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Design of planar antennas based on textile materials

Carla Hertleer UGent (2009)
abstract
The need for textile-based antennas originates from the development of smart textiles that emerged in the nineties. The idea is to increase the functionality of textiles, in most cases clothing, by adding electronic systems. This allows the monitoring of physical (such as heart rate or respiration rate) as well as environmental parameters (e.g. humidity, temperature) through an embedded sensor network. The availability of micro electronics on the one hand, and of new textile materials on the other, stimulates this evolution. A wearable textile system comprises several components: sensors, actuators, a data processing unit, an energy supply, interconnections that combine all the components into an entire system and a communication system that allows wireless data transfer from the garment to a nearby base station. The target of a textile specialist is to manufacture as many components as possible out of textile materials, in order to increase their integration in the textile product in a comfortable way. The development of textile-based sensors and flexible interconnections is a continuously ongoing and extremely promising research area. This research focuses on the expansion of textile-based communication systems. Wireless communication requires the use of antennas. Antennas are available in all sorts of shapes, but for textile applications, especially planar patch antennas are of interest. These antennas are low profile, light weight and have a simple structure, which makes them most suitable to be embedded in apparel in a comfortable and unobtrusive way. This work reveals the feasibility of the design, the manufacturing and the integration of planar textile-based antennas. It is subdivided into two parts: the first part deals with textile-based antennas in general, whereas the second part focuses on textile-based antennas for protective clothing. The planar antennas developed in this dissertation mainly consist out of four pieces: - a conductive antenna patch; - an antenna substrate made out of a nonconducting material; - a ground plane, which is also conductive; - a connector that allows connecting of the antenna to the system. All antennas are designed to operate in the frequency band centered around 2.45 GHz (2.4 - 2.4835 GHz, thus having a bandwidth of 83.5 Mz). This is a dedicated license-free frequency range for the ISM (Industrial, Scientific, Medical) band, in which communication protocols such as Bluetooth and Zigbee operate. In a first step, suitable textile materials were selected and characterized. For the conductive parts (antenna patch and ground plane), commercially available e-textiles were chosen. Apart from that, the feasibility of applying conductive inks through screen printing was examined. Properties such as conductivity and easiness of handling were the main requirements. For the antenna substrate, several conventional, thus nonconductive textile materials were selected. Antenna design requires knowledge of electromagnetic material properties, which are not determined in traditional textile characterization. Relative permittivity and loss tangent of the nonconductive antenna substrate materials were determined. Based on these values and by applying a commercially available field simulator for antenna design, a robust antenna topology was designed. The main requirements were to achieve a -10 dB impedance bandwidth of at least 83.5 MHz in the 2.45 GHz ISM band. The selected textile materials were applied to manufacture antenna prototypes, based on designs obtained with electromagnetic field simulations. Reflection and transmission characteristics of these prototypes were measured and compared to the simulations. In all cases a good agreement between simulations and measurements was obtained. A next research issue was the connection between the antenna and other parts of the textile system. In conventional antenna design rigid connectors are frequently applied, whereas for wearable antennas, flexible, unobtrusive connectors are desired. Some alternatives are discussed and tested in this work. The comfort when wearing textile materials is owed to their ability to absorb moisture. However, the presence of moisture in the antenna substrate can give rise to a shift of the antenna characteristics. Therefore, antennas operating in the 2.45 GHz frequency band are optimally designed on substrate materials that take up few moisture, preferably with a moisture regain of less than 3 %. The second part of this work deals with the design of textile antennas for a specific application, namely protective clothing for rescue workers and firefighters. This research was carried out in the framework of a European project ProeTex (Protection e-Textiles: MicroNanoStructured fibre systems for Emergency-Disaster Wear). This four year lasting project (2006-2010) aims at developing the next generation of protective clothing for rescue workers, based on wearable textile systems. The added value is conceived by enabling monitoring of the physical state of rescue workers in action. In addition, several environmental parameters can by monitored through the garment. Embedded textile antennas permit wireless communication between the protective clothing and the base station. This application demands special requirements of the applied materials comprising the antenna. Within the scope of this research, two substrate materials were examined: on the one hand an aramid fabric (a high performance material often used as outer layer of a firefighter jacket), on the other a flexible foam material. Both materials have proved to be suitable to be applied as antenna substrate, however, flexible foam has some significant benefits. Foam is available in a variety of uniform thicknesses, which facilitates the design of broadband antennas on which the substrate thickness has a substantial influence. In addition, dedicated foams can be selected with respect to their compression, fire retardant or water resistant properties. Flexible foams are commonly used in protective clothing (e.g. as an impact absorbing or isolating layer). The antennas designed for this specific application were subjected to some extra tests, such as operation in bent state (simulating the antenna when integrated into a sleeve or on a shoulder) and covered by extra textile layers (because the antenna is embedded between different textile layers). These phenomena were extensively examined and we concluded that they had no negative effect on the antenna performance. This work clearly establishes the potential of textile materials in the design of wearable antennas. Commercially available e-textiles can be applied, however, without doubt conductive inks are the most promising, because they provide more flexibility to the antenna topology. Flexible foams are more advantageous compared to conventional textile materials, mainly because of their uniform and larger thickness. Within the framework of the ProeTex project, data such as heart rate, respiration rate and body temperature of the rescue workers are wirelessly transmitted to a base station through integrated textile antennas developed in this dissertation. They provide an indispensable link with the base station. A first prototype of the textile system with integrated textile antennas was successfully tested in 2007 by the Paris Fire Brigade.
