Wearable Antennas and Wireless Sensing Systems for e-Textile Applications

  • Yutong Jiang

Student thesis: Phd

Abstract

Smart textile or electro-textile (e-textile) is defined as fabrics constructed entirely or partially by electrically conductive material, which can be integrated with clothing as a part of bodyworn electronics. The main features of e-textile that make it so desirable are its flexibility, durability and high corrosion resistance as a type of daily carry-on electronic device. Over the past decade, e-textile antennas have gained tremendous attention. The close-body nature of such antennas possesses great potential in various fields such as daily communication, personal healthcare and body area networks (BANs). However, due to flexible structures of the e-textile, it can be easily affected by body movements. Therefore, the challenges exist in the application of wearable antennas are the factors that are difficult to predict and control. The purpose of this thesis is to present comprehensive study into multiple types of e-textile integrated antennas and their real-life applications, including NFC antennas integrated body sensing device, RFID antennas and broadband monopole antennas integrated body-worn energy harvesting systems. This thesis is comprised of three main research areas. The first area of this work focuses on the development of novel e-textile embroidered wearable near-field communication RFID antennas, which includes antenna design through full electromagnetic wave simulation, fabrication with conductive treads and textile substrates and measurements under various circumstances such as mechanical bending and human body effects. The measurement results show that the proposed NFC antenna is able to operate under significant degree of bending as well as direct skin contact attributed to its broad operating bandwidth. Distinguished from conventional NFC antennas, e-textile NFC antennas are ensured to be capable of communicating at desired operating frequency of 13.56 MHz while placed on almost any place on clothes. Based on this design, a smart textile integrated wireless powered near field communication (NFC) body temperature and sweat sensing system has also been developed. In this research, temperature and sweat sensors are embedded and powered by an e-textile NFC antenna enabling battery-free and wireless sensing operation. The proposed device is seamlessly integrated with close-fitting garments and the sensor data can be acquired with NFC readers and smart phones, which achieves realtime health monitoring in a convenient and non-intrusive way. The sensor data can be accessed with maximum read distance of 6 cm. The on-body accuracy of the temperature and sweat sensors is measured as ±0.14°C and ±0.2%, respectively. The proposed device aims to 13 provide ubiquitous wireless and battery-free connectivity for daily healthcare and wellbeing monitoring. The second area includes design, fabrication and measurements of e-textile integrated antennas for various applications. Two designs are presented in this part. The first one is a machine embroidered wearable e-textile wideband UHF RFID tag antenna. The antenna read distance is above 6.5 m between 860 MHz and 960 MHz. The tag reading has been tested both in air and on body where the maximum read distance are 7.23 m and 4.71 m, respectively. The second design is a novel e-textile integrated wideband monopole antenna that aims to be applied in body-worn RF energy harvesting systems. The proposed antenna is constructed with silver coated conductive threads woven into cotton substrate. A novel dual circular patch structure is introduced to achieve a wide operating bandwidth which covers GSM bands (range 870.4-915 MHz and 1.7-1.9 GHz), LTE bands (range 0.79–0.96 GHz; 1.71–2.17 GHz; and 2.5–2.69 GHz) and Wi-Fi frequencies (2.4 and 3.6 GHz). The last area under investigation is to develop a functional on-body ambient RF energy harvesting system by combining an e-textile antenna array with a multiband low-input rectifier. The antenna array is constructed with two identical broadband monopole antennas, which achieves relatively high gain and efficiency at most occupied ambient RF frequency bands. A compact six-band rectifier is integrated with the textile antenna with corresponding working frequencies. Experimental results show that the harvesting device performs stably with low input power down to -20dBm, and it is able to generate highest DC power of -11.67 dBm with a wireless power source at a single frequency (0.9 GHz). This work has successfully demonstrated design and performance of a number of novel etextile fabricated antennas and antenna-based electronics (wireless sensors and RF energy harvester). The challenges over this topic such as human body effects and external forces that might be taken by the antennas have been discussed and overcome. This work is believed to be a great contribution to the field of wearable electronics.
Date of Award1 Aug 2021
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorZhirun Hu (Supervisor) & Yi Li (Supervisor)

Keywords

  • Antenna
  • e-textile
  • Wireless sensing
  • Energy harvesting

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