• Journal of Sensor Science and Technology
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• v.13 no.6
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• pp.473-478
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• 2004

This study focused on the charateristic of magnetic fluids, the viscosity deviation of magnetic fluids due to temperature changes, and fabrication of a 'purely' liquid type microvalve. The viscosity of magnetic fluids decreases sharply during increasing of temperature. The viscosity of magnetic fluids is rated 1,000 cP at the room temperature and 25 cP when the temperature reaches $100^{\circ}C$. Briefly, it is remarkable that the fluid flow can be controlled by the temperature and this characteristic can be adopted to the microfluidics as a microvalve. The fabrication of a liquid type microvalve is more easy than solid state microvalves and which can increase an efficiency of the controlability with respect to the thermo-pneumatic micropump which is studied broadly for many years. When the magnetic fluid used as a sealant for high level sealing, the pressure leakage is less than solid state microvalve. The experimental results show that the pressure drop in microchannel, filled with the magnetic fluid, is significant in the temperature range of $20^{\circ}C{\sim}50^{\circ}C$ and this result explains why the use of magnetic fluids is possible as a microvalve searcher uses this characteristics. Well known thermo-pnumatic.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.1
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• pp.49-54
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• 2023

Recently, System in Packaging(SIP) technology needs to meet high frequency (5G and more) communication technology and fine pitch surface treatment. The conventional Electroless Ni/Immersion Au plating(ENIG) is not suitable for high frequency range because of magnetic properties are increasing the transmission loss. Without nickel plating layer, the pattern and pad reliability level must be meet the condition. In this review paper, we investigated research trends on Ni-less surface treatment technology for high-frequency communication and frequency characteristics according to materials.

• Journal of The Korean Astronomical Society
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• v.36 no.spc1
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• pp.7-12
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• 2003

We have studied the magnetic helicity of active regions by using the data from (1) the photo-electric magnetograph of the Okayama Observatory (1983-1995) and (2) the video magnetograph of NAOJ/Mitaka (1992-2000). The latitude distribution of helicity showed a tendency that the regions in the north (south) hemisphere have negative (positive) helicities, respectively, which is already known as the hemispheric sign rule. If we look into the sign of helicity as a function of time, the sign rule was less definite or was reversed sometimes in the sunspot minimum phase. We also studied the relation between the magnetic helicity and the sunspot tilt angles, and found that these two quantities are positively correlated, which is opposite to the expectation of a theoretical model. The implications of this cycle-phase dependence of helicity signs and the correlation between magnetic he Ii city and sunspot tilt angles are discussed.

• Resources Recycling
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• v.11 no.5
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• pp.7-10
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• 2002

Iron nitride magnetic fluid was oxidized by exposing it to the air under normal atmospheric conditions. After exposure of 3.2 hours, the relative saturation magnetization of the iron nitride magnetic fluid is less than 0.4 compared to the value of the unexposed sample, and it is nearly zero after exposure for 1008 hours. The structure of the oxidized iron nitride is considered to be a non-magnetic hematites. The thickness of the oxidation layers of the iron-nitride particles are nearly the same, about 3 nm, regardless of the different particle sizes.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.4
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• pp.41-47
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• 2013

The electrical relay in an essential part of the Smart Grid, Electrical Vehicle (EV) and LED lightning system. For these reasons, research of electrical relay is actively underway. In this paper, analyze of the relationship between the bouncing of relay contact and magnetic flux of permanent magnet. Experiment result, changes the bouncing numbers depending on the magnetic flux of the latching relay. And find the value of the magnetic flux that occurs to minimize the bouncing of the contacts. In additions, by the increasing the magnetic flux, unconditional bounce is not reduced. The bouncing number of latching relay is less than expected the armature relay for present results. Further experiments are need to prove it, bouncing on the armature relays.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.291-298
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• 2004

The observations of rapid motion of bubbles under water for approximately 50 ms or less in high-magnetic fields of 10 T have been carried out successfully for the first time. The observation system constructed is composed of a high-speed video camera, a telescope, a cryostat with a split-type superconducting magnet, a light source, a mirror and a transparent sample cell. Using this system, the influence of magnetic field on the path and shape of single bubbles of O$_2$ (paramagnetism) and N$_2$ (diamagnetism) has been examined carefully. Experimental values describing the path are in good agreement with theoretical values calculated on the basis of the magneto-Archimedes effect, despite the effect of magnetism on the bubble. However, no effect of magnetism on the shape of the bubble is observed. In addition, the influence of magnetic field on drag coefficient of the bubble is discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.11
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• pp.2786-2795
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• 2000

Recently, the technology for internal polishing is needed for ultra-clean machining for the prevention of corrosion and pollution of parts is the area of high technology industries such as semiconductor, electronics, telecommunication optics, aerospace, and motors. In this study, an internal polishing system using the magnetic force was developed for the production of ultra-clean tubes with averaged surface roughness ranging from 0.2㎛ to 0.05㎛ or less, and magnetic abrasives composed of WC/Co powder were developed, After finding the optimal condition on each, machining characteristics using newly developed abrasive were analyzed. Form the results obtained by experimental design method, the optimal polishing condition was analyzed and, thhereafter internal polishing was done.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.6
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• pp.888-893
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• 1998

In this paper, we present a magnetic levitation system which has not a gap sensor with sensor-less realization and stabilizing controller design. For measuring gap between magnet and levitated object we propose a gap sensorless method and adop two-degree-of-freedom controller for robust-ness and performence of the magnetic levitation system. From time responeses we confirm that the proposed sensorless method which can be applied to magnetic levitation system. Also the designed stabilizing controller has good disturbance rejection and reference tracking performance.

• Journal of Power Electronics
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• v.13 no.4
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• pp.552-557
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• 2013

This paper proposed an analytical model for the distributed magnetic field analysis of interior permanent magnet-type blush-less direct current motors under the stator-turn fault condition using the winding function theory. Stator-turn faults cause significant changes in electric and magnetic characteristic. Therefore, many studies on stator-turn faults have been performed by simulation of the finite element method because of its non-linear characteristic. However, this is difficult to apply to on-line fault detection systems because the processing time of the finite element method is very long. Fault-tolerant control systems require diagnostic methods that have simple processing systems and can produce accurate information. Thus analytical modeling of a stator-turn fault has been performed using the winding function theory, and the distributed magnetic characteristics have been analyzed under the fault condition. The proposed analytical model was verified using the finite element method.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.10
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• pp.453-456
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• 2005

We have fabricated superconducting ceramics by chemical process. A high Tc superconducting with a nominal composition of YBaCuO was prepared by the pyrolysis method. The electromagnetic properties in YBaCuO superconductor was studied. In the measurement of current-voltage characteristics, a voltage across the superconducting sample was observed on applying an external magnetic field. The voltage increases with increase in applied magnetic flux, but it becomes constant at about 10$^{-2}$T. The voltage continues to appear the removal of the magnetic field. The appearance of the voltage is ascribed to the trapping of magnetic flux. Depending on the direction of applied magnetic flux less than 2.5$\times$10$^{-5}$ T, the voltage in the magnetized sample increases or decreases.