• Korean Journal of Optics and Photonics
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• v.21 no.1
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• pp.1-5
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• 2010

In this study, we propose a grating structure using guided-mode resonance (GMR) to increase the absorption efficiency of a silicon solar cell. The proposed solar cell design consists of a one-dimensional diffraction grating and a planar waveguide layer of poly-silicon deposited on a silver reflector. We investigate the influence of structure parameters such as grating period, waveguide thickness, grating width and grating depth. Optimal parameters are found using the particle swarm optimization (PSO) algorithm. In the optimized GMR-assisted solar cell, absorption efficiency up to 65.8% is achieved in the wavelength range of 300 nm~750 nm.

• Journal of the Korean Solar Energy Society
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• v.26 no.1
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• pp.7-12
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• 2006

The dish type solar thermal concentrating system can collect the solar energy above $800^{\circ}C$. It has a concentration ratio of 800 and total reflector area of $49m^2$. To operate solar receivers at high temperature, the optimum aperture size is obtained from a comparison between maximizing absorbed energy and minimizing thermal losses. The system efficiency is defined as the absorbed energy by working fluid in receiver divided by the energy coming from the concentrator. We find that system efficiency is stable in case of flow rate of above 6lpm. The system efficiency are 64.9% and 65.7% in flow rate of 6lpm and 8lpm, respectively. The thermal performance showed that the maximum efficiency and the factor of thermal loss in flow rate of 8lpm are 68% and 0.0508.

• ETRI Journal
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• v.41 no.6
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• pp.715-730
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• 2019

We propose a switched beam-forming antenna that satisfies not only ultra-wideband characteristics but also beam-forming in the WLAN frequency band using an ultra-wideband antenna and passive parasitic elements applying a broadband optimal reactance load algorithm. We design a power and phase estimation function and an error correction function by re-analyzing and normalizing all the components of the parasitic array using control system engineering. The proposed antenna is compared with an antenna with a pin diode and reactance load value, respectively. The pin diode is located between the passive parasitic elements and ground plane. An antenna beam can be formed in eight directions according to the pin diode ON (reflector)/OFF (director) state. The antenna with a reactance load value achieves a better VSWR and gain than the antenna with a pin diode. We confirm that a beam is formed in eight directions owing to the RF switch operation, and the measured peak gain is 7 dBi at 2.45 GHz and 10 dBi at 5.8 GHz.

• Journal of electromagnetic engineering and science
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• v.14 no.4
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• pp.360-366
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• 2014

A single-feed composite cavity-backed four-arm curl antenna is presented for use in global positioning systems (GPS). Its primary radiating element is fed by a vacant-quarter printed ring, which helps the antenna directly match to a $50-{\Omega}$ coaxial line and produce a good circular polarization (CP). The cavity-backed reflector is employed to improve the CP radiation characteristics in terms of 3-dB axial ratio (AR) beamwidth and minimum AR value. The optimized design with an overall size of $90{\times}90{\times}25mm^3$ ($0.4725{\lambda}_o{\times}0.4725{\lambda}_o{\times}0.13{\lambda}_o$ at 1,575 MHz) results in a ${\mid}S_{11}{\mid}<-10dB$ bandwidth of 8.66% (1,514-1,651 MHz) and a 3-dB AR bandwidth of 2.23% (1,555-1,590 MHz). The antenna radiates a widebeam right-hand circular polarization and operates with a measured radiation efficiency greater than 90% within its impedance matching bandwidth.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.9
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• pp.908-914
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• 2013

A shaped Cassegrain antenna is designed from the condition of the same path length at the equi-phase surface by using the conservation of energy and Snell's law. In order to improve the phase error efficiency of aperture surface, the surface profile of the main and sub-reflectors is found to satisfy the power distribution and the equi-phase condition at the aperture surface. The sidelobe levels of 36.4 dB and 33.9 dB are achieved at the AZ and EL planes, respectively from numerical calculation by physical optics method at Ku band and the directivity of designed antenna is 10 percent greater than that of conventional antenna.

