• Progress in Superconductivity
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• 제3권2호
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• pp.183-187
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• 2002

In this paper we analyzed the electromagnetic behavior of high $-T_{c}$ superconductor under the quench state using finite element method. Poisson equation was used in finite element analysis as a governing equation and was solved using algebra equation using Gallerkin method. We first investigate d the electromagnetic behavior of U-type superconductor. Finally we applied our analysis techniques to 5.5 kVA meander-line superconducting fault current limiters (SFCL) which are currently developed by many power-system researcher in the world. Meshes of 14,600 elements were used in analysis of this SFCL. Analysis results show that the distribution of current density was concentrated to inner curvature in meander-line type-superconductors and maximum current density 14.61 $A/\m^2$ and also maximum Joule heat was 6,420 W/㎥. We concluded that this meander line-type SFCL was not pertinet fur uniform electromagnetic field distribution.n.

• 대한전기학회논문지:전력기술부문A
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• 제53권1호
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• pp.38-42
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• 2004

In this paper we analyzed the electromagnetic behavior of a superconducting fault current limiter (SFCL) under the quench state using FEM. The analysis model used in this work is 5.5 KVA meander-line type SFCLs which are currently developed by Superconductor Power System Lab in Korea Electric Power Research Institute. Meshes of 3,650 triangular elements were used in the analysis of this SFCL. Analysis results showed that the distribution of current density was concentrated to inner curved line in meander-line type SFCL and the maximum current density was 14.61 A/$m^2$ and also the maximum Joule heat was 2,030 W/$m^2$ in this region. We think that the new and the modified structure must be considered for an uniform distribution of the electromagnetic field.

• 한국세라믹학회지
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• 제28권7호
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• pp.556-560
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• 1991

The behavior of Ni-Zn ferrite/Mn-Zn ferrite composite electromagnetic absorber was investigated. The imaginary part of complex permeability of the composite was higher than that of either ferrite alone at all frequency range (50∼1400MHz) studied. The difference, which was pronounced in low frequency range, was reached the maximum value when the composite consisted of constituent ferrites with equal amount. Since the thickness in inversely proportional to the imaginary part of complex permeability for the ferrite absorber, it was possible to reduce the thickness of electromagnetic absorber by employing a composite of two different ferrites.

• 한국주조공학회지
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• 제25권4호
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• pp.156-160
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• 2005

There are many factors that influence solidification behavior during continuous casting, e.g. include superheat, casting speed, cooling rate and holding time. However, when melt is stirred by electromagnetic force, there would be some changes in its solidification behavior compared to that of the ordinary casting process. In this study, the billets of A356 alloy with a diameter of 3 inch were fabricated with electromagnetic stirring under various conditions of superheat, casting speed and input voltage of electro magnetic stirring (EMS) device. The microstructure was also investigated under the various casting conditions and electromagnetic input voltages. When increase in input voltage, the microstructure was changed from dendritic to rosette type and finally to spheroidal. With pouring temperature, casting speed and electromagnetic input voltage were $650^{\circ}C$, 100 mm/min and 140 V, respectively, the billet with a diameter of 3 inch, which has a uniform dispersed spheroidal particles in the whole area of billet except for the surface area, was manufactured.

• Journal of Magnetics
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• 제13권3호
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• pp.92-96
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• 2008

There are few reports of high frequency loss behavior in the near-field for magnetic films with semiconducting properties, even though semiconducting magnetic materials, such as soft magnetic amorphous alloys and nanocrystalline thin films, have been demonstrated. The electromagnetic loss behavior of multilayer magnetic films with semiconducting properties on the microstrip line in quasi-microwave frequency band was analyzed numerically using a commercial finite-element based electromagnetic solver. The large increase in the absorption performance and broadband characteristics of the semiconducting/insulating layer magnetic films examined in this study were attributed to an increase in the loss factor of resistive loss. The electromagnetic reflection increased significantly with increasing conductivity, and the loss power deteriorated significantly. The numerical results of the magnetic field distribution showed that a strong radiated signal on the microstrip line was emitted with increasing conductivity and decreasing film thickness due to re-reflection of the radiated wave from the surface of the magnetic film, even though the emitted levels varied with film thickness.

