• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2013년도 춘계학술대회 논문집
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• pp.151-152
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• 2013

• 비파괴검사학회지
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• 제21권2호
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• pp.152-162
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• 2001

비파괴 평가 기술들 중의 하나인 레이저 초음파 응용 기술은 각종 구조물에 존재하는 표면결함에 의한 신호를 통해 건전성을 평가하는 기법이다. 따라서 결함의 신뢰성 높은 정량적 평가를 위해서는 결함으로부터의 레이저 초음파 신호특성에 대한 기본적 이해가 필수적이며 따라서 이를 위한 신호해석 연구가 요구된다. 본 연구에서는 레이저유도 초음파에 의한 one-sided 기법을 이용하여 표면균열을 평가하고자 하였다. 하지만 레이저를 이용한 평가방법들은 수신된 신호의 해석이 까다로우며 또한 상당한 전문적인 지식이 요구된다. 웨이블렛 변환(wavelet transform, WT) 기법은 신호처리 분야에서 하나의 새로운 방법으로서 다양한 분야에 적용되고 있으며 특히 한 시점에 대한 주파수 분해가 가능한 신호처리 방법으로서 시간-주파수 분석에 아주 유용하게 이용되고 있다. 본 연구에서는 이러한 레이저 유도 초음파를 이용하여 재료의 표면 결함신호들에 대한 웨이블렛 변환기법을 적용하여 보다 정량적인 결함 크기를 예측하고 그 타당성을 평가하고자 하였다.

• 대한기계학회논문집A
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• 제24권7호
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• pp.1847-1853
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• 2000

A computer simulation technique for 2-dimensional laser generated ultrasonic waves was developed for visualization and investigation of ultrasonic propagation in solids. The technique is similar to a finite difference method (FDM) and a mass-particle model method, but uses a new nodal calculation method based on fundamental consideration of an elastic wave equation. By this method, the propagation behavior oflaser generated ultrasonic wave in thermoelastic and ablation mode is visualized and shows good agreement with previous experimental result or the numerical analysis result by Green function.

• 비파괴검사학회지
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• 제27권3호
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• pp.246-254
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• 2007

The scanning laser source (SLS) technique is a promising new laser ultrasonic tool for the detection of small surface-breaking defects. The SLS approach is based on monitoring the changes in laser-generated ultrasound as a laser source is scanned over a defect. Changes in amplitude and frequency content are observed for ultrasound generated by the laser over uniform and defective areas. The SLS technique uses a point or a short line-focused high-power laser beam which is swept across the test specimen surface and passes over surface-breaking or subsurface flaws. The ultrasonic signal that arrives at the Rayleigh wave speed is monitored as the SLS is scanned. It is found that the amplitude and frequency of the measured ultrasonic signal have specific variations when the laser source approaches, passes over and moves behind the defect. In this paper, the setup for SLS experiments with full B-scan capability is described and SLS signatures from small surface-breaking and subsurface flaws are discussed using a point or short line focused laser source.

• 비파괴검사학회지
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• 제26권3호
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• pp.181-189
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• 2006

A 2D finite-element numerical simulation has been developed to investigate the generation of ultrasonic waves in a homogeneous isotropic elastic slab under a line-focused laser irradiation. Discussing the physical processes involved in the thermoelastic phenomena, we describe a model for the pulsed laser generation of ultrasound in a metal slab. Addressing an analytic method, on the basis of an integral transform technique, for obtaining the solutions of the elastodynamic equation, we outline a finite element method for a numerical simulation of an ultrasonic wave propagation. We present the numerical results for the displacements and the stresses generated by a line-focused laser pulse on the surface of a stainless steel slab.

