• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.97.1-97.1
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• 2011

저온에서 양이온 고분자막을 사용하는 고분자 연료전지의 경우 뛰어난 성능과 다양한 응용분야로 인해 많은 연구와 실증이 이루어지고 있지만 공기극에서의 느린 산소 환원반응으로 인해 백금과 같은 귀금속의 사용이 불가피하고 백금의 제한된 매장량과 높은 가격으로 인해 상용화가 늦어지고 있다. 그래서 많은 연구자들이 합금 촉매 또는 비귀금속 촉매를 이용한 전극 개발에 집중하고 있다. 알칼리 분위기에서 저가의 전이 금속들이 백금과 비슷한 활성을 보이고 고체 음이온 교환막이 개발됨에 따라 최근 알칼리 연료전지가 다시금 큰 주목을 받고 있다. 그러나 고분자 연료전지와는 달리 아직 촉매나 전해질막, 이오노머의 특성 및 메커니즘에 관해 별로 알려진 것이 없다. 본 연구에서는 직접 개발한 세공충진막 형태의 탄화수소계의 음이온 교환막과 비귀금속 공기극 촉매를 이용하여 막전극접합체(MEA)를 개발하였고 촉매 및 이오노머 함량과 같은 전극 조성, 막전극접합체의 제조 및 체결, 가습이나 가스조성 등의 단위전지 운전조건과 같은 다양한 변수에 대해에 최적 조건을 도출하고자 하였다. 공기극 촉매는 Cu-Fe/C를 이용한 상용 촉매를 이용하였고 이오노머의 경우는 탄화수소계의 상용 제품을 사용하였으며 음이온 교환막에 전극층을 형성하기 위해서는 스프레이 공정을 이용하였다. 단위전지를 통해 성능을 확인하였고 임피던스 및 CV를 통해 전기화학적인 특성을 규명하였다. 조건의 최적화를 통해 상당한 성능 향상을 이루었으나 추가적인 성능 향상 및 내구성 확보 등에 대해 계속적인 실험을 진행할 예정이다.

• Journal of Physiology & Pathology in Korean Medicine
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• v.27 no.6
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• pp.717-729
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• 2013

Bioelectrical Impedance Analysis (BIA) is a non-invasive and low-cost technique that estimates body composition based on the distribution of water and electrolytes in the body by analyzing body's electrical responses to source voltages. In this work, we carried out a systematic literature review on BIA researches in traditional East Asian medicine (TEAM). For comparison, firstly we introduced the concept and principle of BIA, and offered a general overview of research trends in western medical perspectives. We searched through the databases of Oriental Medicine Advanced Searching Integrated System and DataBase Periodical Information Academic for the articles published between 1994 and 2013, with keywords such as 'BIA', 'bioelectrical impedance' and 'impedance'. Among the rough-searched 274 articles, we finally selected 21 articles appropriate to the intended research field. The selected articles were categorized into diagnosis in Sasang medicine, impedance analysis in meridian system, and change of body composition after taking herbal medicine. We found that most of BIA researches in TEAM were preliminary and remained in the peripheral levels which is far behind the western medical research activities. Therefore, more efforts are needed to study BIA in association with major subjects such as pattern identification or physiological/pathological phenomena. In addition, methodological breakthrough of BIA is possible by applying the diagnostic concepts of the TEAM in relation to the balance of Qi and Blood.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.33.2-33.2
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• 2011

