• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.6
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• pp.119-126
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• 2014

Micro-holes of conductive ceramic are required in micro structures. Micro-electrical discharge machining (Micro-EDM) is an effective machining method since EDM is as process for shaping hard metals and complex-shaped holes by spark erosion in all kinds of electro-conductive materials. However, as the depth of micro hole increases, the machining condition becomes more unstable due to inefficient removal of debris between the electrode and the workpiece. In this paper, micro-EDM was performed to evaluate machining characteristic such as electrode wear, machining time, taper angle, radial clearance with varying voltage and ultrasonic vibration on 10 vol.% Carbon-nanotube reinforced conductive $Al_2O_3$ composite fabricated by spark plasma sintering in previous research.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.6
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• pp.3-9
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• 2013

Aluminum Oxide($Al_2O_3$) ceramics are excellent candidates for such applications due to their outstanding mechanical, thermal, and tribological properties. However, they are difficult to machine using conventional mechanical methods. Carbon fillers, such as carbon nanotubes(CNT) and graphene nanoplatelets(GNP)can be dispersed in a ceramic matrix to improve the mechanical and electrical properties. In this study, CNT and Graphene reinforced hybrid ceramic composites were fabricated using the spark plasma sintering method at a temperature of $1,500^{\circ}C$, pressure of 40 MPa, and soaking time of 10min. Besides this, the material properties such as microstructure, crystal structure, hardness, and electrical conductivity were analyzed using FE-SEM, XRD, Vickers, and the 4-point probe method. A micro machining test was carried out to compare the effects of the material properties and the machining performance for CNT and Graphene reinforced ceramic composites.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1717-1723
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• 2003

Experimental study is conducted to investigate the cooling performance of impinging jet from microtube using Joule-Thomson effect to apply practical applications. And also the heat transfer characteristics of a impinging jet itself and the impinging jet with Joule-Thomson effect are tested to make a comparative study of the two different general ideas. For this propose, two kinds of copper microtubes which have 200 tim and 300 tim in inner diameter respectively were tested and $N_2$ was used as a working fluid. In case of impinging jet without Joule-Thomson effect, heat transfer coefficients distributions were similar to those of normal impinging jet. But in impinging jet with Joule-Thomson effect, the heat transfer coefficients decrease as jet-to-surface increases contrary to the case of the normal jet. As a result, much higher heat transfer coefficients are obtained with Joule-Thomson effect than those of the normal jet without J-T effect.

• Composites Research
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• v.23 no.3
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• pp.7-12
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• 2010

In order to increase the electrical conductivity and the mechanical properties of carbon fabric composites, multi-walled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) were deposited on carbon fabrics by anodic and cathodic electrophoretic deposition (EPD) processes. In the cathodic EPD, carbon nano-particles and nano-sized Cu particles were simultaneously deposited on the carbon fabric, which gave a synergetic effect on the enhancement of properties as well as the degree of deposition. The hybridization of carbon nano-particles and micron-sized carbon fiber significantly improved the through-the-thickness electrical conductivity. In addition, both MWCNTs and CNFs were deposited onto the carbon fabric for multi-scale hybrid composites. Multi-scale deposition improved the through-the-thickness electrical conductivity, compared to the deposition of either MWCNTs or CNFs.

• Korean Journal of Optics and Photonics
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• v.35 no.1
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• pp.9-17
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• 2024

A plenoptic optical system for microscopy comprises an objective lens, tube lens, microlens array (MLA), and an image sensor. Numerical aperture (NA) matching between the tube lens and MLA is used for optimal performance. This paper extends performance predictions from NA matching to unmatching cases and introduces a computational technique for plenoptic configurations using optical analysis software. Validation by fabricating and experimenting with two sample systems at 10× and 20× magnifications resulted in predicted spatial resolutions of 12.5 ㎛ and 6.2 ㎛ and depth of field (DOF) values of 530 ㎛ and 88 ㎛, respectively. The simulation showed resolutions of 11.5 ㎛ and 5.8 ㎛, with DOF values of 510 ㎛ and 70 ㎛, while experiments confirmed predictions with resolutions of 11.1 ㎛ and 5.8 ㎛ and DOF values of 470 ㎛ and 70 ㎛. Both formula-based prediction and simulations yielded similar results to experiments that were suitable for system design. However, regarding DOF values, simulations were closer to experimental values in accuracy, recommending reliance on simulation-based predictions before fabrication.

