A wirelessly-powered sensor platform using a novel textile antenna

• Main Author: Lui, Kwok Wa
• Other Authors: Toumazou, Christofer ; Murphy, Olive
• Published: Imperial College London 2013
• Subjects: 621.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616858

This thesis describes the design and analysis of a novel wideband circularly-polarized textile antenna to power up a wearable wirelessly-powered sensor system operating in the 2.45 GHz ISM band (2.4-2.5 GHz) and the building of the whole system. The system is constructed using off-the-shelf components and it is shown that the wirelessly-powered sensor system is able to operate when just a few mW are transmitted from a base station at a distance over a metre. Initially, standard linearly-polarized patch antennas are used for power transmission. However, the antennas have to be aligned perfectly for the best efficiency. Subsequently, a circularly-polarized antenna is proposed for enhanced wireless-power transfer due to the freedom of orientation. A wide-slot antenna without a ground plane has been chosen for its simplicity and wide impedance band. The geometry is firstly optimized for wide impedance and 3-dB axial ratio bandwidth on FR-4. The experimental and simulation results have been studied to analyse the characteristics of such an antenna. The wideband circularly-polarized antenna is then constructed using a conductive textile and re-optimized for on-body applications. With a simple antenna geometry and only a single layer of conductive textile layer, the axial ratio and impedance bandwidths are wide enough to cover the whole 2.45 GHz ISM band with plenty of margin and are significantly wider than any other on-body circularly-polarized textile patch antennas which have been reported. The characteristics of this wideband circularly-polarized antenna under different conditions on the human body have been measured and then connected to the wirelessly-powered sensor system to demonstrate the effectiveness of power transfer to the human body.