Flexible, wearable and reconfigurable antennas based on novel conductive materials: graphene, polymers and textiles

Abstract

Due to high demand and ubiquity of novel wireless communication systems, numerous new technical challenges have risen in modern antenna design to satisfy emerging unconventional system requirements. Typical examples include radio frequency identification (RFID) systems and wearable electronic systems. RFID systems usually consist of a reader and a tag integrated with an antenna which is attached to the item(s) to be tracked. Therefore, for the commercial viability of the system, it is desired to have flexible, light-weight, highly integratable and low-cost antennas for the tags. These characteristics are also desired for the antennas used in wearable electronic systems, with an additional critical requirement, namely electrical and mechanical robustness to the loading effect from the human body when worn. Hence traditional metallic conductors and dielectric materials such as ceramics are usually not suitable, as these materials lack mechanical flexibility and resilience while having a high intrinsic cost. In this context, flexible, wearable and reconfigurable antennas based on novel conductive and dielectric materials are of significant interest. This is in line with the goals of this thesis which comprise four main different objectives. Firstly, the dissertation presents the development of non-metallic, highly efficient and flexible antennas based on conductive polymers and graphene thin films as conductors. Through efficiency-driven and material-oriented engineering methods, it is shown that these antennas can overcome the process-related inherent limitations of the non-metallic conductors, demonstrating the excellent potential of these novel materials. Secondly, the thesis also focuses on the investigation of appropriate shorting strategies and connection solutions for textile antennas, in terms of ease of fabrication, connection reliability and antenna efficiency. This work aims to provide reliable and efficient solutions to the critical connection requirement between flexible textile antennas and rigid electronic components. Thirdly, modular and reconfigurable wearable textile antennas which provide passive and/or active system reconfigurability are proposed, based on commercial snap-on buttons operating as shorting vias and connectors. The modular wearable antenna concept utilizes different modules which are designed to achieve specific antenna characteristics and fulfill various functionalities. The reconfigurable antenna is based on a reconfigurable module which integrates varactors and a dedicated bias circuit board inside snap-on buttons. This button module can solve the main challenge in realizing reliable connections between bias circuit, lump components and textiles, which arises because of the very different physical properties of rigid and flexible components. Fourthly, the last part of the thesis presents a compact and high efficiency series-fed microstrip patch array and a flexible dielectric resonator antenna, as examples of novel designs suitable for wearable applications. All the results and findings in this thesis illustrate that, antennas realized in novel conductive and dielectric materials including conductive polymers, graphene, conductive textiles and polydimethylsiloxane (PDMS), can potentially satisfy the unconventional characteristics desired for future wearable electronic systems. Furthermore, the interdisciplinary combination of antenna technology and material science paves a promising path for advanced antenna developments, towards next generations of mobile wireless communication systems.