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Reversible and Continuous Latching Using a Carbon Internanotube Interface
Eun, Youngkee,Choi, Jungwook,Lee, Jae-Ik,Na, Hyungjoo,Baek, Dae-hyun,Kim, Min-Ook,Kim, Jongbaeg American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.15
<P>Mechanical multistability is greatly beneficial in microelectromechanical systems because it offers multiple stable positioning of movable microstructures without a continuous energy supply. Although mechanical latching components based on multistability have been widely used in microsystems, their latching positions are inherently discrete and the number of stable positions is quite limited because of the lithographical minimum feature size limit of microstructures. We report a novel use of aligned carbon nanotube (CNT) arrays as latching elements in a movable micromechanical device. This CNT-array-based latching mechanism allows stable latching at multiple latching positions, together with reversible and bidirectional latching capabilities. The latching element with integrated CNTs on the sidewalls of microstructures can be adopted for diverse microelectromechanical systems that need precise positioning of movable structures without the necessity of continuous power consumption.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-15/am401777u/production/images/medium/am-2013-01777u_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am401777u'>ACS Electronic Supporting Info</A></P>
Eun, Youngkee,Na, Hyungjoo,Jeong, Bongwon,Lee, Jae-ik,Kim, Jongbaeg IOP 2009 JOURNAL OF MICROMECHANICS AND MICROENGINEERING - Vol.19 No.6
<P>This paper presents a novel design of a bidirectional torsional micromirror utilizing vertically driven electrothermal electromagnetic silicon beam actuators to generate large angular motion in both static mode and high-frequency resonance mode with low operational voltages. The microactuators are fabricated on a silicon-on-insulator (SOI) wafer using three photo masks in order to form two different thicknesses of single crystal silicon (SCS) device layer and backside cavities. When the driving bias is applied to the device in the static mode operation, four buckle beams placed alongside the torsion bars are subjected to thermal expansion and buckle in the vertical direction generating torsional displacement of the micromirror with respect to two torsion bars, the center of rotation. The direction of buckle is controlled by the Lorentz force caused by the current flowing through the silicon beams to be buckled in the magnetic field applied, enabling the bidirectional motion of the torsional micromirror. At resonance, Lorentz force itself drives the actuator instead of thermal expansion force from the buckle beams. The maximum static angular displacement of the torsional actuator is 13.42° (26.84°, optical angle) under a driving dc voltage of 7.5 V. In the resonance mode operation, the measured angular displacement is 8.22° (16.44°, optical angle) at 10.64 kHz under sinusoidal driving voltages of 0 to 4.4 V.</P>
Eun, Youngkee,Kim, Jongbaeg IOP 2009 JOURNAL OF MICROMECHANICS AND MICROENGINEERING - Vol.19 No.4
<P>This paper presents one- and two-degree-of-freedom (DOF) torsional micromirrors driven by in-plane thermal actuators for large static angular motion at low operational voltage. The micromirror actuator is fabricated on a silicon-on-insulator (SOI) wafer using three photomasks to form two different thicknesses on the device layer and to define backside holes. The thin layer beam connected to the thick layer torsion bar is pulled by the in-plane thermal actuator, twisting the torsion bar and therefore inducing angular motion of the mirror. The proposed pre-bent torsion bar design enhances the angular motion significantly and suppresses unnecessary translational motion. The fabricated 1-DOF micromirror is driven to the maximum optical scan angle of 6.5° at 13 V dc. For a 2-DOF micromirror, optical scan angles of 5.4° and 5.2° are achieved in each direction of rotation at 11 V dc.</P>
주영기(Youngkee Ju),정다은(Da-eun Jeong),유명순(Myoungsoon You) 한국보건교육건강증진학회 2013 보건교육건강증진학회지 Vol.30 No.5
Objectives: The public relies on the news media to understand health risks. To examine the surveillance function of Korean health journalism, this study compared the rank-order of the 10 most frequently diagnosed cancers with that of the 10 cancers most frequently covered by three major Korean newspapers. Methods: News stories published between 1999 and 2010 by the Chosun-Ilbo, Joong-Ang-Ilbo, and Dong-A-Ilbo were examined. Data on cancer incidence were collected using the epidemiological data published by a governmental public health institution. To compare the level of the crude rates and the amount of news coverage, rank-order correlation tests and regression analyses were employed. Results: A reduction in the rank-ordered correlation coefficient was observed despite an increase in the overall number of cancer news stories released. The significance of the correlation disappeared after 2006. The big difference of the rank order between the crude rate and the amount of news coverage was observed in the cancer of breast, uteri, thyroid, and gallbladder/biliary. Finally, the three newspapers did not follow the amount change in stomach, lung, liver, and uterine cervix cancer. The four cancers’ rank orders of crude rate were lowering, signifying a reduction of the comparative dangerousness of the four cancers. Conclusions: The news media’s customization of news content and the negative bias in journalism are suggested as possible influences on the news media’s inaccurate representation of cancer risk.
