• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.4
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• pp.53-58
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• 2016

A ray tracing method to analyze the propagation channel characteristics for a millimeter-wave indoor wireless communication system is presented. Reflected rays from planar as well as rough surfaces are included. Transmitted rays though a thin dielectric slab are considered. Maps representing received power levels and RMS delay spread from a transmitter in a rectangular room are shown. The received power levels in the empty room for bottom's roughness factors of 0 and 0.13 are represented. The simulation results are well consistent with the calculation of Friis equation with reflection coefficient. Any size of furniture the shape of plane form can be positioned anywhere in the room.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.81-86
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• 2001

126-kHz bistatic sea surface scattering measurements were conducted in the shallow waters off the east coasts of Korea. The range from source to receiver was altered to change the scattering angle at the grazing angles of 38％ and 52％ . Unlike bottom scattering signal, the arrival time and the amplitude of sea surface scattering signals were varied due to the fluctuation of sea surface. The measured forward scattering strengths were compared to model predictions of Kirchhoff approximation and small slope approximation. In overall, the tendency of the scattering strengths showed reasonable agreement among the experimental data, Kirchhoff approximation, and small slope approximation.

• Fisheries and Aquatic Sciences
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• v.3 no.1
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• pp.1-7
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• 2000

Different substrata fixed as the roof (for shadow) on artificial iron reef had been developed as a tool for valuable fishery resources. The experiment was set up on a sandy bottom substratum at 8m depth in Muronohana, Ikata, Japan. Within one month of placement of the plates, diatoms dominated the experimental plates with a coverage of $100\%$ approximately. Enteromorpha intestinalis and Colpomenia sinuosa dominated within three months after the placement. E. intestinalis coverage on substrata was estimated $7\%$ on the plate shaped iron bar, $12-14\%$ on concrete plates, $18\%$ on the plate fixed pebble, $61\%$ on the plate to accumulated wood, and 80-100% on the steel materials plate. Whereas after four months of placement, C. sinuosa coverage on plates became $1-36\%$ on different plates, and $100\%$ on the plate to accumulated wood. The differences in E. intestinalis and C. sinuosa colonization on the different substrata were probably due to variations in their surface roughness influencing the settlement of zoospores, and thus gametophyte. development. After five months of placement, the above two species slowly disappeared.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.20-23
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• 2001

Plasma Display Panel(PDP) is a type of flat panel display utilizing the light emission produced by gas discharge. Barrier Ribs of PDP separating each sub-pixel prevents optical and electrical crosstalks from adjacent sub-pixels. The mold for forming the barrier ribs has been newly researched to overcome the disadvantages of conventional manufacturing processes such as screen printing, sand-blasting and photosensitive glass methods. The mold for PDP barrier ribs have stripes of micro grooves transferring glass-material wall. In this paper, Stripes of grooves of which width 48${\mu}{\textrm}{m}$, depth 124$\mu\textrm{m}$ , pitch 274$\mu\textrm{m}$ was acquired by machining of single crystal silicon with dicing saw blade. Maximum roughness of the bottom of the grooves was 59.6nm Ra in grooving Si. Barrier ribs were formed with silicone rubber mold, which is transferred from grooved Si forming hard mold. Silicone rubber mold has the elasticity, which enable to accommodate the waveness of lower glass plate of PDP. The methods assisted by the microwave and UV was adopted for reducing the forming time of glass paste.

• Journal of Advanced Research in Ocean Engineering
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• v.2 no.3
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• pp.99-111
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• 2016

Seabed affected by scouring, sedimentation, and siltation occurrences often cause exposure, which induces risks to existing structures or crude oil or gas pipeline buried subsea. In order to prevent possible risks, more economical structure installation methodology is proposed in this study by predicting and managing the risk. Also, the seabed does not only consist of sandy material, but clayey soil is also widespread, and the effect of undrained shear strength should be considered, and by cyclic environmental load, pore water pressure will occur in the seabed, which reduces shear strength and allows particles to move easily. Based on previous research regarding sedimentation or erosion, the average value of external environmental loads should be applied; for scouring, a 100-year period of environmental conditions should be applied. Also, sedimentation and erosion are mainly categorized by the bed load and suspended load; also, they are calculated as the sum of bed load and suspended load, which can be obtained from the movement of particles caused by sedimentation or erosion.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.9
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• pp.701-706
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• 2013

We have focused on the conversion efficiency of CIGS thin film solar cell prepared by co-evaporation method as well as the optimization of process condition. The total thickness of back electrode was fixed at 1 ${\mu}m$ and the structural, electric and optical properties of CIGS thin film were investigated by varying the thickness of Mo:Na bottom layer from 0 to 500 nm. From the experimental results, the content of Na was appeared as 0.28 atomic percent when the thickness of Mo:Na layer was 300 nm with compactly densified plate-shape surface morphology. From the XRD measurements, (112) plane was the strongest preferential orientation together with secondary (220) and (204) planes affecting to the crystallization. The lowest roughness and resistivity were 2.67 nm and 3.9 ${\Omega}{\cdot}cm$, respectively. In addition, very high carrier density and hole mobility were recorded. From the optimization of Mo:Na layer, we have achieved the conversion efficiency of 9.59 percent.

