• Journal of Magnetics
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• v.14 no.2
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• pp.75-79
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• 2009

Nickel (Ni) and ferrite ($Fe_3O_4$, $NiFe_2O_4$) nanoparticles were synthesized by LGC using both wire feeding (WF) and micron powder feeding (MPF) systems. Phase evolution and magnetic properties were then investigated. The Ni nanopowder included magnetic-ordered phases. The LGC synthesis yielded spherical particles with large coercivity while the abnormal initial magnetization curve for Ni indicated a non-collinear magnetic structure between the core and surface layer of the particles. Since the XRD pattern cannot actually distinguish between magnetite ($Fe_3O_4$) and maghemite (${\gamma}-Fe_2O_3$) as they have a spinel type structure, the phase of the iron oxide in the samples was unveiled by $M{\ddot{o}}ssbauer$ spectroscopy. The synthesized Ni-ferrite consisted of single domain particles, including an unusual ionic state. The synthesized nanopowder bore an active surface due to the defects that affected abnormal magnetic properties.

• Journal of the Korean institute of surface engineering
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• v.48 no.6
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• pp.335-342
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• 2015

Recently, the production of oil and gas at the arctic ocean and offshore has been growing. Accordingly, S500 steel with the high tensile strength and excellent toughness has been used and flux cored wire that can be welded to the S500 has been required. In this study, we carried out observation of microstructures, mechanical properties and CTOD (crack tip openning displacement) in the weld zone that GMA (gas metal arc) welded with different component of $TiO_2$ flux core wire (the main components, rutile or Ti-slag) for S500 steel. Weld zone produced with Ti-slag flux cored wire has formed a enough acicular ferrite and shown excellent impact toughness at $-40^{\circ}C$, tensile strength at room temperature and CTOD at $-20^{\circ}C$. As a result, the developed flux cored wire was suitable for S500 steel.

• Journal of the Korean Magnetics Society
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• v.9 no.6
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• pp.278-284
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• 1999

The effect of TiO$_2$addition has been studied on the power loss, density, initial permeability, resistivity, and microstructure of Mn-Zn ferrites. TiO$_2$addition increased the density of sintered body and decreased of the initial permeability. Activation energy for electron hopping as well as electrical resistivity increased with TiO$_2$addition. The toroidal core sintered at 1150 $^{\circ}C$ with 1.5 wt% of TiO$_2$demonstrated the power loss of 83 mW/㎤ at 1 MHz, 25 mT, 8$0^{\circ}C$. However, the same specimen sintered at 120$0^{\circ}C$ lead to the power loss, 1168 mW/㎤ at 1 MHz, 25 mT, 8$0^{\circ}C$ and developed an exaggerated grain growth.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.683-686
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• 2000

The chargers for DC power supply of the contro1lers, which have been installed in the relay rooms in 345/154kV substations of KEPCO, lag in both aspects of technique and performance. Moreover, as they are SCR-based, they dont meet the performance requirements of todays digital and automated controllers. Now two controllers are running in pair and one of those is for reservation. There are lots of troubles because the patrol engineering team has to replace them manually whenever they are out of order. So it is expected to bring convenience if the charger replacement is automated. Also, the existing chargers take much space, weight and cost - which have increased the need of development to make them smaller, less expensive, and have high quality. We will develop a charger system which has one fifth of the weight of the existing system by double-integrating the volume. The new system will be ready for a future full unmanned system with integrated pores for remote control, state-of-the-art digital features, and more than 90% efficiency/power factor against 80% efficiency/power factor of the existing system.

• Journal of the Korean Ceramic Society
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• v.35 no.10
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• pp.1055-1060
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• 1998

The effects of particle size distribution have been investigated on the high frequency low loss Mn-Zn fer-rites. The particle size distribution was controlled by milling time. Zirconia ball and engineering plastic jar were employed to avoid iron contamination from the milling media. As increasing the milling time BET value was increased from 0.55 to 3.21m2/g and mean particle size was decreased from 2.1 $\mu\textrm{m}$ to 1.0$\mu\textrm{m}$ The large specific surface area of initial powder resulted in the high density of sintered core. However starting powders with high BET lead to inhomogeneous grain growth as well as poor electromagnetic pro-perties at sintering temperature above 1300$^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.365-368
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• 2000

