• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1702-1703
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• 2011

MEMS 소자의 Wafer level Package 관련하여 Deep cavity를 가진 Cap Wafer와 Polymer bonding 중 cavity 단차로 인한 Polymer Patterning 및 접합 불량의 어려움을 극복할 수 있는 새로운 공정 flow를 제안하였다. Cavity를 형성할 때 사용하는 Si deep etching Mask인 기존의 Photoresist를 접합용 감광성 Polymer로 대체하고, cavity 형성 후, 별도의 추가 공정 없이 이 Polymer를 이용해 Wafer bonding을 진행하였다. 이를 통해 cavity 단차에 따른 문제를 해결함과 동시에 공정이 단순하고 제작 비용이 저렴하며, 신뢰성 있는 Wafer level Package를 구현하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1294-1298
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• 2005

In this study, combined micro press and surface finishing process are proposed to fabricate the micro nozzle array on a stainless steel sheet metal. In micro hole punching process the burr occurs inevitably, but the burr must be minimized in order to improve the quality and accuracy of the product. For this reason, subsequent magnetic field-assisted finishing technique is applied to remove the burr which exists around the nozzles for ink-jet printer head and proved to be a feasible for deburring by experiment. The deburring characteristics of sheet metals were investigated changing with polishing time and magnetic abrasive size. After the deburring, the burr size has remarkably reduced and roundness of the hole also has improved.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.689-693
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• 2005

Inkjet printing is a non-contact and direct writing associated with a computer. In the industrial field, there have been many efforts to utilize the inkjet printing as a new way of manufacturing, especially for electronic devices. For the application of inkjet printing to electronic field, one of the key factors is exact realization of designed images into printed patterns. In this work, micro patterning for conducting line has been studied using the piezoelectric print head and silver nano ink. Dimensions of printed images have been predicted in terms of print resolution and diameter of a single dot. The predicted and the measured values showed consistent results. Using the results, the design capability for industrial inkjet printing could be achieved.

• Structural Engineering and Mechanics
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• v.48 no.2
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• pp.195-205
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• 2013

The buckling problem of linearly tapered micro-columns is investigated on the basis of modified strain gradient elasticity theory. Bernoulli-Euler beam theory is used to model the non-uniform micro column. Rayleigh-Ritz solution method is utilized to obtain the critical buckling loads of the tapered cantilever micro-columns for different taper ratios. Some comparative results for the cases of rectangular and circular cross-sections are presented in graphical and tabular form to show the differences between the results obtained by modified strain gradient elasticity theory and those achieved by modified couple stress and classical theories. From the results, it is observed that the differences between critical buckling loads achieved by classical and those predicted by non-classical theories are considerable for smaller values of the ratio of the micro-column thickness (or diameter) at its bottom end to the additional material length scale parameters and the differences also increase due to increasing of the taper ratio.

• 한국HCI학회:학술대회논문집
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• 2006.02a
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• pp.638-646
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• 2006

유비쿼터스 시대가 도래함에 따라 사회적으로 실내 위치 추적 시스템에 대한 관심이 증가되었다. 하지만 기존 실내 위치 추적 시스템은 실내 환경의 빈번한 변화에 능동적으로 대응하지 못하고, 실내 환경의 NLOS 특성으로 인하여 이동 객체의 정확한 위치 측정이 어려운 문제점이 있다. 본 연구의 목적은 앞으로 유비쿼터스 시대가 도래함에 따라 다양한 사용자의 요구를 만족시키기 위한 서비스를 제공하는데 필수 요소인 실내 이동 객체의 위치를 효과적으로 파악하고, 이동 객체의 위치 정확도를 향상시킨 환경 적응형 위치 추적시스템을 제안한다.

• Steel and Composite Structures
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• v.26 no.4
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• pp.513-531
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• 2018

