• Proceedings of the KSME Conference
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• 2001.06d
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• pp.54-59
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• 2001

OH radical concentration have been measured in a methane-air partially premixed flames using PLIF. Excitation lines were selected $Q_{1}(6)$ branch, (1,0) band. The system is consisted of Nd:YAG laser, dye laser and frequency doubler to make pump beam for OH radical. On the direct photographs, flame height increases as fuel flow rate and equivalence ratio increase. And on the PLIF images, OH radical is distributed from premixed flame front to nonpremixed flame front through the flame structure with all equivalence ratio. OH overall concentrations increase with equivalence ratio. At the stoichiometric equivalence ratio, the peak of OH radical concentration exists strongly near the inner cone. As equivalence ratio is changed to richer, OH radical distribution goes thinly and the peak is increased as longitudinal direction. As the flow goes to the downstream, OH radical concentration decreases and broadens, because OH radical reacts with another species after OH formation at the initial oxidization. This phenomenon resembles radial distribution. At the l00cc fuel flowrate, the radial peak of OH radical exists from x/R=l.0 to 1.5.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.11 s.188
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• pp.108-115
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• 2006

A hydraulic breaker is widely utilized for many civil engineering areas for the purpose of destroying objects such as rocks, concrete, or road. However, since the high-level noise and vibration by a hydraulic breaker is one of the major sources of environmental noise and recently the environmental regulations on construction equipments are also getting more strengthened, in order to solve such problems, it is certainly necessary to design and develop a hydraulic breaker with low noise and low vibration. This research is to understand the noise characteristics through the noise test and acoustic analysis of the bracket housing in a hydraulic breaker and to identify the element part to be modified based on the result of the element contribution analysis. An improved breaker model including X-typed rib shows the result of low-noise level within target frequency band compared with a commercial breaker model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.962-965
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• 2005

A high intensity progressive wave tube is installed at Korea Aerospace Research Institute (KARI) for acoustic environmental tests. The test facility has 700 mm x 800 mm cross-sectional area, and provides acoustic environment of 165 dB over the frequency range of $25Hz{\sim}10,000Hz$. The facility consists of a 6 m long acoustic wave tube, acoustic power generation systems, gases nitrogen supply systems, and acoustic control systems. This paper describes how the basic parameters of the facility and power generation systems are controlled to meet the requirement of the test. The shape and length of the tube has been designed by using the size of test objects and the wave propagation characteristics of the tube. The capacity of acoustic power generation systems is determined by the energy conversion of acoustic wave and the efficiency of acoustic modulators. Moreover, the paper introduces test run results of the tube. Overall of 163dB has been generated by using the test facility.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.9
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• pp.685-690
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• 2010

ZnO with the wide band gap near 3.37 eV is typically an n-type semiconductor in which deviation from stoichiometry is electrically active. It was known that the films with a resistivity of the order of $10^{-4}{\Omega}cm$ is not easy to obtain. In order to improve electrical characteristic of ZnO, we added 1, 3, 5 wt% Ga element in ZnO. The Ga-doped ZnO (GZO) was grown on a glass substrate by radio frequency (RF) magnetron sputtering at the temperature range from 100 to $500^{\circ}C$. X-ray diffraction (XRD) patterns of GZO films showed preferable crystal orientation of (002) plane. The lowest resistivity of the GZO films was $8.9{\times}10^{-4}{\Omega}cm$. GZO films significantly influenced by the working temperature. The average transmittance of the films was over 80% in the visible ranges.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.6
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• pp.760-767
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• 2009

This thesis focuses on the study of high-power, coupled-cavity traveling-wave tube(CCTWT) for radar applications. The CCTWT employed a reentrant double-slot staggered RF cavity structure. Computational analysis of the X-band, double-slot staggered structures is carried out through the use of HFSS code, which solves Maxwell's equations fully in three-dimensions. The non-linear, large-signal performance of CCTWTs are predicted from numerical simulations using a three-dimensional particle-in-cell code, MAGIC3D. With beam voltage set to 12.7~13kV and beam current at 300mA, the CCTWT produces a saturated radiation power of 350~430W, corresponding to an electronic efficiency of 8.9~11.2% and a gain of 23.7~24.2dB within a frequency range of 7.9~8.4GHz.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1914-1917
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• 2001

3D Feed Horn Shape MEMS Antenna Array는 적외선 이미지 소자 또는 Tera hertz band 등에서 많은 응용을 할 수 있는 장점을 가진 MEMS 구조체 이다. 하지만 일반적인 MEMS 공정을 이용해서 3D Feed Horn Shape MEMS antenna array를 구현하기는 적합하지 않았다. 본 논문에서는 마스크와 웨이퍼가 일체 된 형태의 경사된 척이 초 저속으로 회전하면서 노광을 할 수 있는 새로운 방식과 미러 반사구조를 이용해서 평행광을 얻을수 있는 노광장치 (MRPBI : Mirror Reflected Parallel Beam Illuminator) System제작방법을 제안하였다. 3D Feed Horn Shape MEMS Antenna의 구조적인 high apect ratio의 특성에 의해서 SU-8과 PMER Negative Photo resist를 이용한 기본적인 실험을 통해 3D 구조체의 구현 가능성을 증명하였다. 또한 Microbolometer의 성능향상을 위한 이론적인 3D MEMS Antenna Model들을 HFSS(High Frequency Structure Simulator)을 이용해서 그 최적구조를 제안하고 3D MEMS Antenna Gain 값을 비교 분석하였다.

