• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.05a
• /
• pp.23-26
• /
• 2001

The properties of $LiMnO_2$ was studied as a cathode active material for lithium polymer batteries. $LiMnO_2$ cathode active materials were synthesized by the reaction of $LiOH{\cdot}H_2O$ and $Mn_2O_3$ at various temperature under argon atmosphere. The powders were characterized by the X -ray diffraction. For lithium polymer battery applications, the $LiMnO_2$ cell was characterized electrochemically by charge-discharge experiments and a.c. impedance spectroscopy. And the relationship between the characteristics of powders and electrochemical properties was studied in this research. A maximum discharge capacity of 160~170 mAh/g for o-$LiMnO_2$ cell was achieved. The capacity of o-$LiMnO_2$ electrode demonstrated better than of the spinel $LiMnO_2$ by solid-state reaction.

• Journal of the Korean Ceramic Society
• /
• v.32 no.2
• /
• pp.189-196
• /
• 1995

Materials retaining electrolyte of a phosphoric acid fuel cell (PAFC) have been prepared with SiC powder to SiC whisker mixing ratios of 1:1, 1:2, 1:3, 1:4, 0:1 by a tape casting method. When 3wt% dispersant (sorbitan monooleate) is added to a matrix, the porosity of the matrix decreases a little while the bubble pressure and area of the matrix increase remarkably in comparison with no dispersant content. Effect of the electrolyte resistance and the polarization resistance on perfomance of a PAFC has been investigated using A.C. impedance spectroscopy. With the increase of whisker content, the electrolyte resistance decreases due to the increase of porosity and acid absorbancy, and the polarization resistance increases due to the increase of surface roughness. The polarization resistance affects current density predominantly at the higher potential than 0.7V becuase the polarization resistance is considrably larger than the electrolyte resistance. Both the electrolyte resistance and the polarization resistance affect current density near 0.7V of the fuel cell operating potential because they have similar values. The electrolyte resistance affects current density predominantly at the lower potential than the fuel cell operating potential because the electrolyte resistance is larger than the polarization resistance.

• Fire Science and Engineering
• /
• v.10 no.4
• /
• pp.3-12
• /
• 1996

The aim of the present study is to find out the effect of cooling rate on the electrical behavior of ZnO varistors. The microstructure, 1-V characteristics and complex impedance spectra were investigated under the change of cooling rates. It is found that at cooling rate $200^{\circ}$/h, nonlinearity and breakdown voltage reached a maximum value which may show that good intergranular layer is formed as a results of proper cooling rate. Complex Impedance spectras were measured as a function of frequency range 100Hz to 13MHz to determine grain and grainboundary resistance. The semicircles were attributed to the dependence of grain and grainboundary resistance on cooling rates.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.19 no.6
• /
• pp.29-35
• /
• 2005

This paper presents the basic quench protection idea for the HTS(High-Temperature Superconducting) cable. In Korea power system, the transfer capability of transmission line is limited by the voltage stability, HTS cable could be one of the countermeasure to enhance the transfer limit with its higher current capacity and lower impedance[1]. However, the quench characteristic makes not only HTS cable to loss its superconductivity, but also change the impedance of the transmission line and power system operating condition dramatically. This pheonominum threats HTS cable safety as well as power system security, therefore a proper protection scheme and security control counterplan have to be established before HTS cable implementation. In this paper, the quench characteristics of HTS cable for the fault current based on heat balance equation was established and a proper protection method regarding conventional protection system was suggested.

• Journal of the Korean Ceramic Society
• /
• v.38 no.4
• /
• pp.325-330
• /
• 2001

고상반응법으로 이론 밀도의 약 97%의 소결 밀도를 갖는 N $d_{1-x}$S $r_{x}$G $a_{1-x}$M $g_{x}$ $O_{3{\delta}}$(x=0, 0.03, 0.07, 0.1) 고체전해질을 제조하였다. X선 회절 분석 결과, x=0.03일 때의 X선 회절도는 순수한 NdGa $O_3$와 같았으나, x=0.07, 0.1일 때에는 불순물이 나타났다. 교류 복소임피던스는 4$50^{\circ}C$~90$0^{\circ}C$의 온도 범위에서 공기 중에서 측정하였으며, 각 조성에 대하여 상호 비교 분석하기 위하여 복소비저항 스펙트럼으로 변환하여 해석하였다. 전기전도도는 N $d_{0.93}$S $r_{0.07}$G $a_{0.93}$M $g_{0.07}$ $O_{0.97}$(x=0.07) 시편이 90$0^{\circ}C$에서 6$\times$$10^{-3}$ S$cm^{-1}$ /로 가장 우수하였으며, 활성화 에너지는 저온 영역에서는 1 eV, 고온 영역에서는 0.74 eV이었다.다.

