Saft-reconstruction in ultrasonic immersion technique using phased array transducers

Abstract

The two main preconditions for the application of the Synthetic Aperture Focusing Technique (SAFT) are: (i) a large divergence of the sound beam of the transducer and (ii) an exact knowledge about the sound propagation path. These requirements are easily fulfilled for point sources directly mounted on the surface of the specimen. In many cases, however, the transducer is wedge mounted and/or coupled using a water delay line, e.g. in immersion technique. These delay lines change the beam index and the propagation path has to be evaluated for each pixel separately considering Fermat's principle. Using phased array transducers, a sector scan can improve the divergence of the sound beam. The introduced method combines the advantages of using a phased array transducer in immersion technique to improve SAFT reconstruction. An algorithm is presented accounting the influence of the delay line on the reconstruction method. The applicability of the algorithm is shown by validation with simulated echo responses and with experimental results collected from a specimen with artificial flaws.