• Journal of the Optical Society of Korea
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• v.14 no.3
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• pp.260-265
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• 2010

This paper proposes a transflective configuration of the dual operating mode liquid crystal display, which has transmissive dynamic and reflective memory parts in its pixel. By employing a wideband structure and optimizing the cell-gap of the liquid crystal layer, the reflective memory part shows a very low reflectance in the dark state, good dispersion properties for the entire visible range, as well as high reflectance in the bright state. The transmissive dynamic part is designed to have the same cell-gap and rubbing direction as those of the reflective part. The driving voltage of the dynamic part and transmittance of the bright state can also be controlled by using compensation film with a positive a-plate, which can compensate the reflective part. Experimental results in the memory part operation demonstrate that the contrast ratio is over 50:1 and the reflectance in the dark state is reduced to 56% on average of that of the conventional dual mode configuration for the entire visible range. The contrast ratio of the dynamic part is 300:1.

• Journal of Practical Engineering Education
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• v.8 no.1
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• pp.9-14
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• 2016

Depending on the college graduation project and graduation thesis regulations for the certification and graduation requirements, the quadcopter acting as a Li-Po battery that charges by solar energy are proposed a design method and improvements in theory. Quadcopter posture is balanced and confirmed by the position sensor, through a PID (Proportional Integral Differential) control. Battery switching circuit is composed of two Li-Po battery. Driving the quadcopter as one battery, and does not use other battery is charged by solar energy. A battery switching circuit is fabricated in a manner that uses two types of relays. Even if completely not charged to the battery is being driven a certain switch by the battery charging voltage from time to time, it proposes a method for increasing the endurance time and range.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.6
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• pp.504-511
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• 2003

In this paper, inverter type neon power supply using a piezoelectric transformer is fabricated and its characteristic is investigated. Developed neon power supply is composed of basic circuit and blocks, such as rectifier part, frequency oscillation part and piezoelectric transformer and resonant half bridge inverters. In this paper for complement the low power limitation, piezoelectric transformer at parallel connected driving by inverter is studied for noon tubes system of high power. When piezoelectric transformer is connected with parallel, LC filter connection method with parallel and selection of inductance L and capacitor C of primary side is suggested for reduce unbalanced current at the terminal of each transformer. Piezoelectric transformers use piezoelectric ceramic devices. Thus it is wireless therefore it has high power density, high Isolation level, low loss, more light, and miniaturization. In addition, high voltage transfer ratio is expected because there is no leakage inductance. Also, it has economic merit that the electrical loss Is low because structure is simple, small and tighter weight.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.750-754
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• 2011

In this research, the electric characteristic of organic light-emitting diodes(OLEDs) was studied depending on thickness of amorphous fluoropolymer(Teflon-AF) which is the material of hole injection layer to improve electric characteristic of OLEDs. Sample composition was fabricated in double layer. The basic structure was fabricated by ITO/tris(8-hydroxyquinoline) aluminum (Alq3)/Al and the 2 layer was fabricated by ITO/2,2-Bistrifluoromethyl-4,5-Difluoro-1,3-Dioxole(Teflon-AF)/tris(8-hydro xyquinoline) aluminum (Alq3)/Al. The experiment was carried with variation of thickness of Teflon-AF at 1.0, 2.0, 2.5, 3.0 nm. The result showed when Teflon-AF thickness was 2.5 nm, the electric and optical characteristic were well performed. Moreover, when it was compared with Teflon-AF without materials, it was improved 15.1 times more on luminance, 12.7 times more on luminous efficiency and 12.1 times more on external quantum efficiency. Therefore, OLEDs element with optimum hole injection layer reduced energy barrier and driving voltage, and confirmed that it improved efficiency widely.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.11
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• pp.2758-2764
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• 2015

In the field of electronic warfare applications, high voltage power supply(HVPS) for high power phased array transmitters must necessarily have an independent operating characteristics for driving mini TWTs. TWT independent operational characteristics, in order to run without interrupting the electronic warfare mission by maintaining the partial transmission function even when one of the TWT has occurred a failure, is known to be very important. In this paper, we describe the research on high-speed independent control system using a high-density HVPS, including FE modulators, hardware configuration and the FPGA in order to independently operate mini TWTs. Also, we have simulated some possible faults in phased array transmitters, and presents the test results to control a faulted TWT independently.

