Aerospace metamaterials and functional coatings

Abstract

Optically transparent and electrically conductive thin-film coatings are widely used to functionalize surfaces of various high-technology platforms, including mobile phones, displays, detectors, and LEDs. Their integration into aviation transparencies, such as canopies, windshields, and windows, is widely known and used for de-icing purposes. However, there are limited reports or information available about using such thin-film coatings for electromagnetic interference (EMI) shielding, low observability (LO), and solar irradiation protection features. This thesis aims to study and demonstrate optically transparent aviation structures possessing the properties of EMI shielding, LO features, and solar radiation protection altogether. To this end, in this thesis, we specifically addressed the problem of achieving high EMI shielding and solar protection, which require high electrical conductivity, resulting in a trade-off reducing the optical quality and LO performance. Transparent engineering polymers are widely used in structural parts in aviation thanks to their enhanced mechanical performance. However, good-quality films require high-temperature processes, which is not applicable to transparent aviation structures. Therefore, the architecture of layered films can be applied to meet the requirements of well-featured aviation transparencies. For these purposes, in the thesis we also designed monolithic and laminated aviation transparencies with surface modification based on stratified films and their patterned ones using numerical and experimental methods. We developed numerical approaches for the design of aircraft transparencies, including both the optical and electromagnetic requirements and validated our results. We successfully conducted experimental studies for uniform large-area thin-film coatings onto aviation transparencies. The results revealed that EMI shielding and solar control performance were achieved with minimal optical losses for planar structures. LO requirement was incorporated into prototypes built on curved or laminated transparent structures instead of monolithic ones to sustain optical, solar protection, and EMI shielding performance to a possible extent. We showed that the low observability performance of such patterned structures, the metamaterials, is enhanced in terms of bandwidth and attenuation compared to the planar thin-film-coated monolithic counterparts. These multi-functional thin-film coatings are essential in aviation, especially for high-performance 5th-generation fighter jets and other civil applications. This thesis paves the way for thin-film-coated transparent aviation structure designs across different domains, including visible, infrared, and microwaves, to enable their multi-functionality at large scales. The experimental large-area coating method guides the coating of a large and complex area to remove the limitation of metamaterial applications at the industrial level. We believe that our findings in this thesis will help to replace traditional planar thin film coatings with metamaterials at the industry scale, aiming to outperform traditional counterparts.