Three-dimensional thermographic imaging using a virtual wave concept

TL;DR

This paper introduces a novel 3D thermographic imaging method based on ultrasonic image reconstruction techniques, using a virtual wave concept to improve resolution and reduce artifacts in thermographic measurements.

Contribution

It presents a new two-stage algorithm that enables 3D thermographic imaging by transforming temperature data into a virtual signal suitable for ultrasonic imaging methods.

Findings

Resolution is proportional to structure depth.

Artifacts from limited view can be mitigated with multiple measurement planes.

The method is validated through simulations and experiments.

Abstract

In this work, it is shown that image reconstruction methods from ultrasonic imaging can be employed for thermographic signals. Before using these imaging methods, a virtual signal is calculated by applying a local transformation to the temperature evolution measured on a sample surface. The introduced transformation describes all the irreversibility of the heat diffusion process and can be used for every sample shape. To date, one-dimensional methods have been primarily used in thermographic imaging. The proposed two-stage algorithm enables reconstruction in two and three dimensions. The feasibility of this approach is demonstrated through simulations and experiments. For the latter, small steel beads embedded in an epoxy resin are imaged. The resolution limit is found to be proportional to the depth of the structures and to be inversely proportional to the logarithm of the signal-to-noise ratio. Limited-view artefacts can arise if the measurement is performed on a single planar detection surface. These artifacts can be reduced by measuring the thermographic signals from multiple planes, which is demonstrated by numerical simulations and by experiments performed on an epoxy cube.