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Open AccessArticle

A SAFT Method for the Detection of Void Defect inside a Ballastless Track Structure Using Ultrasonic Array Sensors

1
School of Urban Rail Transportation, Shanghai University of Engineering Science, Shanghai 201620, China
2
School of Communication and Information Engineering, Shanghai University, Shanghai 200444, China
*
Author to whom correspondence should be addressed.
Sensors 2019, 19(21), 4677; https://doi.org/10.3390/s19214677
Received: 9 October 2019 / Revised: 27 October 2019 / Accepted: 28 October 2019 / Published: 28 October 2019
High-precision ultrasound imaging of void defects is critical for the performance and safety assessment of ballastless track structures. The sound propagation velocity of each layer in the ballastless track structure is quite different. However, the traditional concrete Synthetic Aperture Focusing Technique (SAFT) ultrasound imaging method is based on the assumption that the concrete has a single constant shear wave velocity. Thus, it is not a suitable method for the ultrasonic imaging of multilayer structures. In this paper, a Multilayer SAFT high-precision ultrasound imaging method is proposed. It is based on the ray-tracing technique and uses the Fermat principle to find the refraction point that minimizes the delay of the acoustic wave propagation path at the interface of the discrete layers. Then, the acoustic wave propagation path is segmented by the position of the refraction point, and the propagation delay of the ultrasonic wave is obtained segment by segment. Thus, the propagation delay of the ultrasonic wave is obtained one by one, so that the propagation delay of the ultrasonic wave in the multilayer structure can be accurately obtained. Finally, the focused image is obtained according to the SAFT imaging algorithm. The finite element simulation and experimental results show that the Multilayer SAFT imaging method can accurately track the propagation path of the ultrasonic wave in ballastless track structures, as well as accurately calculate the propagation delay of the ultrasonic wave and the lengths of void defects. The high accuracy of the Multilayer SAFT imaging represents a significant improvement compared to traditional SAFT imaging. View Full-Text
Keywords: SAFT imaging; ultrasonic array sensors; multilayer structure; ballastless track structure; void defect detection SAFT imaging; ultrasonic array sensors; multilayer structure; ballastless track structure; void defect detection
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MDPI and ACS Style

Zhu, W.-F.; Chen, X.-J.; Li, Z.-W.; Meng, X.-Z.; Fan, G.-P.; Shao, W.; Zhang, H.-Y. A SAFT Method for the Detection of Void Defect inside a Ballastless Track Structure Using Ultrasonic Array Sensors. Sensors 2019, 19, 4677. https://doi.org/10.3390/s19214677

AMA Style

Zhu W-F, Chen X-J, Li Z-W, Meng X-Z, Fan G-P, Shao W, Zhang H-Y. A SAFT Method for the Detection of Void Defect inside a Ballastless Track Structure Using Ultrasonic Array Sensors. Sensors. 2019; 19(21):4677. https://doi.org/10.3390/s19214677

Chicago/Turabian Style

Zhu, Wen-Fa; Chen, Xing-Jie; Li, Zai-Wei; Meng, Xiang-Zhen; Fan, Guo-Peng; Shao, Wei; Zhang, Hai-Yan. 2019. "A SAFT Method for the Detection of Void Defect inside a Ballastless Track Structure Using Ultrasonic Array Sensors" Sensors 19, no. 21: 4677. https://doi.org/10.3390/s19214677

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