• Journal of the Korean Solar Energy Society
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• v.25 no.4
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• pp.85-92
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• 2005

One of the most effective methods for utilizing solar energy is to combine thermal solar and optical energy simultaneously using a hybrid panel. Many systems using various kinds of photovoltaic panels have already been constructed. But utilizing solar energy by means of a hybrid panel with concentrator has not been to be attempted yet. Normally if sunlight is directed on the solar cell, and there is no increase in temperature, the absorption energy of each cell will increase per unit area. In a silicon solar cell. however, cell conversion efficiency decreases according to the increasing temperature. Therefore, to maintain cell conversion efficiency under normal condition, it is necessary to keep the cell at operating temperature. we design and make new hybrid panel with cooling system to prevent increasing of temperature on cell, collect effectively thermal energy. We compared performance of new hybrid panel with PV module and thermal panel. We also evaluated conversion efficiency, electric power and thermal capacity and confirmed cooling effect from thermal absorption efficiency.

• Journal of the Korean Solar Energy Society
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• v.25 no.4
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• pp.93-100
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• 2005

Character and illuminance distribution of daylighting is very important for the architectural plan in museum. Those data show bases for exhibition space design with daylighting and play a decisive role in visual perception of articles and space aesthetic. The goal of this paper was therefore to analyze the illuminance distribution in fine art museum with 3 typical girdle skylight types which are devided according to the art of protection from glare. This Experiment proved that they had a striking contrast with regard to the ratio of daylight illumination and illuminance distribution in spite of the same purpose of those development. The girdle skylight with a translucent glass showed the strongest value of the ratio of daylight illumination, but inequable illuminance distribution in space, excepting the area of the wall. However, the latticed reflector of light refracted daylight in the direction of wall and made illuminance distribution very equable in whole space. The ratio of daylight illumination at the girdle skylight which was located at the verge of the ceiling, was highest at the upper part of the wall and was reduced gradually from there, by way of the middle and under part of the wall, to the center of space.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.10
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• pp.935-940
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• 2016

Directed energy weapon enables to radiate the concentrated energy so as to result in distraction and overload of the target electronics. Analysis on effectiveness of weapon system can be important consideration in order to determine performance and design weapon system. In this paper, air defense weapon system, which is one of directed energy weapon system is studied. In order to analyze the effectiveness, the reflector antenna with high power circularly polarized horn antenna is designed, and power density in axial effective area is simulated and calculated using Friis formula. Through the study, the validity of antenna system is verified, and the effectiveness of directed energy weapon system on the target is evaluated.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.151-155
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• 1999

We proposed the beam tilted antenna by aperture coupled microstrip array, found out the values of design parameters by using Ensemble 5.1 of Ansoft Co., and analysed the performance of fabricated antenna. In order to point to the fixed satellite on the nothern hemisphere, 3 dB beamwidth of this antenna is 25$^{\circ}C$ to 65$^{\circ}C$. Operation bandwidth is 2.51GHz to 2.59GHz. The structure of this antenna is composed by 3 types of squared patches; reflector, driver, and director. The maximum antenna gain is 6.2dB at 2.56GHz and elevation angle of 42$^{\circ}C$. Front-to-Back ratio is more than 13dB at the same condition.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.11
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• pp.1005-1009
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• 2008

A noble infrared $\lambda/4$ absorbing structure using metal reflector was studied for uncooled infrared sensors. This paper described the design and the fabrication of IR uncooled detectors which were composed of 21 by 21 elements using the surface micromachining technology. The characteristics of the array were investigated in the spectral region of 4.26 ${\mu}m$. The fabricated detectors exhibited the thermal mass of $9.75\times10^{-9}$ J/K, the thermal conductance of $1.31\times10^{-6}$ W/K, the thermal time constant of 7.4 ms, the responsivity of $1.07\times10^5$ V/W and the detectivity of $1.04\times10^9$ $cmHz^{1/2}/W$, at the chopper frequency of 10 Hz and the bias current of 9.22${\mu}A$. Finally the absorptance efficiency of $\lambda/4$ absorbing structure was about 23.2 % higher than that of absence absorbing structure.