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phased-array technologies

Surface-Adapting ULtrasound (SAUL)

The SAUL technique enables the transmission of an incident wave-front parallel to any complex surface. One specimen presenting variable geometries (flat, concave or convex surfaces) can be entirely controlled using a unique probe (such as a matrix array with a flat active aperture). This is achieved by means of an iterative algorithm that does not require the knowledge of the geometrical and acoustical properties of the component undergoing inspection. The real-time adaptive processing is illustrated through measurements obtained with typical aircraft composite structures (e.g., CFRP stringers, stiffeners).

The principle of the SAUL algorithm may be decomposed as follows. The first step consists in transmitting a plane wave with the full array and recording elementary signals in parallel for all channels. The B-scan obtained is displayed in the figure below.


SAUL method M2M


As the exited wave is not normally incident on the surface, the consecutive plies inside the material (each ply being approximately parallel to the surface) deviate the transmitted field. This results in a poor image where the back-wall interface of the specimen cannot be identified.

The second step consists in adapting the incident wave to the surface geometry. This process relies on measuring the times of flight between all elements of the array and the surface (e.g., by detecting the maxima of the surface echo envelope). These times of flight are used to extract a delay law that will be applied to a second transmission. A reception delay law can also be applied in order to synchronize received elementary signals and to create several coherent summations of signals via electronic scanning of a sub-aperture. This algorithm is iterative and converges after a couple shots (e.g., 3 shots per position).


SAUL method M2M

Figure: example of surface adapting using the SAUL algorithm

The SAUL algorithm has been implemented on M2M MultiX systems. An industrial application has been achieved with CONTOUR DYNAMICS (formerly MECNOV) and EADS (AIRBUS parts). This method may be extended to many other industrial projects, such as the inspection of turbine blades, wavy plates, and all types of metallic/composite structures presenting irregular surfaces.


N. Dominguez, G. Ithurralde, ‘Ultra-fast Ultrasonic Inspection for Aeronautical Composites using Paintbrush Acquisitions and Data Processing on GPU’, European Conference on NDT, Moscow, 2010.

A. Maurer, W. Haase, W. De Odorico, ‘Phased Array Application in Industrial Scanning Systems’, ECNDT Proceeding, September 2006.

S. Robert, O. Casula, M. Njiki, O. Roy, ‘Assessment of Real-Time Techniques for Ultrasonic Nondestructive Testing’, Review of Progress in QNDE, in press, 2012.

S. Robert, O. Casula, A. Nadim, ‘Procédé de Commande de Transducteurs d’une Sonde à Ultrasons, Programme d’Ordinateur et Dispositif de Sondage par Ultrasons’, France Patent No FR 10/56217, July 2010.

S. Robert, O. Casula, E. Iakovleva, ‘Procédé de Détermination d’une Surface d’un Objet par Sondage Echographique, Programme d’Ordinateur Correspondant et Dispositif de Sondage à Ultrasons’, France Patent No FR 11/60399, November 2011.