• Progress in Medical Physics
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• v.4 no.1
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• pp.41-53
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• 1993

The electron spin resonanec of sigle crystals of L-alanine have been observed at T=300K, 100K and analyzed for different orieantations of the crystal in the magnetic field and at microwave frequency X-band. The stable free radical profuced by the irradiation is proved to be of the form CH$_3$CHR, where R is a group which has no nuclei with detectable coupling A notable dependence on temperature of the absorption was observed in the range from 1100K to 2l0K. It was concluded that the reorietation of the methy group of the radical H$_3$CCHR is quenched at low temperature.

• Information and Communications Magazine
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• v.16 no.10
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• pp.112-124
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• 1999

본 논문에서는 FTTC/VDSL (Fiber-to-the-Curb/Very High-speed Digital Subscriber Line) 전송시스템의 개발동향과 ANSI, ETSI, ITU등의 표준화 위원회에서 현재 진행중인 VDSL 시스템의 표준화 작업에 대해 기술하였다. 특히, POTS (Plain Old Telephone Service), BA-ISDA(Basic Access Integrated Services Digital Network), HDSL(High-rate Digital Subscriber Line), SDSL (Single-pair HDSL), ADSL(Asymmetric Digital Subscriber Line) 등의 다양한 xDSL (Digital Subscriber Line) 서비스들에서 발생하는 NEXT (Near-end Crosstalk)/FEXT (Far-end Crosstalk)와 같은 crosstalk를 최소화하기 위해 제안된 VDSL시스템의 주파수 대역과 PSD (Power Spectral Density) mask에 관해 설명하고, 순방향(down-stream) 채널과 역방향(upstream) 채널의 데이터 전송률이 대칭적인 VDSL전송시스템과 비대칭적인 VDSL 전송시스템 간의 주파수대역의 호환성 문제, RFI(Radio Frequency Interference) ingress/egress 문제의 해결 방안에 관해 기술하였다. 또한, 현재 VDSL Coalition과 VDSL Alliance 간에 논의 중인 VDSL 전송시스템의 변복조 방식에 관한 표준화 작업과정 및 순방향과 역방향에 할당될 band 개수에 따른 시스템 성능의 장단점 등에 관해 살펴보았다. 끝으로 현재 국내에서 개발되고 있는 FTTC/VDSL 전송시스템의 전체구조를 요약하고, 네트워크에서 가입자쪽으로 순방향 데이터 전송에 사용된 51.84 Mb/s 19-CAP (Carrierless Amplitude/Phase Modulation) 전송시스템과 가입자 댁내에서 네트워크 방향으로 역방향 데이터 전송에 사용된 1.62 Mb/s QPSK (Quadrature Phase Shift Keying) burst-mode TDMA (Time Division Multiple Access) 전송시스템 등의 동작 원리 및 구조를 기술하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.13 no.4
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• pp.277-284
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• 1988

A 12GHz low-noise amplifier, a single gate GaAs MESFET mixer, and a low-pass filter have been fabricated for DBS receiver applications by using MIC technology. Each subsystem contains DC block with symmetric line and ship capacitor, respectively. The frequency converter with chip capacitor exhibits a 20-23 dB conversin gain with a RF bandwidth of 11.581-11.981 GHz and an IF bandwidth of 581-981MHz. Rf bandwidth of 12.1GHz and an IF banewidth of 1GHz.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.4
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• pp.534-540
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• 1990

In this paper the characteristics of submicron gate GaAs MESFET's have been studied using a particle model which takes into account the hot-electron transport phenomena, i.e., the velocity overshoot. \ulcornervalley(<000> direction), L valley (<111>direction), X valley (<100>direction) as the GaAs conduction energy band and optical phonon, acoustic phonon, equivalent intervalley, nonequivalent intervalley scattering as the scattering models, have been considered in this simulation. And the GaAs material and the device simulation have been done by determination of the free flight time, scattering mechanism and scattering angle according to Monte-Carlo algorithm which makes use of a particle model. As a result of the particle simulation, firstly the electron distribution, the potential energy distribution and the situation of electron displacement in 0.6 \ulcorner gate length device have been obtained. Secondly, the cutoff frequency, obtained by this method, is k47GHz which is in good agreement with the calculated result of theory. And the current-voltage characteristics curve which takes account of the buffer layer effect has been obtained. Lastly it has been verified that parasitic current at the buffer layer can be analyzed using channel depth modulation.