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Open AccessArticle

Beyond the Page: Solar Loading Thermographic Imaging and Predictive Modeling for Ancient Book Diagnostics—Preliminary Results

by Elena Marini, Gilda Russo, Hai Zhang and Stefano Sfarra

Sensors 2026, 26(4), 1358; https://doi.org/10.3390/s26041358 - 20 Feb 2026

Viewed by 529

Abstract

This study investigates the application of NDTs for the detection of sub-surface defects in an ancient book, with the aim of improving conservation methods in the field of cultural heritage. A sequence of thermographic images in a solar loading thermography (SLT) scenario was acquired during a diagnostic campaign in Harbin, China, to identify four distinct fabricated dowels made of Wool, Rubber, Teflon^®, and Synthetic material. The images were processed in two ways: the first combined advanced image-processing methods: pre-processing via MdFIF, post-processing, PCT and RPCT, applied both to the original sequence and to the MdFIF-filtered thermograms. The second approach employed numerical simulations in COMSOL Multiphysics^® to develop a predictive thermal model. The comparison of localized thermal anomalies obtained from the two approaches demonstrated the capability of NDTs to reliably reveal artificial defects, confirming their suitability for diagnostic conservation. Overall, the integration of advanced image processing with numerical simulation enhances diagnostic accuracy, particularly for subtle or low-contrast anomalies, thereby enabling more informed condition assessment and supporting rapid, targeted, and preventive conservation strategies. Full article

(This article belongs to the Section Physical Sensors)

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21 pages, 2046 KB

Open AccessArticle

Thermographic Diagnosis of Corrosion-Driven Contact Degradation in Power Equipment Using Infrared Imaging and Color-Channel Decomposition

by Milton Ruiz and Carlos Betancourt

Energies 2026, 19(3), 766; https://doi.org/10.3390/en19030766 - 1 Feb 2026

Viewed by 458

Abstract

This study presents a measurement–modeling pathway for diagnosing corrosion-driven contact degradation in power equipment using infrared thermography and color-channel analysis. Thermal data were acquired with a Fluke Ti450 (LWIR, 7.5–14 μm) under typical high-altitude, temperate conditions in Quito, Ecuador. Radiometric parameters (emissivity, distance, ambient/reflected temperature, and humidity) are reported explicitly, and images are processed with a reproducible pipeline that combines adaptive thresholding, morphology, and region-of-interest statistics, including

Δ T

relative to a reference region. A worked example links an observed hotspot to emissivity-corrected temperature and discusses qualitative implications for the effective contact resistance

R_{eff}

. Uncertainty is summarized through a per-case template that propagates

u_{Δ T}

u (R_{eff})

and Weibull characteristic life

η

. Environmental influences (solar load, wind, and emissivity variability) are acknowledged and mitigated. Two field cases illustrate the approach to substation assets. Because the dataset comprises single-visit inspections, formal parameter estimation (e.g., EIS-validated

R_{eff}

and full Weibull/Arrhenius fits) is reserved for longitudinal follow-up. By making radiometry, processing steps, and limitations explicit, the study reduces ambiguity in the transition from temperature contrast to physics-based interpretation and supports auditable maintenance decisions. Full article

(This article belongs to the Section F: Electrical Engineering)

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4 pages, 984 KB

Open AccessAbstract

Multiphysics-Enabled Digital Twin Framework for Solar Loading Thermography-Based Wood Structure Strength Prediction

by Yinuo Ding, Zhiyang Zhang, Gilda Russo, Stefano Sfarra and Hai Zhang

Proceedings 2025, 129(1), 5; https://doi.org/10.3390/proceedings2025129005 - 12 Sep 2025

Viewed by 661

Abstract

In this study, we employ solar loading infrared thermography to non-invasively assess the internal defects and degradation of the millennium-old composite wooden columns at Baoguo Temple [...] Full article

(This article belongs to the Proceedings of The 18th International Workshop on Advanced Infrared Technology and Applications)

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15 pages, 3025 KB

Open AccessArticle

Impacts of Atmospheric and Load Conditions on the Power Substation Equipment Temperature Model

by Osni Silva Junior, Jose Carlos Pereira Coninck, Fabiano Gustavo Silveira Magrin, Francisco Itamarati Secolo Ganacim, Anselmo Pombeiro, Leonardo Göbel Fernandes and Eduardo Félix Ribeiro Romaneli