In this article, static, buckling and free vibration analyses of a sinusoidal micro composite beam reinforced by single-walled carbon nanotubes (SWCNTs) with considering temperature-dependent material properties embedded in an elastic medium in the presence of magnetic field under transverse uniform load are presented. This system is used at micro or sub micro scales to enhance the stiffness of micro composite structures such as bar, beam, plate and shell. In the present work, the size dependent effects based on surface stress effect and modified strain gradient theory (MSGT) are considered. The generalized rule of mixture is employed to predict temperature-dependent mechanical and thermal properties of micro composite beam. Then, the governing equations of motions are derived using Hamilton's principle and energy method. Numerical results are presented to investigate the influences of material length scale parameters, elastic foundation, composite fiber angle, magnetic intensity, temperature changes and carbon nanotubes volume fraction on the bending, buckling and free vibration behaviors of micro composite beam. There is a good agreement between the obtained results by this research and the literature results. The obtained results of this study demonstrate that the magnetic intensity, temperature changes, and two parameters elastic foundations have important effects on micro composite stiffness, while the magnetic field has greater effects on the bending, buckling and free vibration responses of micro composite beams. Moreover, it is shown that the effects of surface layers are important, and observed that the changes of carbon nanotubes volume fraction, beam length-to-thickness ratio and material length scale parameter have noticeable effects on the maximum deflection, critical buckling load and natural frequencies of micro composite beams.

• Structural Engineering and Mechanics
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• v.70 no.3
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• pp.351-365
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• 2019

In this paper, free vibration of Cooper-Naghdi micro sandwich cylindrical shell with saturated porous core and reinforced carbon nanotube (CNT) piezoelectric composite face sheets is investigated by using first order shear deformation theory (FSDT) and modified couple stress theory (MCST). The sandwich shell is subjected to magneto-thermo-mechanical loadings with temperature dependent material properties. Energy method and Hamilton's principle are used for deriving of the motion equations. The equations are solved by Navier's method. The results are compared with the obtained results by the other literatures. The effects of various parameters such as saturated porous distribution, geometry parameters, volume fraction and temperature change on the natural frequency of the micro-sandwich cylindrical shell are addressed. The obtained results reveal that the natural frequency of the micro sandwich cylindrical shell increases with increasing of the radius to thickness ratio, Skempton coefficient, the porosity of the core, and decreasing of the length to radius ratio and temperature change.

• The Journal of Korea Robotics Society
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• v.4 no.3
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• pp.225-232
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• 2009

In the high precision robot systems, the most popular tasks may be handling of micro-scale objects on a surface such as a micromanipulation robot system. In handling of micro-scale objects, the stiction effect becomes a fundamental issue since the micro-contact mechanics dominates the micromanipulation robot system. In the paper, a theoretical non-stick condition derived from the micro-contact mechanics is carried out for the propose of micro-scale object manipulation. To verify the non-stick condition, a micro-manipulation robot system equipped with a high precision stage system and a microscope system is developed. Experimental results show that the proposed non-stick condition guarantees successful micro-scale object manipulation.

• The Journal of Engineering Geology
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• v.4 no.2
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• pp.231-243
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• 1994

To better understand the fundamental problems of the true micro-damage in medium-grained granite under uniaxial compressive stress, micro-damage localization, initiation and propagation have been observed in a great detail in contact portion of two grains such as quartz and feldspar. For this purpose, new experimental system allowing us to observe the micro-damaging process continuously was developed. Earlier studies used the specimens of unloaded state and it is difficult to visualize stress-induced microcracks under unloading state. Thus, direct observation under loading state is very important for understanding the true micro-damage process. The results explain well the mechanism of micro-damage at two grains, and mechanics of the micro-damage is clarified well by Hertzian fracture mechanics.

• Structural Engineering and Mechanics
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• v.71 no.5
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• pp.485-502
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• 2019

In this research, the nonlinear static, buckling and vibration analysis of viscoelastic micro-composite beam reinforced by various distributions of boron nitrid nanotube (BNNT) with initial geometrical imperfection by modified strain gradient theory (MSGT) using finite element method (FEM) are presented. The various distributions of BNNT are considered as UD, FG-V and FG-X and also, the extended rule of mixture is used to estimate the properties of micro-composite beam. The components of stress are dependent to mechanical, electrical and thermal terms and calculated using piezoelasticity theory. Then, the kinematic equations of micro-composite beam using the displacement fields are obtained. The governing equations of motion are derived using energy method and Hamilton's principle based on MSGT. Then, using FEM, these equations are solved. Finally the effects of different parameters such as initial geometrical imperfection, various distributions of nanotube, damping coefficient, piezoelectric constant, slenderness ratio, Winkler spring constant, Pasternak shear constant, various boundary conditions and three material length scale parameters on the behavior of nonlinear static, buckling and vibration of micro-composite beam are investigated. The results indicate that with an increase in the geometrical imperfection parameter, the stiffness of micro-composite beam increases and thus the non-dimensional nonlinear frequency of the micro structure reduces gradually.