Year

2021

Degree Name

Doctor of Philosophy

Department

School of Electrical, Computer and Telecommunication Engineering

Abstract

The demand for flexible and wearable wireless systems is increasing exponentially in today’s information-oriented society. Flexible electronic systems are equally beneficial and have wide applications in communication, medicine, military and radio frequency applications. Beginning with a detailed review of flexible materials which have been used during the last few decades, an overview of some abundantly used polymer substrates is provided, which compares their physical, electrical and mechanical properties. The polymers are highly resistant nonconductive materials made up of repeated subunits of hydrocarbons known as monomers. Polymers are widely used for different antennas and Radio Frequency Identifications (RFID) to facilitate bending and flexibility as a substrate such as polyimides (PI), polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), Rogers RT/ Duroid and Liquid Crystal Polymer (LCP). Flexible substrates have become essential to provide increased flexibility in wearable sensors, including polymers, plastic, paper, textiles and fabrics. This study is to comprehensively summarize the bending capabilities of flexible polymer substrate for general Internet of Things (IoT) applications. Various antennas, applicable for the frequency range between 2 GHz to 10 GHz by using different polymer substrates PI, PET, PDMS, PVC, and PTFE have been designed and fabricated with studies on the bending effects on the radiation performance of antenna designs that use the polymer substrates.

The RFID tags, based on polymers substrates, possess very enticing characteristics like high flexibility, crumpling and stretchability, lightweightedness, ease of processability, corrosion and humidity resistance, and most importantly a low cost with easy fabrication. A novel Flexible Bow Tie Chipless RFID tag is introduced on three flexible polymer substrates PET, PTFE Teflon and PVC, and its design, fabrication, testing and comparative analyses are presented in this research. The tag uses the Frequency Selective Surface (FSS) approach with a frequency ranging from 4 to 18 GHz by using CST studio and then fabricated through a laser etching technique on low-cost polymers. The results are obtained in an anechoic chamber by performing a series of comparative experiments for the Radar Cross Section (RCS) of the Bow Tie Chipless RFID tags. The bow tie design was compared to an Octagonal-shaped tag already published. Furthermore, the Singularity Expansion Method (SEM) based circuit modelling, the transient behaviour and the coupling coefficients of the Bow-Tie shaped tag are evaluated. The maximum read range is evaluated and the Bow Tie RFID tag is proved to be more robust and accurate with the variation of distance up to 1.8 m at 0 dBm, which is extendable to 2.14 m for higher input power. The bending capabilities of the tag are noted for radii curvature of 27 mm and 14 mm. The experimental result shows that the new Bow Tie RFID tag is more robust and accurate with the distance variation of up to 12 cm at 0 dBm power and can be used to encode a bit sequence.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.