Design of new wearable antennas and textile-based transmission lines

Abstract

Flexible wearable antennas and their components are a fast growing research topic in modern communication systems. They are developed for various wearable applica tions, such as health monitoring, fitness tracking, rescuing, and telecommunications. Wearable antennas need to be compact, lightweight, flexible, and robust. In this thesis, two dual-band wearable antennas were developed, each with a differ ent design approach. The first antenna is a dual-band flexible folded shorted patch (FSP) antenna which operates at 400 MHz and 2.4 GHz. It uses polydimethylsilox ane (PDMS), which is low cost, flexible and robust, and is used as a substrate for wearable the FSP antenna. In addition, the FSP antenna also exploits the TM010 and TM001 modes. A comparative study was carried out to analyze the far-field radiation and directivity at the TM010 and TM001 modes between the FSP antenna and a conventional patch antenna using cavity model analysis. The proposed FSP antenna is suitable for military search and rescue operations and emergency services. The second antenna is a dual-band flexible circular polarized (CP) patch antenna operational at 1.575 GHz and 2.45 GHz. Kevlar was used as a substrate for the proposed antenna. The patch consists of truncated corners and four diagonal slits. An artificial magnetic conductor (AMC) plane was integrated within the design in order to reduce the backward scattered radiation towards the human body and also to improve the realized gain of the antenna. The AMC unit cell design consists of square slits, a square ring and was integrated as a 3 × 3 array of square patch AMC unit cells. The proposed antenna developed is suitable for WBAN and WLAN applications. A circular polarized (CP) patch antenna with a PDMS substrate was also designed and fabricated to test the durability and resiliency of PDMS as a polymer-based material suitable for use in wearable antennas. Robustness tests such as bent, wet, and temperature tests were performed and reported. Two prototypes of flexible wearable coaxial transmission lines were also designed and fabricated. Polyester (PES) and polytetrafluoroethylene (PTFE) textile materials were used to design prototypes of these cables. Shielding effectiveness and DC losses were measured and compared for the fabricated cables. The cables were also tested for bending, twisting and for suitability in environmental conditions. The highly flexible nature of these cables makes them suitable to use with wearable antennas for various applications. For example, the proposed cables can be used with previously detailed FPS antenna for military search and rescue operations. It should be mentioned that this thesis was done in collaboration with Leonardo, UK and J&D Wilkie, UK.