The use of ultrasonic arrays in the field of non-destructive evaluation of composites is a recent technique. This method offers the possibility to achieve fast inspection of components having complex geometries. As compared with the single element transducers, arrays configuration yields more effective detection of defects. However, to achieve adequate imaging by ultrasonic array elements, each element should be excited according to a specific sequence which is called the focal law. At each instant a subset of the array elements is activated and the incident waves are better directed to scattered at the defect. The reflected signals can then be more intensified. In this work, two-dimensional approximation of wave propagation problem was supposed. Array elements with linear geometry and with the elements assumed to be fully coupled with the composite panel were considered. A delamination defect was inserted between the plies of the composite panel at a given depth. The forward model enabling to simulate ultrasonic array data was built by means of the FEM. As each focal position requires a different focal law that fixes a proper protocol of excitation and reception, synthesis of these focal laws was studied. Optimization of signal focalization and reception as function of the delamination extent was achieved.

In this work, a numerical method is proposed in order to achieve design optimisation of phased array (PA) probes for the special application of defects detection in thin films. This approach relies on an extended Fourier-based model that was adapted to predict the two-dimensional ultrasonic displacement field taking place in a thin plate under individual excitation of PA probe elements which have arbitrary orientation with respect to the examined part surface. Excitation is applied through a fluid couplant and is operated at scheduled delays that are managed to enable emission of constructive pulses. This gives the possibility to steer sound waves towards a direction and to focalize the beam in a selected point. An optimisation algorithm based on the concept of pattern search that does not require evaluation of a gradient was used to find the best match in the multidimensional analysis space of possibilities including the elements orientation angles, the elements lengths, the inter-elements distances and work frequency. Optimisation was performed with the objective to maximize the displacement amplitude at the focal point while minimizing simultaneously the effect of beam side lobes. The results obtained by this approach reveal that focalisation can be achieved with enhanced features in comparison with previous algorithms assuming linear elements that are parallel to the surface of the plate.