Nondestructive thermographic detection of internal defects using pixel-pattern based laser excitation and photothermal super resolution reconstruction

TL;DR

This paper introduces a novel, high-resolution, nondestructive thermographic method using pixel-pattern laser excitation and numerical reconstruction, significantly improving defect detection speed and accuracy in metal samples.

Contribution

It presents a new approach combining pixel-pattern laser heating with photothermal super resolution, utilizing high-power DLP projectors and a numerical inversion method for defect imaging.

Findings

Outperforms conventional thermographic techniques in defect detection.

Reduces measurement time by a factor of 8.

First application of high-power DLP projectors for structured thermography.

Abstract

In this work, we present a novel approach to photothermal super resolution based thermographic resolution of internal defects using two-dimensional pixel pattern-based active photothermal laser heating in conjunction with subsequent numerical reconstruction to achieve a high-resolution reconstruction of internal defect structures. With the proposed adoption of pixelated patterns generated using laser coupled high-power DLP projector technology the complexity for achieving true two-dimensional super resolution can be dramatically reduced taking a crucial step forward towards widespread practical viability. Furthermore, based on the latest developments in high-power DLP projectors, we present their first application for structured pulsed thermographic inspection of macroscopic metal samples. In addition, a forward solution to the underlying inverse problem is proposed along with an appropriate heuristic to find the regularization parameters necessary for the numerical inversion in a laboratory setting. This allows the generation of synthetic measurement data, opening the door for the application of machine learning based methods for future improvements towards full automation of the method. Finally, the proposed method is experimentally validated and shown to outperform several established conventional thermographic testing techniques while conservatively improving the required measurement times by a factor of 8 compared to currently available photothermal super resolution techniques.