• Journal of electromagnetic engineering and science
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• 제18권2호
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• pp.129-135
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• 2018

This paper proposes a design of small controlled reception pattern antenna (CRPA) arrays using circular microstrip loops with frequency-insensitive characteristics. The proposed array consists of seven identical upper and lower circular loops that are electromagnetically coupled, which results in a frequency-insensitive behavior. To demonstrate the feasibility of the proposed feeding mechanism, the proposed array is fabricated, and its antenna characteristics are measured in a full-anechoic chamber. The operating principle of the proposed feeding mechanism is then interpreted using an equivalent circuit model, and the effectiveness of the circular loop shape is demonstrated by calculating near electromagnetic fields in proximity to the radiator. The results confirm that the proposed feeding mechanism is suitable to have frequency-insensitive behavior and induces strong electric and magnetic field strengths for higher radiation gain in extremely small antenna arrays.

• Journal of Electrical Engineering and Technology
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• 제8권4호
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• pp.824-831
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• 2013

Lightning electromagnetic fields are important issues for the evaluation of lightning induced overvoltage on power lines and for setting the appropriate protection level for power networks. Such electromagnetic fields are strongly dependent on lightning return stroke currents at different heights along the lightning channel. On the other hand, the ground reflection factor due to the difference between the return stroke channel impedance and the equivalent ground impedance at channel base can have an effect on the shape of the return stroke currents by entering additional reflected currents into the channel. In this paper, the effect of the ground reflection factor on the return stroke currents at different heights along a channel and the electromagnetic fields associated with the lightning channel at close distances are considered. Moreover, the behavior of the electromagnetic fields versus the reflection factor changes and the radial distance changes are considered and the results are discussed accordingly. The results illustrate that the reflection factor has a direct relationship with the values of the electromagnetic fields while this is usually ignored in earlier studies.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2002년도 종합학술발표회 논문집 Vol.12 No.1
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• pp.39-43
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• 2002

In this thesis, a λ/4 hair-pin resonator is proposed to reduce the size of resonators. A LTCC MLC bandpass filter is designed using the λ/4 hair-pin resonators. The electromagnetic coupling structure between two planar resonators is analysed. The equivalent circuit is derived to explain the behavior of the LTCC MLC bandpass filter using λ/4 hair-pin resonators. A design procedure is also described. The simulated and measured results of 2-pole bandpass filter are presented.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권2호
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• pp.61-66
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• 2003

The electromagnetic properties and thermal behavior of Mn-Zn ferrite cores used for the blocking filter in he Power Line Communication(PLC) application were investigated as the function of additives. The highest density and permeability of 4.98 g/㎤) and 8,221 respectively were obtained to the specimen with composition of MnO 24 mol%, ZnO 25 mol% and Fe$_2$O$_3$ 51 mol% added MnO$_3$ 400 ppm, SiO$_2$ 100 ppm and CaO 200 ppm since the uniform grains were organized and the microstructures were compacted through reduction of pores. The permeability was increased up to 13,904 as temperature of specimen increased to 11$0^{\circ}C$, however, it was decreased precipitously under 100 over 11$0^{\circ}C$. The exothermic behavior was observed in the frequency range from 1 kHz to 1 MHz that the maximum temperature of specimens became 102$^{\circ}C$ at 1 MHz. In the consequence, the Mn-Zn ferrite core developed by this research will maintain the stable electromagnetic properties since the temperature of ferrite core rose to 93$^{\circ}C$ in the range of 10 kHz to 450 kHz bandwidth qualified for PLC.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 초전도 자성체
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• pp.68-71
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• 2002

The electromagnetic properties and thermal behavior of ferrite cores used in the blocking filter for PLC were investigated as a function of additives. The highest density of 4.98 $g/cm^2$ and permeability of 8221 were obtained to the specimen added $MoO_3$ 400 ppm, $SiO_2$ 100 ppm and CaO 200 ppm since the microstructures were compacted through reduction of pores in the specimen. The permeability was increased up to 13094 at $110^{\circ}C$ with increasing temperature of specimen, however, it was decreased precipitously to under 100 over $110^{\circ}C$. The exothermic behavior was observed that the temperature of specimens became $102^{\circ}C$ at 1MHz. In the consequence, the ferrite core developed by this research will maintain the stable electromagnetic properties since the temperature of ferrite core rose to $93^{\circ}C$ in the range of 10kHz to 450kHz bandwidth qualified for PLC.