Pseudo-noise pulse-compression thermography: a powerful tool for time-domain thermography analysis

TL;DR

This paper introduces a novel pulse-compression thermography method using pseudo-noise excitation and advanced processing to suppress sidelobes, enhancing thermography analysis by improving image clarity and interpretability.

Contribution

It presents a new pulse-compression thermography technique that effectively suppresses sidelobes, addressing a key limitation of previous correlation-based thermography methods.

Findings

Effective sidelobe suppression demonstrated in thermograms

Improved interpretability of thermography data

Enhanced signal-to-noise ratio in measurements

Abstract

Pulse-compression is a correlation-based measurement technique successfully used in many NDE applications to increase the SNR in the presence of huge noise, strong signal attenuation or when high excitation levels must be avoided. In thermography, the pulse-compression approach was firstly introduced in 2005 by Mulavesaala and co-workers, and then further developed by Mandelis and co-authors that applied to thermography the concept of the thermal-wave radar developed for photothermal measurements. Since then, many measurement schemes and applications have been reported in the literature by several groups by using various heating sources, coded excitation signals, and processing algorithms. The variety of such techniques is known as pulse-compression thermography or thermal-wave radar imaging. Even despite the continuous improvement of these techniques during these years, the advantages of using a correlation-based approach in thermography are still not fully exploited and recognized by the community. This is because up to now the reconstructed thermograms' time sequences after pulse-compression were affected by the so-called sidelobes. This is a severe drawback since it hampers an easy interpretation of the data and their comparison with other thermography techniques. To overcome this issue and unleash the full potential of the approach, this paper shows how it is possible to implement a pulse-compression thermography procedure capable of suppressing any sidelobe by using a pseudo-noise excitation and a proper processing algorithm.