Characterization of a parametric loudspeaker and its application in NDT

The parametric loudspeaker combines the high directivity at the audio frequencies with the small size of the transducer, thanks to the nonlinear interaction of finite-amplitude ultrasonic waves. These properties make this class of sources an attractive investigation tool especially for non destructive testing (NDT). Till now the research has been mainly focused on the optimization of the transducer and the signal pre-processing, while only recently actual applications mainly in the field of material's acoustical characterization are emerging. The authors present the analysis of the pressure field generated by a commercial parametric loudspeaker integrated in a system purposely developed for acoustic diagnostics on objects of heritage interest. It was used in an investigation on the renaissance panel painting Annunciazione by the Italian artist Benozzo Gozzoli (XV century) revealing pictorial film detachments. Preliminary results are here presented, disclosing the potential of the parametric loudspeaker for the enhancement of the spatial resolution in the acoustic measurement, of the non invasiveness of the investigation tool, and also of the operator comfort.