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Choi, Hyunjin,Choi, Woohyuk,Lim, Jiseok,Choi, Jungwook Elsevier 2019 Sensors and actuators. A Physical Vol.298 No.-
<P><B>Abstract</B></P> <P>Light-emitting diodes (LEDs) are widely used in many industrial applications owing to their high performance and efficiency compared with conventional lighting systems. However, a considerable amount of input power is inevitably dissipated into heat at the LED junction, which can degrade the performance and reliability of the LED; thus, it is important to monitor the change in the junction temperature of the LED. In this study, we present a micro-temperature sensor-integrated surface-mounted device (SMD) for accurate and real-time measurement of the junction temperature of an LED. The LED is mounted on a microfabricated Pt sensor in a similar way to the typical SMD assembly. The heat generated at the LED junction is conductively transferred to the microsensor, increasing the temperature and changing its electrical resistance. In contrast to the conventional techniques for thermal characterization of LEDs, the integrated microsensor provides real-time information on the junction temperature with high precision, reproducibility, and simplicity. Additionally, the temperature of the solder, which is not easily accessible but is closely related to the reliability of the LED, can be estimated by analyzing the thermal resistance of the LED package. Experimental and numerical results indicate a linear correlation (R<SUP>2</SUP> = 0.988) between the junction and sensor temperatures, which is practically useful for the thermal management of the miniaturized SMD-LED.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Methodology for measuring LED junction temperature is proposed. </LI> <LI> Pt micro-temperature sensor-integrated SMD-LED is designed and fabricated for real-time measurement of junction temperature. </LI> <LI> Highly linear correlation of the temperature between the microsensor and the junction is experimentally found. </LI> <LI> Analysis of structure function, thermal resistance, and numerical calculation of SMD-LED validates measurement accuracy of Pt microsensor. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Hyunjin Choi,Youdan Kim,Hyounjin Kim 한국항공우주학회 2011 International Journal of Aeronautical and Space Sc Vol.12 No.2
Task assignments of multiple unmanned aerial vehicles (UAVs) are examined. The phrase “task assignment” comprises the decision making procedures of a UAV group. In this study, an on-line decentralized task assignment algorithm is proposed for an autonomous UAV group. The proposed method is divided into two stages: an order optimization stage and a communications and negotiation stage. A genetic algorithm and negotiation strategy based on one-to-one communication is adopted for each stage. Through the proposed algorithm, decentralized task assignments can be applied to dynamic environments in which sensing range and communication are limited. The performance of the proposed algorithm is verified by performing numerical simulations.
Choi, Pyungho,Kim, Hyunjin,Kim, Sangsub,Kim, Soonkon,Javadi, Reza,Park, Hyoungsun,Choi, Byoungdeog American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.5
<P>In this study, pulse frequency and reverse bias voltage is modified in charge pumping and advanced technique is presented to extract oxide trap profile in hot carrier stressed thin gate oxide metal oxide semiconductor field effect transistors (MOSFETs). Carrier trapping-detrapping in a gate oxide was analyzed after hot carrier stress and the relationship between trapping depth and frequency was investigated. Hot carrier induced interface traps appears in whole channel area but induced border traps mainly appears in above pinch-off region near drain and gradually decreases toward center of the channel. Thus, hot carrier stress causes interface trap generation in whole channel area while most border trap generation occurs in the drain region under the gate. Ultimately, modified charge pumping method was performed to get trap density distribution of hot carrier stressed MOSFET devices, and the trapping-detrapping mechanism is also analyzed.</P>