• 한국주조공학회지
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• 제9권4호
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• pp.327-335
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• 1989

The matrix structure and the morphology of CV graphite are affected by the addition of many kinds of elements, which are contained in the CV graphite cast iron, additives, fading time and cooling rate. The effects of cooling rate on the matrix structure, the shape of CV graphite, mechanical properties and propagation of ultrasonic wave in hypoeutectic CV graphite cast iron were studied. When the diameters of the samples are 50mm, 35mm and 20mm 1. CV graphite number showed average 17.9% increase and CV graphite length showed 10.3% decrease with decreasing diameter of the samples. 2. The amount of graphite and ferrite showed average 11.2, 4.1 % decrease and the amount of pearlite showed average 15.7% increase. 3. Hardness and tensile strength showed average 3.5%, 11.3% increase and impact strength showed average 1.5% decrease. 4. Ultrasonic wave velocity showed average 1.1% increase.

• 한국주조공학회지
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• 제9권4호
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• pp.336-344
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• 1989

The matrix structure and the morphology of CV graphite are affected by the addition of many kinds of elements, which are contained in the CV graphite cast iron, additives, fading time and cooling rate. The effects of cooling rate on the matrix structure, the shape of CV graphite, mechanical properties and propagation of ultrasonic wave in eutectic CV graphite cast iron were studied. When the diameters of the samples are 50mm, 35mm and 20mm 1. CV graphite number showed average 13.8% increase and CV graphite length showed 12.3% decrease with decreasing diameter of the samples. 2. The amount of graphite and ferrite showed average 10.6, 4.3% decrease and the amount of pearlite showed average 23.4% increase. 3. Hardness and tensile strength showed average 3.2%, 9.5% increase and impact strength showed average 1.3% decrease. 4. Ultrasonic wave velocity showed average 1.1% increase.

• ETRI Journal
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• 제41권2호
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• pp.262-269
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• 2019

This paper introduces a low-cost, high-performance mmWave antenna array module at 77 GHz. Conventional waveguide transitions have been replaced by 3D CPW-microstrip transitions which are much simpler to realize. They are compatible with low-cost substrate fabrication processes, allowing easy integration of ICs in 3D multi-chip modules. An antenna array is designed and implemented using multilayer coupled-fed patch antenna technology. The proposed $16{\times}16$ array antenna has a fractional bandwidth of 8.4% (6.5 GHz) and a 23.6-dBi realized gain at 77 GHz.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.411-411
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• 2010

Cavity mode Whistler wave를 사용하는 자화유도결합플라즈마 (Magnetized Inductively Coupled Plasma, MICP)의 제반 특성을 비등방성 수송계수를 가지는 Drift-Diffusion 근사, 에너지 보존 방정식 및 유도전자계를 self-consistent 하게 고려하여 계산하였다. 이러한 접근법은 비충돌성 전자가열현상을 고려하지 못하는 단점에도 불구하고, 반도체 장비설계에 필수적인 전자온도, 밀도, 플라즈마 전위, 시스템의 임피던스 특성에 대한 경향성 파악에 매우 유용하다. 뿐만 아니라 전자밀도분포가 공간내에 형성되는 R-wave mode에 미치는 영향을 분석할 수 있다. 직경 320 mm를 가지는 작은 반응기에서 시뮬레이션과 실험결과를 비교하여 본 모델링 방법의 타당성을 검증한 후, 450 mm wafer가공에 적합한 대면적 플라즈마 반응기에서 플라즈마 특성을 연구하였다. 수 mTorr의 공정압력에서 약 10 Gauss전후의 약한 자장이 인가됨으로서 반경방향의 전자밀도 균일성이 대폭 향상되었다. 플라즈마 및 안테나의 대면적화에 수반되는 높은 Q값이 자장의 인가로 큰 폭으로 감소함으로서 임피던스메칭의 안정성이 비약적으로 개선되었고 전력전달 효율 또한 크게 증가함을 알 수 있었다. 본 연구 결과는 차세대 450 mm 반도체 공정장비의 개발에 있어 자화유도결합플라즈마가 매우 유용하게 사용될 수 있음을 보여준다.

• 한국공작기계학회논문집
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• 제10권1호
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• pp.133-140
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• 2001

Recently, to assure the integrity of a structural components such as piping pressure vessels and thinning structure, Lamb wave inspection technique has been used in material evaluation. It is very important to select the optimal Lamb wave mode and to analyze the signal accurately because of its unique dispersion properties grnerating several modes within the speci-men. It this study, the feasibility of material evaluation applications using wavelet analysis of Lamb wave has been veir-fied experimentally. These results show as follows; 1)dispersion characteristic of each mode in dispersion curve is demon-strated that A0 mode propagating material surface is useful mode having the lest energy loss and not sensitive to surface condition. 2) it can be detected even the micro defect ($1\times2mm$) fabricated in ultrasonic probe flaw distance (290mm) to axis direction. 3) the wavelet transform which is called "time-frequency analysis" shows the Lamb wave propagation due to the change of materials characterization can be evaluated at each frequency and experimental group velocity of Lamb wave agrees quite well with that of simulated dispersion curve.ion curve.

• 한국전자파학회논문지
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• 제20권6호
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• pp.562-569
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• 2009

최근 DSRC, 협대역 통신 방식을 이용하여 고속도로 톨게이트에 Hi-pass(차량의 무정차 자동 요금 징수)를 운용하고 있지만, 전파의 다중 반사로 인한 전파 간섭이 발생하여 시스템의 오류 및 사고가 발생하고 있다. 이러한 문제들은 전파 흡수체를 사용하여 해결할 수 있다. 본 논문은 전파 흡수 재료인 비정질 재료와 지지재인 CPE를 배합하여 최적의 조성비를 찾고 DSRC용 전파 흡수체를 개발하는 연구를 하였다. 그 결과, 조성비 비정질 재료 :CPE=45:55 wt.%, 두께 2.65 mm인 전파 흡수체가 5.8 GHz에서 40 dB 이상의 흡수능이 얻어지도록 개발하였다.

