• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.8
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• pp.594-598
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• 2018

The tangential electric polarizability of a electrically small square patch, which is commonly used in metasurfaces, is calculated using electric potential continuity. Since the potential at the patch surface is not uniform due to the equivalent electric dipole located at the center, there is a problem in that the polarizability is not uniquely defined. To obtain equivalent polarizability, the meshes in the analysis area are divided on the patch surface, and the equivalent polarizability is calculated by averaging the polarizabilities obtained at each point. The results of the proposed method, third-power series approximation, and experimental equations are compared and verified. Finally, the magnitude and phase of the reflection coefficient of patch metasurface calculated by generalized sheet transition conditions(GSTCs) are in good agreement with the HFSS simulation results.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.3
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• pp.211-217
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• 2003

Recently, with rapid development in marine and shipbuilding industries such as marine structures, ships and chemical plants for ship, there occurs much interest in the study on corrosion characteristics played an important role in mechanical design. This paper was studies on the corrosion characteristics of chromium plating in the marine environment. Under the various specific resistance, the electrochemical polarization test of chromium plating was carried out. And thus corrosion potential, polarization resistance, corrosion current density, control efficiency of corrosion and polarization control behavior of chromium plating are investigated. The main results are as the followed : 1. The polarization resistance of Cr plating and Ni become higher than that of base metal, also and these material become low with decrease of the specific resistance. 2. As the specific resistance decreases, the corrosion current density of Cr and Ni plating is lower than that of base metal. 3. The corrosion reaction of Cr plating, Ni plating and base metal vs. specific resistance is cathodic control.

• Membrane Journal
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• v.11 no.1
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• pp.50-59
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• 2001

Influence of concentration polarization has been investigated on the vapor permeation of VOCs/$N_2$ mixture. Po]y(dimethylsiloxane)(PD,vIS) membrane which had a good affinit~, toward VOCs was emploj,'c'Cl in this study. The chlorinated hydmcarbons which were part of homologous series of chrolomelhane and chrolocthane were used as organic vapor. The vapor permeation experiments were calTied out at various VOCs feed concentrations. operating temperatures and feed flow rates. With decreasing feed flow rate. the membrane perfonnance, that is. penneation rate and selectivity were reduced in the permeation of VOCs/$N_2$ mixture. Especially the reducing of the membrane performance was founel to be more significant when the condensibility of voe was greater. voe content in the feed mixture was higher or operating temperature was lower. These observations were discussed in terms of the influence of con-centration polarizalion on the permeation of VOCSINl mixture through the PDMS membrane.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.179-184
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• 2008

Silt or clay alluvium fully saturated with water generally shows low resistivity. Sometimes it is believe that the low resistivity layer is considered as good aquifer but this makes problems in the development of groundwater. To overcome this problem, we adopted induced-polarization(IP) method with resistivity method. Laboratory experiments and resistivity/IP field surveys with non-polarization electrodes were conducted for the study. Laboratory experiments shows that the increase of clay contents in the sample mixed with sand and clay give low resistivity and high chargeability. We used this experiment results in the interpretation of resistivity/IP field data which were obtained in riverbank filtration. Finally, the layer which has low resistivity and chargeabilty would be regarded as a good aquifer for the development of groundwater intake.

• Geophysics and Geophysical Exploration
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• v.5 no.1
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• pp.56-63
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• 2002

Tracing the history of study, problems of seawater intrusion are commonly investigated with electrical techniques because seawater saturated zone is indicative of the low resistivity anomaly. There we, however, silt and mud layers in the western and southern coastal areas of Korea, so we may make a mistake in case we determine seawater intrusion only with resistivity survey. Hence, reference IP survey was carried out in Kimje, Jeollabuk-Do and Youngkwang, Jeollanam-Do in order to decide whether or not the area is under the influence of seawater intrusion. With the use of a electric field cable to minimize EM coupling, we obtained more accurate results by appling reference If technique measuring simultaneously wavelet of current as well as potential. With the aid of reference IP technique, it is possible that we can exactly evaluate seawater intrusion by discriminating seawater saturated area (no IP effect) from very highly conductive layer composed of clay mineral (high IP effect).

