• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.404-406
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• 2002

We have investigated the contribution of the scattered x rays to the signal imaging in the radiographs acquired with anti-scatter grids of several grid ratios by separating the line spread functions (LSFs) derived from the signal edge image into the primary and the scatter components. By using a 1.0-mm lead plate in the scattering material, the blurred signal edge images were acquired by use of an imaging plate at a tube voltage of 80 kV with the anti-scatter grids of grid ratios for 5:1, 6:1, 8:1, 10:1 and 12:1. The edge profiles of the signal images were scanned and those in relative exposure were differentiated to obtain the LSFs. To investigate the contribution of the scattered x rays to the signal imaging, we proposed a method for separating the LSFs derived from the signal images into the primary and the scatter components, where the scatter component was approximated with exponential function. Our basic approach is to separate the area of the LSFs by ratios of the scattered x-ray exposure to the primary x-ray exposure, which were obtained for the grid ratios by use of a lead disk method. The LSFs and the two components were Fourier transformed to obtain the modulation transfer functions (MTFs) and their two components. As the result, we found that, by using the anti-scatter grids, the scattered x rays were reduced, but the shape of the LSFs of the scatter component hardly changed. The contributions of the scatter component to the MTFs were not negligible (more than 10 %) for spatial frequencies lower than about 1.0 mm$\^$-l/ and that was greater as the grid ratio decreasing. On the other hand, for higher frequencies, the primary component was dominant compared with the scatter component.

• 대한기계학회논문집A
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• 제24권1호
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• pp.163-172
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• 2000

In this study, the scattered far-field due to a cavity embedded in infinite media subjected to the incident SH-wave was calculated by the boundary element method. The effects of cavity shape and distance between internal cavity and internal point in infinite media were considered. The scattered far-field of the frequency domain was transformed into the signal of the time domain by using the Inverse Fast Fourier Transform(IFFT). It was found that the amplitude of scattered signal in time domain decreased with the increase of the distance between the detecting points of ultrasonic scattered field and the center of internal cavity in media. In addition, the time delay was clearly found in time domain waveform as the distance between the detecting points of ultrasonic scattered field and the center of internal cavity was gradually increased.

• 한국통신학회논문지
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• 제38A권11호
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• pp.979-981
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• 2013

본 논문에서는 OFDM 시스템에서 채널을 추정하기 위해 사용하는 분산 파일럿의 위치를 추정하는 방법에 대해 연구하였다. 수신 신호와 4 심볼 지연된 신호의 상호상관을 통하여 위상 오차를 제거함으로 다중 경로 환경에서 정확한 분산 파일럿의 위치를 추정할 수 있다.

• E2M - 전기 전자와 첨단 소재
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• 제8권5호
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• pp.633-639
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• 1995

Dropouts in magnetic media are a primary quality deficiency which is detrimental to magnetic signal quality and thus the major impediment to error-free recording, especially in high density digital recorders. The specific form of defects and causes found to be responsible for signal dropouts occurring in magnetic tape were studied. Dropout occurred when the RF signal falls to low level due to the various types of surface defects. However, the fall in the level of the RF signal in gravure roll coated tapes was most often caused by foreign particles adhering to the magnetic tape. It was also shown from the present study that scattered particles trapped under the tape surface or put on the top can lift it as it crosses the head, creating a spherical tent shaped defect and causing a temporary signal drop. Dropout producing substances were identified through optical and microchemical analyses. The results were correlated with measured electrical signal losses combined with analytical microscopy to clarify source identification of defects.

• 한국추진공학회지
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• 제13권4호
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• pp.36-44
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• 2009

광학 선형 패터네이터 및 광학 토모그래피 기법을 사용하여 높은 주위 기체 압력 조건에서 분무단면을 측정하였다. 레이저 직선광이 분무 영역을 지나도록 하여 발생하는 Mie 산란 신호 및 직선광의 투과율을 측정하였으며, 이로부터 Beer-Lambert 법칙 및 수학적 단면 재구성 기법을 이용하여 분무 단면의 감쇠 계수 분포를 재구성하였다. 높은 주위 기체 압력 조건에서 광학적으로 밀한 분무가 발생하며, 그 결과 산란 신호의 감쇠 효과가 크게 증가한다. 따라서 미 산란 신호를 이용하는 광학 선형 패터네이터의 경우 감쇠 효과를 완화하는 데 한계를 보인다. 광학 토모그래피의 경우 분무를 통과하는 레이저광의 투과율 정보만을 이용하여 성공적으로 분무 단면을 재구성하였다.

