• International Journal of Precision Engineering and Manufacturing
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• v.6 no.3
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• pp.19-23
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• 2005

To minimize the weld defect in manufacturing of the welded tube by using $CO_2$ laser, the monitoring of the welding quality and the seam tracking along the butt-joint lengthwise to the tube axis are studied. The longitudinal butt-joint is shaped from $60kgf/mm^2$ grade steel sheet by 2 roll bending method, and welded by the $CO_2$ laser welding system equipped with the seam tracker and plasma sensor. The laser welded tube has the thickness of 1.5mm, diameter of 105.4mm and length of 2000mm. The precise positioning of the laser beam on the butt-joint to be assembled is obtained within $200{\mu}m$ by the laser vision sensor. The artificial defects in the butt-joint are well observed by the signal of plasma intensity measured from the plasma sensor of UV wavelength range within 400nm. The developed $CO_2$ laser tube welding system has the function of the precision seam tracking and the real-time monitoring of the welding quality. In conclusion, the laser welded tube can be used for manufacturing of automobile chassis and components after hydro-forming.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.795-801
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• 2001

A method of miniaturizing branch line coupler is presented. The method utilizes the microstrip line with overlay(or superstrate). The frequency dependent characteristics, dispersion and characteristic impedance, of this line are obtained by Immitance method in spectral domain and Method of Line. The relevant spectral domain Green's function is given and used to obtain numerical results. The branch line couplers with overlays are designed and fabricated at 2 GHz. The experimental results show that the size of coupler with overlay(${epsilon}_r$=10.2) is 31.4 precent smaller than conventional coupler. This minimized coupler is suitable for Butler Matrix as feeder for mobile communication beam forming antenna.

• Journal of IKEEE
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• v.24 no.3
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• pp.917-920
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• 2020

In this paper, we studied the derivation method of isoflux radiation for a planar array antenna. The presented array antenna was designed for considering of 1U-sized CubeSAT with Ku-band communications. For the presented array antenna, 8×8 radiating elements were arranged, and the distance between radiating elements was set of half-wavelength. The excited current weighting for each radiating elements was calculated by the signal processing technique used in the design of the low-pass filter. As a result of analysis of the method proposed in this paper, it was confirmed that a seamless isoflux pattern can be derived.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.209-210
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• 2006

We have successfully termed brown colored patterns inside of a transparent borosilicate glass generally known as BK7, laying the focus of near infrared Ti: sapphire femtosecond laser beam in the bulk BK7 glass. It is important to keep the laser power well below the damage threshold of BK7 in forming the color center. Thanks to the low laser power, there was no laser induced mechanical damage such as cracks or threads in the color formed area. From the absorbance spectrum and its gaussian fitting, we found the band gap of BK7, 4.21eV, and three absorption edges.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.196-197
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• 2010

NAND형 charge trap flash (CTF) non-volatile memory (NVM) 소자가 30nm node 이하로 고집적화 되면서, 기존의 SONOS형 CTF NVM의 tunnel barrier로 쓰이는 SiO2는 direct tunneling과 stress induced leakage current (SILC)등의 효과로 인해 data retention의 감소 등 물리적인 한계에 이르렀다. 이에 따라 개선된 retention과 빠른 쓰기/지우기 속도를 만족시키기 위해서 tunnel barrier engineering (TBE)가 제안되었다. TBE NVM은 tunnel layer의 전위장벽을 엔지니어드함으로써 낮은 전압에서 전계의 민감도를 향상 시켜 동일한 두께의 단일 SiO2 터널베리어 보다 빠른 쓰기/지우기 속도를 확보할 수 있다. 또한 최근에 각광받는 high-k 물질을 TBE NVM에 적용시키는 연구가 활발히 진행 중이다. 본 연구에서는 Si3N4와 HfAlO (HfO2 : Al2O3 = 1:3)을 적층시켜 staggered의 새로운 구조의 tunnel barrier Capacitor를 제작하여 전기적 특성을 후속 열처리 온도와 방법에 따라 평가하였다. 실험은 n-type Si (100) wafer를 RCA 클리닝 실시한 후 Low pressure chemical vapor deposition (LPCVD)를 이용하여 Si3N4 3 nm 증착 후, Atomic layer deposition (ALD)를 이용하여 HfAlO를 3 nm 증착하였다. 게이트 전극은 e-beam evaporation을 이용하여 Al를 150 nm 증착하였다. 후속 열처리는 수소가 2% 함유된 질소 분위기에서 $300^{\circ}C$와 $450^{\circ}C$에서 Forming gas annealing (FGA) 실시하였고 질소 분위기에서 $600^{\circ}C{\sim}1000^{\circ}C$까지 Rapid thermal annealing (RTA)을 각각 실시하였다. 전기적 특성 분석은 후속 열처리 공정의 온도와 열처리 방법에 따라 Current-voltage와 Capacitance-voltage 특성을 조사하였다.

