[3C1] Lighting the blind zone of ultrasonic phased array probes
L Couret and N Paul
EDF R&D PRISME, France
The context of this work is the non-destructive examination of material that generates significant structural noise. We use an ultrasonic array probe and focus on the first inspected millimetres, usually considered as a ‘blind zone’ because of the sub-surface waves. A first approach was proposed in a previous work, where some post-processing of the imaging results was derived from a learning zone defined on several sensor positions. This approach gives good results, with a significant increase in the signal-to-noise ratio. Yet it requires the difficult definition of a learning area, which has to be defect-free and statistically representative of the noise in the controlled zone. In this work, a new approch is proposed that does not require any learning area. The processing is performed on the full matrix capture (FMC) acquisitions and consists of removing a significant amount of noise from the acquisitions to improve imaging results. To do this, acquisitions are divided into groups in which a principal component analysis (PCA) is performed. Then, we remove from each acquisition the projection of itself on eigenvectors associated with the largest eigenvalues. As a result, the noise component is reduced and the defect information is enhanced.