• 한국안전학회지
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• 제32권2호
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• pp.98-104
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• 2017

The ultrasonic pulse velocities of pressure, shear, and Rayleigh waves ( P-, S-, and R- waves) have been used for the condition evaluation of various concrete structures, but the statistical distribution according to the wave type has not been studied clearly in view of data reliability and validity. Therefore, this study analyzed the statistical distribution of P-, S-, R-wave velocities in concrete wide beams of $800{\times}3100mm$ (width ${\times}$ length) with a thickness of 300 mm. In addition, we investigated an experimental consistency by the Kolmogorov-Smirnov goodness-of-fit test. The experimental data showed that the R-, S- and P- wave velocities in order have better statistical stability and reliability for in situ evaluation because R- and S-waves are less sensitive to confinement and boundary conditions. Also, good correlations between wave velocities and strength and modulus of elasticity were found, which indicate them as appropriate techniques for estimating the mechanical properties.

• 한국항해학회지
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• 제22권4호
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• pp.51-57
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• 1998

According to the rapid development of the electric industry, the demand of the frequency allocation and the usage of electromagnetic wave are increased due to automation of modem society. Electromagnetic wave absorbers for anechoic chamber are needed to broaden the effective frequency bandwidth, reduce the thickness, and decrease the weight. There are various absorbers proposed for the above conditions, but they could not decisively solve the above requirements. The Electromagnetic wave absorber made by a conventional ferrite tile has, for example, broadened the effective frequency bandwidth by the way of forming air layer(practically in urethane foam, etc.) on the ferrite tile. Therefore, an air layer is formed between a reflection plate and a sintered Ni-Zn ferrite tile of 7 mm in thickness, which has reflectivity less than -20 dB from 30 MHz to 400 MHz in bandwidth. In this paper, a broadband electromagnetic wave absorber are designed, which has the reflection characteristics less than -20 dB from 30 MHz to 8,000 MHz in the bandwidth. A super broadband electromagnetic wave absorber is achieved by inserting square Ferrite Cylinders Type with the thickness less than 23.5 mm and with the frequency band from 30 MHz to 8,000 MHz under the above tolerance limits. The purpose of this research is on the development of a universal anechoic chamber for measuring radiated electromagnetic wave or immunity of electronic equipments, GTEM-cell and also a wall material for preventing TV ghost, etc.

• Restorative Dentistry and Endodontics
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• 제42권2호
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• pp.134-139
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• 2017

Objectives: To compare the fatigue life of Tango-Endo, WaveOne GOLD, and Reciproc NiTi instruments under static model via artificial canals with different angles of curvature. Materials and Methods: Reciproc R25, WaveOne GOLD Primary, and Tango-Endo instruments were included in this study (n = 20). All the instruments were rotated in artificial canals which were made of stainless steel with an inner diameter of 1.5 mm, $45^{\circ}$, $60^{\circ}$, and $90^{\circ}$ angles of curvatures and a radius of curvature of 5 mm until fracture occurred, and the time to fracture was recorded in seconds using a digital chronometer. The data were analyzed using Kruskal-Wallis and post-hoc Dunn tests were used for the statistical analysis of data in SPSS 21.0 software. Results: Tango-Endo files were found to have significantly higher values than WaveOne GOLD and Reciproc files in terms of fatigue life (p < 0.05). However, there was no statistically significant difference between fatigue life of Reciproc and WaveOne GOLD files (p > 0.05). It was determined that increasing the angle of curvature of the stainless canals caused significant decreases in fatigue life of all of three files (p < 0.05). Conclusions: Within the limitations of the present study, the cyclic fatigue life of Tango-Endo in canals having different angles of curvature was statistically higher than Reciproc and WaveOne GOLD.

• 지구물리와물리탐사
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• 제14권4호
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• pp.305-315
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• 2011

암석시료에 대한 음파 속도측정의 정확성을 검증하고 정밀한 측정을 위한 기초적인 실험의 일환으로 아크릴과 스테인리스강 재질의 시료에 대하여 길이와 축하중을 달리하여 각각에 대해 3회씩 측정한 총 864 경우에 대하여, 시험편을 통과한 초동 주시를 측정하고 분석하였다. 축하중이 가해진 상태에서의 S-파 측정은 P-파에 비해 측정에 어려움이 있었으며 이에 따라 반복측정, 길이, 축하중에 의한 편차도 S-파가 훨씬 크게 나타났다. 또한, 재질에 따라서는 스테인레스강 시편보다는 아크릴 시편의 초동주시 편차가 약 2배 정도 양호하게 나타났으며 이는 아크릴 시험편의 경우가 트랜스 듀서와 시험편 간의 접촉 coupling이 안정적이며 또한 동일한 시간 분해능이나 유사한 전기적 잡음에 비하여 초동 주시가 길기 때문으로 판단된다. 실험결과, 아크릴 시험편과 스테인리스강 시험편의 탄성파 속도를 측정할 때는 60 ~ 90 mm 정도의 길이를 갖는 시험편을 20 kg (27.7 $N/cm^2$) ~ 30 kg (41.6 $N/cm^2$) 내외의 축하중 하에서 측정하는 것이 가장 좋으며, 스테인리스강 시험편의 S-파 속도는 길이 50 mm 이하의 시험편을 사용하여 측정해야 한다. 이러한 실험 결과는 암석 코어의 속도 측정시 시스템 지연의 측정 및 보정에 활용될 수 있을 것이다.