• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.522-522
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• 1996

An investigation of the effects of transverse magnetic field and Peltier effect on melt convection and macrosegregation in vertical Bridgman crystal grosth of Te doped InSb was been carried out by means of microstructure observation, Hall measurement, electrical resistivity measurement and X-ray analysis. Before the experiments, Interface stability, convective instability and suppression of convection by magnetic field were calculated theoretically. After doping 1018, 1019 cm-3 Te in InSb, the temperature of Bridgman furnace was set up at $650^{\circ}C$. The samples were grown in I.D. 11mm, 100mm high quartz tube. The velocity of growth was about 2${\mu}{\textrm}{m}$/sec. In order to obtain the suppression of convection by magnetic field in the middle of growth, 2-4KG magnetic field was set on the melt. For searching of the shape of solid-liquid interface and the actual velocity of crystal growth, let 2A current flow from solid to liquid for 1second every 50seconds repeatedly (Peltier effect). The grown InSb was polycrystal, and each grain was very sharp. There was no much difference between the sample with and without magnetic field at a point of view of microstructure. For the sample with Peltier effect, the Peltier marks(striation) were observed regularly as expected. Through these marks, it was found that the solid-liquid interface was flat and the actual growth velocity was about 1-2${\mu}{\textrm}{m}$/sec. On the ground of theoretical calculation, there is thermosolutal convection in the Te doped InSb melt without magnetic field in this growth condition. and if there is more than 1KG magnetic field, the convection is suppressed. Through this experiments, the effective distribution coefficients, koff, were 0.35 in the case of no magnetic field, and 0.45 when the magnetic field is 2KG, 0.7 at 4KG. It was found that the more magnetic field was applied, the more convection was suppressed. But there was some difference between the theoretical calculation and the experiment, the cause of the difference was thought due to the use of some approximated values in theoretical calculation. In addition to these results, the sample with Peltier effect showed unexpected result about the Te distribution in InSb. It looked like no convection and no macrosegregation. It was thought that the unexpected behavior was due to Peltier mark. that is, when the strong current flew the growing sample, the mark was formed by catching Te. As a result of the phenomena, the more Te containing thin layer was made. The layer ruled the Hall measurement. The values of resistivity and mobility of these samples were just a little than those of other reference. It was thought that the reason of this result was that these samples were due to polycrystal, that is, grain boundaries had an influence on this result.

• Journal of Magnetics
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• v.20 no.1
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• pp.8-10
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• 2015

The magnetic anisotropy field plays an important role in spin-orbit-torque-induced magnetization dynamics with electric current injection. Here, we propose a magnetometric technique to measure the magnetic anisotropy field in nanostructured ferromagnetic thin films. This technique utilizes a magneto-optical Kerr effect microscope equipped with two-axis electromagnets. By measuring the out-of-plane hysteresis loops and then analyzing their saturated magnetization with respect to the in-plane magnetic field, the magnetic anisotropy field is uniquely quantified within the context of the Stoner-Wohlfarth theory. The present technique can be applied to small nanostructures, enabling in-situ determination of the magnetic anisotropy field of nanodevices.

• Journal of Power System Engineering
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• v.11 no.2
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• pp.72-76
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• 2007

Since the magnetic bearing system has unstability inherently it is necessary to measure the displacement for stable operation. Normally the displacement measurement is implemented by using sensors. The sensor for the displacement measurement is selected by precision, installation space, effect of magnetic field and response speed. And the cost of displacement measurement sensor also is considered. At the cost the hall effect sensor has a large advantage comparing with the others. Therefore this study concern about the basis experimental test for the displacement measurement of the magnetic bearing system that uses the hall effect sensor coupled with a tiny permanent magnet. The experimental results confirm the validity and practicability for this displacement measurement sensor.

• Journal of Space Technology and Applications
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• v.2 no.1
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• pp.41-51
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• 2022

CubeSat is a satellite platform that is widely used not only for earth observation but also for space exploration. CubeSat is also used in magnetic field investigation missions to observe space physics phenomena with various shape configurations of magnetometer instrument unit. In case of magnetic field measurement, the magnetometer instrument should be far away from the satellite body to minimize the magnetic disturbances from satellites. But the accommodation setting of the magnetometer instrument is limited due to the volume constraint of small satellites like a CubeSat. In this paper, we investigated that the magnetic field interference generated by the cube satellite was analyzed how much it can affect the reliability of magnetic field measurement. For this analysis, we used a reaction wheel and Torque rods which have relatively high-power consumption as major noise sources. The magnetic dipole moment of these parts was derived by the data sheet of the manufacturer. We have been confirmed that the effect of the residual moment of the magnetic torque located in the middle of the 3U cube satellite can reach 36,000 nT from the outermost end of the body of the CubeSat in a space without an external magnetic field. In the case of accurate magnetic field measurements of less than 1 nT, we found that the magnetometer should be at least 0.6 m away from the CubeSat body. We expect that this analysis method will be an important role of a magnetic cleanliness analysis when designing a CubeSat to carry out a magnetic field measurement.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.664-667
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• 2009

