High resolution Autofocused Virtual Source Imaging (AVSI)

Synthetic aperture focusing technique with arrays (SAFT) provides improved lateral resolution but, when a coupling medium is between the probe and the part, refraction complicates time-of-flight computations. This slows down the imaging process since there are not general formulae for arbitrarily shaped interface. The approach of the AVSI proposed method is to generate, by conventional delay and sum beamforming, a set of foci at different points of the interface. These act as virtual sources and SAFT processing can be carried out in the second medium only, avoiding refraction complications. Furthermore, an automated process for locating the virtual sources from ultrasound measurements and to compute the adapted focal laws in emission and reception is proposed, so knowledge of the part shape geometry is not required. Theoretical bases of the Autofocused Virtual Source Imaging method (AVSI) are presented, along with experimental data that confirms the expected performance.