Emissivity-independent spatiotemporal thermal anomaly detection in metal components using transmission-mode phase measuring deflectometry

Trivedi R, Sharma S, Trivedi V, Sharma R, Groves RM, Sheoran G, Anand A (2026)

Publication Type: Journal article

Publication year: 2026

Journal

Optics and Laser Technology Elsevier

Book Volume: 203

Article Number: 115664

DOI: 10.1016/j.optlastec.2026.115664

Abstract

Non-destructive evaluation of components often relies on infrared thermography, yet metallic and highly conductive surfaces provide weak radiative contrast and require emissivity calibration. We present an emissivity-independent optical approach for rapid spatiotemporal heat-flow mapping and subsurface anomaly detection using transmission-mode phase measuring deflectometry (PMD). A sinusoidal fringe field is imaged through a transparent sensing medium in thermal contact with a thermally stimulated specimen. Thermal diffusion into the sensing medium creates transient temperature gradients; via the thermo-optic effect, these gradients induce refractive-index gradients that modulate the fringe field, enabling an estimation of the temperature-gradient field from the retrieved phase. A coupled experimental–numerical framework is used for quantitative validation: COMSOL-predicted and PMD-derived ROI-averaged vertical temperature-gradient show close agreement over the 0–3 s early-time window, with a root-mean-square error of 0.074 K/mm. Varying the applied thermal load from 5 K to 55 K yields an approximately linear phase response with a system responsivity of 0.0399 rad per unit applied ΔTapp (defined between the hot-water reservoir and the imaging chamber at t=0). Demonstrations on representative anomaly classes (dissimilar-material interface, localized low-conductivity insert, and void-type discontinuity) show clear localization of subsurface thermal anomalies within the first few seconds after stimulation, supporting rapid anomaly indication when radiative techniques are constrained.

Involved external institutions

National Institute of Technology Delhi / राष्ट्रीय प्रौद्योगिकी संस्थान दिल्ली IN India (IN) Delft University of Technology (TU Delft) NL Netherlands (NL) Sardar Patel University (SPU) IN India (IN)

How to cite

APA:

Trivedi, R., Sharma, S., Trivedi, V., Sharma, R., Groves, R.M., Sheoran, G., & Anand, A. (2026). Emissivity-independent spatiotemporal thermal anomaly detection in metal components using transmission-mode phase measuring deflectometry. Optics and Laser Technology, 203. https://doi.org/10.1016/j.optlastec.2026.115664

MLA:

Trivedi, Ragni, et al. "Emissivity-independent spatiotemporal thermal anomaly detection in metal components using transmission-mode phase measuring deflectometry." Optics and Laser Technology 203 (2026).

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