A theoretical study of the dispersion relations for several types of composite laminates allowed the manufacturing of a couple of transducers described in the paper. These prototypes are designed to work on the surface. Their geometrical parameters correspond to a given set of frequencies for a particular lay-up, but an appropriate electronic allows to work at any frequency according to the <<phased array>> method. The total height is about 3 mm.

As the mobility was essential to characterize the transducers (different plates to inspect, changing the distance between the transmitting and the receiving transducers), it was impossible to stick the piezoelectric elements onto the composite material. Therefore, a glass slide was used as a support and the PZT plate was welded onto it before the cutting it out.

Compared with the angled transducers, the prototypes showed their ability to work at higher frequencies. The Lamb wave generation is improved when the wavelength is equal to a multiple of the element spacing with the <<in-phase>> method (no delay between the signals applied to the piezoelectric elements). Nevertheless, the duration of the response may be increased with this method. Then, it seems to be more suitable to apply the same signal to each element of the array with different phases (<<phase array>> method).

Another problem that crops up during the tests is the wave- propagation in the glass slide. These waves are likely to increase the duration of the signals, and reduce the inspection- resolution. The new prototypes are designed in order to remove the support between the active elements and the plate to be inspected. The results allow the comparison with the transducers previously described.