• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 춘계학술대회 논문집 반도체 재료 센서 박막재료 전자세라믹스
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• pp.60-63
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• 2004

Recently, carbon nanotubes(CNTs) have been demonstrated to possess remarkable mechanical and electronic properties, in particular, for field emission applications. Its high aspect ratio and extremely small diameter, hollowness, together with high mechanical strength and high chemical stability, are advantages for use in field emitter. In this paper, we demonstrate electrical discharge properties from carbon nanotube cathode electrodes to use as an emitter electrode of vacuum gauges. Vertically aligned $2{\times}2mm^2$ CNT arrays on the silicon substrate were synthesized by the thermal CVD method on Fe catalytic metal, and a glass patterning by the sand blast method and the silicon/glass anodic bonding processes were applied to make samples with 2 electrodes. The field emission was examined under the vacuum range of $10^{-3}$ Torr.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
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• pp.681-684
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• 2002

To investigate thermal effects of silicon field emitter, we fabricated and characterized single silicon tips with various tip radii, which generate different joule heating. Through I-V and stability tests, the changes of emission characteristics and tip structures due to different tip heating were observed and discussed. From the results, we confirmed that the changes of emission characteristics due to thermal effects in silicon emitter could occur at relatively small emission currents and concluded that the thermal effects should be also considered under normal operation condition above 1 ${\mu}A$.

• 한국자동차공학회논문집
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• 제10권6호
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• pp.11-18
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• 2002

Residual gas fraction in an engine cylinder affects engine performance, efficiency and emission characteristics. With high residual gas fractions, a flame speed and maximum combustion temperature are decreased and these are deeply related with combustion stability especially at idle and NOx emission at relatively high engine load. In this work, the residual gas fraction was calculated by an engine simulation code, which was validated by the experimental data (cylinder pressure and emissions) obtained from 4-cyliner spark ignition engine. A comparison between experimental and computational calculation results was made. The residual gas is generated mostly at low engine speed by the larger pressure difference between the intake and exhaust port. As the valve overlap duration was increased, the amount of residual gas in the cylinder, the amount of HC emission in the exhaust gas and the variation of power output increased.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.163-167
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• 2007

A field emission electron gun including 3 electrodes including one cathode and two anodes is very important for high resolution electron microscope. To have functions to control the initially-emitted electron beam, two anodes act as an electrostatic lens according to equipotential lines by adjusting the spot size, intensity, and working distance. To verify the action of the electron beam by the electrostatic lens by changing several parameters such as electrode shape, displacement and applied voltage to the electrodes, the two lenses were design and simulated and then their performances were analyzed with angular beam intensity(distribution), electrical optic axis variation and their stability.

• Journal of the Korean Wood Science and Technology
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• 제43권5호
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• pp.672-681
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• 2015

As a part of abating the formaldehyde emission of amino resin-bonded wood-based composite panels, this study was conducted to investigate hydrolytic stability of urea-melamine-formaldehyde (UMF) resin depending on various hydrolysis conditions and hardener types. Commercial UMF resin was cured and ground into a powdered form, and then hydrolyzed with hydrochloric acid. After the acid hydrolysis, the concentration of liberated formaldehyde in the hydrolyzed solution and mass loss of the cured UMF resins were determined to compare their hydrolytic stability. The hydrolysis of cured UMF resin increased with an increase in the acid concentration, time, and temperature and with a decrease in the smaller particle size. An optimum hydrolysis condition for the cured UMF resins was determined as $50^{\circ}C$, 90 minutes, 1.0 M hydrochloric acid and $250{\mu}m$ particle size. Hydrolysis of the UMF resin cured with different hardener types showed different degrees of the hydrolytic stability of cured UMF resins with a descending order of aluminum sulfate, ammonium chloride, and ammonium sulfate. The hydrolytic stability also decreased as the addition level of ammonium chloride increased. These results indicated that hardener types and level also had an impact on the hydrolytic stability of cured UMF resins.

• 한국산학기술학회논문지
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• 제20권1호
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• pp.179-183
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• 2019

