• 연구논문집
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• s.33
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• pp.53-65
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• 2003

Electrostatic micro-motors can be divided into three classes: (i) salient type side drive motor, (ii) radial gap type wobble motor, (iii) axial gap type wobble motor. The working mechanism, torque evaluation, fabrication, and operational characteristics of each micro motors are compared. It is proved that axial gap type wobble motor has the bigger generating torque than that of the other type. The gear ratio of wobble motors increases the driving torque at the cost of a decreasing angular speed and decreases the friction because of the rolling motion instead of sliding at the bearing. Techniques for characterizing micro-motors performance are presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.11
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• pp.881-887
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• 2014

This paper presents numerical study on flow and heat transfer characteristics in micro-gap plate heat exchanger. In particular, we investigate the effect of flow inertia on the flow distribution from single main channel to multiple parallel micro-gaps. The flow regime of the main channel is varied from laminar regime (Reynolds number of 100) to turbulent regime (Reynolds number of 10000) by changing the flow rate, and non-uniformity of the flow distribution and temperature field is evaluated quantitatively based on the standard deviation. The flow distribution is found to be significantly affected by not only the header design but also the flow rate of the main channel. It is also observed that the non-uniformity of the temperature field has its maximum at the intermediate flow regime.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1835-1837
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• 1996

Characteristics of Discharge and nonthermal plasma generation in a micro-air gap spacing between a micro-dielectric barrier and a electrode have been investigated experimentally to chert the potential to be used as a micro-scale nonthermal plasma generator. It is found that the output ozone concentration, as a nonthermal plasma intensity parameter, of the micro-air gnp nonthermal plasma generator depended greatly upon the air gap spacing and thickness of the dielectric barrier. As a result, there is a optimal air gap sparing in the same micro dielectric barrier to generate ozone effectively. And the higher ozone concentration was generated from the thinner micro-barrier.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1202-1205
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• 2005

Micro hole is one of basic elements for micro device or micro parts. By micro ECM, micro holes less than $50\mu{m}$ in diameter can be machined easily. Machining characteristics of micro ECM were investigated according to machining conditions such as electrolyte concentration and pulse conditions. From the investigation, optimal machining conditions were suggested for micro ECM of stainless steel. For the micro machining with high resolution, the change of machining gap should be predicted. By using electrochemical principle equations, the change of machining gap was simulated.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.3
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• pp.22-26
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• 2008

The use of electrical discharge machining (EDM) for micro-machining applications requires particular attention to the machined surface roughness and discharge gap distance, as these factors affect the geometrical accuracy of micro-parts. Previous studies of conventional EDM have shown that selected types of semi-conductive and non-conductive powder suspended in the dielectric reduced the surface roughness while ensuring a limited increase in the gap distance. Based on this, an extension of the technique to micro-EDM was studied Such work is necessary since the introduction of nanopowders suspended in the dielectric is not well understood. The experimental results showed that a statistically significant reduction in the surface roughness value was achieved at particular concentrations of the powder additives, depending on the powder material and the machining input energy setting. The average reduction in surface roughness using a powder suspended dielectric was between 14-24% of the average surface roughness generated using a pure dielectric. Furthermore, when these additive concentrations were used for machining, no adverse increase in the gap distance was observed.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2133-2139
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• 2012

A new system using $TiO_2$ (nano-sized, band-gap 3.14 eV)-impregnated spherical ZnS (micro-sized, band-gap 2.73 eV) nano/micro-composites (Ti 0.001, 0.005, 0.01, and 0.05 mol %/ZnS) was developed to enhance the production of hydrogen from methanol/water splitting. The ZnS particles in a spherical morphology with a diameter of about 2-4 mm which can absorb around 455 nm were prepared by hydrothermal method. This material was used as a photocatalyst with loading by nano-sized $TiO_2$ (20-30 nm) for hydrogen production. The evolution of $H_2$ from methanol/water (1:1) photo splitting over the $TiO_2$/ZnS composite in the liquid system was enhanced, compared with that over pure $TiO_2$ and ZnS. In particular, 1.2 mmol of $H_2$ gas was produced after 12 h when 0.005 mol % $TiO_2$/ZnS nano/micro-composite was used. On the basis of cyclic voltammeter (CV) and UV-visible spectrums results, the high photoactivity was attributed to the larger band gap and the lower LUMO in the $TiO_2$/ZnS composite, due to the decreased recombination between the excited electrons and holes.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.12 s.177
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• pp.163-169
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• 2005

Micro hole is ode of basic elements for micro device or micro parts. Micro electrochemical machining (ECM) can be applied to the machining of micro holes less than 50 ${\mu}m$ in diameter, which it is not easy to apply other techniques to. For the machining of passivating metals such as stainless steel, machining conditions should be chosen carefully to prevent a passive layer. The machining conditions also affect the machining resolution, In this paper, machining characteristics of micro ECM were investigated according to machining conditions such as electrolyte concentration and pulse conditions. From the investigation, optimal machining conditions were suggested for micro ECM of stainless steel.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.12
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• pp.55-61
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• 1998

Recently, the needs of machining technologies of very small parts have been increasing with advent of micro-revolution. These technologies have mostly used the method applied to semi-conductor production process such as LIGA, etc. But they have serious difficulties to settle down in terms of workpiece materials, machining thickness, 3-dimensional structure. Therefore. mciro-machining technology using EDM(Electrical Discharge Machining) was proposed. It is very difficult to machine the micro-parts (microshaft, microhole) using conventional machining. Micro-machining using BDM can machine the micro-parts easily because it requires little machining force. This MEDM(Micro-EDM) need the capabilities to move a electrode and control a discharge energy precisely, and the gap control strategy to maintain the optimal discharge condition is necessary. Therefore, in this study, the new EDM machine with high precision motion stage and high-performance EDM device was developed. Using this MEDM machine, we have machined microshaft and microhole with various shapes and sizes.

• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.267-269
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• 1994

Various types of plasma display panels(PDPs) have been developed to realize the flat panel display device. But, many of its characteristics must be improved before it can be commercialized. In order to investigate tile characteristics of micro discharge in a PDP ceil, we have constructed a micro-gap discharge system whose electrode gap can be adjustable between $100-1000{\mu}m$ within $0.1{\mu}m$ accuracy. We measured the minimum sustain voltage, current, delay time of discharge while changing parameters(electrode gap distance, electrode surface area, pressure) which influence discharge characteristics.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.4
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• pp.101-108
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• 2002

A specially-built EMM (Electrochemical Micro Machining) / PECM (Pulse Electrochemical Machining) cell, a electrode tool filled with non-conducting material, a electrolyte flow control system and a small & stable gap control unit are developed to achieve accurate dimensions of recesses. Two electrolytes, aqueous sodium nitrate and aqueous sodium chloridc arc applied in this study. The farmer electrolyte has better machine-ability than the latter one because of its appropriate changing to the transpassive state without pits on the surface of workpiece. It is easier to control the machining depth precisely by micrometer with pulse current than direct current. This paper also presents an identification method for the machining depth by in-process analysis of machining current and inter electrode gap size. The inter electrode gap characteristics, inc1uding pulse current, effective volumetric electrochemical equivalent and electrolyte conductivity variations, are analyzed based on the model and experiments.