Electronic Textiles

Smart Fabrics and Wearable Technology

Tilak Dias

• Publisher: Woodhead Publishing
• Year: 2015
• ISBN:
  9780081002230
• Topic: Computer Science
• Subtopic: CAD-CAM
• Index: Computer Science

The integration of electronics into textiles and clothing has opened up an array of functions beyond those of conventional textiles. These novel materials are beginning to find applications in commercial products, in fields such as communication, healthcare, protection and wearable technology. Electronic Textiles: Smart Fabrics and Wearable Technology opens with an initiation to the area from the editor, Tilak Dias. Part One introduces conductive fibres, carbon nano-tubes and polymer yarns. Part Two discusses techniques for integrating textiles and electronics, including the design of textile-based sensors and actuators, and energy harvesting methods. Finally, Part Three covers a range of electronic textile applications, from wearable electronics to technical textiles featuring expert chapters on embroidered antennas for communication systems and wearable sensors for athletes.

• Comprehensive overview of conductive fibres, yarns and fabrics for electronic textiles
• Expert analysis of textile-based sensors design, integration of micro-electronics with yarns and photovoltaic energy harvesting for intelligent textiles
• Detailed coverage of applications in electronic textiles, including werable sensors for athletes, embroidered antennas for communication and electronic textiles for military personnel

Part One

Conductive fibres, yarns and fabrics

1

Conductive fibres for electronic textiles

an overview

C.R. Cork Nottingham Trent University, Nottingham, UK

Abstract

The chapter gives an overview of electrically conducting fibres. Electrically conducting fibres have a surprisingly long history and have been used for aesthetics, anti-static and shielding purposes and for applications in electronic textiles. They take many forms, including metal fibres, metallized fibres, electrically conducting strips, inherently conducting polymers and fibres with conducting elements added during extrusion. More recently, electrical conductivity has been achieved using carbon nanotubes and, in the future, fibres doped with graphene hold promise.

Keywords

Electrically conducting fibres

Metal fibres

Metallized fibres

Inherently conducting polymers

Carbon nanotubes

1.1 Introduction

1.1.1 Definition

Electrically conducting fibres have a surprisingly long history and have been used for aesthetics, anti-static and shielding purposes and for applications in electronic textiles.

A fibre may be defined as a structure that is fine, flexible and exhibits a high length-to-width ratio. A conductive fibre can be defined as an electrically conductive element having the structure of a fibre. Thus, a metal nail and thick copper wire are electrically conductive but not fibres, as they are neither fine nor flexible. In contrast, for the present purposes, a fine copper wire and silver-coated polymer fibre can both be categorized as conductive fibres.

The electrical resistance of metals is of the order of 10^{− 5} Ω cm, whereas that of a typical insulator would be 10¹² Ω cm. The electrical resistance of natural fibres is governed by the humidity of the air to which they are exposed (Murphy and Walker, 1928). For example, the specific resistance of wool varies from 1.6 × 10⁹ Ω cm at 53% relative humidity (RH) to 1.3 × 10⁶ at 86% RH (Marsh and Earp, 1933). In contrast, the resistance of polyester at 85% RH is greater than 7 × 10¹² Ω cm (Hersh and Montgomery, 1952). At normal temperatures, the resistance of metals is proportional to the absolute temperature, whereas the resistance of insulators increases as temperatures decrease (Bardeen, 1940). The electrical conductivity of copper, silver and gold at 0 °C are 64, 66 and 49 × 10^{− 4} Ω^{− 1} cm^{− 1}, respectively (Bardeen, 1940).

1.1.2 Archaeological metallized fibres

The first description of static electricity was by Thales of Miletus in the sixth century BCE (Noad, 1859), but the modern science of electricity was not formulated until the eighteenth century. However, electrically conducting textile fibres have a long history that goes back to antiquity. For example, gold-coated threads were produced in ancient times before the modern discovery of electricity but were, of course, designed for aesthetic purposes alone. In a story familiar to Homer, the adventurer Jason goes in search of a golden fleece (Rhodius, 3rd Century B.C.). Could this have been a reference to a fleece used to collect gold or to man-made gold fibres?

Historically, there have been various techniques for producing metal thread for textiles. Metals were hammered and cut into foil strips and then wrapped around a core. Gold threads made by wrapping a flat ribbon of gold around a silk core are reported from a second century sarcophagus in Cyprus (Conroy and García, 2010). Alternatively, metal wires were wound directly around a core. In another approach, leather or paper was coated with gold leaf and then used directly, or again, wound around a core yarn (Hauser-Schäublin and Ardika, 2008). The techniques used often depended on the geographical origin. For example, metal-coated strips of paper were used in China, whilst hammered and cut strips of foil are reported from ancient Egypt and Persia (Hauser-Schäublin and Ardika, 2008).

A paper by Csiszár et al. (2013) describes manufacturing methods for metallized fibres made from the fourth century AD onwards. The metal strips were a few tenths of a millimetre in width and up to 70 mm in length. These might be wound around a textile core or used flat. Csiszár et al. (2013) also describe how silver gilt threads took over from gold around the first millennium. With reference to the literature, Csiszár et al. (2013) report that ~ 70 types of metallized thread are known.

Metal threads with animal hair cores are reported from around 1200 to 1300 AD (Skals, 1991). A paper on the cleaning of copper embroidery threads on an archaeological textile refers to a fabric embroidered with copper threads (Abdel-Kareem and Harith, 2008). Again, these were formed from solid metal strips wound around a cotton core that had been embroidered to produce a motif.

Details of gold and silver threads in Renaissance tapestries are reported by Hacke et al. (2003). Various metallized threads from the seventeenth and nineteenth centuries in South America are described by Muros et al. (2007). Figure 1.1 shows a seventeenth century silver-wrapped silk thread found in Dorchester in the United Kingdom.

Figure 1.1 Silver-wrapped silk thread from the seventeenth century. Figure supplied by Dr. Jane Batcheller of the University of Alberta.

1.1.3 Eighteenth century

After the modern discovery of electricity, various electrically conducting wires such as copper, iron, steel, brass, platinum, silver, German silver and gold have been used (Noad, 1859) in non-textile applications.

1.1.4 Nineteenth century developments

In the nineteenth century, the understanding of electricity was developed further. Michael Faraday, in his volume on experimental research in electricity from 1855, mentions the use of copper, iron, platinum and platina (natural impure platinum; Faraday, 1855).

Fibres specifically designed for electrical conductivity started to appear in the late nineteenth century.

Thomas Edison took out a patent for an electric lamp in 1880. The filament was made from carbonized cotton and linen threads, wood splints and paper (Edison, 1880).

The late nineteenth century saw the introduction of the first combinations of electrical functionality with textiles. For example, an electric corset promised to cure various ailments for ‘ladies of all ages and all stations in life’ (Fishlock, 2001), but the nature of the wiring is not clear. Considering the modern focus on powering wearable devices, it is notable that power was generated by the body using metal discs located next to the skin (Harness, 1891).

1.1.5 Twentieth century developments

The early twentieth century saw thinking focus on more practical combinations of electrical functionality and textiles. For example, a patent from 1911 describes an electrically heated glove (Carron, 1911) for ‘drivers of aeroplanes, automobiles, motor boats and other conveyances which are guided by manually operated steering wheels’. It is proposed that the heating elements be made from German silver or other suitable wire. Another patent (Lemercier...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• Woodhead Publishing Series in Textiles
• Part One: Conductive fibres, yarns and fabrics
• Part Two: Integrating textiles and electronics
• Part Three: Applications
• Index