Plane Wave Imaging for ultrasonic non-destructive testing: Generalization to multimodal imaging

• A Plane Wave Imaging (PWI) method is proposed for ultrasonic non destructive testing.
• The method is applied to multimodal imaging of solids in immersion.
• Comparisons between Plane Wave Imaging and Total Focusing Method are given.
• PWI is less sensitive to incoherent noise and provides better images for cracks.

This paper describes a new ultrasonic array imaging method for Non-Destructive Testing (NDT) which is derived from the medical Plane Wave Imaging (PWI) technique. The objective is to perform fast ultrasound imaging with high image quality. The approach is to transmit plane waves at several angles and to record the back-scattered signals with all the array elements. Focusing in receive is then achieved by coherent summations of the signals in every point of a region of interest. The medical PWI is generalized to immersion setups where water acts as a coupling medium and to multimodal (direct, half-skip modes) imaging in order to detect different types of defects (inclusions, porosities, cracks). This method is compared to the Total Focusing Method (TFM) which is the reference imaging technique in NDT. First, the two post-processing algorithms are described. Then experimental results with the array probe either in contact or in immersion are presented. A good agreement between the TFM and the PWI is observed, with three to ten times less transmissions required for the PWI.