Caratterizzazione di sorgenti acustiche non convenzionali per l'impiego dei test non distruttivi

Innovation in sound source technology gives to the applied acoustics field new opportunities for advanced methods and for modern approaches in non-destructive testing. Specific requirements in the experimental practice orient the research towards smarter and more performing instruments. The researchers look for those technological solutions that guarantee the easiest measuring conditions, are not time consuming while providing very accurate data, or obtain punctual results on non-homogeneous materials, and allow the monitoring of their conservation state through periodic tests. Last generation acoustic sources have been selected for this study, a parametric array operating in air and two plane wave flat panels; their sound emission properties were analyzed, i.e. the width of the characteristic frequency band and the pressure field. These sources are small sized transducers characterized by a very narrow directivity pattern, particularly interesting for field (on site) applications. The objective of the characterization of these sources is the assessment of their suitability for the integration into some measuring systems, in particular those for the determination of the sound absorbing properties of heterogeneous materials and structures. Two specific applications directed both the initial choice of the sources' typology and the final evaluation criteria. The first one is related to a non-invasive diagnostic method of paintings like frescoes, ceramics and panel paintings, for revealing detachments of the pictorial film from the support. Some examples of in situ investigation are presented, where a commercial parametric array is integrated in the experimental apparatus. The second application aims at the determination of the sound absorbing properties of road pavements and acoustic barriers. The authors briefly review the critic aspects of some international standards such as the ADRIENNE method (UNI ISO 13472-1:2004), for which the plane wave flat panels have been selected. In this case, on the basis of the characterization's outcomes, the potential use of the plane wave source is considered, while at present the realization of field measurements are still under examination with other potential partners.