• Advances in materials Research
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• v.1 no.2
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• pp.129-146
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• 2012

Polycrystalline diamond is an ideal material for parts with micro-holes and has been widely used as dies and cutting tools in automotive, aerospace and woodworking industries due to its superior wear and corrosion resistance. In this research paper, the modeling and simultaneous optimization of multiple performance characteristics such as material removal rate and surface roughness of polycrystalline diamond (PCD) with ultrasonic machining process has been presented. The fuzzy logic and taguchi's quality loss function has been used. In recent years, fuzzy logic has been used in manufacturing engineering for modeling and monitoring. Also the effect of controllable machining parameters like type of abrasive slurry, their size and concentration, nature of tool material and the power rating of the machine has been determined by applying the single objective and multi-objective optimization techniques. The analysis of results has been done using the MATLAB 7.5 software and results obtained are validated by conducting the confirmation experiments. The results show the considerable improvement in S/N ratio as compared to initial cutting conditions. The surface roughness of machined surface has been measured by using the Perthometer (M4Pi, Mahr Germany).

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.104-107
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• 1999

We investigated the effects of cooling condition on deep levels and iron precipitate formation in iron-contaminated p-type silicon by DLTS(Deep Level Transient Spectroscopy) and preferential etching technique. Dependency of cooling condition on Bulk Micro-Defect (BMD) and four different iron-related deep traps were observed. For normal cooling condition, T1, T2, T3, T4 traps that related to Fe\ulcorner or Fe-O complex were obtained. However, the trap with activation energy, 0.4 eV was observed for slow cooling condition. The trap caused by the $\textrm{Fe}^{+}\textrm{}^{-}$ pair (H4:0.56eV) were detected only at the case of $\textrm{LN}_{2}$ quenching condition.

• Applied Science and Convergence Technology
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• v.23 no.4
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• pp.192-199
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• 2014

The electronic property of graphene was investigated by hydrazine treatment. Hydrazine ($N_2H_4$) highly increases electron concentrations and up-shifts Fermi level of graphene based on significant shift of Dirac point to the negative gate voltage. We have observed contact resistance and channel length dependent mobility of graphene in the back-gated device after hydrazine monohydrate treatment and continuously monitored electrical characteristics under Nitrogen or air exposure. The contact resistance increases with hydrazine-treated and subsequent Nitrogen-exposed devices and reduces down in successive Air-exposed device to the similar level of pristine one. The channel conductance curve as a function of gate voltage in hole conduction regime keeps analogous value and shape even after Nitrogen/Air exposure specially whereas, in electron conduction regime change rate of conductance along with the level of conductance with gate voltage are decreased. Hydrazine could be utilized as the highly effective donor without degradation of mobility but the stability issue to be solved for future application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.9
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• pp.825-831
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• 2006

As an increase of chip complexity and level of chip integration, chip input/output (I/O) pad pitches are also drastically reduced. With arrival of high complexity SoC (System on Chip) and SiP (System in Package) products, conventional horizontal type probe card showed its limitation on probing density for wafer level test. To enhance probing density, we proposed new vertical type probe card that has the $70{\mu}m$ probe needle with tungsten wire in $80{\mu}m$ micro-drilled hole in ceramic board. To minimize alignment error, micro-drilling conditions are optimized and epoxy-hardening conditions are also optimized to minimize planarity changes. To apply wafer level test for target devices (T5365 256M SDRAM), designed probe card was characterized by probe needle tension for test, contact resistance measurement, leakage current measurement and the planarity test. Compare to conventional probe card with minimum pitch of $50{\sim}125{\mu}m\;and\;2\;{\Omega}$ of average contact resistance, designed probe card showed only $22{\mu}$ of minimum pitch and $1.5{\Omega}$ of average contact resistance. And also, with the nature of vertical probing style, it showed comparably small contact scratch and it can be applied to bumping type chip test.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.12
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• pp.1347-1352
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• 2011

Recently, as the aged population grows around the world, many medical instruments, devices, and their fabrication processes are developing. Among the devices, a drug delivery stent is a good example for precision machining. Conventional drug delivery stent has problem of the remaining polymer because the drug is coated on the surface with it. If the drug is impregnated into the micro hole array on the stent surface, the polymer can be perfectly eliminated. Micro sized holes are generally fabricated by laser machining however, the fabricated holes do not have an enough aspect ratio to contain the drug or a good surface finish to deliver the stend to blood vessel tissue. To overcome these problems, we propose a vibration-assisted machining mechanism with PZT (Piezoelectric Transducers) for abrication of micro sized holes better. The results indicated that the burr size can be significantly decreased with vibration assisted in nanosecond pulse laser drilling test.

