• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.214.2-214.2
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• 2011

In this work, porous carbon based electrodes are prepared by carbonization using poly(vinylidene fluoride) (PVDF)/carbon nanotube (CNT) composites to further increase the specific capacitance for supercapacitors. Electrode materials investigate the aspects of specific capacitance, pore size distribution and surface area: influence of carbonization temperatures of PVDF/CNT composites. The electrochemical properties are investigated by cyclic voltammetry, impedance spectra, and galvanostatic charge-discharge performance with in $TEABF_4$ (tetraethylammonium tetrafluoroborate)/acetonitrile as non-aqueous electrolyte. From the results, the highest value of specific capacitance of ~101 $F{\cdot}g^{-1}$ is obtained for the samples carbonized at $600^{\circ}C$. Furthermore, pore size of samples control be low 7 nm through carbonization process. It is suggested that micropores significantly contribute to the specific capacitance, resulting from improved charge transfer.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.10a
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• pp.323-330
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• 1994

본 연구에서는 다공질 흡음재료 중 closed cell 구조를 갖는 발포수지재료(Foamed Material)에 음(sound)이 입사할 때 발생하는 흡음현상을 보다 정확히 예측하기 위해서 다공질 흡음재료에 대한 Biot 이론에 근거한 Allard의 모델링기법[4]을 이용하여 해석 프로그램을 개발하였고, 이를 이용하여 다공질 흡음재료가 단층(single layer)일 때 이 재료의 Surface Impedance와 흡음률(Absorption Coefficient)을 예측하고, 물성치(parameters)변화에 따른 다공질 흡음재료의 흡음특성을 분석하였으며, 이 재료가 자동차 제조시 사용되는 압연강판(rolled steel piate)에 부착되었을 때의 투과손실(Transmission Loss)을 예측하였고, 또한 다공질 흡음재료는 중고주파 대역의 음에 대한 흡음특성은 좋지만 저주파 대역의 음에 대한 흡음특성은 좋지 않으므로 흡음 재료의 저주파 대역의 흡음특성을 향상시키기 위해서 2층(two layers)으로 하였을 때의 흡음특성을 분석하였다. 본 논문의 연구결과는 자동차 제조시 사용되어지는 다공질 흡음재료는 물론 산업용기계나 건축용등 여러 분야에서 사용되어지는 다공질 흡음재료의 흡음특성 분석에 응용될 수 있으리라 기대된다.

• Electrical & Electronic Materials
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• v.9 no.8
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• pp.831-835
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• 1996

The molten carbonate fuel cell has conspicuous features and high potential in being used as an energy converter of various fuels to electricity and heat. However, the MCFC which use strongly corrosive molten carbonate at 650[.deg. C] have many problem. Systematic investigation on corrosion behavior of Fe-based Cr has been done in ($62{\times}38$)mol % (Li+K)$CO_3$ melt at 923K by using steady state polarization and electrochemical impedance spectroscopy method. It was found that the corrosion current of these Fe-based alloys decreased with increasing Cr content, and this was attributed to the formation of $LiCrO_2$ layer at the surface .

• Korean Journal of Materials Research
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• v.12 no.6
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• pp.442-446
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• 2002

Design of microwave absorbers using high frequency properties of fiber reinforced composites are investigated. Two kinds of composite materials (glass and carbon) are used and their complex permittivity and permeability are measured by transmission/reflection technique using network analyzer. Low dielectric constant and nearly zero dielectric loss are determined in glass fiber composite. However, carbon fiber composites show the high dielectric constant and large conduction loss which is increased with anisotropy of fiber arrangement. It is, therefore, proposed that the glass and carbon fiber composites can be used as the impedance transformer (surface layer) and microwave reflector, respectively. By inserting the foam core or honeycomb core (which can be treated as an air layer) between glass and carbon fiber composites, microwave absorption above 10 dB (90% absorbance) in 4-12 GHz can be obtained. The proposed fiber composites laminates with sandwitch structure have high potential as lightweight and high strength microwave absorbers.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.367-370
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• 1998

A hybrid-integrated SAW(surface acoustic wave) douplexer including transmitter(Tx) filter, receiver(Rx) filter an dantenna terminal has been studied. The prototype duplxer was designed for CDMA system application in the 800 MHz-band. Ladder type SAW filters consisting of one port SAW resonators wer integrated on epoxy substrate to demonstrate the feasiblity of antenna duplexer. In order to perform the duplexing function, a strip line for impedance transformaton with length of .gamma./4 was inserted at rx path. The fabricted duplexer has an insertion loss of 3.0 dB at Tx path and 3.7 dB at Rx path. The attenuation has more than 40dB.

