• Korean Journal of Materials Research
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• v.5 no.2
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• pp.208-214
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• 1995

In order to study on the penetrations of HF solution acording to the geometrical shrinkage of contact-hole pattern size, the wet etch characteristics for oxide in microchannel patterns was investigated. Microchannel patterns of LPCVD oxide surrounded by nitride film, with dimensions of 0.1~1$\mu\textrm{m}$ height and 0.1~20$\mu\textrm{m}$, width, were fabricated. And the etch rates of oxide in HF solution were observed. It was found that oxide etch rate for micro-channel patterns in HF was not affected by pattern sizes and initial aspect ratios up to $0.1 \times 0.1 \mu \textrm{m}^{2} size and 1.2$\mu\textrm{m}$ depth. Finally, it was concluded that there were no special limitations for penetrations of HF solution in wet processes according to the geometrical shrinkage of contact-hole pattern size.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.553-559
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• 2006

Most diesel injector, which is currently used in high-pressure common rail fuel injection system of diesel engine, is driven by the solenoid coil energy for its needle movement. The main disadvantage of this solenoid-driven injector is a high power consumption, high power loss through solenoid coil and relatively fixed needle response's problem. In this study, a prototype piezo-driven injector, as a new injector mechanism driven by piezoelectric energy based on the concept of inverse piezo-electric effect, has been designed and fabricated to know the effect of piezo-driven injection processes on the diesel spray structure and internal nozzle flow. Firstly we investigated the spray characteristics in a constant volume chamber pressurized by nitrogen gas using the back diffusion light illumination method for high-speed temporal photography and also analyzed the inside nozzle flow by a fully transient simulation with cavitation model using VOF(volume of fraction) method. The numerical calculation has been performed to simulate the cavitating flow of 3-dimensional real size single hole nozzle along the injection duration. Results were compared between a conventional solenoid-driven injector and piezo-driven injector, both equipped with the same micro-sac multi-hole injection nozzle. The experimental results show that the piezo-driven injector has short injection delay and a faster spray development and produces higher injection velocity than the solenoid-driven injector. And the predicted simulation results with the degree of cavitation's generation inside nozzle for faster needle response In a piezo-driven injector were reflected to spray development in agreement with the experimental spray images.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1765-1771
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• 2010

In the case of micro.electro-mechanical system (MEMS) devices, the quality of punched via hole is one of the most important factors governing the performance of the device. The common features that affect the laser micromachining of via holes drilled by using Nd:$YVO_4$ laser are described, and efficient optimization methods to measure them are presented. The analysis methods involving an orthogonal array, analysis of variance (ANOVA), and response surface optimization are employed to determine the main effects and to determine the optimal laser process parameters. The significant laser process parameters were identified and their effects on the quality of via holes were studied. Finally, an experiment in which the optimal levels of the laser process parameters were used was carried out to demonstrate the effectiveness of the optimization method.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.751-758
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• 2002

Boreholes that are drilled in soft or unconsolidated materials such as gravels and coals are prone to collapse. To maintain the hole, some kinds of casing pipes are needed. If thereby a plastic pipe e.g. PVC is used for the casing, Televiewer tool is still capable of detecting structural features such as fractures in the borehole wall behind the pipe, whereas other borehole-imaging logging devices such as BIPS (Borehole Image Processing System) and FMS(Formation Micro Scanner) won't provide any information about that. Televiewer's primary component is a piezoelectric transducer centered in the hole. It acts as both a transmitter and receiver, and sends an ultrasonic beam. That is reflected, in the same manner as the seismic wave propagation, from the both sides(inner and outer surfaces) of the casing pipe, transmits through the pipe and then reflected from the borehole wall. With an appropriate choice of time-windowing, it is possible to capture the returning signals from both the borehole wall and the outer side of casing pipe as well. A suite of laboratory tests were performed on various physical models composed of plastic pipes with different diameters. Although the amplitudes of returning signals were reduced to about half the usual value due to the transmission loss, the dynamic range of Televiewer tool was sufficient to observe the structural features behind the casing pipe. Besides, several representative case studies at various research areas in our country are presented. The results demonstrate the usefulness of the transmissivity of Televiewer acoustic km, which will assist in further structural interpretation.

