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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korean Society for Nondestructive Testing
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Journal DOI :
The Korean Society for Nondestructive Testing
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Volume & Issues
Volume 20, Issue 6 - Dec 2000
Volume 20, Issue 5 - Oct 2000
Volume 20, Issue 4 - Aug 2000
Volume 20, Issue 3 - Jun 2000
Volume 20, Issue 2 - Apr 2000
Volume 20, Issue 1 - Feb 2000
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Time-Frequency Analysis of Dispersive Waves in Structural Members Under Impact Loads
Jeong, H. ; Kwon, I.B. ; Choi, M.Y. ;
Journal of the Korean Society for Nondestructive Testing, volume 20, issue 6, 2000, Pages 481~489
A time-frequency analysis method was developed to analyze the dispersive waves caused by impact loads in structural members such as beams and plates. Stress waves generated by ball drop and pencil lead break were recorded by ultrasonic transducers and acoustic emission (AE) sensors. Wavelet transform (WT) using Gabor function was employed to analyze the dispersive waves in the time-frequency domain, and then to find the arrival time of the waves as a function of frequency. The measured group velocities in the beam and the plate were compared with the predictions based on the Timoshenko beam theory and Rayleigh-Lamb frequency equations, respectively. The agreements were found to be very good.
An Improved AE Source Location by Wavelet Transform De-noising Technique
Lee, Kyung-Joo ; Kwon, Oh-Yang ; Joo, Young-Chan ;
Journal of the Korean Society for Nondestructive Testing, volume 20, issue 6, 2000, Pages 490~500
A new technique for the source location of acoustic emission (AE) in plates whose thichness are close to or thinner than the wavelength has been studied by introducing wavelet transform de-noising technique. The detected AE signals were pre-processed using wavelet transform to be decomposed into the low-frequency, high-amplitude flexural components and the high-frequency, low-amplitude extensional components. If the wavelet transform de-noising was employed, we could successfully filter out the extensional wave component, one of the critical errors of source location in plates by arrival time difference method. The accuracy of source location appeared to be significantly improved and independent of the setting of gain and threshold, plate thickness, sensor-to-sensor distance, and the relative position of source to sensors. Since the method utilizes the flexural component of relatively high amplitude, it could be applied to very large, thin-walled structures in practice.
Wavelet Analysis of Ultrasonic Echo Waveform and Application to Nondestructive Evaluation
Park, Ik-Keun ; Park, Un-Su ; Ahn, Hyung-Keun ; Kwun, Sook-In ; Byeon, Jai-Won ;
Journal of the Korean Society for Nondestructive Testing, volume 20, issue 6, 2000, Pages 501~510
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.
Wavelet Transform Based Doconvolution of Ultrasonic Pulse-Echo Signal
Jhang, Kyung-Young ; Jang, Hyo-Seong ; Park, Byung-Yll ; Ha, Job ;
Journal of the Korean Society for Nondestructive Testing, volume 20, issue 6, 2000, Pages 511~520
Ultrasonic pulse echo method comes to be difficult to apply to the multi-layered structure with very thin layer, because the echoes from the top and the bottom of the layer are superimposed. We can easily meet this problem when the silicon chip layer in the semiconductor is inspected by a SAM equipment using fairly low frequency lower than 20MHz by which severe attenuation in the epoxy mold compound of packaging material can be overcome. Conventionally, deconvolution technique has been used for the decomposition of superimposed UT signals, however it has disabilities when the waveform of the transmitted signal is distorted according to the propagation. In this paper, the wavelet transform based deconvolution(WTBD) technique is proposed as a new signal processing method that can decompose the superimposed echo signals with superior performances compared to the conventional deconvolution technique. WTBD method uses the wavelet transform in the pre-stage of deconvolution to extract out the common waveform from the transmitted and received signal with distortion. Performances of the proposed method we shown by through computer simulations using model signal with noise and we demonstrated by through experiments for the fabricated semiconductor sample with partial delamination at the top of silicon chip layer.
Signal Processing in Medical Ultrasound B-mode Imaging
Song, Tai-Kyong ;
Journal of the Korean Society for Nondestructive Testing, volume 20, issue 6, 2000, Pages 521~537
Ultrasonic imaging is the most widely used modality among modern imaging device for medical diagnosis and the system performance has been improved dramatically since early 90's due to the rapid advances in DSP performance and VLSI technology that made it possible to employ more sophisticated algorithms. This paper describes "main stream" digital signal processing functions along with the associated implementation considerations in modern medical ultrasound imaging systems. Topics covered include signal processing methods for resolution improvement, ultrasound imaging system architectures, roles and necessity of the applications of DSP and VLSI technology in the development of the medical ultrasound imaging systems, and array signal processing techniques for ultrasound focusing.