• Journal of Korea Water Resources Association
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• v.31 no.2
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• pp.189-198
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• 1998

Five dam-break floodwave models are t재 field data sets. The models included FLDWAV, SMPDBK, HEC-1, Tr66, and HEC Dimensionless Graph. The field data sets documented the disasters at Teton dam, and Yeunchun dam. The FLDWAV results are uesd to test the sensitivity of the floodwave to variations in Manning's roughness coefficient, breach size, and bottom slope. The HEC-1 analysis includes testing the sensitivity of the results to model parameters. The TR66 model and FLDWAV, with channel routing by TR66 in both cases. SMPDBK and the Dimensionless Graph procedure are applied without particular difficulties being encountered in both real world cases. It is necessary to analyze numerical limit of existing numerical models and then to apply the relatively accurate numerical model in real basin. It is found that FLDWAV model is superior in numerical accuracy and stability to any other model. This study will contribute to improve defect of numerical models and develop more precise numerical model for a efficient and rapid dam breach flood disaster predict.

• Journal of the Korean Solar Energy Society
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• v.28 no.1
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• pp.33-42
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• 2008

Zr-O ($Zr-ZrO_2$) cermets solar selective coatings with a double cermets layer film structure were prepared using a DC (direct current) magnetron sputtering method. The typical film structure from surface to bottom substrate were an $Al_2O_3$ anti-reflection layer on a double Zr-O cermets layer on an Al metal infrared reflection layer. Optical properties of optimized Zr-O cermets solar selective coating had an absorptance of ${\alpha}\;=\;0.95$ and thermal omittance of ${\epsilon}\;=\;0.10\;(100^{\circ}C)$. The absorbing layer of Zr-O cermets coatings on glass and silicon substrate was identified as being amorphous by using XRD. AFM showed that ZF-O cermets layers were very smooth and their surface roughness were approximately $0.1{\sim}0.2 nm$. The chemical analysis of the cermets coatings were determined by using XPS. Chemical shift of photoelectron binding energy was occurred due to the change of Zr-O cermets coating structure deposited with increase in oxygen flow rate. The result of thermal stability test showed that the Zr-O cermets solar selective coating was stable for use at temperature below $350^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.9
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• pp.711-717
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• 1998

BST(70/30) and BST(50/50) thin films were prepared by Sol-Gel method and studied about the microstructural and dielectric properties with Pt and ITO bottom electrodes. The stock solution was synthesized and spin coated on the Pt/Ti$SiO_2$/Si and Indium Tin Oxide(ITO)/ glass substrate. the coated films were dries at 350$^{\circ}C$ for 10 minutes and annealed at $750^{\circ}C$ for 1 hour for the crystallization. The thin films coated on ITO substrate were crystallized easily and the packing density and roughness of surface were better that those of films coated on Pt substrates. In the BST(50/50) composition the structural properties were similar to the BST(70/30) composition and grain size were decreased with increasing the contents of Sr. The dielectric constant was higher in the BST(50/50) composition compared with the BST(70/30) composition. Using the ITO substrate, the dielectric constant was higher than the Pt substrate while the dielectric loss was showed a reverse trend. The dielectric constant with and increase of temperature was decreased slowly.

• Proceedings of the KIEE Conference
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• 1998.07g
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• pp.2515-2517
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• 1998

The micro fresnel lens(MFL) was modeled and fabricated on a XY-stage electrostatically driven by comb actuator. The modeled MFL was approximated as a step shape with 4-phase and 4-zone plate. The focal length and diameter of the MFL is 20mm and 912${\mu}m$, respectively. The XY-stage suspending the MFL is designed to generate a large static displacement up to about 20${\mu}m$. On SOI substrates, we first fabricated MFL using the RIE(reactive Ion etching) technology and then patterned and etched bulk silicon to make XY-stage. After the fabrication of all structures on top side of the SOI substrates. $Si_3N_4$ was deposited for passivation of all structures using PECVD(plasma enhanced chemical vapor deposition). All the MFL systems width comb drive actuator were released by KOH etching from the bottom side of the SOI wafer using double-sided alignment technique. In fabrication of MFL, a dry etching conditions is established in order to improve surface roughness and to control the etched depth.