The use of pulse-compression thermography for detecting defects in paintings

S Laureti,S Sfarra,H Malekmohammadi,P Burrascano,D.A Hutchins,L Senni,G Silipigni,X.P.V Maldague,M Ricci

doi:10.1016/j.ndteint.2018.05.003

Abstract

Interest in the conservation of paintings grows year by year. Their periodic inspection is essential for their conservation over the time. Thermographic non-destructive inspection is one technique useful for paintings, but it is essential to be able to detect buried defects while minimising the level of thermal stimulus. This paper describes a pulse-compression infrared thermography technique whereby defect detection is optimized while minimising the rise in temperature. To accomplish this task, LED lamps driven by a coded waveform based on a linear frequency modulated chirp signal have been used on paintings on both a wooden panel and a canvas layer. These specimens contained artificially fabricated defects. Although the physical condition of each painting was different, the experimental results show that the proposed signal processing procedure is able to detect defects using a low temperature contrast.

Highlights

Active Thermography (AT) is a Non-Destructive Evaluation (NDE) technique widely used in different fields of research and industrials applications, as in material characterization [1], food inspection [2] and in cultural heritage diagnostic [3]
This paper describes a pulse-compression infrared thermography technique whereby defect detection is optimised while minimising the rise in temperature
The use of low-power excitation is desirable in such cases, but this leads to a significant reduction of the Signal to Noise Ratio (SNR) that could affect the effectiveness of the Pulsed Thermography (PT) analysis

Summary

Introduction

Active Thermography (AT) is a Non-Destructive Evaluation (NDE) technique widely used in different fields of research and industrials applications, as in material characterization [1], food inspection [2] and in cultural heritage diagnostic [3]. PT is relatively simple to use, care should be taken when applying a pulsed stimulus to cultural objects such as paintings This is because abrupt variations of the sample temperature could create thermal shocks and damage to the sample, these can be anticipated using numerical simulations centred on heat transfer phenomena [14,15]. The frequency content of the coded signal can be tailored to suit the investigation of a given sample, while T can be increased almost arbitrarily to achieve the desired SNR [34,35,36,37] These properties can be usefully applied to inspect paintings, using low-power heating sources to keep surface temperatures relatively low. In [38] the thermal source consisted of halogen lamps driven by a pseudo-random code while in the present paper the heating stimulus is realized with LEDs driven by a chirp signal

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Results

Conclusion