• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.579-582
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• 2016

Recently, wireless communication system has been widely used in a variety of fields along with the remarkable advancement of communication technology. Sound communication system in underwater wireless communication is utilized in underwater communication since it has better transmission capacity than the existing RF. However, sound communication system has the problems such as low speed communication, transmission delay and limited bandwidth, and the studies have been actively conducted on the visible light communication underwater to improve these problems. Therefore, the visible light communication underwater using ASK modulation is suggested for the effective communication in this article.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.5
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• pp.339-347
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• 2019

The power circuit design of an on-board S-band transmitter for KSLV-II with derating(operation of a component at less than its maximum rated specification to enhance reliability) is investigated. The power circuit of the transmitter consists of linear voltage regulators, DC/DC converters for regulating the DC supply, and diodes for reverse voltage protection. After analyzing the load current of the components, derating requirements are explored. Furthermore, power dissipation and junction temperature rise are considered with respect to the load current. The analysis is compared to the results from an engineering model of the transmitter. The temperature of the components is derated by >$40^{\circ}C$ in an environment where the ambient temperature is $+60^{\circ}C$, which is the acceptance test specification of high temperature.

• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.683-690
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• 2008

In order to develop transparent electrodes for high efficiency GaN-based light emitting diodes (LEDs), the electrical and optical properties of the electron beam evaporated ITO contacts have been investigated as a function of the deposition temperature and flow rate of oxygen during the deposition. As the deposition temperature increases from $140^{\circ}C$ to $220^{\circ}C$, the resistivity of the ITO films decreases slightly from $4.0{\times}10^{-4}{\Omega}cm$ to $3.3{\times}10^{-4}{\Omega}cm$, meanwhile the transmittance of the ITO films significantly increases from 67% to 88% at the wavelength of 470 nm. When the flow rate of oxygen during the deposition increases from 2 sccm to 4 sccm, the resistivity of the ITO films increases from $3.6{\times}10^{-4}{\Omega}cm$ to $7.4{\times}10^{-4}{\Omega}cm$, meanwhile the transmittance of the ITO films increases from 86% to 99% at 470 nm. Blue LEDs fabricated with the electron beam evaporated ITO electrode show that the ITO films deposited at $200^{\circ}C$ and 3 sccm of the oxygen flow rate give a low forward-bias voltage of 3.55 V at injection current of 20 mA with a highest output power.

• New Physics: Sae Mulli
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• v.68 no.11
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• pp.1268-1274
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• 2018

Aircraft-warning lights are lights that are used to inform pilots in flight about the presence of buildings or dangerous objects. Currently, the light sources of most aircraft-warning lights have been replaced by light-emitting diodes (LEDs). However, the aircraft-warning lights that are installed do not meet the optical performance standards and may cause airplane collisions. Therefore, the use of such light poses a risk to aviation safety. In order to solve this problem, we designed a Fresnel lens with the same luminous intensity distribution ovef $360^{\circ}$ direction; thus, we collimated the light beam from the LED light source with a narrow beam divergence angle in the form of an array of aspheric pieces. After that, we designed and simulated an aircraft-warning-light optical system with a center luminous intensity of 20,000 cd and a vertical divergence angle of $3^{\circ}$ or more by optimizing the lens' tilt and the distance between the LED and the Fresnel lens.

• Journal of IKEEE
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• v.25 no.2
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• pp.322-329
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• 2021

In this study, a method for improving the light extraction efficiency of organic light emitting diodes was presented using the polymer Poly(vinylidenefluoride-co-trifluoroethylene) [P(VDF-TrFE)] having an island surface structure after annealing. Polydimethylsiloxane (PDMS) imprinted on the island-structured P(VDF-TrFE) surface has a spike structure, which improves the external light extraction efficiency aroud 20%. It was confirmed that the produced film showed a low haze characteristic of 8.2, and the Current and external quantum efficiency could be improved without pixel blur due to the excellent transmittance of 93.4%.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.4
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• pp.47-54
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• 2020

Integration of active and passive waveguides is an essential component of the photonic integrated circuit and its elements. Butt joint is one of the important technologies to accomplish it with significant advantages. However, it suffers from high optical loss at the butt joint junction and need of accurate process control to align both waveguides. In this study, we used beam propagation method to simulate an integrated device composed of a laser diode and spot size converter (SSC). Two SSCs with different mode properties were combined with laser waveguide and optical coupling efficiency was simulated. The SSC with larger near field mode showed lower coupling efficiency, however its far field pattern was narrower and more symmetric. Tapered passive waveguide was utilized for enhancing the coupling efficiency and tolerance of waveguide offset at the butt joint without degrading the far field pattern. With this technique, high optical coupling efficiency of 89.6% with narrow far field divergence angle of 16°×16° was obtained.

