Won-Sik Choi

Flexible InGaN LEDs on a Polyimide Substrate Fabricated Using a Simple Direct-Transfer Method

An array of InGaN-based flexible light-emitting diodes (FLEDs) was fabricated on a full-scale 2-in polyimide substrate. An InGaN epitaxial layer on a sapphire substrate was directly bonded with a polyimide substrate, and the sapphire substrate was then removed via a laser lift-off process. A subsequent n-GaN etching process for a chip isolation finished LED chips over the entire 2-in polyimide substrate. Using this simple direct-transfer process, we obtained a production yield of over 97%. The FLED device operated linearly up to an input current level of 500 mA. Output power, operating voltage, and wavelength shift of the FLED up to 400-mA driving current were nearly the same as for a vertical LED on metal substrate.

Study on Compound Humidifier Employing UV-LED using Environmental Life Cycle Assessment

In this study, we assessed environmental impacts of compound humidifiers using environmental life cycle assessment and presented the ways to improvements in energy consumption of them. We found eco-design parameters and -eq emissions in each stage of raw material acquisition, manufacturing, transportation, use and disuse in life cycle of the compound humidifiers. The highest emission is found to be in the stage of use among all stages of life cycle, which is mainly due to power consumption in thermal heating of heating coil for sterilization during humidification. The power consumption and emission in the stage of use can be reduced to 1/4 and 1/3 at the highest estimate through improvement of sterilization method, respectively. We suggested the replacement of conventional thermal heating coil by ultra violet light-emitting diodes (UV-LED) for sterilization and then presented the experimental results on the sterilization effects of UV-LEDs.

Use of Beam Spoiler to Improve Build-up of Photon Beam Using Low Strength Magnetic Field

Woo Sang Ahn, Wonsik Choi, Jungwon Kwak*, Young Ran Ka, Cheol-soo Park, and Seong Soo Shin Department of Radiation Oncology, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung 25440, Republic of Korea 2 Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, Republic of Korea 3 Department of Radiological Technology, Jefferson State Community College, Birmingham, AL 35242, USA 4 Department of Radiological Science, Hallym Polytechnic University, Chuncheon 24210, Republic of Korea