• 한국자기학회지
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• 제22권6호
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• pp.210-215
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• 2012

단층형 전자파 흡수체의 흡수 성능은 입사파의 반사 손실(return loss)이 최대가 되는 두께 정합 조건 및 주파수 정합 조건에서 최적화 된다. 본 연구에서는 재료의 복소 투자율과 복소 유전율에 의존하는 전송선 이론을 적용하여 광대역 흡수체의 정합 조건을 계산하였다. 그 결과 주파수에 따른 복소 투자율 감소 특성이 두께 정합 조건을 광대역으로 확대하는 효과를 지니기 때문에 광대역 전자파 흡수체에 자성 재료가 이용될 수 있다는 것을 알 수 있었다. 따라서 향후 확대될 EMC(Electromagnetic compatibility) 규격을 대비한 차세대 광대역 전자파 흡수체를 만들기 위하여 현재 사용되고 있는 NiZn 페라이트 소결체 보다 포화 자화량이 크고 유전율 값이 작은 자성 재료들을 사용하여야 한다는 것을 보였다.

• 한국자기학회지
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• 제10권1호
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• pp.11-15
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• 2000

수분사법으로 제조된 13Cr-1.5Nb-Fe 합금분말을 수소분위기 하에서 환원처리 하였다. 분말특성이 조사된 환원분말을 이용하여 자기코아를 제작한 후 약 $10^{-5}$Torr의 진공분위기에서 소결하였다. 자기코아의 교류자기특성을 조사하기 위하여 투자율과 자기손실을 조사하였다. 환원분말의 입도분포는 약 70$\mu\textrm{m}$에서 50% vol.을 나타내며, 포화자화 값은 약160 emu/g이었다. 10ton/$\textrm{cm}^2$ 성형압력, 1,20$0^{\circ}C$ 소결온도에서 제작된 자기코아의 교류투자율은 주파수, f=1 kHz, 인가자장, H$_{a}$ =5 Oe에서 400이다. 또한 동조건에서 제작된 자기코아의 교류자기이력손실은 유도자화, B$_{m}$ =80G에서 0.12mW/cc이다.

• Advances in nano research
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• 제1권4호
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• pp.183-192
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• 2013

One-dimensional multiferroic nanostructured composites have drawn increasing interest as they show tremendous potential for multifunctional devices and applications. Herein, we report the synthesis, structural and dielectric characterization of barium titanate ($BaTiO_3$)-bismuth ferrite ($BiFeO_3$) composite fibers that were obtained using a novel sol-gel based electrospinning technique. The microstructure of the fibers was investigated using scanning electron microscopy and transmission electron microscopy. The fibers had an average diameter of 120 nm and were composed of nanoparticles. X-ray diffraction (XRD) study of the composite fibers demonstrated that the fibers are composed of perovskite cubic $BaTiO_3$-$BiFeO_3$ crystallites. The magnetic hysteresis loops of the resultant fibers demonstrated that the fibers were ferromagnetic with magnetic coercivity of 1500 Oe and saturation magnetization of 1.55 emu/g at room temperature (300 K). Additionally, the dielectric response of the composite fibers was characterized as a function of frequency. Their dielectric permittivity was found to be 140 and their dielectric loss was low in the frequency range from 1000 Hz to $10^7$ Hz.

• 조명전기설비학회논문지
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• 제26권2호
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• pp.27-33
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• 2012

In this paper, we researched the heat transfer analysis of 1.2[kW] BLDC motor on the condition of the external flow. The BLDC motor is fallen under influence of some heat generated by rotationg motor speed and it changes the life and confidence of motor. The heat makes to reduce the life of insulation and the magnetization. So motor can't make own performance. Therefore we calculated the losses about number of revolutions of motor. And then, we analyzed the heat transfer of BLDC motor by using the results when a fan attached to motor makes the external flow or not. The results showed that the temperature of motor increased constant values irrespective of external air temperature. The temperature of motor decreased very lower values than prior researches when the fan makes the external flow. In this method we can analyze the performance, losses and heat transfer of motor applied in the many industries.

• Progress in Superconductivity
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• 제14권2호
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• pp.82-86
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• 2012

A sensitive eight-channel high-Tc Superconducting Interference Device (SQUID) detection system for magnetic contaminant in a lithium ion battery anode was developed. Finding ultra-small metallic foreign matter is an important issue for a manufacturer because metallic contaminants carry the risk of an internal short. When contamination occurs, the manufacturer of the product suffers a great loss from recalling the tainted product. Metallic particles with outer dimensions smaller than 100 microns cannot be detected using a conventional X-ray imaging system. Therefore, a highly sensitive detection system for small foreign matter is required. We have already developed a detection system based on a single-channel SQUID gradiometer and horizontal magnetization. For practical use, the detection width of the system should be increased to at least 65 mm by employing multiple sensors. In this paper, we present an 8-ch high-Tc SQUID roll-to-roll system for inspecting a lithium-ion battery anode with a width of 65 mm. A special microscopic type of a cryostat was developed upon which eight SQUID gradiometers were mounted. As a result, small iron particles of 35 microns on a real lithium-ion battery anode with a width of 70 mm were successfully detected. This system is practical for the detection of contaminants in a lithium ion battery anode sheet.

