• Proceedings of the KSR Conference
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• 2010.06a
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• pp.872-879
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• 2010

High rock-fill embankment is relatively flexible, which makes crest of embankment subject to excessive amplification in displacement due to earthquake loading. To overcome problems related with site response in high embankment, it is essential to evaluate shear-wave velocity profile of the embankment with improved accuracy and reliability. In this aspect, an experimental research was performed to answer how to perform surface-wave tests and to analyze measurements at an embankment site with a sloping ground surface. Unlike flat ground surface, sloping ground may hamper and slow down propagation of surface waves due to multiple reflections and refractions in embankment. To figure out this reasoning for the effect of multiple reflections and refractions due to sloping surface, surface wave tests were performed at a reservoir embankment of Chung-Song in North KyeongSang Province. Parameters involved in surface wave tests at non-flat surface, including source directionality, geometry-related constraint and frequency components in source function, were investigated using field measurements.

• Korean Journal of Computational Design and Engineering
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• v.3 no.4
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• pp.293-303
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• 1998

The objective of this study is to develop a PC level freeform surface modeling system which explicitly represents information of part geometry. Surface modeler uses nonuniform rational B-spline (NURBS) function with nonuniform knot vector for the flexible modeling work. The results of this study are as follows. 1) By implementation surface modeler through applying representation scheme proposed to represent free-form surface explicity, the technical foundation to develop free-from surface modeling system using parametric method. 2) Besides the role to model geometric shape of a surface, geometric modeler is developed to model arbitrary geometric shape. By doing this, the availability of the modeling system is improved. Geometric modeler can be utilized application fields such as collision test of tool and fixture, and tool path generation for NC machine tool.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.549-556
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• 2010

In general, materials that can be used to form elastic pads, such as urethane and rubber, are often used in flexible forming processes by inserting the pads between a blank and flexible die for smoothing the forming surface that is formed by a reconfigurable die. In this study, the effects of the elastic pad on formability in the flexible forming process for sheet metals are investigated by performing numerical simulations. In the simulation, the hyperelastic material model is used, where the urethane elastic pads serve as elastic cushions. Case studies are carried out for elastic materials with different hardness values and thicknesses. The results are used to evaluate formability by comparing the configuration of the deformed blank and its major cross-sectional profiles. It is verified that the elastic pad used in the flexible forming process for sheet materials should be hard and that its thickness should be chosen appropriately.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.314-314
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• 2013

Recently, flexibility is one of the hottest issues in the field of electronic devices. For flexible displays or solar cells, a development of transparent conductive electrodes (TCEs) with flexibility, bendability and foldability is an essential element. Hundreds of nanometers indium-tin-oxide (ITO) films have been widely used and commercialized as a transparent electrode, but their brittleness make them difficulty to apply flexible electronics. Many researchers have been studying for flexible TCEs such as a few layers of graphene sheets, carbon nanotube networks, conductive polymer films and combinations among them. Although gained flexibility, their transmittance and resistivity have not reached those of commercialized ITO films. Metal grids electrode cannot act as TCEs only, but they can be used to lower the resistance of TCEs with few losses of transmittance. However, the possibility of device shortage will be rise at the devices with metal grids because a surface flatness of TCEs may be deteriorated when metal grids are introduced using conventional methods. In our research, we have developed hybrid TCEs, which combined tens of nanometers ITO film and metal grids which are embedded in flexible substrate. They show $13{\Omega}$/${\Box}f$ sheet resistance with 94% of transmittance. Moreover, the sheet resistance was maintained up to 1 mm of bending radius. Also, we have verified that flexible organic light emitting diodes and organic solar cells with the TCEs showed similar performances compared to commercial ITO (on glass substrate) devices.

• Applied Chemistry for Engineering
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• v.32 no.4
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• pp.403-408
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• 2021

In this study, a thin and flexible planar supercapacitor (PSC) was fabricated by coating polyaniline (PANI) on a screen-printed carbon electrode. Carbon ink was coated onto the flexible polyethylene terephthalate using a screen-printing method; subsequently, a thin film of PANI was coated onto the carbon surface using a dilute polymerization method. A thin flexible PANI electrode in an interdigitated structure was assembled with a polymer gel electrolyte that resulted in planar-shaped supercapacitor (PSC) devices. The as-obtained PANI/PSC was very thin and flexible, exhibiting a high areal capacitance of 409 µF/cm was obtained at a rate of 10 mV/s. This capacitance retains 46% of its original value at 500 mV/s. The flexible PANI/PSC exhibited an excellent capacitance retention of 82% even under bent states of 180° and 100 repetitive bent cycles.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.1
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• pp.21-28
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• 2008

