Wideband Nonuniformly Excited Focused Transducers — Theory and Experiments

In an earlier study [1], we discussed the interest of wideband nonuniform transducers in nondestructive testing (NDT). Only flat transducers were studied. Since that, we have developed a new technique that combines in a single probe three different modes: a conventional uniform mode, a mode favoring the plane wave component leading to a diffractionless beam and a mode favoring the edge diffracted wave leading to a focusing effect. This original technique is fully described in [2]. Here, we study the influence of nonuniform source profile on the characteristics of the field radiated by wideband focused transducers, as compared to conventional focused transducers with uniform profile. Classically, the transient field radiated by a conventional spherically focused transducer is described as the superposition of a geometric wave (a spherical wave converging to the focal point then diverging) and of diffracted edge wave [3]. Two nonuniform profiles are studied, both theoretically and experimentally which favor either one or the other contribution.