Real-time 3D imaging with Fourier-domain algorithms and matrix arrays applied to non-destructive testing

International audience; Real-time 3-D ultrasound imaging with matrix arrays remains a challenge in Non-Destructive Testing (NDT) due to the time-consuming reconstruction algorithms based on delay-and-sum operations. Other algorithms operating in the Fourier domain have lower algorithmic complexities and therefore higher frame rates at the cost requiring more storage space, which may limit the number of reconstruction points. In this paper, we present a 3-D real-time implementation of the Total Focusing Method (TFM) and the Plane Wave Imaging (PWI), as well as of their Fourier-domain counterparts, referred to as k-TFM and k-PWI. For both acquisition types, the Fourier-domain algorithms are used to increase frame rates, and they are compared to the time-domain TFM and PWI in terms of image quality, frame rates and memory requirements. In order to greatly reduce their memory requirements, a new implementations of k-TFM and k-PWI are proposed. The four imaging methods are then evaluated in real time on a block of stainless steel made by additive layer manufacturing using a laser powder bed fusion process and containing a 3-D network of spherical porosities.