Abstract:
Non-destructive inspection technologies for consumer goods, industrial products, and infrastructure have increasingly focused on millimetre-wave, terahertz, and infrared imaging due to their non-invasive transparency and extensive material identification capabilities. Among various inspection devices available, photo-thermoelectric (PTE) image sensor sheets fabricated from carbon nanotube (CNT) thin films stand out. CNT film sensors demonstrate consistently high absorption rates exceeding 90% from millimetre-wave through infrared and even into the visible spectrum, despite film thicknesses of only a few micrometres. Additionally, these devices exhibit excellent mechanical stability, with variations in photo-detection sensitivity limited to within 5%, even after repeated bending and stretching. These attributes allow the application of CNT sensors in complex curved surfaces or harsh environments, where conventional sensors may not be practical.
However, the potential reuse of CNT-based image sensors in contaminating environments, such as those encountered with industrial oils, requires further evaluation, particularly concerning their durability and suitability for repeated liquid-based cleaning processes. This work addresses this critical gap by developing an ultrabroadband, highly transparent protective coating that maintains the intrinsic optical and mechanical properties of CNT film sensors, enabling repeated washing and reuse.
The fabrication process involves coating a 25 µm-thick polyurethane sheet with a hydrophilic layer, followed by applying a polyimide mask. A semiconductor CNT dispersion solution is applied at elevated temperatures to achieve p-type doping, covered by an additional polyurethane sheet. Finally, a polydimethylsiloxane (PDMS) coating (400 µm thick) and a fluoropolymer coating are applied to encapsulate and protect the sensor. The fabricated device is then subjected to contamination with oil- based substances, followed by washing procedures in water and ethanol.
Infrared sensing tests conducted on these sensors show a significant reduction in optical response when contaminated, dropping to 10% of the initial value. Water washing partially recovers sensor performance, achieving around 30% of the original sensitivity. In contrast, ethanol washing fully restores the optical response to its initial state, demonstrating the sensor's capability for complete recovery after contamination.
This research demonstrates the successful integration of conductive polymer electrodes and protective coatings, resulting in a flexible, robust sensor capable of high-sensitivity imaging across an ultra-wide spectral range from millimetre-wave to visible light. The device maintains performance even after repeated cleaning cycles in liquid environments, proving its suitability for practical non-destructive inspection applications in contamination-prone industrial settings. This work not only establishes a reusable sensor technology but also provides essential insights into sensor design for sustainable and cost- effective non-destructive inspection systems.
Biography:
Mr. Junyu JIN is a master's student at Chuo University (Kawano Laboratory), Japan. His research focuses on non-destructive inspection, carbon nanotubes, and ultrabroadband thin-film devices. He has presented at the 21st Thin Film Materials and Devices Workshop in Kyoto and co-authored a peer-reviewed article in Advanced Sensor Research on microwave monitoring using CNT PTE sensors. Originally from China, he is currently pursuing his graduate studies in Japan.
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