We have studies on the Microstructures and densities as a function of forming pressures and the magnetic properties of the specimens with additive Bi$_2$O$_3$ that sintered at 95$0^{\circ}C$ for 4.5 hours for synthesizing optimal Ni-Cu-Zn ferrite. Green density rose generally as Forming pressure increased from 1.7 ton/cm$^2$to 2.5 ton/cm$^2$and Cold Isostatic Pressure(CIP) method was more effective than Die Pressure(DP) method to high green density. Forming pressure had no influence on apparent density but on the other hand Bi$_2$O$_3$contents were strongly dominant to appaernt density than forming pressure. Bi$_2$O$_3$liquid phases created during sintering process promoted sintering and grain growth so that apparent density, grain size and permeability increased compared to that of the specimens which were sintered with non-additive Bi$_2$O$_3$.

• Journal of the Korean Magnetics Society
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• v.25 no.1
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• pp.22-26
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• 2015

In this paper, a magneto-inductive wave generated in a chain of LC resonators fabricated with Ni-Zn ferrite cores and chip capacitors is presented. RF signal propagates to neighbor resonator one by one as a consequence of the magnetical coupling between two resonators in the device. The magnetical coupling is due to the mutual inductances along the chain of resonators. So, the signal amplitude (${\approx}$ coupling intensity) is dependent of the mutual inductance which can be adjusted by applied magnetic field. In order to demonstrate the device, some experiments have been carried out systemically. The transmission characteristics of a magneto-inductive wave could be controlled by applied external magnetic field. The device composed of 5 resonators; the center frequencies were estimated to be 32 MHz and 38 MHz with the external magnetic flux density of 75 Oe and 222 Oe, respectively. We expect that the reported results could open a promising way to a high variety of applications in one- and two-dimensional functional devices, such as transducers, delay lines, power dividers and couplers.

• Korean Journal of Materials Research
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• v.6 no.1
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• pp.22-28
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• 1996

고주파 이동통신의 효용이 증가할수록 고주파 회로에 들어가는 부품들의 소형화가 중요한 과제로 대두되고 있다. 인덕터는 전자회로에 이용되는 주요 부품의 하나이며, 현재 교주파용 소형 인덕터를 박막화하려는 시도가 진행중이다. 본 연구에서 열산화시킨 Si(100)기판위에 성공적으로 박막형 인덕터를 제조하였다. Core 물질로는 ion beam sputtering 법으로 증착한 Ni-Zn 페라이트와 PECVD법으로 증착한 SiO2를 사용하였다. 고온산화분위기의 박막 증착과정을 고려하여 귀금속류인 Au를 전극으로 이용하였으며, life-off법으로 미세회로를 구현하였다. 상하부 전극의 안정적인 연결을 위하여 2차 전극배선 전에 via를 채워넣었다. 제조된 박막 인덕터의 고주파 특성은 network analyzer로 측정한 후 HP사의 Mecrowave Design System으로 분석하였다.

• Journal of Magnetics
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• v.21 no.3
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• pp.450-459
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• 2016

Experimental results and data of numerical simulations are presented, concerning generation of wideband radio frequency (RF) oscillations in a nonlinear transmission line (NLTL) which contains a pre-magnetized core of ferrite material. Emphasis is made on the means for extracting the RF signal from the line, in order to radiate it into free space. Antennas of two types that can be used for the purpose are considered, both featuring a coaxial design. This permits availing of the principal advantages of coaxial systems, such as operation in the mode of a traveling TEM wave; wide range of the transmitted frequencies, and a reasonably simple design. The antennas studied, specifically a disc-cone dipole (DCD) and an impulse reflector antenna ('Half-IRA', or HIRA type) differ significantly in effective width of the radiated spectrum and in spatial characteristics of the radiated field in far region.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.211-214
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• 2004

The advantage of ring-shaped electrodeless fluorescent lamp is the removal of internal electrodes and heating filaments that are a light-limiting factor of conventional fluorescent lamps. Therefore, the life time of ring-shaped electrodeless fluorescent lamps is substantially higher than that of conventional fluorescent lamps and last up to 60,000 hours and is intended as a high efficacy replacement for the incandescent reflector lamp in many applications. In this paper, maxwell 3D finite element analysis program(Ansoft) was used to obtain electromagnetic properties associated with the coil and nearby structures. The electromagnetic emitting properties were presented by 3D simulation software operated at 250[kHz] and some specific conditions