• 한국안전학회지
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• 제22권6호
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• pp.13-19
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• 2007

Diesel car's smoke measurement equipment and method were investigated based on the exhaust gas regulations. Reflection photo method and light extinction method for measuring smoke were compared under conditions of both no load mode and Lug-down 3 mode. Free acceleration mode at no load condition was used for regular inspection of diesel car, and Lug-down 3 mode was used for fine inspection of the diesel car. A correlation between no load mode and Lug-down 3 mode was investigated in this research. The smoke measured with reflection photo method was 1.5${\sim}$2 times higher than that of light extinction method The correlation coefficient between reflection photo method and light extinction method for measuring smoke was 0.83, which shows comparatively high correlation between the two methods for measuring smoke in diesel engines.

• 한국의학물리학회지:의학물리
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• 제32권4호
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• pp.179-184
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• 2021

This study aimed to determine the optimal thickness of the active layer and scan mode for a flexible radiochromic film (F-RCF) based on the active lithium salt of pentacosa-10,12-diynoic acid (LiPCDA). F-RCFs of 90, 120, 140, and 170-㎛ thickness were fabricated using LiPCDA. Several pieces of the F-RCFs were exposed to doses ranging from 0 to 3 Gy. Transmission and reflection modes were used to scan the irradiated F-RCFs. Their dose-response curves were obtained using a second-order polynomial equation. Their sensitivity was evaluated for both scanning modes, and the uniformity of the batch was also examined. For both the transmission and reflection modes, the sensitivity increased as the film thickness increased. For the reflection mode, the dose response increased dramatically under 1 Gy. The value of the net optical density varied rapidly as the thickness of the film increased. However, the dose-response curves showed a supralinear-curve relationship at doses greater than 2 Gy. The sensitivity of the reflection scan at doses greater than 2 Gy was higher than that of the reflection scan within 0-2 Gy. The sensitivity steadily decreased with increasing doses, and the sensitivity of the two modes was within 0.1 to 0.2 at 2 Gy and was saturated beyond that. For the transmission scan, the sensitivity was approximately 0.2 at 3 Gy. For the intra-batch test result, the maximum net optical density difference of the intra-batch was 5.5% at 2 Gy and 7.4% at 0.2 Gy in the transmission and reflection scans, respectively. In the low-dose range, film thickness of more than 120-㎛ was proper in the transmission mode. In contrast, the transmission mode showed a better result compared to the reflection mode. Therefore, the proper scan mode should be selected according to the dose range.

• Smart Structures and Systems
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• 제32권4호
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• pp.253-266
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• 2023

The time-reversal method is employed to improve the ability of pipeline defect detection, and a new approach of identifying the pipeline defect depth is proposed in this research. When the L(0,2) mode ultrasonic guided wave excited through a lead zirconate titinate (PZT) transduce array propagates along the pipeline with a defect, it will interact with the defect and be partially converted to flexural F(n, m) modes and longitudinal L(0,1) mode. Using a receiving PZT array attached axisymmetrically around the pipeline, the L(0,2) reflection signal as well as the mode conversion signals at the defect are obtained. An appropriate rectangle window is used to intercept the L(0,2) reflection signal and the mode conversion signals from the obtained direct detection signals. The intercepted signals are time reversed and re-excited in the pipeline again, result in the guided wave energy focusing on the pipeline defect, the L(0,2) reflection and the L(0,1) mode conversion signals being enhanced to a higher level, especially for the small defect in the early crack stage. Besides the L(0,2) reflection signal, the L(0,1) mode conversion signal also contains useful pipeline defect information. It is possible to identify the pipeline defect depth by monitoring the variation trend of L(0,2) and L(0,1) reflection coefficients. The finite element method (FEM) simulation and experiment results are given in the paper, the enhancement of pipeline defect reflection signals by time-reversal method is obvious, and the way to identify pipeline defect depth is demonstrated to be effective.

• 비파괴검사학회지
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• 제30권3호
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• pp.194-199
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• 2010

Based on the idea of eigen-mode expansion, a method to analyze the reflection of Lamb wave from a finite vertical discontinuity of plate is theoretically derived and verified by experiment. The theoretical prediction is in good agreement with the experimental result, and this strongly suggests that eigen-mode expansion method could be used for solution of inverse scattering problem for ultrasonic testing using Lamb wave.

