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Open AccessArticle

Defect Visualization of a Steel Structure Using a Piezoelectric Line Sensor Based on Laser Ultrasonic Guided Wave

by Sang-Hyeon Kang 1,2, Dae-Hyun Han 1,2 and Lae-Hyong Kang 1,2,3,*
1
Department of Mechatronics Engineering, Jeonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju-si 54896, Korea
2
LANL-JBNU Engineering Institute-Korea, Jeonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju-si 54896, Korea
3
Department of Flexible and Printable Electronics, Jeonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju-si 54896, Korea
*
Author to whom correspondence should be addressed.
Materials 2019, 12(23), 3992; https://doi.org/10.3390/ma12233992
Received: 31 October 2019 / Revised: 28 November 2019 / Accepted: 29 November 2019 / Published: 2 December 2019
We studied the detection and visualization of defects in a test object using a laser ultrasonic guided wave. The scan area is irradiated by a laser generated from a Nd:YAG 532 nm Q-switched laser generator through a galvanometer scanner. The laser irradiation causes the surface temperature to suddenly rise and then become temporarily adiabatic. The locally heated region reaches thermal equilibrium with the surroundings. In other words, heat energy propagates inside the object in the form of elastic energy through adiabatic expansion. This thermoelastic wave is typically acquired by a piezoelectric sensor, which is sensitive in the ultrasonic domain. A single piezoelectric sensor has limited coverage in the scan area, while multi-channel piezoelectric sensors require many sensors, large-scale wiring, and many channeling devices for use and installation. In addition, the sensors may not acquire signals due to their installed locations, and the efficiency may be reduced because of the overlap between the sensing areas of multiple sensors. For these reasons, the concept of a piezoelectric line sensor is adopted in this study for the first time. To verify the feasibility of the line sensor, I- and L-shaped sensors were attached to a steel structure, and the ultrasound signal from laser excitation was obtained. If the steel structure has defects on the back, the ultrasonic propagation image will be distorted in the defect area. Thus, we can detect the defects easily from the visualization image. Three defects were simulated for the test. The results show that the piezoelectric line sensor can detect defects more precisely and accurately compared to a single piezoelectric sensor. View Full-Text
Keywords: defect visualization; piezoelectric; line sensor; laser ultrasonics; guided wave defect visualization; piezoelectric; line sensor; laser ultrasonics; guided wave
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Kang, S.-H.; Han, D.-H.; Kang, L.-H. Defect Visualization of a Steel Structure Using a Piezoelectric Line Sensor Based on Laser Ultrasonic Guided Wave. Materials 2019, 12, 3992.

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