Please use this url to cite or link to this publication:
author
promoter
UGent and UGent
organization
alternative title
Ontwerp van vlakke antennes uit textielmaterialen
year
type
dissertation (monograph)
subject
keyword
Textile antennas, Wearable textile system, Smart textiles, Wireless communication
pages
XV, 167 pages
publisher
Ghent University. Faculty of Engineering
place of publication
Ghent, Belgium
defense location
Gent : Faculteit Ingenieurswetenschappen (Jozef Plateauzaal)
defense date
2009-09-14 16:00
ISBN
9789085782971
language
English
UGent publication?
yes
classification
D1
additional info
dissertation in parts contains copyrighted material
copyright statement
I have transferred the copyright for this publication to the publisher
id
789983
handle
http://hdl.handle.net/1854/LU-789983
alternative location
http://lib.ugent.be/fulltxt/RUG01/001/351/358/RUG01-001351358_2010_0001_AC.pdf
date created
2009-11-26 10:43:55
date last changed
2010-09-29 12:23:30
@phdthesis{789983,
  abstract     = {The need for textile-based antennas originates from the development of smart textiles that emerged in the nineties. The idea is to increase the functionality of textiles, in most cases clothing, by adding electronic systems. This allows the monitoring of physical (such as heart rate or respiration rate) as well as environmental parameters (e.g. humidity, temperature) through an embedded sensor network.  The availability of micro electronics on the one hand, and of new textile materials on the other, stimulates this evolution. A wearable textile system comprises several components: sensors, actuators, a data processing unit, an energy supply, interconnections that combine all the components into an entire system and a communication system that allows wireless data transfer from the garment to a nearby base station. 
The target of a textile specialist is to manufacture as many components as possible out of textile materials, in order to increase their integration in the textile product in a comfortable way. The development of textile-based sensors and flexible interconnections is a continuously ongoing and extremely promising research area. This research focuses on the expansion of textile-based communication systems. 
Wireless communication requires the use of antennas. Antennas are available in all sorts of shapes, but for textile applications, especially planar patch antennas are of interest. These antennas are low profile, light weight and have a simple structure, which makes them most suitable to be embedded in apparel in a comfortable and unobtrusive way. This work reveals the feasibility of the design, the manufacturing and the integration of planar textile-based antennas. It is subdivided into two parts: the first part deals with textile-based antennas in general, whereas the second part focuses on textile-based antennas for protective clothing. 
The planar antennas developed in this dissertation mainly consist out of four pieces:
- a conductive antenna patch;
- an antenna substrate made out of a nonconducting material;
- a ground plane, which is also conductive;
- a connector that allows connecting of the antenna to the system. 

All antennas are designed to operate in the frequency band centered around 2.45 GHz (2.4 - 2.4835 GHz, thus having a bandwidth of 83.5 Mz). This is a dedicated license-free frequency range for the ISM (Industrial, Scientific, Medical) band, in which communication protocols such as Bluetooth and Zigbee operate. 
In a first step, suitable textile materials were selected and characterized. For the conductive parts (antenna patch and ground plane), commercially available e-textiles were chosen. Apart from that, the feasibility of applying conductive inks through screen printing was examined. Properties such as conductivity and easiness of handling were the main requirements. For the antenna substrate, several conventional, thus nonconductive textile materials were selected. 
