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Sparse-TFM Imaging of Lamb Waves for the Near-Distance Defects in Plate-Like Structures

1,2,*, 1,2, 1,2, 1,2, 3 and 4,*
1
School of Communication and Information Engineering, Shanghai University, Shanghai 200444, China
2
School Institute for Advanced Communication and Data Science, Shanghai University, Shanghai 200444, China
3
School of Urban Railway Transportation, Shanghai University of Engineering Science, Shanghai 201620, China
4
School of Mechatronic and Automation Engineering, Shanghai University, Shanghai 200444, China
*
Authors to whom correspondence should be addressed.
Metals 2019, 9(5), 503; https://doi.org/10.3390/met9050503
Received: 5 April 2019 / Revised: 23 April 2019 / Accepted: 26 April 2019 / Published: 29 April 2019
(This article belongs to the Special Issue Opto-Acoustic Characterization of Metals)
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Abstract

The ultrasonic phased array total focusing method (TFM) has the advantages of high imaging resolution and high sensitivity to small defects. However, it has a long imaging time and cannot realize near-distance defect imaging, which limits its application for industrial detection. A sparse-TFM algorithm is adopted in this work to solve the problem regarding rapid imaging of near- distance defects in thin plates. Green’s function is reconstructed through the cross-correlation of the diffuse full matrix captured by the ultrasonic phased array. The reconstructed full matrix recovers near-distance scattering information submerged by noise. A sparse array is applied to TFM for rapid imaging. In order to improve the imaging resolution, the location of active array elements in the sparse array can be optimized using the genetic algorithm (GA). Experiments are conducted on three aluminium plates with near-distance defects. The experimental results confirm that the sparse-TFM algorithm of Lamb waves can be used for near-distance defects imaging, which increases the computational efficiency by keeping the imaging accuracy. This paper provides a theoretical guidance for Lamb wave non-destructive testing of the near-distance defects in plate-like structures. View Full-Text
Keywords: Lamb waves; diffuse field; sparse-TFM algorithm; near-distance defects imaging Lamb waves; diffuse field; sparse-TFM algorithm; near-distance defects imaging
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Zhang, H.; Liu, Y.; Fan, G.; Zhang, H.; Zhu, W.; Zhu, Q. Sparse-TFM Imaging of Lamb Waves for the Near-Distance Defects in Plate-Like Structures. Metals 2019, 9, 503.

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