• Composites Research
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• v.20 no.2
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• pp.17-20
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• 2007

Superhydrophobic polytetrafluoroethylene ($Teflon^{(R)}$, Dupont) sub-micro and nanostructures were fabricated by the dipping method, based on anodization process in oxalic acid. The polymer sticking phenomenon during the replication creates the sub-microstructures on the negative polytetrafluoroethylene nanostructure replica. This process gives a hierarchical structure with nanostructures on sub-microstructures, which looks like the same structures as lotus leaf and enables commercialization. The diameter and the height of the replicated nano pillars were 40 nm and 40 um respectively. The aspect ratio is approximately 1000. The fabricated surface has a semi-permanent superhydrophobicity, the apparent contact angle of the polytetrafluoroethylene sub-micro and nanostructures is about $160^{\circ}$, and the sliding angle is less than $1^{\circ}$.

• Journal of Powder Materials
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• v.21 no.4
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• pp.301-306
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• 2014

Titanium alloys are extensively used in high-temperature applications due to their excellent high strength and corrosion resistance properties. However, titanium alloys are problematic because they tend to be extremely difficult-to-cut material. In this paper, the powder synthesis, spark plasma sintering (SPS), bulk material characteristics and machinability test of hybrid $Ti_2AlC$ ceramic bulk materials were systematically examined. The bulk samples mainly consisted of $Ti_2AlC$ materials with density close to theoretical value were synthesized by a SPS method. Random orientation and good crystallization of the $Ti_2AlC$ was observed at $1100^{\circ}C$ for 10 min under SPS sintering conditions. Scanning electron microscopy results indicated a homogeneous distribution and nano-laminated structure of $Ti_2AlC$ MAX phase. The hardness and electrical conductivity of $Ti_2AlC$ were higher than that of Ti 6242 alloy at sintering temperature of $1000^{\circ}C{\sim}1100^{\circ}C$. Consequently, the machinability of the hybrid $Ti_2AlC$ bulk materials is better than that of the Ti 6242 alloy for micro-EDM process of micro-hole shape workpiece.

• 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.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.8 s.197
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• pp.116-121
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• 2007

The length of root canal has to be measured for endodontic treatment. Several electronic apex locators were developed to measure the length of root canal by other researchers. And their accuracies were verified by X-ray or micrometer method. But these methods did not consider the non-linear bends of pulp and had ${\pm}0.5mm$ error which was large enough to measure the length of root canal. The purpose of this study is the introduction of a new method to measure the length of root canal and the verification of the accuracy of an electronic apex locator using a Micro-CT. The length of root canal of 6 teeth were measured with the electronic apex locator. When the electronic apex locator reads 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 mm length of the file which was inserted in the hole of the tooth to measure the length of root canal. The average (${\pm}$Standard deviation) length of root canal of 6 teeth measured by the Micro-CT was $0.49{\pm}0.03,\;0.59{\pm}0.04,\;0.68{\pm}0.03,\;0.78{\pm}0.03,\;0.90{\pm}0.04\;and\;1.01{\pm}0.03mm$, respectively. The maximum error of the electronic apex locator was 0.06 mm.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.623-631
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• 2007

In this paper, dynamic elastic module of banded gneiss were calculated on the basis of SPS velocity logging data obtained from a geotechnical test-hole in Pungsan-dong, Hanam, Gyeonggi Province, Korea. This study mainly focuses on the velocity analysis, Q factor calculation relative to attenuation factor, and generation of crack information and its relation with seismic velocity. As a result, P-wave and S-wave velocity of fresh hard rock was 5,559m/s and 3,063m/s, respectively, with Poisson's ratio being 0.28. With these results, dynamic modules were prepared, and crack information analyzed by acoustic televiewer was incorporated to identify the correlation among and between delay of first arrival by crack amplitude ratio, and velocity. The results of this study revealed that the analyzed logging hole mainly consisted of micro crack and a number of cracks and the size of crack aperture, functioned as a variable to seismic velocity in the micro crack area of this type of hard rock.