• Journal of Hydrogen and New Energy
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• v.20 no.4
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• pp.317-322
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• 2009

To investigate degradation mechanism of PEMFC operated with repetitive startup/shutdown cycling, i-V characteristics, impedance, cyclic voltamograms were measured. OCV decreased from 0.967 to 0.951 V while the cell voltage at 800mA/$cm^2$ from 0.657 to 0.563V, implying that the electrodes rather than membrane electrolyte was damaged during the cycling operation. Electrochemical analyses supported that the performance degradation could be mainly attributed to degradation of the electrodes such as a decrease in electrochemical active surface area rather than degradation of membrane.

• Biotechnology and Bioprocess Engineering:BBE
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• v.8 no.4
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• pp.252-256
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• 2003

In this paper we describe the status of a silicon-based microelectrode for neural recording and an advanced neural interface. We have developed a silicon neural probe, using a combination of plasma and wet etching techniques. This process enables the probe thickness to be controlled precisely. To enhance the CMOS compatibility in the fabrication process, we investigated the feasibility of the site material of the doped polycrystalline silicon with small grains of around 50 nm in size. This silicon electrode demonstrated a favorable performance with respect to impedance spectra, surface topography and acute neural recording. These results showed that the silicon neural probe can be used as an advanced microelectrode for neurological applications.

• Journal of information and communication convergence engineering
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• v.16 no.3
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• pp.197-202
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• 2018

This paper reveals the impact of the insertion of electromagnetic band gap (EBG) structures on the performance of circularly polarized (CP) patch-slot antenna with offset slot. Several optimizations are necessary to precise physical parameters in the aim to fix the resonance frequency at 3.2 GHz. The proposed antenna possesses lightweight, simplicity, low cost, and circular polarization ensured by two feeding sources to permit right-hand and left-hand circular polarization process (RHCP and LHCP). The measured results compared with simulation results of the proposed circularly polarized EBG antenna with offset slot show good band operations with –10 dB impedance bandwidths of 9.1% and 36.2% centered at 3.2 GHz, which cover weather radar, surface ship radar, and some communications satellites bands. Our investigation will confirm the simulation and experimental results of the EBG antenna involving new EBG structures.

• Journal of Hydrogen and New Energy
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• v.8 no.1
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• pp.31-41
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• 1997

In order to investigate the mechanism of electrochemical hydrogenation reaction on Zr-based Laves phase hydrogen storage alloy electrodes, electrochemical charge/discharge characteristics, potentiostatic/dynamic polarizations and electrocehmical impedance spectroscopy(EIS) of Zr-Ti-Mn-Ni and Zr-Ti-Mn-Ni-M(M=Fe, Co, Al) alloys were examined. Electrochemical discharge capacities of the alloys were quite different with gas charge capacities. Therefore, it was considered that discharge capacities of the alloys depend on electrochemical kinetic factors rather then thermodynamic ones. Discharge efficiencies were increased linearly with exchange current densities. The results of potentiostatic/dynamic polarization measurements showed that electrochemical charge and discharge reaction of Zr-based Laves phase hydrogen storage alloys is controlled by charge transfer process at the electrode surface. The EIS measurements also confirmed this result.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.12
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• pp.23-30
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• 1994

In this paper, we present an antenna which can be used for subsurface continuous wave electromagnetic probing. Its input impedance and transmission coefficient of the two port scattering parameters, S$_{21}$, are calculated numerically and the numerical results are compared with measured values from laboratory scale-down experiment. Scale-down experiemtn results using this antenna show that we can detect a metallic pipe, which has 0.8 cm in diameter and buried at a depth of 5.7cm in saline solution, in frequency range from 200 MHz to 1000 MHz.