Nondestructive Inspection of Steel Structures Using Phased Array Ultrasonic Technique
Shin, Hyeon-Jae ; Song, Sung-Jin ; Jang, You-Hyun ;
Journal of the Korean Society for Nondestructive Testing, volume 20, issue 6, 2000, Pages 538~544
A phased array ultrasonic nondestructive inspection system is being developed to obtain images of the interior of steel structures by modifying a medical ultrasound imaging system. The medical system consists of 64 individual transceiver channels that can drive 128 array elements. Several modifications of the system were required mainly due to the change of sound speed. It was necessary to fabricate array transducers for steel structure and to obtain A-scan signal that is necessary for the nondestructive testing. Boundary diffraction wave model was used for the prediction of radiation beam field from array transducers, which provided guidelines to design array transducers. And a RF data acquisition board was fabricated for the A-scan signal acquisition along a selected un line within an image. For the proper beam forming in the transmission and reception for steel structure, delay time was controlled. To demonstrate the performance of the developed system and fabricated transducers, images of artificial specimens and A-scan signals for selected scan lines were obtained in a real time fashion.
Reconstruction and Deconvolution of X-Ray Backscatter Data Using Adaptive Filter
Kim, Noh-Yu ;
Journal of the Korean Society for Nondestructive Testing, volume 20, issue 6, 2000, Pages 545~554
Compton X-ray backscatter technique has been used to quantitatively assess the impact damage in quasi-isotropic laminated composites and to obtain a cross-sectional profile of impact-damaged laminated composites from the density variation of the cross section. An adaptive filter is applied to the Compton backscattering data for the reconstruction and noise reduction from many sources including quantum noise, especially when the SNR(signal-to-noise ratio) of the image is relatively low. A nonlinear reconstruction model is also proposed to overcome distortion of the Compton backscatter image due to attenuation effects, beam hardening, and irregular distributions of the fibers and the matrix in composites. Delaminations masked or distorted by the first few delaminations near the front surface are detected and characterized both in width and location, by application of an error minimization algorithm.
Quantitative Evaluation of Remote Field Eddy Current Defect Signals
Jeong, Jin-Oh ; Yi, Jae-Kyung ; Kim, Hyoung-Jean ;
Journal of the Korean Society for Nondestructive Testing, volume 20, issue 6, 2000, Pages 555~561
The remote field eddy current (RFEC) inspection was performed on the ductile cast iron pipes with nominal outer diameter of 100mm, which were machined with various shapes and sizes of defects. Ductile cast iron pipes which are used as water supply pipe have the non-uniform thickness and asymmetric cross section due to relatively high degree of allowable errors during the manufacturing processes. These characteristics of ductile cast in pipes cause the long range background noises in RFEC signals along the pipe. In this study, tile machined defects in pipes were effectively classified by the moving window average (MWA) method which eliminated the long-range noise. The voltage plane polar plots (VPPP) method was used to quantitatively evaluate the depth and circumferential degree of defects. The VPPP signatures showed that the angle between defect signature and the normalized in-phase component on the VPPP is linear to the depth of defects. The nondestructive RFEC technique proved to be capable of quantitatively evaluating the machined defects of underground water supply pipe.
Development of Ultrasonic Inspection System and Application to Overlay Weld Flaw Detection
Nam, Young-Hyun ; Seong, Un-Hak ;
Journal of the Korean Society for Nondestructive Testing, volume 20, issue 6, 2000, Pages 562~567
Many pressure vessels for power and industrial plant are fabricated from low alloy carbon steels. The inner sides of pressure vessels are commonly weld-cladded with austenitic stainless steels to minimize problems of corrosive attack. Disbonding cracks are often detected at the transition region of welding interlayer, which is serious problem to reliability of pressure vessels. We have developed C-scan system to high speed inspection of overlay weld using DSP(digital signal processor). This system consists of signal processing parts (oscilloscope, pulser/receiver, digitizer, DSP), scanner, program and position controller. The developed system has been applied to a practical ultrasonic testing in overlay weld, and demonstrated high speed with precision
On Wavelet Method for Image Processing: Compression, Noise Removal, and Reconstruction
Lee, Nam-Yong ;
Journal of the Korean Society for Nondestructive Testing, volume 20, issue 6, 2000, Pages 568~573