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

Haiyan Zhang,Yaqun Liu,Hui Zhang,Guopeng Fan,Wenfa Zhu,Qi Zhu

doi:10.3390/met9050503

Haiyan Zhang, Yaqun Liu + Show 4 more

Open Access

https://doi.org/10.3390/met9050503

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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.

Highlights

Ultrasonic phased arrays have been widely used in industries due to its strong flexibility and high imaging resolution
A sparse-total focusing method (TFM) algorithm for the near-distance imaging of aluminum plates was presented in this paper, and the influence of sparse receiving elements on computational efficiency and defect quantification accuracy was discussed
To maximize the reduction of the data processing times, the sparse-TFM proposed in this paper was similar to the TFM algorithm, but not all elements were used

Summary

Introduction

Ultrasonic phased arrays have been widely used in industries due to its strong flexibility and high imaging resolution. It has become a research hotspot in the field of ultrasonic non-destructive testing [1,2]. By changing the pulse emission time of a single element according to a certain time sequence, the ultrasonic waves emitted by different elements will be superimposed to form a new wave front. Such a technique can perform linear scanning, sector scanning, and dynamic focusing without probe displacement [3]. The impulse response received by the transducer includes the scattering information from the transmitter to the receiver, and the ultrasonic reverberation

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