Fast-VTFM based on two-layer scanned ultrasonic arrays

The total focusing method (TFM) based on full matrix capture data (FMC) has an extremely high detection resolution in the field of ultrasonic non-destructive testing. TFM is however unable to determine the direction of defects and has difficulty in detecting sub-wavelength defects. Vector total focusing method (VTFM) is an advanced post-processing method capable to represent the normal direction of defects and has higher detection resolution. Nevertheless, the current VTFM has huge computational burden and is only applicable to single-medium scenarios. In this paper, a fast vector total focusing method (Fast-VTFM) for two-medium scenarios is proposed based on the scanned ultrasonic arrays. Additionally, hybrid of sliding window method and calibration method with sound field are introduced in the process of implementing Fast-VTFM. Comparative experiments have been conducted on various test blocks. The results show that the proposed Fast-VTFM can accurately characterize the normal direction of reflectors in which reducing the computation time by 46%. Thus, the proposed calibration method can be used not only for small-aperture calibration of VTFM but also for real-time detection. Demo code will be updated on https://github.com/Horizon-line/Fast-VTFM.