• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.6
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• pp.152-158
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• 2013

The purpose of this study is to investigate cooling performance of high power LEDs from 100 to 200 W class by using a jet impingement cooling module. The numerical analysis of forced convection cooling inside cooling module is carried out using a multi-purpose CFD software, FLUENT 6.3. In the experiments, the LED cooling system consists of jet impingement module, heat exchanger, water reservoir, and pump. In the present study, the cooling performance of jet impingement cooling module is investigated to determine the effect of the heat sink types on the impinging surface, the space and length of fins. Numerical and experimental studies show the reasonable agreement of LED metal PCB temperature between those results and give the optimized design parameters such as the space of fin and the length of fin. Also, the pin fin type of heat sink is found to be more efficient than the plate type heat sink in jet impingement cooling.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.124-124
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• 2010

Much interest has been focused on InGaN-based materials and their quantum structures due to their optoelectronics applications such as light emitting diode (LED) and photovoltaic devices, because of its high thermal conductivity, high optical efficiency, and direct wide band gap, in spite of their high density of threading dislocations. Build-in internal field-induced quantum-confined Stark effect in InGaN/GaN quantum well LED structures results in a spatial separation of electrons and holes, which leads to a reduction of radiative recombination rate. Therefore, many growth techniques have been developed by utilizing lateral over-growth mode or by inserting additional layers such as patterned layer and superlattices for reducing threading dislocations and internal fields. In this work, we investigated various characteristics of InGaN multiple quantum wells (MQWs) LED structures grown on selectively wet-etched porous (SWEP) GaN template layer and compared with those grown on non-porous GaN template layer over c-plane sapphire substrates. From the surface morphology measured by atomic force microscope, high resolution X-ray diffraction analysis, low temperature photoluminescence (PL) and PL excitation measurements, good structural and optical properties were observed on both LED structures. However, InGaN MQWs LED structures grown on SWEP GaN template layer show relatively low In composition, thin well width, and blue shift of PL spectra on MQW emission. These results were explained by rough surface of template layer, reduction of residual compressive stress, and less piezoelectric field on MQWs by utilizing SWEP GaN template layer. Better electrical properties were also observed for InGaN MQWs on SWEP GaN template layer, specially at reverse operating condition for I-V measurements.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.10a
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• pp.323-325
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• 2022

In this paper, after administration of Chlorin e6 to kill cervical cancer cells, PDT (photodynamic therapy) using laser or LED was studied for Ce6 concentration and apoptosis by administration time. After photostimulation was applied to cervical cancer cells, qualitative and quantitative evaluation through imaging and quantitative evaluation using CCK-8 were performed. As a result of the experiment, as the concentration of Ce6 increased, a large amount of cells were killed, and it was confirmed that the Ce6+PDT test group killed more. When comparing the LED and the laser, the laser was able to kill cells only at a local location, and the LED showed the result that it was possible to kill the cells in a wide range. In addition, when irradiating a local location, such as a laser, when measuring the cell viability, it is judged to be accurate to image processing the location.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.3
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• pp.115-121
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• 2012

Sapphire single crystals have been highlighted for epitaxial gallium nitride films in high-power laser and light emitting diode (LED) industries. Among the many crystal growth methods, the Kyropoulos process is an excellent commercial method for growing larger, high-optical-quality sapphire crystals with fewer defects. Because the properties and growth behavior of sapphire crystals are influenced largely by the temperature distribution and convection of molten sapphire during the manufacturing process, accurate predictions of the thermal fields and melt flow behavior are essential to design and optimize the Kyropoulos crystal growth process. In this study, computational fluid dynamic simulations were performed to examine the effects of the crucible geometry aspect ratio on melt convection during Kyropoulos sapphire crystal growth. The results through the evolution of various growth parameters on the temperature and velocity fields and convexity of the crystallization interface based on finite volume element simulations show that lower aspect ratio of the crucible geometry can be helpful for the quality of sapphire single crystal.

• Journal of the Korean Society of Food Science and Nutrition
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• v.44 no.11
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• pp.1725-1732
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• 2015

The bactericidal effects of 642, 521, and 461 nm LED were investigated on Escherichia coli O157:H7 and Staphylococcus aureus strains in TSB with pH 7.2, 4.0, and 3.5 for 10 h at $15^{\circ}C$. The bactericidal effect of 461 nm blue LED was the most pronounced compared to 642 nm and 521 nm LEDs at pH 3.5. When E. coli was exposed to pH 3.5 with 461 nm LED, populations of E. coli O157:H7 ATCC 43894 and 35150 decreased by 4 and 5 log CFU/mL for 2 h, respectively. Populations of E. coli ATCC 8739 decreased by 5 log CFU/mL for 2 h. Further, S. aureus ATCC 27664, 43300, and 19095 were inactivated by 4, 5 and 5 log CFU/mL for 2 h, respectively, at pH 3.5 with 461 nm LED. In conclusion, combined treatment with 461 nm LED and acidic conditions at low-temperature ($15^{\circ}C$) showed the greatest antimicrobial effects. This study suggests that LEDs may be potentially used as a method to maintain the safety of the food preservation technology.

