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Symmetric Current-Balancing Circuit for LED Backlight With Dimming
Sungjin Choi,Taehoon Kim IEEE 2012 IEEE transactions on industrial electronics Vol.59 No.4
<P>One of the key challenges in driving multiple light-emitting-diode (LED) strings for a liquid-crystal-display (LCD) backlight system is to ensure uniform current control. Unequal current sharing between the strings is due to manufacturing spread and temperature variations. In this paper, a novel current-balancing circuit for LED backlights is proposed. A smart combination of an inherent symmetry of circuit and capacitive balancing mechanism enables an efficient and cost-effective current balancing. The operating principle of the proposed method is analyzed, and an appealing generalization is made. The feasibility of the proposed scheme is verified by developing a hardware prototype with a dimming feature to drive a 100-W edge-type backlight system, having six LED strings for a large-scale LCD panel.</P>
Inkjet-Printed Electromagnet-Based Touchpad Using Spiral Resonators
Choi, Sungjin,Eom, Seunghyun,Tentzeris, Manos M.,Lim, Sungjoon Institute of Electrical and Electronics Engineers 2016 Journal of microelectromechanical systems Vol. No.
<P>In this paper, an inkjet-printed electromagnet-based touchpad employing spiral resonators is proposed. The proposed touchpad is fabricated by a direct patterning method using an inkjet printer with a conductive silver nanoparticle ink. The conductive patterns are easily printed on a paper substrate and sintered for achieving good conductivity. The proposed touchpad is composed of two spiral resonators that resonate at 0.94 GHz (f(1)) and 1.83 GHz (f(2)), respectively. When the first resonator is touched, f(1) decreases from 0.94 to 0.81 GHz because of electromagnetic (EM) coupling between the finger and the spiral resonator. Similarly, when the second resonator is touched, f(2) decreases from 1.83 to 1.55 GHz. Owing to the EM coupling distance between the spiral resonator and the finger, the frequency changes although the finger does not reach beyond a height of 1.27 mm on the spiral resonator. The performance of the proposed touchpad is validated using simulation and measurement results. [2016-0035]</P>
Thermally stable, planar hybrid perovskite solar cells with high efficiency
Choi, Kyoungwon,Lee, Junwoo,Kim, Hong Il,Park, Cheol Woong,Kim, Guan-Woo,Choi, Hyuntae,Park, Sungjin,Park, Sang Ah,Park, Taiho The Royal Society of Chemistry 2018 ENERGY AND ENVIRONMENTAL SCIENCE Vol.11 No.11
<P>We report a highly effective interface engineering strategy for thermally stable perovskite solar cells (PSCs) by employing a zwitterion-modified SnO2 electron transport layer (ETL) and a dopant-free hole transport layer (HTL). A zwitterionic compound, 3-(1-pyridinio)-1-propanesulfonate, is used to modify the SnO2 ETL. The zwitterion, which forms interfacial dipoles, plays a few important roles: (1) it causes shifts in the work function of SnO2 resulting in more efficient charge extraction and an increase in the built-in potential. (2) It pulls electrons from perovskite layers to the ETL/perovskite interface, enhancing the electron transport ability. (3) Interfacial dipoles prevent back transfer of electrons from the ETL to the perovskite and suppress charge recombination. (4) Positively charged atoms in the zwitterion passivate Pb-I antisite defects, improving the stability of devices. With these desirable properties, the PSC with doped Spiro-OMeTAD obtained a power conversion efficiency of 21.43%. In addition, the PSC with the dopant-free HTL exhibited a record high efficiency of 20.5% among dopant-free polymeric HTLs using green solvents. The resulting PSCs without encapsulation showed excellent thermal stability. Accordingly, this work suggests that the use of a modified ETL and a dopant-free HTL is a promising strategy to overcome the thermal instability of planar-PSCs (P-PSCs).</P>
Sungjin Choi,Wenjing Su,Tentzeris, Manos M.,Sungjoon Lim IEEE 2015 IEEE microwave and wireless components letters Vol.25 No.2
<P>In this letter, a novel fluid-reconfigurable advanced and delayed phase line using a microfluidic composite right/left-handed (CRLH) transmission line (TL) is proposed. A CRLH-TL prototype is inkjet-printed on a photo-paper substrate. In addition, a laser-etched microfluidic channel in poly(methyl methacrylate) (PMMA) is integrated with the CRLH TL using inkjet-printed SU-8 as a bonding material. The proposed TL provides excellent phase-tuning capability that is dependent on the fluidic materials used. As the fluid is changed, the proposed TL can have negative-, zero-, and positive-phase characteristics at 900 MHz for different fluids. The performance of the TL is successfully validated using simulation and measurement results.</P>
A Reliable Communication Protocol for Multiregion Mobile Agent Environments
SungJin Choi,MaengSoon Baik,HongSoo Kim,EunJoung Byun,Hyunseung Choo IEEE 2010 IEEE transactions on parallel and distributed syst Vol.21 No.1
<P>A mobile agent system is regarded as an attractive technology when developing distributed applications. However, mobility makes it more difficult to trace agents. It is also more complex for agents to communicate with each other in a reliable manner. Therefore, a reliable communication protocol is necessary to control and monitor mobile agents and deliver messages between them. In this paper, a new reliable communication protocol (RCP) is proposed for a multiregion mobile agent computing environment. RCP is implemented on the ODDUGI mobile agent system. Analysis and evaluation show that RCP fulfills the following design goals: reliability, asynchrony, timeliness, location dependency, scalability, and communication cost.</P>