• Transactions on Electrical and Electronic Materials
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• v.12 no.6
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• pp.253-257
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• 2011

This study was carried out to solve problems such as radio frequency band depletion, confusion risk, and security loss in existing visible wireless communication systems, and to determine the applicability of next-generation networks. A light-emitting diode (LED) light communication system was implemented with a controlling switching light module using the ATmega16 micro-controller. To solve the existing modulation effect and disturbance in visible light communication, an integrated interface was evaluated with a driving light module and analyzes its reception property. A transmitter/receiver using the ATmel's micro-controller, high-intensity white LED-6 modules, and infrared sensor KSM60WLM and visible sensor TSL250RD were designed. An experiment from the initial value of distance to 2.5 m showed 0.46 V of the voltage loss, and if in long distance, external light interference occurred and light intensity was lost by external impact and thus data had to be modified or reset repeatedly. Additionally, when we used 6 modules through the remote controller's lighting dimming, data could be transmitted up to 1.76 m without any errors during the day and up to 2.29 m at night with around 2~3% communication error. If a special optical filter can reduce as much external light as possible in the integrated interface, the LED for lighting communication systems may be applied in next generation networks.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.3
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• pp.71-74
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• 2019

In this study, we fabricated two standard and inverted quantum dot light emitting diodes (QLEDs) using $TiO_2$ nanoparticles (NPs) with lower electron mobility than ZnO NPs as inorganic electron transport layer to suppress electron injection into the emitting layer. Current density was much higher for the inverted QLEDs than the standard ones. The inverted QLEDs were brighter, but showed low current efficiency due to the high current density. In addition, as the current density was higher, the driving voltage was higher, and the red shift was confirmed in the emission wavelength spectrum. The low current density in the standard structured devices showed that the possibility that $TiO_2$ NPs could suppress the electron injection in the QLEDs.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.5
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• pp.325-333
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• 2021

A 3 kW grid-tied PV inverter with Gallium nitride high-electron mobility transistor (GaN HEMT) for domestic commercialization was developed using boost converter and full-bridge inverter with LCL filter topology. Recently, many GaN HEMTs are manufactured as surface mount packages because of their lower parasitic inductance characteristic than standard TO (transistor outline) packages. A surface mount packaged GaN HEMT releases heat through either top or bottom cooling method. IGOT60R070D1 is selected as a key power semiconductor because it has a top cooling method and fairly low thermal resistances from junction to ambient. Its characteristics allow the design of a 3 kW inverter without forced convection, thereby providing great advantages in terms of easy maintenance and high reliability. 1EDF5673K is selected as a gate driver because its driving current and negative voltage output characteristics are highly optimized for IGOT60R070D1. An LCL filter with passive damping resistor is applied to attenuate the switching frequency harmonics to the grid-tied operation. The designed LCL filter parameters are validated with PSIM simulation. A prototype of 3 kW PV inverter with GaN HEMT is constructed to verify the performance of the power conversion system. It achieved high power density of 614 W/L and peak power efficiency of 99% for the boost converter and inverter.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.4
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• pp.349-358
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• 2019

This paper aimed at collecting sensor signals to extract characteristic parameter of the rotor. A vibration test rig has been developed to perform model tests. Signal characteristics were analyzed when driving normally. Envelope FFT Analysis is used to extract vibration components caused by periodic impacts from other vibration factors. Signal analysis was performed when load changes were given to speed sensors and vibration test rigs that show low frequency characteristics of the rotor and signal analysis according to rotational speed. The acceleration signal measured in the bearing housing has a small amplitude and produces only the rotational frequency component and harmonic component of the motor. As the number of rotations increases, the amplitude of acceleration can be seen. As the rotational speed increases, it can be seen that there is a difference in the shape of the original data and compared with the acceleration FFT graph, it can be seen that the noise is strong at low frequencies and the corresponding rotational frequency components are clearly represented. It can be seen that changing the load does not increase the main rotational frequency component.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.1
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• pp.58-65
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• 2022

The field of liquid crystal display (LCD) is constantly in the spotlight and the process of depositing an alignment layer in the LCD manufacturing process is very important to obtain excellent performance such as low-power driving and high-speed response to improve LCD performance. Therefore, research on liquid crystal (LC) alignment is being actively conducted. When manufacturing LCD, it is necessary to consider the effect of the alignment layer thickness as one of the factors affecting various LCD performances. In addition, previous studies confirmed the LC alignment characteristics correlate with the rotation speed in the spin coating process. Therefore, the electro-optical properties of the LCD were investigated by manufacturing a polyimide alignment layer by varying the rotation speed in the spin coating process in this study. It was confirmed that the thickness of the polyimide alignment layer was controlled according to the spin coating conditions. The average transmittances of anti-parallel LC cells at the spin coating speed of 2,500 rpm and 3,000 rpm are about 60%, which indicates that the LC cell has relatively higher performance. At the spin coating speed of 3,000 rpm, the voltage-transmittance curve of twisted nematic (TN) LC cell was below 1.5 V, which means that the TN LC cell operated at a low power. In addition, high-speed operating characteristics were confirmed with a response time of less than 30 ms. From these derived data, we confirmed that the ideal spin coating speed is 3,000 rpm. And these results provide an optimized polyimide alignment layer process when considering enhanced future LCD manufacturing.