In the field of non-destructive evaluation, defect detection and visualization can be performed exploiting different
techniques relying either on an active or a passive approach. In the following paper the passive technique is investigated
due to its numerous advantages and its application to thermography is explored.
In previous works, it has been shown that it is possible to reconstruct the Green’s function between any pair of points
of a sensing grid by using noise originated from diffuse fields in acoustic environments. The extraction of the Green’s
function can be achieved by cross-correlating these random recorded waves. Averaging, filtering and length of the
measured signals play an important role in this process. This concept is here applied in an NDE perspective utilizing
thermal fluctuations present on structural materials. Temperature variations interacting with thermal properties of the
specimen allow for the characterization of the material and its health condition. The exploitation of the thermographic
image resolution as a dense grid of sensors constitutes the basic idea underlying passive thermography. Particular
attention will be placed on the creation of a proper diffuse thermal field, studying the number, placement and excitation
signal of heat sources. Results from numerical simulations will be presented to assess the capabilities and performances
of the passive thermal technique devoted to defect detection and imaging of structural components.
Margherita Capriotti, Simone Sternini, Francesco Lanza di Scalea, and Stefano Mariani, "Extraction of thermal Green's function using diffuse fields: a passive approach applied to thermography," Proc. SPIE 9803, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2016, 98030U (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 22, 2016; Published: 20 April 2016); https://doi.org/10.1117/12.2218998.
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