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

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 mo-dality 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 pro-posed 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 sur -face, 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.

Automated summary

This paper proposes an efficient phase shift migration method for ultrasonic full-matrix imaging of multilayer structures. By treating FMC as data in three dimensions and transforming it into frequency-wavenumber (f-k) space using a three-dimensional fast Fourier transform, the method can reconstruct wavefields at arbitrary depths and produce defect images. The proposed method has low computational complexity and is six times faster than existing methods.