Polydimethylsiloxane-embedded conductive fabric for realisation of robust flexible passive and active wearable antennas

This thesis presents polydimethylsiloxane (PDMS)-embedded conductive fabric as a new approach to realise robust flexible wearable antennas. The approach combines the use of conductive fabric as the antenna radiator and ground plane, with PDMS which acts as the antenna substrate and a protective encapsulation. This allows for a simple yet effective approach to achieve robust flexible wearable antennas. Initially, a thorough characterisation of the mechanical and electrical properties of the PDMS-embedded conductive fabric was demonstrated with four potential combinations of PDMS-conductive fabric considered in this thesis. This characterisation provides valuable insight into the mechanical robustness of the proposed approach, the constraints associated with selection of the conductive fabric for various parts of the antenna, and the effective modelling of the antenna. Upon gathering the characterisation results, several wearable antenna designs were developed as concept demonstrations. To verify the designs, their performance was then investigated experimentally, including RF performance tests both in free space and on fabricated ultra-wideband (UWB) human-muscle equivalent phantoms, and mechanical stability tests e.g. bending tests on the aforementioned phantoms and machine-washing tests. As the first concept demonstration, four simple inset-fed rectangular patches were designed using the four combinations of PDMS-conductive fabric characterised before, thus verifying the properties obtained from the characterisation process. Next, a new dual-band dual-mode antenna design suitable for off- and on-body communication was developed as the second demonstration. Different from previously reported works, the dual-band dual-mode operation was achieved by utilising inherently generated higher order modes of a patch antenna, allowing for a much simpler design that only used a single patch fed by a simple probe feed. Further, a novel planar UWB antenna design was developed to demonstrate the applicability of the PDMS-embedded conductive fabric technique for UWB and high-frequency applications. In contrast to previously reported flexible UWB antennas, the design maintains a full ground plane which provides a high isolation between the antenna and the human body when worn. The antenna time-domain analysis in both free-space and on-body environments was also conducted, demonstrating its suitability for UWB pulse transmission. Lastly, the application of PDMS-embedded conductive-fabric technology was expanded further to cover, for the first time, the realisation of robust flexible electronically tunable wearable antennas. A frequency-reconfigurable patch antenna that can stand physical deformation and even machine-washing has been successfully developed. Its miniaturised version, incorporating a PDMS-ceramic composite substrate, was also investigated to show the versatility of the proposed PDMS-embedded conductive fabric. In all four concept demonstrations, a good agreement between simulated and measured results is shown. Consistent performance including reconfigurability was obtained even after the antennas were exposed to harsh environments, e.g. extreme bending and machine-washing. This validates the applicability of the proposed approach for realisation of robust flexible antennas for wearable applications.