• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.501-510
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• 2000

Recently, advanced signal analysis which is called "time-frequency analysis" has been used widely in nondestructive evaluation applications. Wavelet transform(WT) and Wigner Distribution are the most advanced techniques for processing signals with time-varying spectra. Wavelet analysis method is an attractive technique for evaluation of material characterization nondestructively. Wavelet transform is applied to the time-frequency analysis of ultrasonic echo waveform obtained by an ultrasonic pulse-echo technique. In this study, the feasibility of noise suppression of ultrasonic flaw signal and frequency-dependent ultrasonic group velocity and attenuation coefficient using wavelet analysis of ultrasonic echo waveform have been verified experimentally. The Gabor function is adopted the analyzing wavelet. The wavelet analysis shows that the variations of ultrasonic group velocity and attenuation coefficient due to the change of material characterization can be evaluated at each frequency. Furthermore, to assure the enhancement of detectability and naw sizing performance, both computer simulated results and experimental measurements using wavelet signal processing are used to demonstrate the effectiveness of the noise suppression of ultrasonic flaw signal obtained from austenitic stainless steel weld including EDM notch.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.591-597
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• 2001

Ti alloy is used for essential parts of aircraft for high temperature environment. Although Ti alloy has excellent performance in regard to mechanical properties, it is difficult ot find fatigue cracks by nondestructive ultrasonic inspection due to its two-phase microstructure, which consists of hard alpha and beta phases. Sound energy reflected from microstructural features in the component produces a background inspection noise which is seen even when no defects are present. This noise can inhibit the detection of critical internal defects such as pores cracks or inclusions. To obtain fundamental data on ultrasonic inspection of Ti alloy, ultrasonic testing was performed using a specimen with small drill holes and ultrasonic wave propagation velocites were measured.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.2
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• pp.152-162
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• 2001

Laser-generated ultrasonic technique which is one of the reliable nondestructive evaluation techniques has been applied to evaluate the integrity of structures by analyzing the characteristics of signal obtained from surface crack. Therefore, the signal analysis of the laser-generated ultrasonics is absolutely necessary for the accurate and quantitative estimation of the surface defects. In this study, one-sided measurement by laser-generated ultrasonic has been applied to evaluate the depth of the surface-breaking crack in the materials. However, since the ultrasonic waveform excited by pulse laser is very difficult to distinguish the defect signals, it is necessary to consider the signal analyses of the transient waveform. Wavelet Transform(WT) is a powerful tool for processing transient signals with temporally varying spectra that helps to resolve high and low frequency transient components effectively. In this paper, the analyses of the surface-breaking crack of the ultrasonic signal excited by pulse laser are presented by employing the WT analyses.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.203-213
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• 2023

In medical ultrasound imaging systems, Side lobes may appear if signals outside the imaging point are not completely removed during receive focusing. If the time signal of the side lobe overlaps with the time signal (main lobe) from the image point, it is difficult to completely remove it using filter processing in the time domain. However, In the receive focusing process, when time-channel signals are Fourier-transformed, the main lobe and side lobe signals are spatially separated in the spectral domain. Therefore, the side lobes can be suppressed by multiplying the image with magnitude weights, which are determined by the magnitudes of the main and side lobes calculated in the spectral domain. In addition, when the main lobe and the side lobe spectrum are adjacent, the distance weight was applied based on the distance between them. In a 5 MHz ultrasound imaging system using a 64-channel linear transducer, point reflector and speckle images with cysts of various brightness were synthesized and weights were applied to the ultrasound image. Using computer simulations, we confirmed that the side lobes were greatly reduced without affecting the spatial resolution in the point reflector image, and the contrast was significantly improved in the cyst image with computer simulations.

• Proceedings of the Korea Contents Association Conference
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• 2010.05a
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• pp.16-18
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• 2010

