• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.454-455
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• 2018

The impedance of an underwater acoustic transducers constituting a multi-channel array structure could be changed in real time by various transmission modes. A power amplifier for driving the transducers usually use a voltage control method, so the transducer and power amplifier may be damaged by over-power due to changeable load conditions. Therefore, the drive controller of the power amplifier should have the function of limiting the power. This paper propose the new voltage control method for limiting the driving power of transducers with variable impedance characteristics.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1204-1207
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• 2009

We investigated the device performance of bulk heterojunction solar cells depending on the active layer thickness. For the systematic comparison, the polymer solar cells comprising RR-P3HT:PCBM (1:0.8 (wt%:wt%)) blend films with different thickness were characterized by impedance spectroscopy, and J-V measurement in dark and solar simulated illumination. The device with 120 nm thickness of active layer exhibited maximum power conversion efficiency of 3.5 % under AM 1.5 100mW/$cm^2$ illumination condition.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.3
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• pp.528-531
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• 1994

Digitalization in electronic system is required the capacitor which have a large capacitance with small size, low impedance at high frequency, and high reliability. The fabrication and its properties of aluminum solid electrolytic capacitor are investigated. Employing conduction polymer film such as, polypyrrole as solid electroylte, solid type aluminum electrolytic capacitors were made. The surface of insulationg oxide is covered with conducting polymer layer prepared by chemical oxidative polymerization. Thereafter this conducting layer is covered with conducting polymer prepared by electrochemical polymerization. The dielectric properties of these capacitors were also measured and discussed. Regarding on frequency characteristics of the trial made capacitor, impedance and ESR at high frequency is lower than those of the stacked type film capacitor. It is alo confirmed that temperature coefficient of capacitance and dissipation factor of the capacitor are lower than those of film capacitor and liquid type aluminum electrolytic capacitor.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.137-138
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• 2006

In this paper, we study the algorithm for the multiport measurements using the 2port VNA(Vector network Analyzer). We explain the conversion algorithm which the open impedance to the matched impedance(50 ohm), and then we apply this algorithm to the 4 port VNA measurement. Finally, we discuss the reliability of this algorithm.

• Corrosion Science and Technology
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• v.6 no.1
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• pp.12-17
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• 2007

Portland cement incorporating supplementary cementing material develops excellent mechanical properties and long term durability characteristics. India is a leading rice producing country and rice husk is considered as waste in the rice milling industries. In this present work, the rice husk ash (RHA) was added to concrete as cement replacement from 0 to 30%. Corrosion performance of reinforcing steel embedded in RHA blended concretes was studied using linear polarization, AC impedance and gravimetric methods. The corrosion rate of steel bars embedded in RHA concretes were compared with control concrete. The results clearly indicate that the corrosion rate of reinforcing steel embedded in concrete is significantly reduced with the incorporation of RHA. A good correlation among gravimetric method and electrochemical methods was observed. Electrochemical impedance study showed 98 percentage reduction in corrosion rate to the RHA blended concrete with 15% replacement than control concrete.

• Corrosion Science and Technology
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• v.5 no.3
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• pp.99-105
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• 2006

This paper is to investigate feasibility on quantitative aging state of epoxy coating on concrete wall in containment structure under operation of nuclear power plants. For evaluating the physical characteristics of the epoxy coating, adhesion strengths of two kinds of degraded epoxy coating systems on both steel surfaces and concrete surfaces were measured via accelerated aging. Comparatively impedance data taken by ultrasonic test were also taken to relate with adhesion data. After aging, in case of concrete, from half of specimens, aging of epoxy coating was developed. As for steel, on $4^{th}$ inspection day, adhesion force was failed. To improve reliability on quality degradation of epoxy, relationship between adhesion and impedance was analyzed. By tracing to co-respond to these data, it was possible to Fig. out physical state of as-built epoxy coating. The possibility to develop new methodology of time - dependent aging state on epoxy coating was found and discussed.

• Corrosion Science and Technology
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• v.9 no.6
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• pp.300-309
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• 2010

The influences of sensitization on localized corrosion resistance of 304 stainless steel, were investigated, using micro-dropletcell techniques. Micro-droplet cell allows one to align the micro-electrode to the desired spot of the working electrode and measure directly local current with the potentiodynamic polarization, linear polarization and a.c. impedance. Micro-electrochemical tests were carried out inside of the grain and on grain boundaries separately. It was found that sensitization decreased the pitting potential, increasing corrosion current density around grain boundaries. Galvanic current density was also measured between grain and grain boundaries.

• Smart Structures and Systems
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• v.7 no.1
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• pp.27-40
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• 2011

Geopolymer concrete is finding a growing number of niche applications in the field of civil engineering due to its high compressive strength and strength gain rate, retainage of structural properties in elevated temperature environments, chemical stability in highly acidic conditions and environmental benefits. Combining the above mentioned characteristics with induced electrical conductivity, could enable geopolymer cement to serve as a smart and sustainable cementitious material suitable for health monitoring of civil structures. Carbon fibers were added to fresh geopolymer and OPC (ordinary Portland cement) mixes to enhance their electrical conductivities. AC-impedance spectroscopy analysis was performed on the specimens with fiber fraction ranging from 0.008 to 0.8 with respect to the weight of cementitious binder, to measure their electrical resistivity values and to determine the maximum beneficial fiber content required to attain electrical percolation. Experimental observations suggest that CFR-geopolymer cement exhibits superior performance to CFR-OPC in terms of conducting electrical current.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.3B no.4
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• pp.159-164
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• 2003

In this paper, a three-dimensional finite element method and construction of equivalent-circuit for a linear ultrasonic motor are presented. The validity of three-dimensional finite element routine in this paper is experimentally confirmed by analyzing impedance of a piezoelectric transducer. Using this confirmed finite element routine, impedance and vibration mode of a linear ultrasonic motor are calculated. Elliptical motion of contact point between vibrator and rail of the linear ultrasonic motor is shown for determination of contact points. By using the finite element method and analytic equations, characteristics of the linear ultrasonic motor, such as thrust force, speed, losses, powers and efficiency, are calculated. The results are confirmed by experiment. Finally, equivalent circuit parameters of the linear ultrasonic motor are obtained using the three-dimensional finite element method and analytic equations.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2004.05a
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• pp.565-569
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• 2004

This paper deals with the characteristics of potential rise and effective impulse impedance of deep-driven ground rods that are used in high resistivity soil or in confined places such as downtown. Also the effects of the impulse and fault currents on the deep-driven ground rods combined with different type grounding electrodes like as mesh grids and counterpoises are described. The $8/20{\mu}s$ impulse current and other wave currents with different rise times are injected into the test ground rod and the effective impedances are examined. The most effective way to obtain the fine transient impedance behaviors of deep-driven ground rods is to reduce the inductive component of grounding electrode systems combined with other ground electrodes.