Antenna design requires knowledge of electromagnetic material properties, which are not determined in traditional textile characterization. Relative permittivity and loss tangent of the nonconductive antenna substrate materials were determined. Based on these values and by applying a commercially available field simulator for antenna design, a robust antenna topology was designed. The main requirements were to achieve a -10 dB impedance bandwidth of at least 83.5 MHz in the 2.45 GHz ISM band. 
The selected textile materials were applied to manufacture antenna prototypes, based on designs obtained with electromagnetic field simulations.  Reflection and transmission characteristics of these prototypes were measured and compared to the simulations. In all cases a good agreement between simulations and measurements was obtained. 
A next research issue was the connection between the antenna and other parts of the textile system. In conventional antenna design rigid connectors are frequently applied, whereas for wearable antennas, flexible, unobtrusive connectors are desired. Some alternatives are discussed and tested in this work.
The comfort when wearing textile materials is owed to their ability to absorb moisture. However, the presence of moisture in the antenna substrate can give rise to a shift of the antenna characteristics. Therefore, antennas operating in the 2.45 GHz frequency band are optimally designed on substrate materials that take up few moisture, preferably with a moisture regain of less than 3 \%.

The second part of this work deals with the design of textile antennas for a specific application, namely protective clothing for rescue workers and firefighters. This research was carried out in the framework of a European project ProeTex (Protection e-Textiles: MicroNanoStructured fibre systems for Emergency-Disaster Wear). This four year lasting project (2006-2010) aims at developing the next generation of protective clothing for rescue workers, based on wearable textile systems. The added value is conceived by enabling monitoring of the physical state of rescue workers in action. In addition, several environmental parameters can by monitored through the garment. Embedded textile antennas permit wireless communication between the protective clothing and the base station. This application demands special requirements of the applied materials comprising the antenna. Within the scope of this research, two substrate materials were examined: on the one hand an aramid fabric (a high performance material often used as outer layer of a firefighter jacket), on the other a flexible foam material. Both materials have proved to be suitable to be applied as antenna substrate, however, flexible foam has some significant benefits. Foam is available in a variety of uniform thicknesses, which facilitates the design of broadband antennas on which the substrate thickness has a substantial influence. In addition, dedicated foams can be selected with respect to their compression, fire retardant or water resistant properties. Flexible foams are commonly used in protective clothing (e.g. as an impact absorbing or isolating layer). The antennas designed for this specific application were subjected to some extra tests, such as operation in bent state (simulating the antenna when integrated into a sleeve or on a shoulder) and covered by extra textile layers (because the antenna is embedded between different textile layers). These phenomena were extensively examined and we concluded that they had no negative effect on the antenna performance. 
This work clearly establishes the potential of textile materials in the design of wearable antennas. Commercially available e-textiles can be applied, however, without doubt conductive inks are the most promising, because they provide more flexibility to the antenna topology. Flexible foams are more advantageous compared to conventional textile materials, mainly because of their uniform and larger thickness. Within the framework of the ProeTex project, data such as heart rate, respiration rate and body temperature of the rescue workers are wirelessly transmitted to a base station through integrated textile antennas developed in this dissertation. They provide an indispensable link with the base station.
A first prototype of the textile system with integrated textile antennas was successfully tested in 2007 by the Paris Fire Brigade.},
  author       = {Hertleer, Carla},
  isbn         = {9789085782971},
  keyword      = {Textile antennas,Wearable textile system,Smart textiles,Wireless communication},
  language     = {eng},
  pages        = {XV, 167},
  publisher    = {Ghent University. Faculty of Engineering},
  school       = {Ghent University},
  title        = {Design of planar antennas based on textile materials},
  url          = {http://lib.ugent.be/fulltxt/RUG01/001/351/358/RUG01-001351358\_2010\_0001\_AC.pdf},
  year         = {2009},
}

Chicago
Hertleer, Carla. 2009. “Design of Planar Antennas Based on Textile Materials”. Ghent, Belgium: Ghent University. Faculty of Engineering.
APA
Hertleer, C. (2009). Design of planar antennas based on textile materials. Ghent University. Faculty of Engineering, Ghent, Belgium.
Vancouver
1.
Hertleer C. Design of planar antennas based on textile materials. [Ghent, Belgium]: Ghent University. Faculty of Engineering; 2009.
MLA
Hertleer, Carla. “Design of Planar Antennas Based on Textile Materials.” 2009 : n. pag. Print.