• Smart Structures and Systems
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• v.4 no.6
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• pp.727-740
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• 2008

A down hole vertical seismic array is a sequence of instruments installed at various depths in the earth to record the ground motion at multiple points during an earthquake. Numerous studies demonstrate the unique utility of vertical seismic arrays for studying in situ site response and soil behavior. Examples are given of analyses made at two sites to show the value of data from vertical seismic arrays. The sites examined are the Lotung, Taiwan SMART1 array and a new site installed at Jingliao, Taiwan. Details of the installation of the Jingliao array are given. ARX models are theoretically the correct process models for vertical wave propagation in the layered earth, and are used to linearly map deeper sensor input signals to shallower sensor output signals. An example of Event 16 at the Lotung array is given. This same data, when examined in detail with a Bayesian inference model, can also be explained by nonlinear filters yielding commonly accepted soil degradation curves. Results from applying an ARMAX model to data from the Jingliao vertical seismic array are presented. Estimates of inter-transducer soil increment resonant frequency, shear modulus, and damping ratio are presented. The shear modulus varied from 50 to 150 MPa, and damping ratio between 8% and 15%. A new hardware monitoring system - TerraScope - is an affordable 4-D down-hole seismic monitoring system based on independent, microprocessor-controlled sensor Pods. The Pods are nominally 50 mm in diameter, and about 120 mm long. An internal 16-bit micro-controller oversees all aspects of instrumentation, eight programmable gain amplifiers, and local signal storage.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.498-502
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• 2010

Aluminium titanate($Al_2TiO_5$) has extremely anisotropic thermal expansion properties in single crystals, and polycrystalline material spontaneously microcracks in the cooling step after sintering process. These fine intergranular cracks limit the strength of the material, but provide an effective mechanism for absorbing strain energy during thermal shock and preventing catastrophic crack propagation. Furthermore, since machinable BN-ceramics used as an insulating substrate in current micro-electronic industry are very expensive, the development of new low-cost machinable substrate ceramics are consistently required. Therefore, cheap $Al_2TiO_5$-machinable ceramics was studied for the replacement of BN ceramics. $Al_2O_3-Al_2TiO_5$ ceramic composite was fabricated via in-situ reaction sintering. $Al_2O_3$ and $TiO_2$ powders were mixed with various mol-ratio and sintered at 1400 to $1600^{\circ}C$ for 1 h. Density, hardness and strength of sintered ceramics were systematically measured. Phase analysis and microstructures were observed by XRD and SEM, respectively. Machinability of each specimens was tested by micro-hole machining. The results of research showed that the $Al_2TiO_5$-composites could be used for low-cost machinable ceramics.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.251-251
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• 2012

A lot of studies are undergoing on the magneto-optical (MO) properties of patterned magnetic systems for the reason that they have potential application to information technology such as ultrahigh-speed computing. Moreover, they can be considered as the future candidates for high-density MO storage devices. Not only the technical aspects, but there have been also tremendous interests in studying their properties related to the fundamental physics. The MO Kerr-rotation effects (both in reflected and the diffracted modes) and the magnetic force microscopy (MFM) are very useful techniques to investigate the micromagnetic properties of such periodic structures. Hence, in this study, we report on the MO properties of bilayered Cobalt (Co)/ nickel (Ni) micro-patterned anti-dot arrays. Such a ferromagnetic structure was made by sequentially depositing co (40 nm)/Ni (5 nm) bilayer on a Si substrate. The anti-dot patterning with hole diameter of $1{\mu}m$ was done only on the upper Co layer using photolithography technique, while the Ni underlayer was kept uniform. The longitudinal Kerr rotation (LKR) of the zeroth- and the first-order diffracted beams were measured at an incidence of $30^{\circ}$ by using a photoelastic modulator method. The external magnetic field was applied perpendicularly to the reflected and the diffracted beams using an electromagnet capable of a maximum field of ${\pm}5$ kOe. Significantly, it was observed that the LKR of the first-order diffracted beam is nearly 4 times larger than that of the zeroth-order beam. The simulated results for the hysteresis loops matched qualitatively well with the experimentally obtained ones. In conjunction with the LKR, we also investigated the magnetic-domain structure by using a MFM system, which were analyzed to elucidate the origin of the enhanced MO rotation.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.581-585
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• 2012