• Journal of electromagnetic engineering and science
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• v.2 no.2
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• pp.117-123
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• 2002

This paper describes the design for the resistive FET mixer with low If for the 4-Ch DBF(Digital Beam Forming) receiver This DBF receiver based on the direct conversion method is generally suitable for high-speed wireless mobile communications. A radio frequency(RF), a local oscillator(LO) and an intermediate frequency(If) considered in this research are 2.09 GHz, 2.08 CHz and 10 MHz, respectively. This mixer is composed of band pass filter, a low pass filter and a DC bias circuit. Super low noise HJ FET of NE3210S01 is considered in design. The RE input power, LO input power and Vcs are used -10 dBm, 6 dBm and -0.4 V, respectively. In the 4-Ch resistive FET mixer, the measured If and harmonic components of 10 MHe, 20 MHz and 2.087 CHz are about -19.2 dBm, -66 dBm and -48 dBm, respectively The If output power observed at each channel of 10 MHz is about -19.2 dBm and it is higher 28.8 dBm than the maximum harmonic component of 2.087 CHz. Each If output spectrum of the 4-Ch is observed almost same value and it shows a good agreement with the prediction.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.6
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• pp.598-604
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• 2011

A method of miniaturizing branch line coupler with connected coupled lines is presented. The quarter-wavelength transmission lines in the typical microstrip branch line coupler are replaced with the connected coupled lines with same characteristics of ones for compact size. The connected coupled line is analyzed by T-equivalent circuit and Z parameters based on the even-odd mode analysis. The proposed branch line couplers with connected coupled line are designed and fabricated on FR4 substrate at 2.4 GHz. The measured results show good agreement with theoretical prediction. And the experimental results show that the size of coupler is 37 precent smaller than conventional coupler. This minimized coupler is suitable for Butler Matrix as feeder for mobile communication beam forming antenna.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.162-165
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• 2007

AAO(Anodic Aluminum Oxidation) method has been known that it is practically useful for the fabrication of nano-structures and makes it possible to fabricate the highly ordered nano masters on large surface and even on the 2.5 or 3D surface at low cost comparing to the expensive e-beam lithography or the conventional silicon processing. In this study, by using the multi-step anodizing and etching processes, highly ordered nano patterned master with concave shapes was fabricated. By varying the processing parameters, such as initial matter and chemical conditions; electrical and thermal conditions; time scheduling; and so on, the size and the pitch of the nano pattern can be controlled. Consequently, various alumina/aluminum nano structures can be easily available in any size and shape by optimized anodic oxidation in various aqueous acids. In order to replicate nano patterned master, the resulting good filled uniform nano molded structure through electro-forming process shows the validity of the fabricated nano pattern masters.

• Journal of Korean Association for Spatial Structures
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• v.4 no.1 s.11
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• pp.77-86
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• 2004

It is the buckling of the compression portions of the deckplate that govern its behaviour under wet concrete construction loading. The size and position of intermediate stiffeners in the compression flanges of thin-plate steel decks exert a strong influence on the dominant buckling mode of the flange. Test sections composed of high-strength steel were brake pressed with a variety of Flat-hat intermediate stiffeners in the compression flange forming a progression from small to large stiffeners. The ABAQUS program to determine the effectiveness of intermediate stiffeners in controlling buckling modes is undertaken. A series of specimens are loaded with simple beam. Various buckling wave forms prior to ultimate failure through a plastic collapse mechanism. The experimentally determined buckling stresses are found to be comparable with studies performed using the ABAQUS program analysis and using each country code.

• Journal of Communications and Networks
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• v.15 no.4
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• pp.362-369
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• 2013

The optimal number of users achieving the maximum sum throughput is analyzed in zero-forcing (ZF) based multiuser multiple-input multiple-output (MIMO) systems with a large number of base station (BS) antennas. By utilizing deterministic ergodic sum rates for the ZF-beam forming (ZF-BF) and ZF-receiver (ZF-R) with a large number of BS antennas [1], [2], we can obtain the ergodic sum throughputs for the ZF-BF and ZF-R for the uplink and downlink frame structures, respectively. Then, we can also formulate and solve the optimization problems maximizing the ergodic sum throughputs with respect to the number of users. This paper shows that the approximate downlink sum throughput for the ZF-BF is a concave function and the approximate uplink sum throughput for the ZF-R is also a concave function in a feasible range with respect to the number of users. The simulation results verify the analyses and show that the derived numbers of users provide the maximum sum throughputs for the ZF-BF as well as ZF-R in multiuser MIMO systems with a large number of BS antennas.