• Progress in Superconductivity and Cryogenics
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• v.15 no.2
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• pp.20-23
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• 2013

For sensitive measurements of micro-Tesla nuclear magnetic resonance (${\mu}T$-NMR) signal, a low-noise superconducting quantum interference device (SQUID) system is needed. We have fabricated a liquid He dewar for an SQUID having a large diameter for the pickup coil. The initial test of the SQUID system showed much higher low-frequency magnetic noise caused by the thermal magnetic noise of the aluminum plates used for the vapor-cooled thermal shield material. The frequency dependence of the noise spectrum showed that the noise increases with the decrease of frequency. This behavior could be explained from a two-layer model; one generating the thermal noise and the other one shielding the thermal noise by eddy-current shielding. And the eddy-current shielding effect is strongly dependent on the frequency through the skin-depth. To minimize the loop size for the fluctuating thermal noise current, we changed the thermal shield material into insulated thin Cu mesh. The magnetic noise of the SQUID system became flat down to 0.1 Hz with a white noise of 0.3 $fT/{\surd}Hz$, including the other noise contributions such as SQUID electronics and magnetically shielded room, etc, which is acceptable for low-noise ${\mu}T$-NMR experiments.

• Proceedings of the KIEE Conference
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• 1990.11a
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• pp.49-52
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• 1990

In this paper, we proposed a new electrothermal shield model with slits for the purpose of applying to the Superconducting Generator with Quick-Response Excitation. Via experimental and finite element analysis, we compared the magnetic shielding effects of the proposed electrothermal shield model with the conventional one. It is considered that he proposed models meet the needs for the electrothermal shields of the Superconducting Generator with Quick-Response Excitation.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.932-934
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• 2002

In this paper, we proposed a method to shield perpendicular magnetic fields in high Tc superconductor(HTS) tape of a shell-type HTS transformer with double pancake windings. A diamagnetism of characteristics of superconductor is used to shield magnetic field. For a shielding experiment, a proper shielding model is chosen, and several kinds of HTS are used such as a monofilament HTS tape, two kinds of multifilament HTS tapes and YBCO film disk. The effect of shielding for the perpendicular magnetic field is measured with HTSs for shielding and their utility for shielding is proved.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.151-153
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• 1996

An optimal design approach is presented for high homogeneity superconducting magnet with superconducting active shield especially for use in magnetic resonance imaging system. This paper is investigated phenomena for the stray magnetic field to get a basic reduction techniques of the unwanted stray magnetic field from the magnet. The present method obtains optimal coil configuration considering constraints for magnetic field homogeneity and leakage field.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.81-86
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• 2003

This paper presents a numerical analysis of transient magnetic diffusion in a melt-cast-processed BSCCO-2212 tube subjected to sinusoidal applied fields. The nonlinear f-$\lrcorner$ relation obtained by experiments in liquefied $N_2$ is used to find the magnetic diffusion coefficient. The magnetic flux density, shield current density and p-J$^2$ loss are considered. According to the result of this study, the shielding current density is varied with external applied field and coordinate in the superconductor tube. The result of analysis can be used to explain the response of a Supercon -ductor-Shield-Core-Reactor subjected to sinusoidal applied fields.

• Journal of Welding and Joining
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• v.20 no.1
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• pp.76-82
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• 2002

In these days, many advanced nations have enforced import restrictions against things emitting electromagnetic wave which has report that it is so harmful. In general, electromagnetic wave is composed of electric wave and magnetic wave. The reflection of electromagnetic wave is mainly reflected by conductive materials and the magnetism loss is generated by magnetic ferrite. The magnetism loss of ferrite is separated by eddy current loss, residual magnetism loss and hysteresis loss. Thermal sprayed coating is intended to manufacture because of simple processes and high efficient electromagnetic wave shielding. The high efficient thermal sprayed coatings were made from the magnetic ferrite materials that characterizes absorption of electromagnetic wave, and the electric conductive materials that characterize emitting of electromagnetic wave. This study was manufactured thermal sprayed coatings to improve absorption-efficiency, and measured the electromagnetic wave shielding efficiency. As the experimental results, high electromagnetic wave shield efficiency was obtained at wave frequency 2GHz to thermal sprayed ferrite coatings manufactured by size distribution range of spray powders, $38~88\mu\textrm{m}$.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.2
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• pp.48-53
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• 2014

The shield effect of 4 layered shield case was investigated in this paper. The material of the case was non-oriented SiFe sheet with a thickness of 0.5mm. The size of the case was 100mm wide, 100mm high and 300mm long. Relative permeability of SiFe sheet was needed to calculate shield effect. It was obtained from the measurement by a ferrite yoke and from the calculation by eddy current FEM analysis. Three configurations were used to connect both ends of SiFe sheet. First one is a connection by double-welded butt. Second one is to put the sheet the same material above the confronted both ends of the sheet to avoid a leakage magnetic flux. The last one is ideally without any connection. The shield effect of the second one agreed well with the last one and showed the shield effect of -40dB.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.3
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• pp.433-438
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• 2012

We have studied on welding dissimilar materials of Carbon steel SCP1-S by using laser beam. In this research we have performed some experiments to know the possibility of welding dissimilar materials using laser beam and magnetic fields by adjusting the power output of 35W laser. Other conditions of the experiments were as follows : the welding speed was varied in the range 10 m/min nitrogen gas was used as shield gas, the flow value of shield gas was ranged 10 L/min. In order to ascertain of the welded surface, we have done the tensile strength testing, the hardness testing and the microscope observation. As a result, we have found that tensile strength was the highest at the condition of the welding speed of 10mm/s, the flow value of 10 L/min, the gap of two materials 0, and the use of nitrogen gas. Above testings have also showed that the tensile strength was generally satisfactory since the penetration of welding was almost complete due to the thinness of the materials. In addition, the formation of the welded area was excellent when it had the highest tensile strength.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.4
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• pp.166-171
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• 2005

Shielding methods on ELF(Extremely Low Frequency) magnetic fields may include the use of induced currents, modification of magnetic field flux patterns using high permeability and/or high conductivity materials, and others. The magnetic shielding properties of enclosures can be utilized to reduce the magnetic field of current carrying conductors. In this paper, to get a more practical understanding of shielding phenomena, we have investigated the magnetic field reduction by means of 3 dimensional numerical analysis and experiments. We found copper could reduce flux density more then permalloy in both cases of box shield and cylindrical shield. Iron under l0$\mu$T of 1 phase could reduce flux density about $20\%$ more than silicon steel, but both of them under 50$\mu$T has a similar reduction rate of $10\%$. The 3 phase horizontal model gave the highest reduction rate and the 1mm thickness iron under 10$\mu$T of 3 phase lines did lowest.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.551-552
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• 2011

In this study new evaluation method of eddy currents in conductive shielding sheets are introduced. This method is based on the magnetic flux linkage in rectangular cells. According to this method the allocated amount of memory and the calculation time can be reduced. In this method calculation of magnetic field in any space can be performed by summing contributions of source currents and eddy currents in conductive shielding sheets. This method is applicable to the design of magnetic field-shield.