• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.147-148
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• 2006

A research on scaffold fabrication has been progressed in many research groups. However, the mechanical properties of existing biodegradable materials are still not satisfactory. But, PPF (poly (propylene fumarate)) has a good mechanical property in comparison to other biodegradable materials. Nevertheless, the viscosity of the synthesized PPF is too high to fabricate structures using micro-stereolithography. Therefore, the viscosity of the resin was made low by adding the diethyl fumarate and this material could be used in micro-stereolithography apparatus. Then, a photoinitiator was added for photo crosslinking of the DEF/PPF resin. 2.5D and 3D scaffolds were fabricated our system and curing characteristics of the resin were analyzed through the experiment.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.1
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• pp.83-90
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• 2014

EHD (electro-hydro-dynamics) patterning was performed under atmospheric pressure at room temperature in a single step. The drop diameter smaller than nozzle diameter and applied high viscosity conductive ink in EHD patterning method provide a clear advantage over the piezo and thermal inkjet printing techniques. The micro electrode pattern was printed by continuous EHD patterning method using 3-type control parameters (input voltage, patterning speed, nozzle pressure). High viscosity (1000cps) conductive ink with 75wt% of silver nanoparticles was used. EHD cone type nozzle having an internal diameter of $50{\mu}m$ was used for experimentation. EHD jetting mode by input voltage and applied 1st order linear regression in stable jet mode was analyzed. The stable jet was achieved at the amplitude of 1.4~1.8 kV. $10{\mu}m$ micro electrode pattern was created at optimized parameters (input voltage 1.6kV, patterning speed 25mm/sec and nozzle pressure -2.3kPa).

• Korea-Australia Rheology Journal
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• v.19 no.2
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• pp.89-95
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• 2007

The flow characteristics of chicken blood in a micro-tube with a $100{\mu}m$ diameter are investigated using a micro-Particle Image Velocimetry (PIV) technique. Chicken blood with 40% hematocrit is supplied into the micro-tube using a syringe pump. For comparison, the same experiments are repeated for human blood with 40% hematocrit. Chicken blood flow has a cell-free layer near the tube wall, and this layer's thickness increases with the increased flow speed due to radial migration. As a hemorheological feature, the aggregation index of chicken blood is about 50% less than that of human blood. Therefore, the non-Newtonian fluid features of chicken blood are not very remarkable compared with those of human blood. As the flow rate increases, the blunt velocity profile in the central region of the micro-tube sharpens, and the parabolicshaped shear stress distribution becomes to have a linear profile. The viscosity of both blood samples in a low shear rate condition is overestimated, while the viscosity in a high shear rate range is underestimated due to radial migration and the presence of a cell-depleted layer.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.850-853
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• 2000

It is well-known that Electro-rheological(ER) fluid is a material(suspension) which shows the dramatic change of rheological properties under an electric field. Using these properties, the concept that variable apparent viscosity of ER fluid could be applicable to the polishing for micro parts was introduced. It was investigated that how it works for polishing and how it affects ER effect when abrasives were mixed with an ER fluid. Therefore a few structures for polishing using ER fluid was suggested and evaluated by means of experiments. In this paper, fundamental mechanism and experimental results are described.

• Journal of the Korean Society of Combustion
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• v.5 no.1
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• pp.81-89
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• 2000

An experimental study has been carried on single fuel droplets of water-in-light oil emulsions in an electric furnace to elucidate the dominant factor for the occurrence of micro-explosions. The tests were carried out by changing the following four parameters; the surfactant, the ratio of water to light oil, ambient temperature in electric furnace, and four kinds of fuels having different viscosity(light-oil, kerosene, iso-octane, bunker fuel). The result shows that micro-explosion phenomena is dominated without surfactant and below 30% of water content. Explosion-time is affected by ambient temperature and viscosity of used fuel.