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.133.2-133.2
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• 2010

현재 융융탄산염 연료전지의 공기극으로 다공성의 lithiated NiO를 사용하고 있는데 이 재료의 경우 크게 두 가지의 문제점을 안고 있다. 첫 번째는 Ni이 전해질 내로 용해하는 것이고, 두 번째는 낮은 활성으로 인한 높은 공기극의 분극이다. Ni이 전해질로 용해되는 문제는 Co나 Fe를 코팅하여 공기극 표면에 $Li_x(Ni_yCo_{1-y})1-xO_2$나 $Li_x(Ni_yFe_{1-y})_{1-x}O_2$를 형성시켜 NiO의 전해질 내로 용해되는 것을 억제하는 방법이나 ZnO, MgO, $La_2O_3$ 등의 산화물을 NiO 표면에 코팅하여 전해질과 접촉을 막는 방식으로 해결하는 등 많은 연구가 이루어져 왔다. 하지만 연료극의 비해 상당히 높은 공기극의 분극으로 인해 큰 전압손실이 일어나 용융탄산염 연료전지 성능이 낮아지는 문제의 경우 이를 해결하고자 하는 연구는 상대적으로 많이 진행되지 못한 상태이다. 특히 현재 용융탄산염 연료전지의 장기수명화를 위해 기존의 작동온도인 $650^{\circ}C$ 보다 다소 낮은 온도인 $600{\sim}620^{\circ}C$에서 작동하려는 움직임이 있다. 작동 온도가 내려가면 전해질이 휘발되는 속도가 낮아져 전해질 부족에 따른 운전시간이 줄어드는 문제를 해결할 수 있어 장기 수명화를 위해서는 작동온도를 낮추는 것이 매우 유리하다. 하지만 작동 온도가 내려가면서 양 전극에서 일어나는 전기화학 반응 속도가 느려지기 때문에 각 전극에서의 활성화 분극으로 인한 전압손실은 더욱 커질 수밖에 없다. 특히 연료극의 수소산화반응 속도는 공기극의 산소환원반응에 비해 매우 빠르기 때문에 작동 온도가 내려감에 따라 연료극의 분극이 커지는 것에 비해 공기극의 분극이 급격히 커지게 된다. 따라서 운전온도가 낮아지는 상황에서는 낮은 작동온도에서도 성능감소가 적게 일어나 0.8V 이상 운전(150mA/$cm^2$, 단위전지 기준)이 가능한 공기극의 개발이 매우 필요한 실정이다. 이를 해결하고자 본 연구에서는 고체 산화물 연료전지의 공기극의 재료로 많이 연구되고 있는 혼합전도성 물질의 페로브스카이트 구조의 물질을 기존 NiO 전극에 코팅하여 새로운 공기극을 개발하였다. 페로브스카이트 구조의 물질로 대표적인 LSCF 물질을 사용하였으며 LSCF를 코팅한 공기극을 이용한 단위전지에서 150mA/$cm^2$의 전류를 흘려주었을 때 0.84V의 성능을 1000hr 유지하였다. 이는 기존의 NiO 전극을 사용했을 때보다 15~20mV 높은 값이다. 낮은 작동온도에서도 좋은 성능을 보였는데, 기존의 NiO 전극의 경우 $630^{\circ}C$에서 0.79V의 성능을 보인 반면 LSCF가 코팅된 공기극의 경우 $620^{\circ}C$에서 0.811V의 매우 좋은 성능을 보였다. 이는 LSCF의 산소이온전도성 및 전기전도성이 공기극에서의 분극을 낮추어 성능을 증가시키는 것으로 보인다.

• Journal of the Korean Electrochemical Society
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• v.4 no.3
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• pp.125-131
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• 2001

