An overview of the development of the acoustic imaging ACEADD technique: the sound of frescoes

A review of the fifteen years experience in the development of an acoustic imaging technique, denominated ACoustic Energy Absorption Diagnostic Device - ACEADD, is presented in order to analyze the key factors addressing innovation in the field of Conservation Science. To extensively characterize complex and heterogeneous structures such as mural paintings on site, an experimental method and the relative device were purposely implemented. The equipment uses back reflection geometry and a non contact setup, scans a portion of the investigated painting, radiating towards the surface an acoustic wave with audible frequency content and recording the reflected wave. Applying a suitable signal processing, the system provides acoustic images of the surface, localizing the defects where the acoustic energy absorption is considerable [1-3]. Firstly the laboratory validation of the method was functional to the patenting process, afterwards the activity was oriented to field validation facing different experimentations. Mainly it was focused on the optimization of the measurement setup and procedure, the automation and software customization for data acquisition and processing, the device portability [1-3]. The investigations have examined the applicability to different kinds of artefacts, ranging from frescoes to glazed ceramic tiles and to panel paintings, while the spatial resolution was recently improved employing a last generation and highly directive sound source. Some important metrological aspects such as the repeatability of measurements, the evaluation of the uncertainty and the device calibration procedure were carefully analyzed, gathering evidences for facing a potential standardization process [4-9]. Thus few key factors for the advancement of an innovative technology can be identified: a suitable metrological approach for the assessment of the method's applicability; the construction of a joint environment for a systematic and participated field experimentation; an accurate planning of significant comparisons between different methodologies; a constant attention towards measuring procedure optimization and technical innovations. Keywords: Acoustic Imaging; Detachments; Frescoes; Glazed Ceramic Tiles; Panel Paintings. References: [1] G. B. Cannelli, P. Calicchia, Nondestructive acoustic method and device, for the determination of detachments of mural paintings, European Patent EP1190243B1 (2006); US Patent US 6728661 (2004); PCT N. PCT/IT00/00244 (2000); Italian Patent N. RM 99 A000410 (1999). [2] P. Calicchia, G. B. Cannelli, Revealing surface anomalies in structures by in situ measurement of acoustic energy absorption, Applied Acoustics, vol 63, issue 1, 43-59 (2002). [3] P. Calicchia, G. B. Cannelli, Detecting and mapping detachments in mural paintings by non-invasive acoustic techniques: measurements in antique sites in Rome and Florence, Journal of Cultural Heritage, 6 (2), 2005, pp. 115-124. [4] G. B. Cannelli, P. Calicchia, Non-invasive method for detecting detachments in mural paintings: validation of laboratory models and application to frescoes, The frescoes of Casa Vasari in Florence Umberto Baldini, Pietro Alessandro Vigato, Edizioni Polistampa, 2006, p. 99. [5] P. Calicchia, P. Tiano, I principii della metrologia scientifica nelle metodologie applicate ai beni culturali: aspetti critici e peculiarità, Proceedings of the 35th National Congress of the Associazione Italiana di Acustica, 2009 (Torino). [6] P. Calicchia, J. M. Mimoso, Investigation on the presence of detachments of glazed ceramic tile panels by means of non destructive acoustic mapping, LNEC Report 134/2010, 2010. [7] P. Calicchia, J. M. Mimoso, D. M. Rodrigues Costa, In situ acoustic imaging to reveal glaze delaminations, in the early stages, in Portuguese azulejos, Proceedings of the International Conference ART'11, April 2011 (Florence). [8] P. Calicchia, M. Favaro, P. Bison, E. Grinzato, P. A. Vigato, Acoustic diagnostics versus Thermography: comparison and integration as a basic approach for cultural heritage preservation. Proceedings of the 5th International Congress: Science and Technology for the safeguard of Cultural Heritage in the Mediterranean Basin, Nov 2011 (Istanbul), pp. 22-25 [9] P. Calicchia, S. De Simone, L. Di Marcoberardino, J. Marchal, Near- to far-field characterization of a parametric loudspeaker and its application in non-destructive detection of detachments in panel paintings, Applied Acoustics 73 (12), 2012, pp. 1296-1302, Special Issue: Parametric Acoustic Array: Theory, Advancement and Applications.