TY - JOUR
T1 - Ultrasonic pulse-echo subwavelength defect detection mechanism
T2 - Experiment and simulation
AU - Yin, Xiangtao
AU - Morris, Scott A.
AU - O'Brien, William D.
N1 - Funding Information:
This work was supported by the Illinois Council on Food and Agricultural Research (C-FAR) Competitive Grants Program. The authors would like to thank Dr. James F. Zachary and Mr. James P. Blue, Jr., for their professional assistance with the optical microscopic image and Dr. Michael L. Oelze for his helpful discussion with the acoustic impedance measurement experiment.
PY - 2003/9
Y1 - 2003/9
N2 - The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique [IEEE Trans. UFFC, 45:30 (1998)] has demonstrated sensitive detection of subwavelength channel defects (38-μm diameter reliably and 6-μm diameter occasionally) in flexible 220-μm-thick food package seals (17.3 MHz, λ ≈ 86 μm). However, the underlying subwavelength defect detection mechanism is poorly understood. In this contribution, a theoretical modeling study was undertaken to elucidate the mechanism. The subwavelength diameter channel was fused in-between two plastic package films by applying heat from one side of the films. The sample cross-section microstructure was characterized from both optical and acoustic images. The cross-section impedance profiles along sample thickness dimension were determined. Although identical in nominal impedance properties before sealing, the two binding films showed an asymmetric impedance profile after sealing. Transient finite-element heat conduction analysis and impedance profiles of multiple-sealed package samples showed that the single-sided heating process caused an asymmetric impedance profile. A generalized impedance model was proposed based on these observations. An efficient two-dimensional simulation tool using a finite-difference time-domain method and the perfectly matched layer numerically evaluated the defect detection behavior of the radio-frequency (rf) echo waveforms. The normalized correlation coefficients between the simulated and the measured rf echo waveforms were greater than 95% for this generalized model, which suggested the validity of the proposed impedance model.
AB - The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique [IEEE Trans. UFFC, 45:30 (1998)] has demonstrated sensitive detection of subwavelength channel defects (38-μm diameter reliably and 6-μm diameter occasionally) in flexible 220-μm-thick food package seals (17.3 MHz, λ ≈ 86 μm). However, the underlying subwavelength defect detection mechanism is poorly understood. In this contribution, a theoretical modeling study was undertaken to elucidate the mechanism. The subwavelength diameter channel was fused in-between two plastic package films by applying heat from one side of the films. The sample cross-section microstructure was characterized from both optical and acoustic images. The cross-section impedance profiles along sample thickness dimension were determined. Although identical in nominal impedance properties before sealing, the two binding films showed an asymmetric impedance profile after sealing. Transient finite-element heat conduction analysis and impedance profiles of multiple-sealed package samples showed that the single-sided heating process caused an asymmetric impedance profile. A generalized impedance model was proposed based on these observations. An efficient two-dimensional simulation tool using a finite-difference time-domain method and the perfectly matched layer numerically evaluated the defect detection behavior of the radio-frequency (rf) echo waveforms. The normalized correlation coefficients between the simulated and the measured rf echo waveforms were greater than 95% for this generalized model, which suggested the validity of the proposed impedance model.
KW - Channel defect
KW - Material characterization
KW - Plastic seals
KW - Pulse-echo detection
KW - Ultrasonic nondestructive evaluation (NDE)
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U2 - 10.1023/B:JONE.0000010737.63227.f4
DO - 10.1023/B:JONE.0000010737.63227.f4
M3 - Article
AN - SCOPUS:3943088429
VL - 22
SP - 103
EP - 115
JO - Journal of Nondestructive Evaluation
JF - Journal of Nondestructive Evaluation
SN - 0195-9298
IS - 3
ER -