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Balasubramanian, Vishal

University of British Columbia

The degradation of protective coatings due to erosion, delamination, and corrosion compromises the structural integrity of critical assets in aviation, marine, and infrastructure industries. Existing non-destructive testing (NDT) methods lack real-time monitoring capabilities, suffer from environmental interference, and exhibit poor spatial localization, limiting their effectiveness in industrial applications. This thesis presents the design, development, and experimental validation of microwave-based coating health monitoring systems, focusing on enhancing detection accuracy, spatial localization, and environmental robustness through differential and multi-resonant sensor architectures. Firstly, a wired differential split-ring resonator (SRR) sensor was developed and validated for coating wear detection in homogeneous mono-layered, and heterogeneous multi-layered protective coatings with a sensitivity in the order of 10s of μm. The system demonstrated a 4 MHz increase in resonant frequency per ~25 μm of wear for coating thicknesses less than 1 mm. Additionally, in multi-layered protective coatings, the system accurately distinguished wear depth and layer-specific erosion while self-compensating for environmental fluctuations. Subsequently, the developed microwave sensor was expanded for simultaneous coating wear detection and localization. A wired multi-resonant SRR sensor was developed, employing three resonators operating at distinct frequencies, alongside a shielded reference SRR. This system achieved an average sensitivity of 35 MHz per 125 µm of coating wear, effectively localizing wear regions while mitigating environmental noise. Additionally, a passive frequency-selective surface (FSS)-based wireless sensor was developed for wear detection over large surfaces, while being integrated with artificial intelligence methods for coating damage localization and augmented reality technology to visualize the damaged region. Finally, a passive differential FSS system was designed to minimize environmental fluctuations. The system maintained minimal hysteresis while detecting coating wear in real-time. The developed FSS sensor could detect coating delamination, in addition to integration with a multi-resonant FSS system for damage localization without the need for post-processing. This thesis advances the body of knowledge in microwave-based non-destructive testing by integrating for the first time a differential microwave sensor, a multi-resonant architecture, AI-driven wear localization, and augmented reality visualization for real-time, passive, and environmentally robust coating health monitoring, thus promising its application in aerospace, and civil infrastructure industries.

Text

2025-05-01

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90935

Electrical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/