• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.57.2-57.2
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• 2010

투명전도 산화막(Transparent conducing oxide: TCO)은 태양 전지, 터치패널, 가스 센서 등 여러 분야에 적용할 수 있는 물질로서 전기 전도성과 광 투과성을 동시에 가진다. 높은 전기 전도성과 광 투과성을 가지는 Sb:$In_2O_3$(ITO)는 투명전도 산화막 재료로써 가장 일반적으로 사용되고 있으나 인듐의 매장량 한계로 인해 가격이 높다는 단점이 있다. 본 연구에서는 ITO 대체 TCO 물질인 Al doped ZnO(AZO)를 rf magnetron sputter를 이용하여 최적의 수소 도핑량을 찾아 ITO의 전기적 광학적 성질과 비교하였다. AZO 박막은(ZnO:Al2O3 2wt.%)타겟을 이용하여 heater 온도 250도에서 슬라이드 글래스 및 코닝 글래스에 증착시켰고 비교군인 ITO박막은 (In2O3:$SnO_2$ 10wt.%)타겟을 이용하여 수소 도핑 없이 350도로 증착시켰다. AZO 및 ITO 박막의 전기적 특성은 hall measurement를 이용하여 측정하였고, UV-VIS spectrophotometer로 광학적 특성을 측정하였다. 수소 도핑량이 증가함에 따라 AZO 박막의 캐리어 농도가 증가하여 전기적 특성이 향상되었고, 가시광 영역에서 높은 평균 투과도를 유지 하였다. AZO 박막과 ITO 박막의 전기적 및 광학적 특성을 비교한 결과, 최적 수소 도핑량을 가진 AZO 박막은 ITO 박막에 준하는 특성을 보였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.10
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• pp.843-852
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• 2016

The autorotative flight of maple seeds(Acer palmatum) is numerically simulated based on the 3D geometry and the motion parameters of real seeds. The nominal values of the motion parameters are 1.26 m/s for descent velocity, 133.6 rad/s (1,276 rpm) for spinning rate, $19.4^{\circ}$ for coning angle, and $-1.5^{\circ}$ for pitch angle. A compact leading-edge vortex (LEV) positioned at the inner span of the seed blade causes a large suction pressure on its leeward surface. The suction pressure peaks occur near the leading region of inner span sections. The flow pattern characterized by the prominent LEV and the values of aerodynamic force coefficients obtained in the present study are in good agreement with experimental data measured for a dynamically-scaled robot maple seeds. A spiraling vortex developed in the leeward region advances toward the seed tip and merges with the tip-passing flow, which is considered to be a mechanism of maintaining stable and attached LEV for the autorotating maple seeds.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.12
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• pp.2989-2994
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• 2000

A mechanical face seal is a tribo-element intended to control leakage of working fluid at the interface of a rotating shaft and its housing. Leakage of working fluid decreases drastically as the clearance between mating seal faces gets smaller. But the very small clearance may result in an increased reduction of seal life because of high wear and heat generation. Therefore, in the design of mechanical face seals a compromise between low leakage and acceptable seal life is important, ant it present a difficult and practical design problem. A fluid film or sealing dam geometry of the seal clearance affects seal lubrication performance very much, and thereby is optimization is one of the main design consideration. in this study the Reynolds equation for the sealing dam of mechanical face seals is numerically analyzed, using the Galerkin finite element method, which is readily applied to various seal geometries, to give lubrication performances, such as opening force, restoring moment, leakage, and axial and angular stiffness coefficients. Then, to improve the seal performance an optimization is performed, considering various design variables simultaneously. For the tested case the optimization ha successfully resulted in the optimal design values of outer and inner seal radii, coning, seal clearance, and balance radius while satisfying all the operation subjected constraints and design variable side-constraints, and improvements of axial and angular stiffness coefficients by 16.8% and 2.4% respectively and reduction of leakage by 38.4% have been achieved.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.10
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• pp.888-895
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• 2015

This paper shows an approximate equation which calculates a flapping angle of blade for verification of KUH safety area. The flapping behavior of blade must be reviewed in an aspect of safety because of a collision possibility with airframe. However, it is difficult to measure an exact flapping angle during flight. A prediction equation of a coning angle is derived from aeromechanics and that of a dynamic flapping angle is derived from analysis results in development phase, respectively. Following, the equations are verified by comparison the flapping angle through an aircraft simulation test to a calculation. Finally, the safety area, which was established in development phase, is verified by calculating a flapping angle during the flight which is required by the terms of safety based on AC29 and FAR29.