• Journal of Convergence for Information Technology
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• v.11 no.3
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• pp.167-173
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• 2021

There is an increasing interest in manufacturing various electronic devices on a bendable substrate. In this paper, we observed a surface morphology by annealing for 20 minutes at temperatures of 150 ℃, 350 ℃, and 550 ℃, respectively, with samples coated by chromium and aluminum. Data on surfaces are investigated using high-resolution SEM and AFM that can measure roughness up to nm. There is no difference from the sample without heat treatment up to 350 ℃, but the change of crystal grains can be observed at 550 ℃. In the future, for application to the flexible optoelectronic field, additional characteristics such as electrical conductivity and reflectivity will be analyzed and optical devices will be manufactured. In conclusion, we will explore the possibility of applying metal materials to flexible electronic devices.

• Journal of Advanced Navigation Technology
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• v.24 no.6
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• pp.557-565
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• 2020

In order for thermal degradationIn, excore nuclear flux monitoring system, as a monitoring and signal processing methodology of reactor power, monitors neutron pulses generated during nuclear fission as frequency status, and converts them into DC voltage, and then log values resultantly. The methods realy applied in the nuclear power plant are to construct combination of counters and flip-flops, or diodes and capacitors up to now. These methodes are reliable for relative high frequencies, while not credible for reasonable low frequencies or extreme low values. Therefore, we developed the circuit that converts frequencies into DC voltages, into and into log DC values in the wide range from low Hz to several hundred high kHz. We proved their validities through testing them using real data used in nuclear power plant and analyzed their results. And, these methods will be used to measure the neutron level of excore nuclear flux monitoring system in nuclear power plant.

• Fashion & Textile Research Journal
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• v.23 no.6
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• pp.860-868
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• 2021

Clothing has a very important role in human life, and it is the most human-friendly platform because humans wear it in almost all the time. In the recent years, smart clothing integrated with various functions is solidifying its position as the core of next-generation Information and Communications Technology(ICT). With this global trend, the smart textiles, textiles embedded with electronic devices that are capable of performing various functions, have been attracting a lot of attention. Therefore, various research activities on the smart textiles are in progress, and the global market outlook for the smart textiles is also showing rapid growth. Among the various smart textile technologies, the textile/fiber-based wearable display has been attracting more attention because it is an essential element for wearers to intuitively control the functions integrated in the smart textiles. This paper provides insightful information and the technological elements of organic light emitting diodes(OLEDs) display, which have been evaluated as the most ideal device for luminescent clothing. Since, OLEDs have many advantages such as light weight, extremely thin thickness and great flexibility, the textile/fiber-based wearable OLEDs can be worn without any inconvenience. In addition, by introducing previous studies on the textile/fiber-based OLED displays, we intend to consider the commercial potential of the textile/fiber-based smart luminescent clothing using the OLED technologies.

• Journal of Sensor Science and Technology
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• v.31 no.4
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• pp.249-254
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• 2022

To achieve high-performance colloidal quantum dot light-emitting diodes (QD-LEDs), the use of a densely packed QD film is crucial to prevent the formation of leakage current pathways and increase in interface resistance. Spin coating is the most common method to deposit QDs; however, this method often produces pinholes that can act as short-circuit paths within devices. Since state-of-the-art QD-LEDs typically employ mono- or bi-layer QDs as an emissive layer because of their low conductivities, the use of a densely packed and pinhole-free QD film is essential. Herein, we introduce the Langmuir-Blodgett (LB) technique as a deposition method for the fabricate densely packed QD films in QD-LEDs. The LB technique successfully transfers a highly dense monolayer of QDs onto the substrate, and multilayer deposition is performed by repeating the transfer process. To validate the comparability of the LB technique with the standard QD-LED fabrication process, we fabricate and compare the performance of LB-based QD-LEDs to that of the spin-coating-based device. Owing to the non-destructiveness of the LB technique, the electroluminescence efficiency of the LB-based QD-LEDs is similar to that of the standard spin coating-based device. Thus, the LB technique is promising for use in optoelectronic applications.