Energies 2023, 16(11), 4295; https://doi.org/10.3390/en16114295 - 24 May 2023

Cited by 4 | Viewed by 2704

Abstract

Infrared thermography is a predictive maintenance tool used in substations to identify a disturbance in electrical equipment that could lead to poor operation and potential failure in the future. According to Joule’s law, the temperature of electrical equipment is proportional to the current flowing through it. Other external factors, such as solar incidence, air humidity, wind speed, and air temperature, can interfere with its operating temperatures. Based on this premise, this article aims to analyze the influence of atmospheric and load conditions on the operational cycle of thermography-monitored equipment in order to describe the operating temperature of the object using only external data and to show the impacts of external influences on the final temperature reached by the object. Five multivariate time series regression models were developed to describe the maximum equipment temperature. The final model achieved the best fit between the measured and model temperature based on the Akaike information criterion (AIC) metric, where all external variables were used to compose the model. The proposed model shows the impacts of each external factor on equipment temperature and could be used to create a predictive maintenance strategy for power substations to avoid failure. Full article

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12 pages, 6569 KB

Open AccessArticle

Estimating Thermal Material Properties Using Step-Heating Thermography Methods in a Solar Loading Thermography Setup

by Samuel Klein, Tobias Heib and Hans-Georg Herrmann

Appl. Sci. 2021, 11(16), 7456; https://doi.org/10.3390/app11167456 - 13 Aug 2021

Cited by 5 | Viewed by 2463

Abstract

This work investigates solar loading thermography applications using active thermography algorithms. It is shown that active thermography methods, such as step-heating thermography, present good correlation with a solar loading setup. Solar loading thermography is an approach that has recently gained scientific attention and is advantageous because it is particularly easy to set up and can measure large-scale objects, as the sun is the primary heat source. This work also introduces the concept of using a pyranometer as a reference for the evaluation algorithms by providing a direct solar irradiance measurement. Furthermore, a recently introduced method of estimating thermal effusivity is evaluated on ambient-derived thermograms. Full article

(This article belongs to the Special Issue Non-destructive Testing in Civil Engineering)

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20 pages, 9146 KB

Open AccessCommunication

Multiscale Analysis of Solar Loading Thermographic Signals for Wall Structure Inspection

by Katherine Tu, Clemente Ibarra-Castanedo, Stefano Sfarra, Yuan Yao and Xavier P. V. Maldague

Sensors 2021, 21(8), 2806; https://doi.org/10.3390/s21082806 - 16 Apr 2021

Cited by 7 | Viewed by 2922

Abstract

Infrared thermography has been widely adopted in many applications for material structure inspection, where data analysis methods are often implemented to elaborate raw thermal data and to characterize material structural properties. Herein, a multiscale thermographic data analysis framework is proposed and applied to building structure inspection. In detail, thermograms are first collected by conducting solar loading thermography, which are then decomposed into several intrinsic mode functions under different spatial scales by multidimensional ensemble empirical mode decomposition. At each scale, principal component analysis (PCA) is implemented for feature extraction. By visualizing the loading vectors of PCA, the important building structures are highlighted. Compared with principal component thermography that applies PCA directly to raw thermal data, the proposed multiscale analysis method is able to zoom in on different types of structural features. Full article

(This article belongs to the Special Issue Feature Papers in Physical Sensors Section 2020)

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13 pages, 6166 KB

Open AccessFeature PaperArticle

Estimating Thermal Material Properties Using Solar Loading Lock-in Thermography

by Samuel Klein, Henrique Fernandes and Hans-Georg Herrmann

Appl. Sci. 2021, 11(7), 3097; https://doi.org/10.3390/app11073097 - 31 Mar 2021

Cited by 3 | Viewed by 3253

Abstract

This work investigates the application of lock-in thermography approach for solar loading thermography applications. In conventional lock-in thermography, a specimen is subjected to a periodically changing heat flux. This heat flux usually enters the specimen in one of three ways: by a point source, a line source or an extended source (area source). Calculations based on area sources are particularly well suited to adapt to solar loading thermography, because most natural heat sources and heat sinks can be approximated to be homogenously extended over a certain region of interest. This is of particular interest because natural heat phenomena cover a large area, which makes this method suitable for measuring large-scale samples. This work investigates how the extended source approximation formulas for determining thermally thick and thermally thin material properties can be used in a naturally excited setup, shows possible error sources, and gives quantitative results for estimating thermal effusivity of a retaining wall structure. It shows that this method can be used on large-scale structures that are subject to natural outside heating phenomena. Full article

(This article belongs to the Special Issue Non-destructive Testing in Civil Engineering)

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