Efficient phase shift migration for ultrasonic full-matrix imaging of multilayer composite structures

• Published in: Mechanical systems and signal processing Vol. 174; p. 109114
• Main Authors: Ji, Kaipeng, Zhao, Peng, Zhuo, Chaojie, Jin, Haoran, Chen, Mu, Chen, Jian, Ye, Sheng, Fu, Jianzhong
• Format: Journal Article
• Language: English
• Published: Berlin Elsevier Ltd 15-07-2022; Elsevier BV
• Subjects: Composite structures; Defects; Fast Fourier transformations; Fourier transforms; Frequency-wavenumber space; Full matrix imaging; Imaging; Mechanical properties; Multilayer structures; Multilayers; Phase shift; Phase shift migration; Phased array; Wavelengths; Phased array; Phase shift migration; Multilayer structures; Frequency-wavenumber space; Full matrix imaging
• ISSN: 0888-3270; 1096-1216
• DOI: 10.1016/j.ymssp.2022.109114

•Double-square-root wavenumber is introduced in wavefield extrapolation directly.•Imaging condition is directly applied in the frequency-wavenumber space.•The method outperforms existing methods in computational complexity and efficiency.•The method has great potential in online detection for large multilayer structures.•The proposed method is well adaptable to the continuous-layered media.
Multilayer composite structures are essential for various fields but void defects inside will greatly reduce its mechanical properties. Ultrasonic full-matrix capture (FMC) is a useful imaging modality to detect defects in multilayer structures, but it also brings heavy computational burden. Though great progress has been made in the full-matrix imaging for homogeneous medium, most of these methods are invalid or inefficient for the cases of multilayer structures. To amend it, an efficient phase shift migration for ultrasonic full-matrix imaging of multilayer structures is proposed in this paper. The method regards FMC as data in three dimensions: receiver position, transmitter position and time, and transforms it into frequency-wavenumber (f-k) space by a three-dimensional fast Fourier transform. By downward extrapolating the wavefield on the surface, the wavefield at arbitrary depth in the measuring region is reconstructed, with a firstly introduced double-square-root vertical wavenumber. Then the imaging condition t = 0 is directly applied in the f-k space to produce the defect image. Computational complexity was reduced greatly, and the calculation time of the proposed method was only 1/6 of that of the well-established extended phase shift migration, in the case of the same resolution. Therefore, the proposed method has great potential in on-line ultrasound defect detection, especially for cases of large multilayer structures.