• Smart Structures and Systems
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• 제10권3호
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• pp.253-269
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• 2012

A split spectrum processing (SSP) method is proposed to accurately determine the time-of-flight (ToF) of damage-scattered waves by comparing the instantaneous amplitude variation degree (IAVD) of a wave signal captured from a damage case with that from the benchmark. The fundamental symmetrical ($S_0$) mode in aluminum plates without and with a notch is assessed. The efficiency of the proposed SSP method and Hilbert transform in determining the ToF of damage-scattered $S_0$ mode is evaluated for damage identification when the wave signals are severely contaminated by noise. Broadband noise can overwhelm damage-scattered wave signals in the time domain, and the Hilbert transform is only competent for determining the ToF of damage-scattered $S_0$ mode in a noise-free condition. However, the calibrated IAVD of the captured wave signal is minimally affected by noise, and the proposed SSP method is capable of determining the ToF of damage-scattered $S_0$ mode accurately even though the captured wave signal is severely contaminated by broadband noise, leading to the successful identification of damage (within an error on the order of the damage size) using a triangulation algorithm.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 하계종합학술대회 논문집
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• pp.629-632
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• 1989

The scattered light intensity from a spherical particle passing through the cross-over region of two coherent laser beams, varies periodically. Photodetection of this light beams produces a periodic signal of varying amplitude. The phase of the signal varies with the particle size and refractive index, the beam crossing angle and wavelength, and the position and size of the scattered ligth collecting aperture. In this paper the phase variation with respect to the particle absorptive index of retraction, collecting lens size and beam crossing angle is calculated using both Mie scattering theory and reflection theory. The two theories show good agreement in phase predictions, especially for large absorptive indices and for small collection lenses. Both theories predict phase to be inversely proportional to the beam crossing angle.

• 한국음향학회지
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• 제38권5호
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• pp.549-557
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• 2019

표적의 음향 산란 특성은 표적의 재료 특성과 구조적 특성에 영향을 받으며, 이는 음향을 이용하여 수중에서 표적을 탐지, 식별하고자 할 때 매우 중요한 정보가 된다. 특히, 얇은 탄성체의 경우 램파(Lamb wave)에 의해 표적 주변 유체에 산란파가 생성된다. 본 논문에서는 계단 주파수 스윕 사인 파형을 이용하여 수조에서 알루미늄 구의 산란 신호를 측정한 결과를 제시한다. 특히 알루미늄 구의 내부에 물이 채워져 있는 경우와 공기가 채워져 있는 경우에 대하여 산란 신호의 차이를 측정하고 이론 모델과 비교하였다. 또, 내부 물질에 따른 표적 산란 신호 차이를 유사 위그널-빌 분포를 이용하여 분석하고, 유도파의 평균 주파수, 주파수 분포, 에너지의 차이를 비교하였다. 분석 결과, 구의 내부에 물이 채워진 경우가 공기가 채워진 경우에 비해 유도파의 평균 주파수, 주파수 분포, 에너지가 증가하는 것을 확인하였으며 이는 이론적인 예상과 부합한다.

• 비파괴검사학회지
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• 제19권5호
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• pp.333-339
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• 1999

가장 널리 이용되고 있는 대표적인 비파괴 평가 기술들 중의 하나인 초음파 응용 기술은 각종 구조물에 존재하는 내부결함에 의한 산란신호를 통해 건전성을 평가하는 기법이므로 결함의 신뢰성 높은 정량적 평가를 위해서는 결함으로부터의 초음파 산란신호특성에 대한 기본적 이해가 필수적이며 따라서 이를 위한 모델링 수치해석 연구가 요구된다. 본 연구에서는 동탄성 경계요소법을 이용하여 무한체 내부에 존재하는 기공 결함에 의한 초음파 수평횡파의 근거리 및 원거리 산란특성에 대하여 결함으로부터의 거리 영향을 고려하여 해석하였다. 이때 경계요소해석으로 구한 주파수 영역의 원거리 산란장을 실제 결함 탐상시 관찰할 수 있는 시간영역의 신호로 나타내기 위하여 IFFT처리를 하였다. IFFT처리하여 얻은 파형으로부터 원형 기공결함과의 거리가 증가할수록 진폭은 감소하고 시간지연이 나타남을 알 수 있었다.

• 대한기계학회논문집A
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• 제24권1호
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• pp.52-61
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• 2000

The role of quantitative nondestructive evaluation of defects is becoming more important to assure the reliability and the safety of structure, which can eventually be used for residual life evaluation of structure on the basis of fracture mechanics approach. Although ultrasonic technique is one of the most widely used techniques for application of practical field test among the various nondestructive evaluation technique, there are still some problems to be solved in effective extraction and classification of ultrasonic signal from their noisy ultrasonic waveforms. Therefore, crack size determination through a neural network based on the back-propagation algorithm using back-scattered ultrasonic signals is established in this study. For this purpose, aluminum plate containing vertical or inclined surface breaking crack with different crack length was used to receive the back-scattered ultrasonic signals by pulse echo method. Some features extracted from these signals and sizes of cracks were used to train neural network and the neural network's output of the crack size are compared with the true answer.