Ultrasonic leaky rayleigh wave imaging using extended phase shift migration and image fusion

Ultrasonic leaky Rayleigh wave enables easy automated detection of surface or sub-surface defects due to its non-contact detection advantages. The existing leaky Rayleigh wave detection methods using single transducer suffer from low focused energy and short detection range. To solve these problems, this paper adopts the detection method of leaky Rayleigh wave generated by phased array, and proposes an imaging algorithm using extended phase shift migration (EPSM) and image fusion. Firstly, the virtual source-based extended phase shift migration (VSEPSM) algorithm is proposed to enhance the effective detection distance by increasing the energy of the transmitting elements. Then, the fast Fourier transform (FFT) interpolation algorithm is employed to enhance the lateral detail representation in EPSM and VSEPSM imaging, improving the imaging quality. Finally, a custom image fusion method is used to perform arithmetic processing on the imaging amplitudes at corresponding positions in EPSM and VSEPSM imaging, merging the detection advantages of EPSM and VSEPSM at different distances. Compared to traditional time-domain full focusing (TFM) imaging, the imaging algorithm proposed in this paper achieves better imaging performance for defects at relatively distant locations, with a 5.94 dB increase in average signal-to-noise ratio (SNR) and a 61.4% improvement in imaging efficiency. This provides an effective method for detecting surface and sub-surface defects in the industrial field.