Improving elevation resolution in phased-array inspections for NDT

The Phased Array Ultrasonic Technique (PAUT) offers great advantages over the conventional ultrasound technique (UT), particularly because of beam focusing, beam steering and electronic scanning capabilities. However, the 2D images obtained have usually low resolution in the direction perpendicular to the array elements, which limits the inspection quality of large components by mechanical scanning. This paper describes a novel approach to improve image quality in these situations, by combining three ultrasonic techniques: Phased Array with dynamic depth focusing in reception, Synthetic Aperture Focusing Technique (SAFT) and Phase Coherence Imaging (PCI). To be applied with conventional NDT arrays (1D and non-focused in elevation) a special mask to produce a wide beam in the movement direction was designed and analysed by simulation and experimentally. Then, the imaging algorithm is presented and validated by the inspection of test samples. The obtained images quality is comparable to that obtained with an equivalent matrix array, but using conventional NDT arrays and equipments, and implemented in real time.