CMP (Chemical-Mechanical Planarization) 공정이란 화학적 반응과 기계적 힘을 동시에 이용하여 표면을 평탄화하는 공정으로, 반도체 산업에서 회로의 고집적화와 다층구조를 형성하기 위해 CMP 공정이 도입되었으며 반도체 패턴의 미세화와 다층화에 따라 CMP 공정의 중요성은 더욱 강조되고 있다. CMP 공정은 압력, 속도 등의 공정조건과, 화학적 반응을 유도하는 슬러리, 기계적 힘을 위한 패드 등에 의해 복합적으로 영향을 받는다. CMP 공정에서, 폴리우레탄 패드는 많은 기공들을 포함한 그루브(groove)를 형성하고 있어 웨이퍼와 직접적으로 접촉을 하며 공정 중 유입된 슬러리가 효과적으로 연마를 할 수 있도록 도와주는 역할을 한다. 하지만, 공정이 진행 될수록 그루브는 손상이 되어 제 역할을 하지 못하게 된다. 패드 컨디셔닝이란 컨디셔너가 CMP 공정 중에 지속적으로 패드 표면을 연마하여 패드의 손상된 부분을 제거하고 새로운 표면을 노출시켜 패드의 상태를 일정하게 유지시키는 것을 말한다. 한편, 금속박막의 CMP 공정에 사용되는 슬러리는 금속박막과 산화반응을 하기 위하여 산화제를 포함하는데, 산화제는 금속 컨디셔너 표면을 산화시켜 부식을 야기한다. 컨디셔너의 표면부식은 반도체 수율에 직접적인 영향을 줄 수 있는 scratch 등을 발생시킬 뿐만 아니라, 컨디셔너의 수명도 저하시키게 되므로 이를 방지하기 위한 노력이 매우 중요하다. 본 연구에서는 컨디셔너 표면에 연마 잔여물 흡착을 억제하고, 슬러리와 컨디셔너 표면 간에 일어나는 표면부식을 방지하기 위하여 소수성 자기조립 단분자막(SAM: Self-assembled monolayer)을 증착하여 특성을 평가하였다. SAM은 2가지 전구체(FOTS, Dodecanethiol를 사용하여 Vapor SAM 방법으로 증착하였고, 접촉각 측정을 통하여 단분자막의 증착 여부를 평가하였다. 또한 표면부식 특성은 Potentiodynamic polarization와 Electrochemical Impedance Spectroscopy (EIS) 등의 전기화학 분석법을 사용하여 평가되었다. SAM 표면은 정접촉각 측정기(Phoenix 300, SEO)를 사용하여 $90^{\circ}$ 이상의 소수성 접촉각으로써 증착여부를 확인하였다. 또한, 표면에너지 감소로 인하여 슬러리 내의 연마입자 및 연마잔여물 흡착이 감소하는 것을 확인 하였다. Potentiodynamic polarization과 EIS의 결과 분석으로부터 SAM이 증착된 표면의 부식전위와 부식전류밀도가 감소하며, 임피던스 값이 증가하는 것을 확인하였다. 본 연구에서는 컨디셔너 표면에 SAM을 증착 하였고, CMP 공정 중 발생하는 오염물의 흡착을 감소시킴으로써 CMP 연마 효율을 증가하는 동시에 컨디셔너 금속표면의 부식을 방지함으로써 내구성이 증가될 수 있음을 확인 하였다.

• Journal of the Korea Society of Computer and Information
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• v.15 no.10
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• pp.99-104
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• 2010

In this paper, the internal antenna for mobile communication handset which is able to control both coupling coefficient and resonant frequency without any major modification of radiator and ground plane of PIFA(Planner Inverted F Antenna). The resonant frequency as well as amount of coupling between feeding point and shorting post can be adjusted by changing inductance. Because the inductor is connected on shorting post where the strength of electric field is weak, the performance reduction of the proposed antenna is very small enough to neglect. For the variation of the inductance value within 3.3nH, the resonant frequency of antenna can have operating range of 1650MHz ~ 1830MHz. And as be increased the inductance, the coupling coefficient of antenna is over coupled. This means that it can be electrically controlled the resonant frequency and input impedance of antenna by inductance and minimized the mismatch loss. Size reduction of 10% for PIFA is obtained without any major modifications of antenna elements. For the frequency range from 1650 to 1830MHz, reduction of the measured antenna gain is within 0.93dB as varying the value of inductance from 0 to 3.3nH.

• 한국ITS학회:학술대회논문집
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• v.2006 no.10
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• pp.187-190
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• 2006

In this paper, the equivalent circuit of tapped-line that is applied in the feeding of the band-pass filter with high coupling is suggested and the value of an equivalent circuit is mathematically defined. An equivalent circuit of tapped-line is composed by open stub and additional transmission line, and the electrical lengths of stub and line can be obtained by the impedance of resonator and the inverter. The new equivalent circuit of tapped-line can be simply applied of design of band-pass filter and leads to very good agreement compared with theoretical value. The coupled-line band-pass filter using equivalent circuit of tapped-line shows the insertion loss of 1.97 dB and the return loss of 18.5 dB at the center frequency of 5.8 GHz.

