New method for real-time dynamic focusing through interfaces

In nondestructive evaluation (NDE) a coupling medium (wedge) is frequently inserted between the array probe and the object being evaluated. In this situation, focal law computing is complicated by the refraction effects at the interface. Furthermore, there are not known techniques to perform dynamic focusing by hardware in these conditions. This work addresses these problems by following a two-step procedure. First, a virtual array that operates in a single medium with nearly equivalent time-of-flight to the foci is obtained. Then, simple hardware is proposed to perform dynamic focusing in real-time. It operates with arrays of any geometry as required by the virtual array in presence of arbitrarily shaped interfaces. The paper describes the theory and evaluates the timing errors of the approximations made. These errors are low enough to allow use of the new technique in most NDE and some specific medical applications. The new technique is validated by simulation and experimentally.