3D ultrasonic full matrix capture imaging for cylindrical scans with wavenumber-domain reconstruction

Ultrasonic imaging of cylindrical structures using linear array scanning is a promising nondestructive testing technique. The image resolution in the axial direction of a cylinder has significantly improved through 2D total focusing algorithms employing single-frame full matrix capture (FMC) data. Further enhancement in circumferential resolution is achievable with synthetic aperture focusing using multiple FMC frames. However, conventional methods suffer from time-consuming computational complexity when focusing in both directions. This paper introduces an efficient 3D wavenumber-domain reconstruction method for both axial total and circumferential focusing in cylindrical FMC scans. Key steps include cylindrical scan phase shift migration (CSPSM) for rapid image migration and subsequent deconvolution for high image resolutions. In CSPSM, the imaging model can be simplified for wavefield extrapolation through appropriate distance approximations and the principle of stationary phase. The extrapolation is applicable to multilayered structures, considering constant transmission coefficients. A 3D imaging rate of 5 Hz is attainable with 32 frames of FMC data in the circumferential direction, each acquired by a 32-element linear array. Experimental results demonstrate achieving an axial resolution of 1.684 mm and a circumferential resolution of 0.37∘. This method holds potential for real-time 3D imaging in the inspection of wrapped pipelines.