Automatic dynamic focusing through interfaces

An interface between the coupling medium and the inspected part is frequently found in Non Destructive Testing (NDT). When phased array technology is used, the focal laws must be obtained considering the refraction at the interface, which requires computationally intensive iterative procedures since no closed formulae exist for the general case. This work presents a new two-step approach. In the first step, the two propagation media scenario is converted into a single homogeneous medium by computing a virtual array with nearly equivalent flight times to the foci. In the second step, a focusing hardware, conveniently initialized, evaluates in real-time the sampling instants that correspond to the focal laws. Focusing errors are small enough to validate the new technique for a wide range of applications. In fact, for active apertures currently used in NDT, the resolution and dynamic range are almost not affected as it is experimentally shown. Furthermore, focal law computing time is dramatically reduced by evaluating a few parameters instead of focusing delays for every output sample, element and steering direction. The instrument focal law storage requirements become significantly reduced as well.