• Korean Journal of Crystallography
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• v.7 no.2
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• pp.175-182
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• 1996

ZnO thin films were deposited on Corning 7059 glass substrates to study fundamental properties of films. According to the experimental results, (002) preferred ZnO thin films were grown by purging Ar/O2 mixed gas, but not without oxygen gas. The structure and the orientation of ZnO thin films were much affected by the substrate temperature and rf power. High quality ZnO films were obtained by increasing their values. Optimum deposition parameters were : 300W rf power, 300℃ substrate temperature, Ar/O2=70/30. To characterize SAW propagation properties, IDT was fabricated by etching Al films deposited on diamond/Si wafer with RIE. Measured λ(wavelength) was 24μm and experimental results were well matched with simulation. Center frequency was 250MHz, and the calculated phase velocity of ZnO/ diamond structure was about 6000m/s.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.8
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• pp.653-660
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• 2017

In this paper, the author analyzes direction finding accuracy based on phase comparisons to estimate elevation and azimuth angles of arrival signals. This paper considers the uniform array configurations using four and three elements. In that direction finding structures, I present the analytic expressions for estimated elevation and azimuth angles and then analyze the direction finding errors. And one presents the design guideline of direction finding system in comparison with aspects of accuracy, structure, the number of channels in that structures. The analysis result is similar with simulation one and has difference within $1.2^{\circ}RMS$. From the proposed analysis results, one knows that when SNR is 20 dB and the baseline is half of wavelength, the estimated elevation accuracy of the uniform array using four elements is 1.15 times better than the one of the uniform array using three elements and the estimated azimuth accuracy is same each other. In addition, one knows coning error is eliminated in 2-D direction finding structure.

• Journal of Navigation and Port Research
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• v.41 no.6
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• pp.389-394
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• 2017

In this paper, the captive model test of a submarine using the RA test was carried out in a square basin. The target model submarine consisted of four types varying according to the position of conning tower and control planes. Hydrodynamic derivatives were acquired by multi-regression analysis. As a result, horizontal dynamic stability indexes of the four types presented positive values and satisfied dynamic stability requirements. In addition, the stability index of type 1 and type 4 - each with the same cruciform configuration of the aft planes - scored within the acceptable range of motion stability.

• Journal of the Korean Magnetics Society
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• v.20 no.4
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• pp.129-133
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• 2010

Two-layered ferromagnetic alloy films (NiFe, CoFe) with a Conetic (NiFeCuMo) intermediately soft magnetic layer of different thickness were investigated to correlate the coercivity values and magnetization process with the strength of saturation field of hard axis. Thickness dependence of the $H_{EC}$ (coercivity of easy axis), $H_{HS}$ (saturation field of hard axis.), and X (susceptibility) of NiFe and NiFeCuMo thin films for the glass/Ta(5 nm)/[CoFe or NiFe(5 nm-t/2)]/NiFeCuMo(t = 0, 4, 6, 8, 10 nm)/[CoFe or NiFe(5 nm-t/2)]/Ta(5 nm) films prepared by the ion beam deposition method was measured. The magnetic properties $H_{EC}$, $H_{HS}$, and X of two-layered ferromagnetic CoFe, NiFe films with a NiFeCuMo intermediately super-soft magnetic layer were strongly depended on the thickness of NiFeCuMo layer. The value of the coercivity and magnetic susceptibility of the NiFeCuMo film decreased by 25% and doubled relative to that of the NiFe film.

• Journal of Sensor Science and Technology
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• v.9 no.2
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• pp.146-152
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• 2000

Lithium doped zinc oxide(ZnO:Li) films are prepared by rf magnetron sputtering on Corning 7059 glass substrate using specifically designed ZnO targets containing different amount of $Li_2CO_3$ powder as the Li doping source. The structural properties of the Li doped ZnO films are investigated by XRD, SEM and AFM. The electrical properties of the ZnO:Li films are measured for various deposition conditions, such as the substrate temperature, $O_2$/Ar gas ratio and rf power. The effects of the $Li_2CO_3$ content in target and the deposition conditions on the structural and electrical properties were studied. When ZnO:Li films were sputtered at the substrate temperature of $200^{\circ}C$, $O_2$/Ar gas ratio of 100% and rf power of 100W with a target containing less than 1wt% content of $Li_2CO_3$, showed good surface morphology, strong c-axis orientation and high resistivity of more than $10^8{\Omega}cm$.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.4
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• pp.110-115
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• 2010

Transparent conducting gallium-doped zinc oxide (GZO) thin films which were deposited on Corning glass substrate using an Gun-type rf magnetron sputtering deposition technology. The GZO thin films were fabricated with an GZO ceramic target (Zn : 97[wt%], $Ga_2O_3$ : 3[wt%]). The GZO thin films were deposited by varying the growth conditions such as the substrate temperature, oxygen pressure. Among the GZO thin films fabricated in this study, the one formed at conditions of the substrate temperature of 200[$^{\circ}C$], Ar flow rate of 50[sccm], $O_2$ flow rate of 5[sccm], rf power of 80[W] and working pressure of 5[mtorr] showed the best properties of an electrical resistivity of $2.536{\times}10^{-4}[{\Omega}{\cdot}cm]$, a carrier concentration of $7.746{\times}10^{20}[cm^{-3}]$, and a carrier mobility of 31.77[$cm^2/V{\cdot}S$], which indicates that it could be used as a transparent electrode for thin film transistor and flat panel display applications.