Development, experimental validation and tuning of a contact-less technique for the health monitoring of antique frescoes

Monitoring of the health and the conservation state of artistic heritage is nowadays of great interest. It involves various fields of the applied research. In particular, several techniques aimed to determine the state of preservation of antique frescoes through non-invasive (NI) and non-destructive (ND) methods have been recently subjected to a considerable evolution.In this work the authors show the results of some experimental validation of a NI&ND vibro-acoustic technique. The diagnostic technique, based on the application of the Laser Doppler Vibrometry with acoustic excitation, is a non-invasive method of measurement of superficial vibrations.This methodology is still scarcely available due to the lack of experimental data needed for a reasonable choice of operating parameters. Therefore, this set of methods has been applied in many laboratory tests with a proper variety of specimens, in such a way to reproduce many of the characteristic sub-superficial detachments of a damaged antique frescos. The laboratory tests have been carried out using two main sources of excitation: contact excitation (impact test) and contact-less excitation (acoustic test). Thought impact test is not adoptable in the “real life”, it has been used as a benchmark to validate the contact-less method.Through the comparison of different zones' dynamic behavior, it is possible to distinguish among surely non-damaged zones, damaged by detachment zones, uncertain zones. One of the targets of this work, in fact, has been to properly tune the method in order to restrict as much as possible the uncertain zone.