• Journal of KSNVE
• /
• v.11 no.2
• /
• pp.276-284
• /
• 2001

In apartment buildings, floor-impact sound has been regarded as the major source that causes complaints from residents. It is mainly due to the use of light-weight structures and the lack of researches in terms of floor-impact sound. The purposes of this study are analyzing the characteristics of vibration response and sound radiation of 12type void slabs in the improvements void slab by impedance method and finding the fittest improvements void slab on the 12type void slab. The main results of this study are summarized as below: (1) In the $\frac{1}{3}$ octave band level of sound radiation, $\frac{1}{3}$ octave band levels, measured from four-divided improvement void slab(No.8) and eight-divided improvement void slab(No.12), are 10~25 dB lower than that of standard void slab(No.1) in the 1250 Hz. Especially, eight-divided improvement void slab(No.12) is the best void slab in terms of radiation efficiency of sound level. (2) In the correlation relation of acceleration and sound radiation, standard void slab(No.1), four-divided improvement void slab(No.8), SK standard four-hole void slab(No.10), and eight-divided improvement void slab(No.12) are positive correlation relation.

• International Journal of Vascular Biomedical Engineering
• /
• v.1 no.1
• /
• pp.41-47
• /
• 2003

The patency rates of small diameter vascular grafts are disappointing because of the formation of thrombus and intimal hyperplasia. Among the various factors influencing the success of graft surgery, the compliance and the size of a graft are believed to be the most important physical properties of a vascular graft. Mismatch of compliance and size between an artery and a graft alters anastomotic flow characteristics, which may affect the formation of intimal hyperplasia. Among the hemodynamic factors influencing the development of intimal hyperplasia, the wall shear stress is suspected as the most important one. The wall shear stress distributions are experimentally measured near the end-to-end anastomosis models in order to clarify the effects of compliance and diameter mismatch on the hemodynamics near the anastomosis. The effects of radial wall motion, diameter mismatch and impedance phase angle on the wall shear rate distributions near the anastomosis are considered. Compliance mismatch generates both different radial wall motion and instantaneous diameter mismatch between the arterial portion and the graft portion during a flow cycle. Mismatch in diameter seems to be affecting the wall shear rate distribution more significantly compared to radial wall motion. The impedance phase angle also affects the wall shear rate distribution.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.466-466
• /
• 2013

Quantum-dot materials have introduced novel applications in organic light-emitting diodes and solar cells. The size controllability and structure modifications have continuously been upgrading the applicability to optoelectronic and flat-panel displays. In particular, quantum-dot organic light-emitting diodes (QLEDs) are a device driven through the electrical field applied to the electrical diodes. The QLEDs are affected by the constituent materials and the corresponding device structures. Conventionally, the electrical properties are characterized only in terms of dc-based current-voltage characteristics. The dynamic change in light-emitting diodes should be characterized in emitted and non-emitted states. Therefore, the frequency-dependent impedance can offer different information on the electrical performance in QLED. The current work reports an auxiliary information on the electrical and optical features originating from quantum-dot organic light-emitting diodes. The empirical characterizations are discussed towards an experimental tool in optimizing the light-emitting diodes.

• Journal of Astronomy and Space Sciences
• /
• v.18 no.2
• /
• pp.119-128
• /
• 2001

The oscillation frequency tuning range of waveguide Gunn oscillator and its stability depend sensitively on the dimensions of the resonator. Therefore the embedding impedances with the various dimensions of the resonator for Q-band (33 ∼ 50 GHz) Gunn oscillator are calculated by using HFSS (High Frequency Structure Simulator). In this paper the comparisons between theoretical results of embedding impedances as a function of frequency and that of experimental results are described. And the oscillation frequency range could be predicted by using the theoretical evaluation methods which were proposed in this paper It shows that post size has an effect on the frequency tuning characteristics of Gunn oscillator.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.18 no.9
• /
• pp.856-862
• /
• 2005

A flux-lock type SFCL consists of two coils, which are wound in parallel each other through an iron core, and a HTSC thin film connected in series with coil 2. If the current of the HTSC thin film exceeds its critical current by the fault accident, the resistance generated of the HTSC thin film, and thereby the fault current can be limited by the impedance of the flux-lock type SFCL. The amplitude of fault current can be set by the impedance of the flux-lock type SFCL. In this paper, we investigated the variance of the limiting current due to the ratio of inductances between coil 1 and coil 2 in the flux-lock type SFCL through the computer simulations and short circuit tests. In addition, both the simulation results and experimental ones were compared each other. From the comparison of both the results, the simulation results agreed well with the experimental ones.