• 한국분말재료학회지
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• 제16권4호
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• pp.249-253
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• 2009

3-D shape soft magnetic composite parts can be formed by general compaction method of powder metallurgy. In this study, the results on the high density nanostructured Fe-Si/Fe composite prepared by a warm compaction method were presented. Ball-milled Fe-25 wt.%Si powder, pure Fe powder and Si-polymer were mixed and then the powder mixture was compacted at various temperatures and pressures. Pore free density of samples up to 95% theoretical value has been obtained. The warm compacted sample prepared at 650 MPa and 240$^{\circ}C$ had highest compaction properties in comparison with other compacts prepared at 300, 400 MPa and room temperature and 120$^{\circ}C$. The magnetic properties such as core loss, magnetization saturation and coercivity were measured by B-H curve analyzer and vibration sample magnetometer.

• Journal of Magnetics
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• 제11권4호
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• pp.164-166
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• 2006

We have investigated the dielectric and magnetic properties of ferroelectric-antiferromagnetic $BaTiO_{3}-LaMnO_{3}$ composite with changing relative mole percents. Due to high sintering temperature, i.e. $1150^{\circ}C$, the Ba ion in $BaTiO_{3}$ seems to diffuse into $LaMnO_{3}$; resulting in $BaTiO_{3}-(La,Ba)MnO_{3}$ ferroelectric-ferromagnetic composite. At room temperature, $0.9BaTiO_{3}-0.1LaMnO_{3}$ composite exhibits considerable magnetization (${\sim}0.7\;emu/g\;at\;2000\;Oe$) and low coercive field (${\sim}5\;Oe$). Also it exhibits high dielectric constant (${\sim}560$) and low loss (${\sim}0.08$) at 10 kHz. This result may imply that $BaTiO_{3}-LaMnO_{3}$ could be suitable for a low leakage multiferroic composite.

• 대한화학회지
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• 제56권5호
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• pp.609-616
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• 2012

Ba-ferrite ($BaFe_{12}O_{19}$) nanoparticles were synthesized by chemical coprecipitation method in an aqueous solution. The particle size and the crystallization temperature of the Ba-ferrite nanoparticles were controlled varying the precipitation temperature. The precipitate that was prepared at $0^{\circ}C$ showed the crystal structure of Ba-ferrite in X-ray diffraction when it was calcined at the temperature above $580^{\circ}C$, whereas what was prepared at $50^{\circ}C$ showed the crystallinity when it was calcined at the temperature higher than about $700^{\circ}C$. The particle sizes of the synthesized Ba-ferrite were in a range of about 20-30 nm when it was prepared by being precipitated at $0^{\circ}C$ and calcined at $650^{\circ}C$. When the precipitation temperature increased, the particle size also increased even at the same calcination temperature. The magnetic properties of the Ba-ferrite nanoparticles were also controlled by the synthetic condition of precipitation and calcination temperature. The coercive force could be appreciably lowered without a loss of saturation magnetization when the Ba-ferrite nanoparticles were prepared by precipitation and calcination both at low temperatures.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.621-622
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• 2008

This paper deals with the magnetic properties under the rotational magnetic field on the electrical steel sheet by using Single Sheet Tester with two excitation coils. Actually, the magnetic flux of stator cores in running motors have the behaviour of rotating and alternating flux. In order to improve motor characteristics, it is require to estimate these magnetic properties. When the magnetic field vectors are rotating around in the plane of the sheet during one period of cycle, the magnetization properties and the core loss are measured and then, the results are compared with the magnetic properties obtained by the alternating magnetic fields.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.808-809
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• 2008

22.9kV 50MVA HTS power cable has been developed and tested by Korea Electrotechnology Research Institute and LS Cable Company and it was supported by a grant from Center for Applied Superconductivity Technology of the 21st Century Frontier R&D Program. In this paper, DC Ic of 100m HTS cable which is installed at Kochang testing station was measured and analyzed. A measurement technique of DC Ic used by resistance and inductance removal method is established. The HTS power cable is composed of 2 layers for transmission and 1 layer for shield. For the analysis of AC losses in an HTS power cable, 2-dimensional numerical calculation was carried out to define the magnetic field distribution. We calculated the magnetization losses in the HTS core of that cable from these fields. These calculated results are in accordance with those of experiment.