Non-Destructive Detection of Coating Delamination Using Reflected Time-Domain Terahertz Waveforms

Non-Destructive Detection of Coating Delamination Using Reflected Time-Domain Terahertz Waveforms | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Non-Destructive Detection of Coating Delamination Using Reflected Time-Domain Terahertz Waveforms Daniel Tobar, Sri Kambhampati, Anthony J. Fitzgerald, Brett Nener, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7248594/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 27 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted 9 You are reading this latest preprint version Abstract Delamination of anti-corrosion coatings from substrates compromises structural integrity by introducing thin gaps that allow ingress of corrosive agents like water. This study investigates the capability of terahertz pulsed imaging to detect air gaps thinner than a THz system's minimum resolvable thickness by measuring apparent thickness changes in overlying layers. The minimum resolvable thickness in terahertz pulsed imaging, referred to as the axial resolution, is determined by the system’s bandwidth. To test this approach, THz measurements were conducted on a 2 mm thick quartz window positioned above a metal substrate with an intervening 19 µm air gap. An increase in the apparent quartz window thickness was observed, consistent with theoretical expectations, despite the air gap remaining undetectable as a distinct reflection. This analysis was extended to multi-layered paint systems consisting of top, mid, and base coatings on steel plates. Cyclic ageing induced a delamination layer between the metal substrate and base coating, measured to be 10 µm by scanning electron microscopy. Terahertz pulsed imaging analysis showed a corresponding 9.9-13 µm increase in the apparent base coating thickness, consistent with the quartz window results. These findings demonstrate that terahertz pulsed imaging offers a non-destructive method for identifying sub-resolution air gaps, enabling early-stage detection of delamination in protective coatings. Physical sciences/Engineering Physical sciences/Materials science Physical sciences/Optics and photonics Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 27 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 05 Sep, 2025 Reviews received at journal 03 Sep, 2025 Reviews received at journal 14 Aug, 2025 Reviewers agreed at journal 13 Aug, 2025 Reviewers agreed at journal 11 Aug, 2025 Reviewers invited by journal 11 Aug, 2025 Editor assigned by journal 02 Aug, 2025 Submission checks completed at journal 01 Aug, 2025 First submitted to journal 30 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7248594","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":501248691,"identity":"53bbfab2-f16f-4c4e-b196-b7da515ed2d4","order_by":0,"name":"Daniel Tobar","email":"data:image/png;base64,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","orcid":"","institution":"University of Western Australia","correspondingAuthor":true,"prefix":"","firstName":"Daniel","middleName":"","lastName":"Tobar","suffix":""},{"id":501248692,"identity":"907decad-dd63-4886-8697-1ae1ca265f1b","order_by":1,"name":"Sri Kambhampati","email":"","orcid":"","institution":"Curtin University","correspondingAuthor":false,"prefix":"","firstName":"Sri","middleName":"","lastName":"Kambhampati","suffix":""},{"id":501248693,"identity":"d314009d-e8b1-4262-9a89-25941ee67af2","order_by":2,"name":"Anthony J. 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This study investigates the capability of terahertz pulsed imaging to detect air gaps thinner than a THz system's minimum resolvable thickness by measuring apparent thickness changes in overlying layers. The minimum resolvable thickness in terahertz pulsed imaging, referred to as the axial resolution, is determined by the system’s bandwidth. To test this approach, THz measurements were conducted on a 2 mm thick quartz window positioned above a metal substrate with an intervening 19 µm air gap. An increase in the apparent quartz window thickness was observed, consistent with theoretical expectations, despite the air gap remaining undetectable as a distinct reflection. This analysis was extended to multi-layered paint systems consisting of top, mid, and base coatings on steel plates. Cyclic ageing induced a delamination layer between the metal substrate and base coating, measured to be 10 µm by scanning electron microscopy. Terahertz pulsed imaging analysis showed a corresponding 9.9-13 µm increase in the apparent base coating thickness, consistent with the quartz window results. 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