• Applied Chemistry for Engineering
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• v.26 no.1
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• pp.40-46
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• 2015

Microcapsules containing the suspension of conducting materials such as carbon nanotube (CNT) or polyaniline (PANI) were prepared by in-situ polymerization of melamine and formaldehyde. Stable microcapsules were prepared and the mean diameter of the observed microcapsules was in the range of $10-20{\mu}m$. The surface morphology and chemical structure of microcapsules were investigated using optical microscope (OM), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FT-IR). The thermal properties of samples were investigated by thermogravimetric analysis (TGA). The conductivity of ruptured microcapsule containing the suspension of CNTs or PANIs in tetrachloroethylene and Isopar-G was measured. As the amount of CNTs and PANIs in the core of microcapsules increased, the measured current increased. Conductivity measurement results suggest that poly (melamine-formaldehyde) based core-shell microcapsules could be applied to self-healing electronic materials systems, where CNTs or PANIs bridge a broken circuit upon release.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.5
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• pp.637-645
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• 2009

The main purpose of this study lies on the improvement of micro dilution tunnel based on the typical porous tube type chamber. The characteristics of flow and temperature fields for steady state has been obtained by numerical analysis using FLUENT. Three different geometrical variations of the porous tube; a) increase of thickness at center, b) step increase of thickness at center and downstream, c) tapered increase of thickness, have been proposed. Accordingly results are obtained and compared in terms of penetration velocity and velocity ratio to therrmophoretic velocity for improvement against particulate deposition inside the tube. The penetration velocity and velocity ratio distributions in the upstream portion and portion of impinging of dilution air are apparently shown to be improved for the case of the step and tapered change of porous tube. The tapered change of tube thickness addition are shown to be the most effective among three geometrical changes. In addition, the considerable improvement against deposition are shown that its thickness should be at least 2mm.

• Journal of the Korean Vacuum Society
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• v.15 no.1
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• pp.103-109
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• 2006

A target for a high-brightness microfocus x-ray tube, which is based on carbon nanotubes (CNT) as electron source, is designed. The x-ray tube has the following specifications: brightness of $1\times10^{11}phs/s.mm^2. mrad^2$, spot size $\~5{\mu}m$, and average x-ray energy of $20\~40 keV$. In order to meet the specifications, the design parameters of the target, such as configuration, material, thickness of the target as well as the required beam current, were optimized using computer code MCNPX. The design parameters were determined from the calculation of both x-ray spectrum and intensity distribution for a transmission type configuration. For the thin transmission type target to withstand vacuum pressure and localized thermal loading, the structural stability and temperature distribution were also considered. The material of the target was selected as molybdenum(Mo) and the optimized thickness was $7.2{\mu}m$ to be backed by $150{\mu}m$ beryllium (Be). In addition, the calculations revealed that the maximum temperature of the transmission target can be maintained within the limits of stable operation.

• Journal of the Microelectronics and Packaging Society
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• v.28 no.2
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• pp.89-94
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• 2021

The mechanical reliability of flexible devices has become a major concern on their commercialization, where the importance of reliable bonding is highlighted. In terms of component materials' properties, it is important to consider thermal damage of polymer substrates that occupy large area of the flexible device. Therefore, room temperature bonding process is highly advantageous for implementing flexible device assemblies with mechanical reliability. Conventional epoxy resins for the bonding still require curing at high temperatures. Even after the curing procedure, the bonding joint loses flexibility and exhibits poor fatigue durability. To solve this problems, low-temperature and adhesive-free bonding are required. In this work, we develop a room temperature bonding process for polymer substrates using carbon nanotube heated by microwave irradiations. After depositing multiple-wall carbon nanotubes (MWNTs) on PET polymer substrates, they are heated locally with by microwave while the entire bonding specimen maintains room temperature and the heating induces mechanical entanglement of CNT-PET. The room temperature bonding was conducted for a PET/CNT/PET specimen at 600 watt of microwave power for 10 seconds. Thickness of the CNT bonding joint was very thin that it obtains flexibility as well. In order to evaluate the mechanical reliability of the joint specimen, we performed lap shear test, three-point bending test, and dynamic bending test, and confirmed excellent joint strength, flexibility, and bending durability from each test.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1079-1083
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• 2009

In this study, the distribution of $CO_2$ in an evaporator with 10 parallel micro channel aluminum tubes are experimentally investigated. Each tube has 6 circular micro channels with a diameter of 0.8mm. The tubes are heated with electric resistance wires, and the distribution of $CO_2$ into each tube is investigated by measuring the outer wall temperature. The outer wall temperature was found to be higher at the exit part of the top tube. It is thought that the $CO_2$ vapor at the upper part of the header reduces the mass flow rate of $CO_2$ into the top tube.