• Journal of the Korean Ceramic Society
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• v.39 no.6
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• pp.540-549
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• 2002

In this work, the hydration behaviour of portland cement pastes containing fly ash, blast-furnace slag and silica fume is investigated by Impedance Spectroscopy(IS). As fly ash or blast-furnace slag was added to portland cement, the values of R$_{t(s+1)}$ and R$_{t(s+1)}$ were decreased in the early hydration period. It showed that hydration of cement containing blending components was slower than it of the reference cement paste with the same W/C ratio. However, the cement paste containing silica fume had a large value of R$_{t(s+1)}$ and R$_{t(int)}$due to very rapid pozzolanic reactivity of silica fume in the hydration time. In OPC-fly ash system, a characteristic plateau region appeared between straight-line and semicircle. The plateau region continued to grow in range with the content of fly ash and the hydration time.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.42 no.3 s.303
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• pp.71-80
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• 2005

This paper proposes a new circuit topology of the half-bridge resonant inverter and presents its digital control scheme. As the proposed half-bridge inverter can be operated in the load-freewheeling modes, pulse width modulation (PWM) control method can be used for the output power control. The proposed half-bridge inverter can keep unity output displacement factor under the load-impedance varying conditions, if a new PWM control scheme based on the resonant frequency tracking algorithm is adopted. In this paper, the operation principle, electrical characteristics and detailed digital control scheme of the proposed half-bridge resonant inverter and loss analysis comparing with a conventional half bridge inverter is described. The experimental results of the proto-type experimental setup to verify the validity of the proposed half-bridge resonant inverter are presented and discussed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.1 s.104
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• pp.60-66
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• 2006

In this paper, a circular microstrip patch antenna for switchable polarization is presented. For the switchable polarization, pairs of tuning stubs and two PIN diodes are utilized. By independently setting the PIN diodes on or off, the antenna produces either linear polarization or circular polarization. From the results, the -10 dB impedance bandwidths of 57.0 MHz($2.4\%$) and 50.0 MHz($2.1\%$) when operated in the linear polarization, and the 3 dB axial ratio bandwidth of $1.3\%$ with minimum of 0.2 and 0.9 dB in the circular polarization have been observed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.9
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• pp.938-943
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• 2014

The scattered field by a gap/crack on the PEC surface of a large object having low-observable RCS cannot be negligible, but may not be analyzed by the known high-frequency technique. If the electrical width of the crack is very small, the crack can be modeled by an impedance strip, whose scattering formulation can be analytically obtained based on a low-frequency approximation. The scattering solution is formulated for the 2D strip and TE(Transverse Electric) or TM(Transverse Magnetic) wave incidence, from which a 3D ILDC(Incremental Length Diffraction Coefficients) can be extracted. Using the ILDC formulation, the scattering by any arbitrary shaped crack can be estimated. In this paper, an improved ILDC equations are proposed, which combine the known TE and TM solutions. The improved accuracy of the proposed solution is numerically verified.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.192-193
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• 2005

Magnesium thin films were prepared on cold-rolled steel substrates by RF(Radio Frequency) magnetron sputtering technique.$^{1)}$ The crystal orientation and monitoring of the deposited films were investigated by using XRD(X-ray Diffraction) and EIS(Electrochemical Impedance Spectroscopy), respectively. The corrosion rates of Mg thin films deposited with different argon gas pressure and substrate bias voltage were monitored by AC impedance method under a cyclic wet-dry condition, which was conducted by exposure to alternate conditions of 1h immersion in 3%NaCl solution and 5h drying at 60% RH and 25$^{\circ}C$. The result of corrosion rate of Mg thin films deposited at various Ar gas pressures and substrate bias voltage under wet-dry cyclic exposure in chloride-containing solutions was showed the following conclusions. At the region I during the onset of the wet cycle, corrosion rate showed relatively low value. The increase in the Corrosion rate of region II is due to the increase in the chloride concentration. Corrosion rate of region III during the onset of the cycle zero and salt crystals remain on the metal surface.$^{2)}$