The final polishing process is based on slurry, pad, conditioner, equipment. Therefore, the concept of wafer final polishing is also necessary for repeatability of results between polished wafers. In this study, the machining conditions have a pressure, table speed, machining time and slurry ratio. This research investigated the surface characteristics that apply variable machining conditions and response surface methodology was used to obtain more flexible and optimumal condition base on Taguchi method. On the base of estimated response surface curvature from the equation and results of Taguchi method, combined design of experiment was considered to lead to optimumal condition. Finally, polished wafer was obtained mirror like surface.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.2
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• pp.113-119
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• 2022

In order to improve the mechanical reliability of next-generation electronic devices including flexible, wearable devices, a high level of mechanical reliability is required at various flexible joints. Organic adhesive materials such as epoxy for bonding existing polymer substrates inevitably have an increase in the thickness of the joint and involve problems of thermodynamic damage due to repeated deformation and high temperature hardening. Therefore, it is required to develop a low-temperature bonding process to minimize the thickness of the joint and prevent thermal damage for flexible bonding. This study developed flexible laser transmission welding (f-LTW) that allows bonding of flexible substrates with flexibility, robustness, and low thermal damage. Carbon nanotube (CNT) is thin-film coated on a flexible substrate to reduce the thickness of the joint, and a local melt bonding process on the surface of a polymer substrate by heating a CNT dispersion beam laser has been developed. The laser process conditions were constructed to minimize the thermal damage of the substrate and the mechanism of forming a CNT junction with the polymer substrate. In addition, lap shear adhesion test, peel test, and repeated bending experiment were conducted to evaluate the strength and flexibility of the flexible bonding joint.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.1
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• pp.92-98
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• 2014

In this paper, the reconfigurable frequency selective surface for C-band was designed using patch array and grid structure. Frequency reconfigurability was obtained by varying the capacitance from varactor diode. From the optimized design parameters, we fabricated the reconfigurable frequency selective surface using the FPCB(Flexible Printed Circuit Board) and commercial varactor diode and measured the frequency reconfigurability for different bias voltage. From the measurement results, proposed structure has the wideband operating frequency of 6.6~7.6 GHz. We can applied this proposed structure to the smooth curved surface like as radome of aircraft or warship.

• Korean Journal of Metals and Materials
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• v.49 no.8
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• pp.657-663
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• 2011

This study represents the results of the peel strength and surface morphology according to the preprocessing times of polyimide (PI) in a Cu/Ni/PI structure flexible copper clad laminate production process based on the polyimide. Field emission scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to analyze the surface morphology, crystal structure, and interface binding structure of sputtered Ni, Cu, and electrodeposited copper foil layers. The surface roughness of Ni, Cu deposition layers and the crystal structure of electrodeposited Cu layers were varied according to the preprocessing times. In the RF plasma times that were varied by 100-600 seconds in a preprocessing process, the preprocessing applied by about 300-400 seconds showed a homogeneous surface morphology in the metal layers and that also represented high peel strength for the polyimide. Considering the effect of peel strength on plastic deformation, preprocessing times can reasonably be at about 400 seconds.

• Journal of Adhesion and Interface
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• v.24 no.2
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• pp.54-59
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• 2023

Silver nanowire-based transparent electrodes are very attractive as a next-generation flexible and transparent electrode that can replace ITO-based flexible electrodes because they have excellent conductivity, transmittance and mechanical flexibility. However, weak understanding of the silver nanowire solution for the fabrication of silver nanowire-based transparent electrodes often cause abnormal operation of the electrical device or peeling problem of the electrode films when applied to electronic devices. Here, we studied a Hydroxypropyl Methylcellulose (HPMC) adhesion promoter, which is one of the additives for silver nanowire solution, to improve the understanding of silver nanowire solution. In detail, it is characterized how the HPMC changes the properties of silver nanowire solution and silver nanowire film, which is fabricated with silver nanowire solution including the HPMC adhesion promoter. As the characteristics of solution, polar surface tension and dispersive surface tension were measured. As the film characteristics, surface energy, surface morphology, silver nanowire density, and sheet resistance were analyzed.