Investigation of Interfacial Adhesion between the Top Ends of Carbon Nanotubes
Choi, Jungwook,Eun, Youngkee,Kim, Jongbaeg American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.9
<P>Understanding the interfacial forces of carbon nanotubes (CNTs) is fundamental to the development of electromechanical systems based on the contact of CNTs. However, experimental studies on the adhesion properties between CNTs are scarce despite the remarkable contact quality of CNTs. Here, we present an experimental investigation of the adhesion between the top ends of aligned, self-adjusted CNTs using a CNT-integrated microelectromechanical actuator. The pull-out and pull-in behaviors of the contact as a function of the applied force by the actuator are precisely identified by measuring the contact resistance between the CNTs. The adhesion between the top ends of individual CNTs is extracted from the measured adhesive strength between the CNT arrays, and it agrees with the theoretical values of the van der Waals interactions. By exploiting the adhesion of the CNT-to-CNT contact, a programmable and reliable microelectromechanical switching device is demonstrated. Our results offer design strategies for diverse CNT-based nano- and microelectromechanical devices that need repeatable contacting interfaces.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-9/am500252s/production/images/medium/am-2014-00252s_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am500252s'>ACS Electronic Supporting Info</A></P>
Han, HyukSu,Nam, Hyun Nam,Eun, Youngkee,Lee, Su Yeon,Nam, Jeongho,Ryu, Jeong Ho,Lee, Sung Yoon,Kim, Jungin The Korea Association of Crystal Growth 2016 한국결정성장학회지 Vol.26 No.5
Foam reaction injection molding (FRIM) is a widely used process for manufacturing polyurethane foam with complex shapes. Numerical model for polyurethane foam forming reaction during FRIM process has been intensively investigated by a number of researchers to precisely predict final shapes of polyurethane foams. In this study, we have identified a problem related with a previous theoretical model for polyurethane foam forming reaction. Thus, previous theoretical model was modified based on experimental and computational results.
Song, Youngsup,Lee, Jae-Ik,Pyo, Soonjae,Eun, Youngkee,Choi, Jungwook,Kim, Jongbaeg IOP Pub 2016 Nanotechnology Vol.27 No.20
<P>A novel carbon nanotube (CNT)-based flexible strain sensor with the highest gauge factor of 4739 is presented. CNT-to-CNT contacts are fabricated on a pair of silicon electrodes fixed on a PDMS specimen for both flexibility and electrical connection. The strain is detected by the resistance change between facing CNT bundles. The proposed approach could be applied for diverse applications with a high gauge factor.</P>
Han, HyukSu,Nam, Hyun Nam,Eun, Youngkee,Lee, Su Yeon,Nam, Jeongho,Ryu, Jeong Ho,Lee, Sung Yoon,Kim, Jungin The Korea Association of Crystal Growth 2016 韓國結晶成長學會誌 Vol.26 No.6
Foam reaction injection molding (FRIM) is a widely used process for manufacturing polyurethane foam with complex shapes. The modified theoretical model for polyurethane foam forming reaction during FRIM process was established in our previous work. In this study, using the modified model, parametric study for FRIM process was performed in order to optimize experimental conditions of FRIM process such as initial temperature of mold, thickness of mold, and injection amount of polymerizing mixture. In addition, we applied the modified model to real application of refrigerator cabinet to determine optimal manufacturing conditions for polyurethane FRIM process.
Yongkeun Oh,Dae-Sung Kwon,Youngkee Eun,Wondo Kim,Min-Ook Kim,Hee-Jin Ko,Seong Gu Kang,Jongbaeg Kim 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.4
In this paper, we present a flexible hybrid energy harvester for single- or multi-source energy collection. To increase harvesting power, piezoelectric and thermoelectric conversions are used simultaneously. The piezoelectric portion of the harvester collects energy from low-frequency kinetic motion using frequency up-conversion. The thermoelectric part is suitable for harvesting energy from a curved surface, thanks to its flexibility. By harvesting from two different energy sources (kinetic and thermal), the harvester allows for sustainable energy harvesting. The average power density obtained was 28.57 and 0.64 μW/cm2 by piezoelectric and thermoelectric conversion, respectively.