We would like to show a measuring technique of azimuthal anchoring energy of the nematic liquid crystals. The electro-optical setup of liquid crystal cell, crossed polarizers and magnetic field was assumed. The planar or hybrid alignment cells were prepared. The director in the light entering substrate and the polarization of light was adjusted into parallel to the magnetic field. The director orientation of exit substrate and analyser maintained perpendicular to the magnetic field. As the magnetic field strength is increased, the director deviates from the easy axis and rotates to the field direction. We obtained an equation calculating the change of transmission with the field and measured experimentally the transmission. By comparing the calculating and experimental data, we obtained the azimuthal anchoring strength.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.1018-1021
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• 2003

This dissertation is reference to measure visual information about the configuration of magnetic field automatically and materialize the new magnetic field mapping system for the rapid and clear measure by using of the mediocrity orthogonal robot in the three- dimensional space required the measure of magnetic field concurrently. The measuring sensor is composed to be available for the measure of three-dimensional direction of magnetic field by vertically conjoining each of three hall sensors utilized of the hall effect and installed Gaussmeter, which is devised to receive the sensor result and the robot controller, away from the measuring robot in order to minimize the affection of magnetic field. Also, the controller and Gaussmeter are composed of Use interface, RS-232C and IEEE-488.2 communication. Interface system is written in NI's LabVIEW and composed to be able to set up a measuring area, the measuring number of times, two and three-dimensional graph, the velocity of robot and the magnetic field distribution graph of each element by inputting parameters. The materialized magnetic field mapping system expert the collection of the data easily and the effect of utilizing data.

• Korean Journal of Clinical Laboratory Science
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• v.37 no.2
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• pp.123-128
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• 2005

Magnetoencephalography (MEG) is the measurement of the magnetic fields produced by electrical activity in the brain, usually conducted externally, using extremely sensitive devices such as Superconducting Quantum Interference Device (SQUID). MEG needs complex and expensive measurement settings. Because the magnetic signals emitted by the brain are on the order of a few femtoteslas (1 fT = 10-15T), shielding from external magnetic signals, including the Earth's magnetic field, is necessary. An appropriate magnetically shielded room is very expensive, and constitutes the bulk of the expense of an MEG system. MEG is a relatively new technique that promises good spatial resolution and extremely high temporal resolution, thus complementing other brain activity measurement techniques such as electroencephalography (EEG), positron emission tomography (PET), single-photon emission computed tomography (SPECT) and functional magnetic resonance imaging (fMRI). MEG combines functional information from magnetic field recordings with structural information from MRI. The clinical uses of MEG are in detecting and localizing epileptic form spiking activity in patients with epilepsy, and in localizing eloquent cortex for surgical planning in patients with brain tumors. Magnetoencephalography may be used alone or together with electroencephalography, for the measurement of spontaneous or evoked activity, and for research or clinical purposes.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2004.05a
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• pp.559-564
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• 2004

This paper deals with the device for measuring the time-varying magnetic fields and induced voltages caused by lightning discharges. The two magnetic field measuring systems were designed and made. One consists of the loop-type magnetic field sensor with the active integrator operated by a differential amplifier. The other consists of the loop-type magnetic field sensor and Labview software. The loop-type magnetic field sensor detects the time derivative of the magnetic field being measured, and the signal detected is integrated by the Labview software. As a consequence, from the calibration experiments, the frequency bandwidth of the full measuring system ranges from 400 [Hz] to 1 (MHz) and the response sensitivity are 0.98 (mV/nT) and 22 (mV/nT) for the magnetic field sensor of 2 turns and 6 turns, respectively. Also, the results obtained by the two measuring devices well agreed with each other.

• Journal of the Korea Institute of Military Science and Technology
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• v.9 no.2 s.25
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• pp.11-19
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• 2006

The underwater electromagnetic signatures of a naval ship are mainly generated from three sources which are the permanent and induced magnetic field in the ship's hull and other ferrous components, the cathodic current electromagnetic field established by the Impressed Current Cathodic Protection(ICCP) system or the Sacrificial Anode and the stray electromagnetic fields generated by onboard equipment. These signatures can be minimized by certain design methods or installation of signature reduction equipment. In this paper, we represented the characteristic of the underwater electromagnetic signature and the signature reduction techniques for a naval ship. Also, we measured the electromagnetic field changes emitted from the real ship using the Electric and Magnetic field Measurement System(EMMS). We found that the underwater electromagnetic signature for a naval ship can be used as input or trigger signal in a surveillance system and an influence mine.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.515-518
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• 2002

In this study, the ellipsoidal cap type magnetic pole structure was proposed for the electro-magnet in B-H curve tracer. From the simulation for the electro-magnet without specimen, the area of effective uniform field(99% range for the central field value) was considerably increased in case of the newly proposed ellipsoidal cap type magnetic pole than that of the conventional simple-inclined cap type magnetic pole. Also, through the simulation for the electro-magnet with permanent magnet specimen(NaFe30), the optimal Positions of the magnetic field measurement sensor(Hall sensor) were found out in each case and the errors were decreased in case of the newly proposed ellipsoidal cap type magnetic pole.