Machinability is important in engineering applications, especially in the current micro-electronics industry. Most ceramic components have complex shapes and hence require machining generally with diamond tools, which incurs a high production cost. Recently, h-BN-containing machinable ceramics have been developed, but these materials are very expensive due to the high raw materials and production costs. Therefore, the development of low-cost machinable ceramics is necessary. In this study, inexpensive $Al_2TiO_5$ was studied as a replacement for h-BN. $Al_2O_3$, $TiO_2$ and partially stabilized $ZrO_2$(PSZ) powders were mixed with various mole ratios and were sintered at $1500^{\circ}C$ for 1 h. The density, hardness and strength were then measured. The phase analysis and microstructures were observed by XRD and SEM, respectively. The machinability of each specimen was tested by micro-hole machining. The results of this research showed that the produced composites could be used as low-cost machinable ceramics.

• Journal of IKEEE
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• v.23 no.3
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• pp.947-953
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• 2019

The purpose of this paper is to explore an ASIC design for estimating sizes and concentrations of airborne micro-particles by the means of integrating, amplifying and digitizing electric charge signals generated by photo-sensors as it receives scattered photons by the presence of micro-particles, consisting of a pre-amplifier that detects and amplifies voltage or current signal from photo-sensor that generates charges (hole-electron pairs) when exposed to visible rays, infrared rays, ultraviolet rays, etc. according to the intensity of rays; a shaper for shaping the amplified signal to a semi-gaussian waveform; two discriminators and binary counters for outputting digital signals by comparing the magnitude of the shaped signal with an arbitrary reference voltages. The ASIC with the proposed architecture and functional blocks in this study was designed with a 0.18um standard CMOS technology from Global Foundries and the operation and performances of the ASIC has been verified by the silicons fabricated by using the process.

• Smart Structures and Systems
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• v.29 no.3
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• pp.445-455
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• 2022

Steel anchor bolts are installed in concrete using a variety of methods. One of the most common methods of anchor bolt installation is using epoxy resin as an infill material injected into the drilled hole to act as a bonding material between the steel bolt and the surrounding concrete. Typical design standards assume uniform stress distribution along the length of the anchor bolt accompanied with single crack leading to pull-out failure. Experimental evidence has shown that the steel anchor bolts fail owing to the multiple failure patterns, hence these design assumptions are not realistic. In this regard, the presented research work details the analytical model that takes into consideration multiple micro cracks in the infill material induced via impact loading. The impact loading from the Schmidt hammer is used to evaluate the bond condition bond condition of anchor bolt and the epoxy material. The added advantage of the presented analytical model is that it is able to take into account the various type of end conditions of the anchor bolts such as bent or U-shaped anchors. Through sensitivity analysis the optimum stiffness and shear strength properties of the epoxy infill material is achieved, which have shown to achieve lower displacement coupled with reduced damage to the surrounding concrete. The accuracy of the presented model is confirmed by comparing the simulated deformational responses with the experimental evidence. From the comparison it was found that the model was successful in simulating the experimental results. The proposed model can be adopted by professionals interested in predicting and controlling the deformational response of anchor bolts.