A long-term variation of electrode polarization in the MCFC has been analyzed successfully using a single cell with a Au, $CO_2/O_2$ reference electrode Four different cells with different components were operated and their electrode polarizations were analyzed. As published in the literatures, the cathode polarization was larger than that of the anode. The more stable operation of a single cell with the Al-coated cell frame up to 6,000hrs indicates that the corrosion at the cell frame, particularly wet seal area, plays an important role to determine the lifetime of a MCFC. At the initial stage of the cell operation, the voltage of the cell using a cathode stabilized by the $LiCoO_2$ coating was relatively low due to the high cathode polarization. As the cell was operated and the stabilized cathode was lithiated sufficiently, the cathode polarization decreased and the cell voltage was recovered. It was observed that the voltage of the cell using the $Li_2CO_3/Na_2CO_3$ electrolyte fluctuated with operation time and the cathode polarization fluctuated along with the cell voltage quite similarly. Although the mechanisms of the voltage fluctuation were not clear yet, the results imply that the voltage fluctuation was related with a reaction in the cathode side. After testing every single cell, the cathode polarization increased with the steep decrease in the cell voltage. Thus, the cathode should be improved in order to develop more durable MCFC.

• Geophysics and Geophysical Exploration
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• v.19 no.4
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• pp.212-219
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• 2016

The development of more advanced geophysical exploration techniques is necessary because the orebodies as yet discovered are increasingly changing in characteristics from shallow/high-grade to deep/low-grade. In this work, laboratory measurement of physical properties of rock samples and a field survey and interpretation of spectral induced polarization (SIP) have been conducted in a skarn metallic deposit, Gagok mine. The purpose of this study is that the applicability of SIP in the exploration of skarn metallic deposits is verified by the comprehensive interpretation between SIP characteristics of rocks obtained from the laboratory measurements and inverted survey results from the field data. In order to understand the SIP characteristics of each lithology, the data of eighty nine rock samples utilized in the previous studies were revaluated. The field survey was carried out using frequency of 0.25 Hz along a survey line designed for intersecting lithological boundaries and evaluating mineralized zones. The mineralized rocks were more conductive (low-resistivity) and capacitive (high-chargeability or strong-phase) than other rocks. Thus, SIP can be one of the very useful tools for the mineral exploration of the skarn deposits.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.5
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• pp.1-1
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• 2001

비휘발성 메모리 소자로의 응용의 관점에서, sol-gel 방법으로 La 을 10mo1% 로 고정시킨 PLZT (10/y/z) 박막을 제작하여 Zr/Ti 조성비에 따른 구조적 및 전기적 특성을 조사하였다. PLZT(10/40/60) 박막은 로제트와 파이로클로르 상이 관찰되었으며, Zr/Ti 조성비에서 Ti 함유량이 증가함에 따라, (100) 배향성, 결정립 크기와 표면 거칠기는 증가되었다. 또한 Zr/Ti 조성비에서 Ti 함유량이 증가함에 따라, 10㎑ 에서 비유전율은 600 에서 400 으로 감소된 반면, 유전손실은 0.028 에서 0.053 로 증가되었으며, 170 ㎸/cm 에서 누설전류밀도는 1.64×$10^{-6}$ 에서 1.26×$10^{-7}$A/㎠ 으로 감소되었다. 그리고 ± 170㎸/㎝ 에서 측정한 PLZT 박막의 이력곡선을 측정한 결과, Zr/Ti 조성비가 40/60 에서 0/100 로 변화함에 따라 PLZT 박막의 잔류분극과 항전계는 6.62 에서 12.86 μC/cm2, 32.15 에서 56.45㎸/㎝ 로 각각 증가되었으며, 피로와 retention 특성 역시 개선되었다. PLZT 박막에 ±5V 의 사각펄스를 $10^9$ 회 인가하여 피로특성을 측정한 결과, PLZT(10/40/60) 박막의 잔류분극은 초기분극값으로부터 50% 감소된 반면, PLZT(10/0/100) 박막은 30% 감소되었다. 또, $10^5$ 초의 retention 결과에서 PLZT(10/0/100) 박막은 초기분극값에서 오직 11% 만이 감소된 반면, PLZT(10/40/60) 박막은 40% 감소되었다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.12
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• pp.2741-2746
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• 2012

In this study, we propose a novel structure based on AlGaN substrate or buffer layer to implement a normally-off mode transistor that was difficult to be realized by conventional AlGaN/GaN heterojunction structures. The channel under the gate can be selectively depleted by growing an upper AlGaN barrier with a higher Al mole fraction and a top GaN charge elimination layer on AlGaN substrate or buffer layer. The proposed AlGaN heterojunction field effect transistor can achieve a threshold voltage of > 2 V, which is generally required in power device specification.