유비쿼터스 컴퓨팅 환경에서 다양한 위치 기반 서비스(LBS)를 위해 객체 식별은 필수적인 기술이다. 객체 식별을 위해서 영상 분석 식별, 무선 신호(RF: Radio Frequency) 식별, MIT Cricket 시스템의 RF 신호와 초음파를 활용한 객체 식별 등의 시스템들이 제안되었다. 그 중 가장 널리 이용되는 Cricket 시스템은 RF 신호에 객체의 식별 정보를 포함시켜 초음파 신호와 동시에 송신하고, 수신단에서 RF 신호의 정보를 통해 객체를 식별하는 방식을 이용한다. 하지만 유비쿼터스 컴퓨팅 환경에서 이용되는 단말 노드의 소형의 특성을 유지하기위해 다수의 장치 모듈을 내장하기 힘들다. 본 논문에서는 신호의 정확도가 높은 초음파를 활용하여 RF 통신모듈 없이 신호 중첩 분석으로 통해 다중 객체를 인식하기 위한 기술을 제안한다. 본 논문에서 제안하는 알고리즘의 가능성을 시뮬레이션을 통해 입증하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.363-366
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• 1999

본 논문은 움직이는 물체의 거리와 속도측정을 위한 고전력 쏘나(SONAR)시스템 개발에 목적을 두었다. 고전력 딘나 시스템은 이동하는 물체에 주파수가 190kHz이고, 1.6ms 만큼의 시간차를 가지는 두 개의 정현 구동신호를 보내, 되돌아오는 초음파의 시간차를 이용했다. 초음파 센서의 송신부에는 고전력 엠프를 사용하여 ${\pm}60V$의 정현 구동 신호가 송신 초음파 센서에 전달 되도록 하였다. 초음파 센서의 신호 발진 및 수신된 신호의 저장을 위하여 IM RAM을 활용하였다. 150-250kHr 대역의 아날로그 BP필터를 거쳐 RAM에 저장된 수신신호는 송신신호와 함께 Cross-correlation을 행하여 시간지 연값을 계산하였고, 이로부터 거리 및 속도를 측정했다. 이 실험에서 설계 제작된 쓰나 시스템으로부터 측정된 값은 오실로스코프와 광 센서를 이용하여 직접 측정한 값들과 비교했다. 그 결과 $2\%$의 오차로 근접함을 확인하였다.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.319-320
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• 2006

본 기술개발의 목표는 기존의 Side Scan Sonar 시스템에서 적용된 초음파 수신 신호의 직접적인 모선으로의 전송과 달리 수중 견인체에서 초음파 수신 신호를 취득하여 전력선을 통한 고속 통신 전이중 방식을 통하여 모선의 신호처리 장치로 전송하는 고속 통신 모들의 성능 및 소형화이다.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.04a
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• pp.183-186
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• 2011

본 논문에서는 모바일 초음파(mobile ultrasound) 영상신호의 빔포밍 알고리즘에서 요구되는 고성능 및 저전력을 만족시키는 매니코어 프로세서에 대한 디자인 공간 탐색 방법을 소개한다. 매니코어 프로세서의 디자인 공간 탐색을 위해 매니코어의 각 프로세싱 엘리먼트(Processing Element, PE)당 초음파 영상신호 데이터의 수를 변화시키는 실험을 통해 실행시간, 에너지 효율 및 시스템 면적 효율을 측정하고, 측정된 결과를 바탕으로 최적의 매니코어 프로세서 구조를 선택하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.3
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• pp.251-260
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• 2001

Damage Profess of CFRP laminates under monotonic tensile test was characterized by the correlation between Acoustic Emission(AE) and Ultrasonic Test(UT). The amplitude distribution of AE signal from a specimens is an aid to the determination of the extent of the different fracture mechanism such as matrix crack, debonding, fiber pullout and fiber fracture as load is increased. In addtion, the characteristics of ultrasonic amplitude attenuation are useful lot analysis of the different type of fracture mechanism. Different orientation of carbon fiber reinforced plastic specimens were used to investigate the AE amplitude range and ultrasonic amplitude attenuation. Finally, loading-unloading tests were carried out to check Felicity effect. During the tests, ultrasonic amplitude attenuation was investigated at the same time and compared with AE parameters. The result showed that two parameters of both AE and UT could be effectively used for analysis of fracture mechanism in CFRP laminates.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.230-237
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• 2012

The ultrasonic resonance method was applied to detect the disbond interface and empty layer between steel and FRP of the exit cone. The ultrasonic resonance method can easily detect the disbond interface and empty layer by amplifying the ultrasonic signal, but pulse echo method is difficult to distinguish adhesive interface from disbond interface or empty layer. The resonance frequency was predicted using the pressure reflection coefficient of 3-layered medium, and measured from ultrasonic signal of the test block using Fast Fourier Transform. The ultrasonic resonance proved that the predicted resonance frequency was in good agreement with the measured resonance frequency.