• 한국공작기계학회논문집
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• 제14권4호
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• pp.49-54
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• 2005

Measuring defects on the inside and on the surface of a steel structure is very important technology in order to predict the life span of the structure. In particular, a place with a high probability that it may contain defects is a welded part and it is very important to check defects in the part, absence/presence of non-uniform substances, its shape, and the location. Many non-destructive tests can be applied, but the ultrasonic flow detection test is widely used with some advantages. The ultrasonic flow detection test, however, cannot be applied when there is a problem by a contact medium between PZT and a specimen, in case of a small and complicated shape or a moving object or when the specimen is hot. In this study, to solve the problems of the contact ultrasonic flow detection test, the non-contact ultrasonic flow detection test for sending/receiving ultrasonic waves using lasers was described. I intended to develop a non-destructive detection system applying the laser application ultrasonic test to a steel structure by detecting the defects inside of and on the surface of the specimen.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.415-418
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• 2005

In the semiconductor and optical industry, a new transport system which can replace the conventional transport systems is required. The transport systems are driven by the magnetic field and conveyer belts. The magnetic field may damage semiconductor and the contact force may scratch the optical lens. The ultrasonic wave driven system can solve these problems. In this semiconductor and optical industry, the non-contact system is required fur reducing the damages. The ultrasonic transportation is the solution of the problem. In this paper, the ultrasonic levitation system fur levitating object are proposed. The 3D vibration profiles of the beam are measured by Laser scanning Vibrometer fur verifying the vibration characteristics of the system and the amplitudes of the beam and the levitation heights of object are measured for evaluating the performance.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.959-962
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• 2005

In the semiconductor and optical industry. a new transport system which can replace the conventional transport system is required. The Transport systems are driven by the magnetic field and conveyer belts. The magnetic field may damage semiconductor and the contact force may scratch the optical lens. The ultrasonic wave driven system can solve these problems. In this semiconductor and optical industry, the non-contact system is required for reducing the damages. The ultrasonic transportation is the solution of the problem. In this paper, the ultrasonic levitation system for levitation object are proposed. The 3D vibration profiles of the beam are measured by Laser Scanning Vibrometer for verifying the vibration characteristics of the system and the amplitudes of the beam and the levitation heights of object are measured fore evaluating the performance.

• Smart Structures and Systems
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• 제26권5호
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• pp.657-666
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• 2020

A rotational pulse-echo ultrasonic propagation imager that can inspect cylindrical specimens for material nondestructive evaluations is proposed herein. In this system, a laser-generated ultrasonic bulk wave is used for inspection, which enables a clear visualization of subsurface defects with a precise reproduction of the damage shape and size. The ultrasonic waves are generated by a Q-switched laser that impinges on the outer surface of the specimen walls. The generated waves travel through the walls and their echo is detected by a Laser Doppler Vibrometer (LDV) at the same point. To obtain the optimal Signal-to-Noise Ratio (SNR) of the measured signal, the LDV requires the sensed surface to be at a right angle to the laser beam and at a predefined constant standoff distance from the laser head. For flat specimens, these constraints can be easily satisfied by performing a raster scan using a dual-axis linear stage. However, this arrangement cannot be used for cylindrical specimens owing to their curved nature. To inspect the cylindrical specimens, a circular scan technology is newly proposed for pulse-echo laser ultrasound. A rotational stage is coupled with a single-axis linear stage to inspect the desired area of the specimen. This system arrangement ensures that the standoff distance and beam incidence angle are maintained while the cylindrical specimen is being inspected. This enables the inspection of a curved specimen while maintaining the optimal SNR. The measurement result is displayed in parallel with the on-going inspection. The inspection data used in scanning are mapped from rotational coordinates to linear coordinates for visualization and post-processing of results. A graphical user interface software is implemented in C++ using a QT framework and controls all the individual blocks of the system and implements the necessary image processing, scan calculations, data acquisition, signal processing and result visualization.

• Composites Research
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• 제31권5호
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• pp.246-250
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• 2018

본 연구에서는 곡면 복합재 구조물의 모서리에 위치한 결함을 검사하고 가시화하기 위해 제안된 레이저 초음파 기반 회전식 검사 기법을 소개한다. 모서리 부위에 결함이 위치한 L 형 복합재 구조물을 레이저 초음파 기반 회전식 검사 기법을 이용하여 검사하였다. L 형 시편은 층간분리 손상을 모사하기 위해 각기 다른 세 가지 깊이에 위치한 인공 결함을 포함하고 있다. 모든 인공 결함이 각각의 위치한 깊이에 따라 다른 시간대에 선명하게 탐지되었다. 검사결과는 제안된 방법이 어떠한 특별한 도구 없이도 곡면 복합재 구조물의 모서리 부위의 검사에 적합하다는 것을 보여준다.