• Journal of the Korean institute of surface engineering
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• v.42 no.1
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• pp.41-46
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• 2009

The fit between dental implant fixture and zirconia abutment is affected by many variables during the fabrication process by CAD/CAM program and milling working. The purpose of this study was to evaluate the surface compatibility and electrochemical behaviors of zirconia abutment for prosthodontics. Zirconia abutments were prepared and fabricated using zirconia block and milling machine. For stabilization of zirconia abutments, sintering was carried out at $1500^{\circ}F$ for 7 hrs. The specimens were cut and polished for gap observation. The gap between dental implant fixture and zirconia abutment was observed using field-emission scanning electron microscopy (FE-SEM). The hardness and corrosion resistance of zirconia abutments were observed with vickers hardness tester and potentiostat. The gap between dental implant fixture and zirconia abutment was $5{\sim}12{\mu}m$ for small gap, and $40{\sim}60{\mu}m$ for large gap. The hardness of zirconia surface was 1275.5 Hv and showed micro-machined scratch on the surface. The corrosion potentials of zirconia abutment/fixture was .290 mV and metal abutment/fixture was .280 mV, whereas $|E_{pit}-E_{corr}|$ of zirconia abutment/fixture (172 mV) was higher than that of metal abutment/fixture (150 mV). The corrosion morphology of metal abutment/fixture showed the many pit on the surface in compared with zirconia abutment/fixture.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.11
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• pp.17-23
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• 2010

Titanium alloy is one of the hard processing materials made by the traditional manufacturing method because of the excellent mechanical strength. Ablation of titanium alloy is investigated by using a femtosecond laser which is a regenerative amplified Ti:sapphire laser with 1kHz repetition rate, 184fs pulse duration time and 785nm wavelength. Experiments are carried out under various ablation conditions with different pulse overlap ratios for the rectangular shape and micro hole. Test results show that the ablation characteristic according to pulse overlap ratio of titanium alloy seems to be as non-linear type at the different zone of energy fluence. The optimal condition of rectangular shape processing is obtained at the laser peak power 1.3mW, pulse overlap ratio of 90%, beam gap of $1\;{\mu}m$. The micro hole has a good quality from the pulse overlap ratio of 99% at the same laser peak power. With the optimal processing condition, the fine rectangular shape and micro hole without burr and thermal damage are achieved.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1527-1530
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• 2009

A LCoS micro-display using polymer dispersed liquid crystals (PDLCs) for light switching layer was fabricated. The Si backplane of SVGA ($800{\times}600$) with a pixel size of $14{\times}14mm^2$ was prepared by a $0.35{\mu}m$ 18V CMOS process. PDLCs were filled in the gap between backplane and ITO glass by conventional vacuum filling method. The prepared panels were driven by a field sequential color (FSC) scheme at the frequency of 180Hz and were successful in modulating LED lights to show projection images. The preparation and performance of PDLC-LCoS are presented.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.6 s.348
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• pp.46-52
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• 2006

We report on a high performance 94 GHz MMIC resistive mixer using 70-nm metamorphic high electron mobility transistor (MHEMT) and micro-machined W-band ring coupler. A novel 3-dimensional structure of resistive mixer was proposed in this work, and the ring coupler with the surface micro-machined dielectric-supported air-gap microstrip line (DAMLs) structure was used for high LO-RF isolation. The fabricated mixer showed an excellent LO-RF isolation of -29.3 dB and a low conversion loss of 8.9 dB at 94 GHz. To our knowledge, compared to previously reported W-band mixers, the proposed MHEMT-based resistive mixer using micro-machined ring coupler has shown superior LO-RF isolation as well as similar conversion loss.

• Journal of Sensor Science and Technology
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• v.9 no.3
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• pp.177-181
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• 2000

The tunneling current is exponentially dependent on the separation gap between a pair of conductors. The detection of displacement can be, therefore, carried out by measurment of a variation in the tunneling current. In this experiment, we fabricated pyramid-type silicon tunneling devices in which a tunneling current flow between a micro-tip and $Si_3N_4$ thin film membrane. A MEMS process was used for the fabrication of the tunneling devices. The micro-tips were formed on Si wafers by undercutting a differently oriented square of $SiO_2$ with KOH. The stiffness of the $Si_3N_4$ films were observed and the model for the stiffness calculation, which is useful in predicting the stiffness even when the stiffness ranges beyond the scope of the normal experimental condition, was suggested.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.540-543
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• 2011

This work is devoted to an experimental investigation on conceptual design of dual consecutive stage micro plasma thruster (${\mu}PT$). Optimization study on the thruster configuration has been performed for various electrode gap distances from 1 mm to 2 mm and the hole diameter from 0.3 mm to 2 mm depending on desired operating conditions and corresponding nozzle design requirement. The operation of ${\mu}PT$ at low pressure from $10^{-1}$ Torr to $10^{-4}$ Torr and at various argon flow rates ranging from 5 sccm to 300 sccm has been studied to understand the physic of plasma and the gas dynamics in details. The specific impulse can reach up to 3000-4000 seconds at low power consumptions from 1 to 5 W. Image of exhaust plume from ${\mu}PT$ will be provided and electrical characteristics is also mentioned in this paper.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.323-324
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• 2012

Flammability limits of opposed flow diffusion flame in a narrow channel was investigated experimentally and theoretically. There were three different extinction modes corresponding to high strain rate (HSR), low strain rate (LSR) and dilution ratio (DR) limits. To investigate these limits, a theoretical study was followed by focusing on flow and heat transfer characteristics. Consequently, a dead space concept that has been used for premixed flames was important to reveal the heat loss mechanism in a narrow channel especially for LSR conditions even in the case of diffusion flames.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.103-104
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• 2003

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.7
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• pp.1218-1222
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• 2008

We investigate the effect of rise time of a pulse bias voltage on atmospheric plasma generation. With the faster rise time of the pulse bias, the glow discharge appears to be more uniformly generated along the electrodes. I-V measurement confirms that higher loading power can be obtained using the faster rise time. A new understanding for atmospheric plasma generation at a micro-gap electrode is suggested.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.540-541
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• 2005