Gradual total focusing method ultrasonic imaging in frequency-wavenumber domain

In order to improve the speed and quality of total focusing method,a Gradual Total Focusing Method ultrasonic imaging in Frequency-Wavenumber domain（GTFM-FW） is proposed.The method starts with a full-matrix capture by collecting the full aperture echo data preceded by sequentially activating each element on the ultrasonic transducer.The echo data located on one or multiple diagonals of the full matrix is selected and transformed to frequency-wavenumber domain spectrums by Fourier transform,which is then aligned and summed together.The final image is produced by a Stolt mapping and inverse Fourier transform.To verify the validity of this algorithm,detailed imaging experiments are performed both on simulated point targets and ultrasonic test blocks.The results show that the method proposed in this article enables imaging quality trade-off between image resolution and sidelobe interference by adjusting the proportion of full-matrix data used for imaging.Furthermore,the frequency-wavenumber approach yields better resolution performance than traditional total focusing method as well as lower computational cost.