• Journal of Sensor Science and Technology
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• v.15 no.5
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• pp.334-340
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• 2006

A compact biosignal monitoring device was developed. Electrodes for electrocardiogram (ECG) and a LED and silicon detector for photoplethysmogram (PPG) were used. A lead II type was arranged for ECG measurement and reflected light was measured at the finger tip for PPG. A single chip microprocessor (model ADuC812, Analog Device) controlled a measurement protocol and processed measured signals. PPG and ECG had a sampling rate of 300 Hz with 8-bit resolution. The maximum power consumption was 100 mW. The microprocessor computed pulse transit time (PTT) between the R-wave of ECG and the peak of PPG. To increase the resolution of PTT, analog peak detectors obtained the peaks of ECG and PPG whose interval was calculated using an internal clock cycle of 921.6 kHz. The device was designed to be operated by 3-volt battery. Biosignals can be measured for $2{\sim}3$ days continuously without the external interruptions and data is stored to an on-board memory. Our system was successfully tested with human subjects.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.3
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• pp.1136-1151
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• 2018

This paper proposes a new hybrid scheme to decrease the high peak to average power ratio (PAPR) of optical orthogonal frequency division multiplexing (OFDM) signals in visible light communication (VLC) systems. The PAPR causes nonlinear signal distortions and high power requirements for the VLC transmitter (light emitting diode, LED). The proposed method is applicable for both direct current-biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM). In the proposed scheme, the PTS method is firstly modified to fit both optical OFDM approaches transmission and then combined with signal clipping method for further PAPR reduction and bit error rate (BER) improvement of the VLC system. The performance of hybrid scheme has been evaluated and compared with the original OFDM based VLC system, conventional PTS and clipping methods. The results show that the hybrid scheme outperforms other methods in terms of both the PAPR reduction and BER performance.

• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.34-39
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• 2012

In the present study, oxygen transfer process across gas-liquid interface in a Y-shape micro-channel is quantitatively visualized using the micro laser induced fluorescence (${\mu}$-LIF) technique. Diffusion coefficient of Oxygen ($D_L$) is estimated based on the experimental results and compared to its theoretical value. Tris ruthenium (II) chloride hexahydrate was used as the oxygen quenchable fluorescent dye. A light-emitting diode (LED) with wavelength of 450 nm was used as the light source and phosphorescence images of fluorescent dye were captured by a CMOS high speed camera installed on the microscope system. Water having dissolved oxygen (DO) value of 0% and pure oxygen gas were injected into the Y-shaped microchannel by using a double loading syringe pump. In-situ pixel-by-pixel calibration was carried out to obtain Stern-Volmer plots over whole flow field. Instantaneous DO concentration fields were successfully mapped according to Stern-Volmer plots and DL was calculated as $2.0675{\times}10^{-9}\;m^2/s$.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2227-2229
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• 1999

As a direct-view flat panel displays, there are many devices, such as plasma display panels(PDPs), vacuum fluorescent displays (VFDs), and light emitting diode(LED). Among these, a PDP is the first type of panel display to be made commercially available. A 'Plasma display' is the general term for a flat display utilizing the light emission that is produced by gas discharge. However, the brightness and Luminous efficiency are still not adequate for consumer television. So, the new sustain electrode type of ac PDP was proposed. By arranging the transparent electrode of quadrangle by zigzag, the area of electrode are reduced, and the length of electrode gap is increased. It generates a high luminous efficiency(corresponding to a 40% improvement of standard type), the same discharge voltage characteristics, and the low power consumption at same luminance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.25-27
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• 2007

$Eu^{2+}$-doped $Ca_2Si_5N_8$ was grown on Si(100) substrate using metal-organic deposition (MOD) method and post-annealed at $900^{\circ}C$ in various atmosphere. Luminescence properties of these thin films were investigated with variations of $Eu^{2+}$-doped concentrations and annealing atmosphere. Thin film was formed with clean surface and uniform thickness of about 72 nm. From the measurements of luminescence properties of thin films, film must be post-annealed in nitrogen or mixture of nitrogen and hydrogen atmosphere to emit a sufficient light. For $Ca_{1.5}Eu_{0.5}Si_5N_8$ thin film annealed at $900^{\circ}C$ in nitrogen atmosphere, excitation band from 380 to 420 nm was detected with the maximum intensity at 404 nm and two broad emission bands from 530 to 630 nm were observed. These broad excitation and emission bands must be attributed to the nitrogen incorporations into the films. From the results, $Ca_{2-x}Eu_xSi_5N_8$ thin film has probability for next generation thin film lighting applications such as light emitting diode (LED) or electro-luminescence (EL).