전력 변환에는 전력 효율과 함께 전력 변환시스템의 소형화를 위해 적용하는 스위칭에 의한 잡음으로부터 시스템 안정성이 보장되어야 한다. 따라서 전력 변환시 스위칭 잡음을 감소시킬 수 있는 대책이 필수적이다. 따라서 이전 논문에는 MPS사의 MPQ4432 드라이버를 이용하여 DC/DC Buck Converter회로를 구성한 후 이를 reference plane을 갖는 4층 PCB 회로 구조에서 부품의 배치가 서로 다른 경우 발생하는 스위칭 잡음특성을 시뮬레이션 하였다. 본 논문에서는 시뮬레이션을 진행한 서로 다른 두 회로를 제작하여, 시뮬레이션과 동일하게 Conducted Emission특성과 Radiated Emission 특성을 분석하였다. 또한 측정결과와 시뮬레이션 결과와 비교하였다. 그 결과 Current Return Path의 구성에 따라 Conducted Emission특성이 저주파대역에서는 2~9dB, 고주파대역에서는 6~7dB 감소됨을 확인하였다. 그리고 Radiated Emission특성은 9dB 감소됨을 확인하였다. Conducted Emission 시뮬레이션 결과 저주파대역에서 6~7dB이고, 측정 결과는 2~9dB로 다소차이가 있음을 확인하였고, 고주파대역에서는 실험과 시뮬레이션에서 모두 7dB정도임을 확인하였다. 그리고 Radiated Emission은 시뮬레이션에서 12dB 감소를 확인하였지만, 측정결과 9dB의 감소를 확인하였다. 이로써 다소 감소량에는 차이가 확인되었지만 전력변환회로를 설계할 경우 Current return path의 구성에 따라 잡음 특성을 향상시킬 수 있음을 확인하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.150-150
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• 2010

Carbon nanotubes have drawn attention as one of the most promising emitter materials ever known not only due to their nanometer-scale radius of curvature at tip and extremely high aspect ratios but also due to their strong mechanical strength, excellent thermal conductivity, good chemical stability, etc. Some applications of CNTs as emitters, such as X-ray tubes and microwave amplifiers, require high current emission over a small emitter area. The field emission for high current density often damages CNT emitters by Joule heating, field evaporation, or electrostatic interaction. In order to endure the high current density emission, CNT emitters should be optimally fabricated in terms of material properties and morphological aspects: highly crystalline CNT materials, low gas emission during electron emission in vacuum, optimal emitter distribution density, optimal aspect ratio of emitters, uniform emitter height, strong emitter adhesion onto a substrate, etc. We attempted a novel approach to fabricate CNT emitters to meet some of requirements described above, including highly crystalline CNT materials, low gas emission, and strong emitter adhesion. In this study, CNT emitters were fabricated by filtrating an aqueous suspension of highly crystalline thin multiwalled CNTs (Hanwha Nanotech Inc.) through a metal mesh. The metal mesh served as a support and fixture frame of CNT emitters. When 5 ml of the CNT suspension was engaged in filtration through a 400 mesh, the CNT layers were formed to be as thick as the mesh at the mesh openings. The CNT emitter sample of $1{\times}1\;cm^2$ in size was characteristic of the turn-on electrical field of 2.7 V/${\mu}m$ and the current density of 14.5 mA at 5.8 V/${\mu}m$ without noticeable deterioration of emitters. This study seems to provide a novel fabrication route to simply produce small-size CNT emitters for high current emission with reliability.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.154-154
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• 2008

Although the screen printing technology using photosensitive carbon nanotube (CNT) paste has many advantages such as low cost, simple process, uniform emission, and capability of mass production, the CNT paste needs to be improved further in CNT dispersion, printability, adhesion, electrical conductivity, population of CNT emitters, etc. Ball milling has been frequently employed to prepare the CNT paste as ball milling can mix its ingredients very well and easily cut the long, entangled CNTs. This study carried out a parametric approach to fabricating the CNT paste in terms of low-energy ball milling and a paste composition. Field emission properties of the CNT paste was characterized with CNT dispersion and electrical conductivity which were measured by a UV-Vis spectrophotometer and a 4-point probe method, respectively. Main variables in formulating the CNT paste include a length of milling time, and amounts of CNTs and conductive inorganic fillers. In particular, we varied not only the contents of conductive fillers but also used two different sizes of filler particles of ${\mu}m$ and nm ranges. Among many variations of conductive fillers, the best field emission characteristics occurred at the 5 wt% fillers with the mixing ratio of 3:1 for ${\mu}m$-and nm-sizes. The amount and size of fillers has a great effect on the morphology, processing stability, and field emission characteristics of CNT emitter dots. The addition a small amount of nm-size fillers considerably improved the field emission characteristics of the photosensitive CNT paste.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2005년도 제29회 학술발표회 초록집
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• pp.76-77
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• 2005

• 한국항공운항학회지
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• 제18권4호
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• pp.59-66
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• 2010

Aerospace structures need high stability and long life because many personal injuries can result from an accident and securing structural integrity for various external environments is more important than any other thing. So first of all we must prove the destruction properties for operating environment, have prediction technology about damage evolution and life, and develop an economical non-destructive technology capable of detecting structure damage. Acoustic emission (AE) have no need of artificial environment like ultrasonic inspection or radio fluoroscopy to emit a certain energy, is a testing technique using seismic signal resulting from interior changes of solids, and enables to observe if any fault is appeared and it grows seriously or not while running. In this study we suggest the method of structural integrity evaluation for aerospace structures through the acoustic emission technique, for which a model plane was manufactured and an actual operation test was conducted.