• 한국전자파학회논문지
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• 제29권1호
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• pp.28-31
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• 2018

본 논문에서는 균일원형배열(UCA) 안테나를 이용한 궤도각운동량(OAM) 다중모드 전송시스템의 채널용량에 대하여지면 반사가 미치는 영향을 수치적으로 분석하였다. 지면 반사는 OAM 다중모드 간 간섭을 유발하고 시스템의 심각한 성능 저하를 가져온다. 전송거리가 증가함에 따라 OAM 다중모드 채널용량은 지면 반사의 영향으로 인하여 매우 작아진다. 지면 반사의 영향을 줄이기 위해서는 UCA의 높이를 높이고, 배열 소자의 지향성을 높이는 것이 필요하다.

• 동력기계공학회지
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• 제15권3호
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• pp.18-24
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• 2011

In this study, the reflection of the L(0,2), axially symmetric guided elastic wave from defects in pipes above ground is examined using finite element method. Phase and group velocity dispersion curves for the pipe were presented for the selection of the excitation mode. Some simple signal processing was applied to determine the amplitude of each of the reflected waves and to calculate the reflection coefficient. The results show the reflection coefficient of this mode is very close to a linear function of the circumferential extent of the defect. The motivation for the work was the development of a technique for inspecting chemical plant pipelines, but the study addresses the nature of the reflection function and its general applicability.

• 한국광학회지
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• 제23권1호
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• pp.36-41
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• 2012

표면 플라즈몬-폴라리톤(surface plasmon-polaritons, SPP)의 외부-전반사(total external reflection, TER) 현상은 유전체 만으로 된 경계 면에서는 일어나지 않는 SPP 만의 독특한 특성이다. 금속 면 위에 놓인 낮은 굴절률 유전체 선이 도파로 코어 역할을 하여 파장 이하의 크기를 갖는 도파모드를 형성하는 SPP-TER 도파로 구조를 제안하였다. 코어 단면적 변화에 따른 SPP-TER 모드의 전파 특성을 기존의 높은 굴절률 유전체 도파로 및 금속 도파로 구조와 비교 분석하였다. 코어의 면적이 작아짐에 따라 SPP-TER 모드의 크기가 파장보다 수십 배 작아질 수 있으면서도, 주변에 이득물질을 갖는 경우에는 기존의 도파로 구조보다도 높은 이득을 가질 수 있음을 보였다. 따라서, 제안된 SPP-TER 구조는 나노 크기의 레이저 구현에 기여하리라 기대된다.

• 한국도로학회논문집
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• 제7권2호
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• pp.1-12
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• 2005

본 연구는 노후된 시멘트 콘크리트 포장 위에 덧씌운 아스팔트 혼합물의 반사균열 지연을 위하여 바인더 2가지 일반과 개질, 바닥 보강재로 그리드 3종류와 Fabric 2종류의 효과를 평가하기 위하여 수행하였다. 보강재는 공시체 제조시 미리 슬래브 몰드 바닥에 깔고 가열 아스팔트 혼합물을 몰드에 부은 후 다짐을 하여 아스팔트 슬래브 공시체와 일체화시켜 콘크리트 블록 위에 덧씌우기 형태로 택코팅하여 부착하였다. 본 연구를 위하여 휨파괴(mode I) 및 전단파괴(mode II)반사균열 시험을 수행하였다. 시험결과, 일부의 그리드의 보강이 휨파괴 및 전단파괴에 의한 반사균열의 지연에 효과가 있는 것으로 나타났다. 특히 LDPE 개질아스팔트와 함께 사용하면 반사균열 지연에 큰 효과가 있음을 알 수 있었다.

• 한국광학회:학술대회논문집
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• 한국광학회 2009년도 동계학술발표회 논문집
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• pp.459-460
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• 2009

In this study, surface structure and near-field distribution of a surface acoustic wave filter were measured with both reflection mode and collection mode near-field scanning optical microscopes, and there results were compared with each other.

• 한국소음진동공학회논문집
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• 제24권8호
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• pp.636-642
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• 2014

The sensor configuration of the magnetostrictive guided wave system can be described as a single continuous transducing element which makes it difficult to separate the individual modes from the reflected signal. In this work we develop the mode decomposition technique employing chirplet transform, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor, and to estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize defects. The reflection coefficients are calculated using the modal energies of the separated mode. Results from experimental results on a carbon steel pipe are presented, which show that the accurate and quantitative defect characterization could become enabled using the proposed technique.