Cylindrical and quasi-cylindrical focalization of air-coupled single element and linear array transducers

The availability of better air-coupled transducers have made possible many different applications. In particular, air-coupled ultrasound is a good solution for the inspection/study of flat/plate materials than can not be wetted by working in through transmission, but experience some problems with curved surfaces. Another successful application is for the generation/reception of Lamb waves using the coincidence principle. However, this technique tunes the energy to one particular mode and is very sensitive to thickness variations, roughness of the plate, local anisotropy or when the system is subjected to vibrations. Some other times, when several modes are to be observed simultaneously (e.g. laser generation) this can also become a problem.