage in peripheral lymphocytes of workers occupationally exposed to EMFs in electric transformer and distribution stations. In conclusion, our findings suggest that EMFs possess genotoxic capability, as measured by CA and MN assays; CA analysis appeared more sensitive than other cytogenetic end-points. It can be concluded that chronic occupational exposure to EMFs may lead to an increased risk of genetic damage among electrical workers.

• Proceedings of the KIEE Conference
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• 2003.10b
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• pp.137-140
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• 2003

To the optimization design of molded case circuit breakers(MCCBs), it is necessary and important to calculate the electro-dynamic repulsion force acting on the movable conductor. With 3-D finite element nonlinear analysis, according to the equations among current-magnetic field-repulsion force and taking into account the ferromagnet, contact bridge model is introduced to simulate the current constriction between contacts, so Lorentz and Holm force acting on the movable conductor and contact, respectively, can be integrated to calculate. Coupled with circuit equations, the opening time of movable contact also can be obtained using iteration with the restriction of contact force. Simulation and experiment for repulsion forte and opening time of five different configuration models have been investigated. The results indicate that the proposed method is effective and capable of evaluating new design of contact systems in MCCBs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.7
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• pp.625-630
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• 2009

In this paper, we introduce the analysis and counter-measure of signal distortion of search radar equipped on the ship. Using ShipEDF program, the search radar's main antenna and ship structures are modeled in the view of electromagnetism. Ray tracing method is used for analysis of the search radar's radiation patterns in free space and ship condition. From analyzed radiation patterns, we can conclude that the search radar's signal distortion is due to radiation pattern distortion. We also analyze the surface current distribution of the mast to propose the counter-measure to reduce electro-magnetic field reflection of mast.

• Smart Structures and Systems
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• v.20 no.3
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• pp.329-342
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• 2017

In this paper, the dispersion characteristics of elastic waves propagation in sandwich nano-beams with functionally graded (FG) face-sheets reinforced with carbon nanotubes (CNTs) is investigated based on various high order shear deformation beam theories (HOSDBTs) as well as nonlocal strain gradient theory (NSGT). In order to align CNTs as symmetric and asymmetric in top and bottom face-sheets with respect to neutral geometric axis of the sandwich nano-beam, various patterns are employed in this analysis. The sandwich nano-beam resting on Pasternak foundation is subjected to thermal, magnetic and electrical fields. In order to involve small scale parameter in governing equations, the NSGT is employed for this analysis. The governing equations of motion are derived using Hamilton's principle based on various HSDBTs. Then the governing equations are solved using analytical method. A detailed parametric study is conducted to study the effects of length scale parameter, different HSDBTs, the nonlocal parameter, various aligning of CNTs in thickness direction of face-sheets, different volume fraction of CNTs, foundation stiffness, applied voltage, magnetic intensity field and temperature change on the wave propagation characteristics of sandwich nano-beam. Also cut-off frequency and phase velocity are investigated in detail. According to results obtained, UU and VA patterns have the same cut-off frequency value but AV pattern has the lower value with respect to them.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.1
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• pp.60-67
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• 2004

In this paper, a rectangular ring microstrip patch antenna has been analyzed by using desegmentation method and evaluation impedance matrices from Green's functions fur rectangular segment and desegmentation method for analysis of planar electro-magnetic structures is discussed. As the rectangular ring cavity could be seen as a structure subtracted a small rectangular cavity from a large one, the overall impedance matrix was obtained by applying a multiport connection method to the individual impedance matrices expressed as a term of Green's function fer rectangular segment. The electromagnetic fields can be solved from a vector potential which is satisfied it's eight boundary conditions. The electric field distribution at each edges was expressed as a histogram table with exciting modes. These results can be used to analyze the operational modes for a rectangular ring microstrip antennas.