• Journal of the Korean Magnetics Society
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• v.25 no.3
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• pp.79-82
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• 2015

The design parameter study about the magnetic pulse forming is performed using finite element analysis with MAXWELL. The first case of design parameters is about the initial charging voltage and the capacitance and the second case of design parameters are about the winding turns and the spacing of electromagnetic coil. The 3D finite element model of electromagnetic forming system is created and the magnetic force is calculated. The effects of design parameters on the magnetic forming force are investigated.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.3
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• pp.729-736
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• 2010

In this study, a magnetic stimulation (MS) device with controllable pulse forming technology and pulse shape (MS) is described. The MS device uses an IGBT with appropriate snubbers to switch coil currents up to 6 kA, enabling pulse forming technology control from 5 s to over 100 s. The induced electric field pulses use 2% - 34% less energy and generate 57% - 67% less coil heating compared to matched conventional cosine pulses. MS is used to stimulate rhesus monkey motor cortex in vivo with pulse forming technology of 20 to 100 s, demonstrating the expected decrease of threshold pulse amplitude with increasing pulse forming technology. The technological solutions used in the MS prototype can expand functionality, and reduce power consumption and coil heating in MS, enhancing its research and therapeutic applications.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.34-35
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• 2003

고에너지적 Nd-Fe-B계 소결자석 제조를 위한 펄스자장 성형시, 금형 및 다양한 성형조건이 자석의 이방화율 향상에 미치는 영향에 대하여 조사하였다. 일반적으로 butterfly, disk or coin 형태의 자석을 제조하는 방법으로는, 종축자장성형법(Axial Die Press, ADP)을 이용하여 최종제품의 near-net shape으로 성형 및 소결하는 방법과, 횡축자장성형법(Transverse Die Press, TDP)을 이용하여 blick or cylinder 형태로 제조한 후 여러 단계의 가공공정을 거쳐 최종제품으로 제조하는 방법이 적용되고 있다. 그러나, ADP의 경우 분말의 자장정렬 후 성형단계에서 성형밀도가 증가함에 따라 배향의 틀어짐 현상이 증가하므로 이방화율 향상의 한계가 있어 (BH)$_{MAX}$+iHc=54 이상의 자석은 제조되기 어렵고, TDP의 경우 고이방화 자석의 제조가 가능하나 복잡한 형상의 제품을 직접 성형할 수 없어 성형/소결 후 복잡한 가공공정을 거쳐야 하므로 재료의 손실뿐만 아니라 고가의 가공비용이 소요되므로 경제적인 문제점을 갖게 된다. 반면에, 펄스자장 종축성형방법(PDP)은 3T~5T의 펄스자장을 이용하여 분말의 정렬 및 성형을 동시에 수행함으로써 TDP보다 향상된 배향율이 얻어질 수 있으며, ADP으로만 실현 가능한 복잡한 형성의 자석을 near-net shape으로 제조가 가능한 잇점이 있다.다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.153-153
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• 2003

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.48.2-48.2
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• 2011

열전재료는 열과 전기에너지의 상호 변환이 가능한 재료로 이를 이용한 응용제품의 개발이 크게 주목을 받고 있으며, 특히 $Bi_2Te_3$계 합금의 경우 상온에서 가장 우수한 성능지수를 가지는 재료로 많은 연구가 진행되고 있다. 그러나 기존의 $Bi_2Te_3$계 합금은 일방향응고법으로 제조되어 많은 시간과 비용을 필요로 하고, 특히 C축의 Van der Waals 결합으로 인해 기계적 강도가 약하다는 단점이 있었다. 최근 분말야금법을 이용하여 기계적강도를 높이고, 격자산란에 의한 열전도도의 감소로 성능지수를 높일수 있는 방법들이 제시되고 있다. 본 연구에서는 급속응고공정인 가스분무법을 이용하여 n-type의 $95%Bi_2Te_3-5%Bi_2Se_3$분말을 제조하였고, 이 재료의 경우 성형조건에 따라 조직이 쉽게 변하기 때문에 이를 제어하기 위해 단시간동안 고압으로 성형가능한 자기펄스압축성형법(Magnetic Pulsed Compaction)을 이용하여 성형체를 제조하였다. 제조된 성형체는 밀도를 증가시키고 결정립성장을 억제시킬수 있는 방전플라즈마소결법(Spark Plasma Sintering)을 이용하여 소결체로 제조되었으며, 각각의 공정이 열전성능에 미치는 영향을 고찰하였다. OM (Optical Microscope) 및 SEM (Scaning Electric Microscope)을 이용하여 미세구조를 관찰하였고 XRD (X-Ray Diffraction)를 이용하여 상의 변화를 분석하였으며, 상온에서 경도를 측정함으로서 공정조건에 따른 기계적강도를 비교하였다. Seebeck계수는 시편의 양단에 온도차를 주어 발생하는 기전압을 측정하여 계산하였고, 전기비저항은 4point probe방법으로 측정하였다. 전하이동도 및 전하농도는 Hall측정으로부터 구하였고 열전도도를 측정하여 종합적인 열전성능을 평가하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2002.05a
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• pp.89-89
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• 2002

• Journal of the Korean Magnetics Society
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• v.21 no.5
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• pp.180-184
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• 2011

The changes in the blood flow in the peripheral vascular system under strong pulsed magnetic fields (pMF) were studied by digital infrared thermal imaging (DITI). After pMF stimulus temperatures in stimulated area were commonly increased in both groups of age and gender. In order to reduce heat generated from coil in pMF stimulus system plastic moldings were fabricated, so that certain distance was kept between stimulus system and the skin and to prevent direct contact to the skin. It is believed that skin temperature is increased by internal electromagnetic energy stimulated the peripheral vascular system by non-contact method.

• Journal of the Korean Magnetics Society
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• v.13 no.4
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• pp.182-186
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• 2003

A new axial pressing method using pulse magnetizing field was studied to improve the remanence of Nd-Fe-B sintered magnets. In order to make near-net shape green compacts of butterfly, disk, or coin magnets, conventional axial-type pressing has been normally used. However, compared to the transverse-type pressing, it is not possible to obtain higher remanence by this method because the magnetic alignment of powder begins to deteriorate when the density of green compacts increases over a critical value. On the other hand, we found that an axial pressing under pulse magnetizing field was very effective to increase the degree of magnetic alignment of powder, yielding remanences even higher than those obtained by the transverse pressing. In this study, it was revealed that appropriate tapping density and how to apply pulse magnetic held were important to improve the grain alignment and thus remanence of Nd-Fe-B sintered magnet.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.459-461
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• 2009

In this research, a new method for consolidation of Al-20wr%Si powders using a magnetic pulsed compaction (MPC) was introduced. A wide Range of experimental studies were carried out to characterize the mechanical properties and microstructure of the MPCed materials by means of SEM, TEM and tensile test. It was found that the effective properties like higher strength and full density were achieved while maintaining a fine microstructure. Consolidated bulk by MPC showed higher density without any crack than that of the general process. With increasing the number of MPC compaction, the density and mechanical properties were also greatly improved.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.390-393
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• 2008

In this research, we introduce a new process for the consolidation of different types of powders such as metal and ceramic powders by using a magnetic pulsed compaction (MPC). The successful consolidation of many kinds of powers including nanopowder by MPC has been presented. A wide range of experimental studies were carried out for characterizing mechanical properties and microstructure of the MPCed materials. It was found that effective properties of high strength and full density maintaining nanoscal microstructure were achieved. finally, optimization of the compaction parameters and sintering conditions could lead to the good consolidation of powders (metal, ceramic, nano-powder) with higher density, and even further enhanced mechanical properties.