• Journal of the korean academy of Pediatric Dentistry
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• v.42 no.4
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• pp.281-290
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• 2015

The aim of this study was to evaluate shear bond strength (SBS) of bulk-fill resin composites (RCs) to dentin and their micro-leakage. One high-viscosity bulk-fill RC and 2 low-viscosity bulk-fill RCs were compared with 1 conventional RC. 7thgenerationbondingagentswereused. In order to evaluate SBS values, 40 permanent molars were selected and divided into 4 groups. The bulk-fill RCs were applied in 4 mm thickness, whereas the conventional RC was applied in 2 mm thickness. In order to evaluate micro-leakage, class I cavities ($5{\times}2{\times}4mm$) were prepared in 32 permanent molars. The teeth were divided into 4 groups and restored with resin composites in an increment of 4 mm for the bulk-fill RC and in 2 horizontal increments of 2 mm for the conventional RC. The mean SBS value of conventional RC showed no statistically significant difference when compared with those of low-viscosity bulk-fill RCs. However, the mean SBS value of high-viscosity bulk-fill RC was significantly lower than that of conventional RC (p < 0.05). There were no statistically significant differences in micro-leakage between the 4 groups. For SBS and micro-leakage, the use of low-viscosity bulk-fill RCs might help clinicians simplify the procedure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.147-150
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• 2003

The purpose of this research was to develope components of micro solid propellant thruster. Micro solid propellant thruster had four basic components: combustion chamber, nozzle, solid propellant and micro heater for ignition. A performance of micro heater and characteristic of solid propellant was investigated. Micro heater was fabricated by conventional MEMS process and Platinum layer was used for heating element. Effect of geometry parameters on micro heater was tested. The temperature responses of heater with respect to each parameters was compared for a given electrical power. The characteristic of solid propellant(HTPB/AP) was investigated to obtain burning velocity in small chamber. Additionally, a capacity of filling propellant with high viscosity in small chamber was checked to guarantee for the micro fabrication.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.38-42
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• 2002

In the recent, electro-rheological fluid has been used for micro polishing of the 3-dimensional micro-aspherical lens and some sectional parts with defects on the wide flat wafer. The ER fluid has the properties that its viscosity has drastic changed under some electric fields. Therefore, ER fluid can be applicable to the micro polishing fur some parts using these properties. In this paper, the experimental device has been constructed using the precision milling machine in order to micro polishing far some sectional parts of a 4 inches wafer It is consisted of a small steel electrode, a wafer fixture, DC10mA and 5KV power supply unit, and a controller unit. Using the ER experimental device, possibility of amending for wide flat wafer and micro polishing of some micro part has been analyzed.

• Transactions of Materials Processing
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• v.24 no.2
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• pp.83-88
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• 2015

For chromaticity correction, it is necessary to dispense high viscosity phosphor slurry since it greatly affects the performance of white LEDs. However, it is quite difficult to dispense high viscosity fluorescent materials. In the current study, micro-discharge electrostatic printing has been used for dispensing various high viscosity phosphor slurries. We have achieved dispersions of up to 50 µg using drop on demand (DOD) discharge experiments. The experiments were conducted with different combinations of process variables such as applied voltage, pneumatic pressure, and frequency.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.27-33
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• 2004

Electro-theological fluid is recently used for the micro polishing of 3-dimensional micro-aspherical lens. It's also used for polishing small area defects on the wide flat wafer. Since ER fluid shows a behavior of viscosity changing under certain electric fields. micro polishing efficiency may be enhanced for certain cases. In this paper, a perfluorinated carbonyl fluoride oil based ER fluids was used to improve surface polishing rate and submicron-scale accuracy. As the polishing electrodes, micro size cylindrical tools had been used for maximizing the electric field. An experimental device, which was applied for micro polishing a number of wafers of 4inches in size and other workpiece. was made on a precision polishing system. It consisted of a steel electrode. a wafer fixture. l0㎃ current and DC 5㎸ power supply unit, and a controller unit. From the Experiments. the ER fluid is applicable for micro polishing of small parts.