• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1647-1649
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• 2003

The electric fields of the sheath region in an argon do discharge were measured using a laser optogalvanic spectroscopy in a pressure range from 0.88 to 10 Torr, where collisions are significant in the sheath region. The sheath width is estimated as the position where the electric field becomes zero, and the pressure dependence of the measured sheath width was obtained to be $(pressure)^{-1/3}$. The measured electric fields agree well with one-dimensional simulation results but are slightly different from collisional sheath theory in the mobility limited region.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.427-428
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• 2009

The authors investigated anomalous nanoporous structures of aluminum oxides during the Al anodization process. We implemented two-steps anodizing process for the electrolyte of oxalic acid. As increasing DC voltages, lattice constants are proportionally increased. For the curved surface, the surface electric field was distorted so that the nanoporous pipe channel changed to a cone-type shape. We confirmed the periodicity by using the FFT(Fast Fourier Transform) analysis.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.620-623
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• 2003

Non-linear behaviors of multilayer piezoelectric ceramic actuator (MCA) were investigated under electrical and mechanical stress. DC 100 V bias was applied to the MCA to obtain displacement. Laser vibrometer, which using Doppler effect, was employed to characterize displacement caused by $d_{33}$ mode of MCA. To understand this non-linear behavior of MCA, displacement was measured and compared under different load states. By increasing load, electric field-induced strain and piezoelectric constant($d_{33}$) of MCA was decreased. We attribute this phenomenon to the domain wall motion and depoling of MCA under heavy load.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.69-71
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• 2014

MLCCs are used broadly in electronic industry like smart phone and TV. Although they are fabricated in small size and have high capacitance, there are acoustic noise problems to reduce comfort of user. Acoustic noise results from linear piezoelectricity and nonlinear electrostriction of $BaTiO_3$ in MLCC and there are some researches on MLCC vibration under AC electric field. When only AC electric field without DC bias is applied to MLCC, fundamental frequency response is affected by piezoelectricity and second-harmonic frequency response shows electrostrictive vibration. In this study we get vibration shape of MLCC under AC electric field for each frequency and analysis on the mechanism of MLCC vibration affected by piezoelectricity and electrostriction.

• Journal of Sensor Science and Technology
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• v.31 no.4
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• pp.194-213
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• 2022

This study comprehensively reviewed four types of integrated-optic electric-field sensors based on titanium diffused lithium-niobate waveguides: symmetric and asymmetric Mach-Zehnder interferometers, 1×2 directional couplers, and Y-fed balanced-bridge Mach-Zehnder interferometers. First, we briefly explain the crystal properties and electro-optic effect of lithium niobate and the waveguide fabrication process. We theoretically analyzed the key parameters and operating principles of each sensor and antennas. We also describe and compare the design, simulation, implementation, and performance tests: dc and ac characteristics, frequency response, dynamic range, and sensitivity. The experimental results revealed that the sensitivity of the sensor based on the Y-fed balanced bridge Mach-Zehnder interferometer (YBB-MZI) was higher than that of the other types of sensors.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.1885-1891
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• 2010

Recently metropolitan local governments is actively introducing urban railway's expand and light rail transit as a means of new transport system. DC electricity feeder system operating in the domestic urban railway is typically a feedback circuit consisted of the contact wire and electric railway vehicle via rail. But stray current is to be defined as a current flowing on a structure that is not part of the intended electrical circuit with respect to a given structure. Stray current is generally results from the leakage of return currents from large DC traction systems that are grounded or have a bad earth-insulated return path. At the place where the current leaves the rail and metallic structures, electrolytic corrosion may take place. This paper presents comparison analysis of field test methods based on criteria of electrolytic corrosion protection of buried metallic structures adjacent to DC traction systems.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.286-293
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• 2008

DC transit system has been adopted in the metropolitan area, Korea since 1974. EMU in this system always reiterates that acceleration and retardation. When EMU decelerates using electric breaking, regenerative power occurs. Regenerative power can be consumed in vicinity EMC on the same line or in resistor. If DC transit system has inverter for reusing regenerative power, Energy efficiency in DC transit system will be increased. This paper present the developed inverter for regenerative power and its field test. Test result of developed inverter is presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1062-1068
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• 2002

In our previous study, it was proven that the mean size and the total number concentration of carbon soot particles emitted from a $C_2$H$_4$ normal diffusion flame decreased when a DC corona was discharged to pin-pin electrodes. In this work the effect of AC corona discharge on soot emission was investigated and compared with that of DC corona discharge. For the pin-pin electrodes the size of soot particles and the number concentration decreased by the AC voltage. There were only slight changes in size distribution with frequencies, while the magnitude of applied voltage was constant. When the electric field was applied to plate-plate electrodes, the size and the number concentration also decreased with the applied AC voltages. For applied voltages above 2kV the effect of frequency increase on the soot emission was effective.

• Proceedings of the KIEE Conference
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• 2005.10c
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• pp.276-278
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• 2005

For over 25 years, the stray currents from DC electric railroads have caused serious interference problems with underground metallic infrastructures in Korea. The most serious interference is reported at the pipelines near the depot areas. Our field survey proves that this phenomena is mainly due to the missing of dedicated rectifiers for mainline, depot and/or workshop areas. Because it takes so much time and costs too much to replace the traction power system, we consider a stray current confinement method which collects the stray currents and drains them to the negative terminal of the rectifier. This can be realized by installing a stray current collecting wire along the depot boundary. Moreover, we found the stray current collecting reinforcement bar located beneath the rails of concrete slab tracks. Using this bar, we arc going to draing the stray currents from mainline rails. In this paper we show the result of field survey on railroad facilities and present the stray current confinement method under field test.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1682-1691
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• 2018

Natural ester is a suitable substitute for mineral oil and has been widely used in AC transformer in many countries. In order to further application of natural ester in direct current (DC) equipment, it is needed to investigate its long term insulation property under DC condition. In this paper, a thermal ageing experiment was conducted for both mineral oil-paper and natural ester-paper insulation. The DC breakdown and space charge characteristics of insulation paper impregnated with natural ester and mineral oil was compared. Results show that the resistivity of the paper immersed in natural ester and mineral oil both increase as the ageing goes on. While insulation paper impregnated with natural ester has higher resistivity and DC breakdown voltage than the paper impregnated with mineral oil. The DC breakdown voltage for the oil impregnated insulation paper being DC pre-stressing is higher than that without pre-stressing. The average DC breakdown field strength difference between the test with pre-stressing and without pre-stressing clearly shows that there is an apparent enhancement effect for the homo-charge injection on the DC breakdown.