Truly smart textiles

Dan Rogers - 19 Mar 2010

Though smart textiles create a fertile area of development for organic electronics, much of what is being made is lacking the comfort and wearability to appeal to end users. Kunigunde Cherenack, senior research fellow at the ETH Wearable Computing Lab, who is working on the TecInTex smart textile project, explains how electronic textiles are changing this.

Scientists are excited about integrating electronic and optical functions into textiles, since this is a ubiquitous, large-area material that can be mass-produced at staggeringly large quantities and high speeds.

So, what exactly are smart textiles? A common definition of smart textiles - also known as electronic or e-textiles - is that they are 'materials and structures that sense and react to environmental conditions or stimuli, such as those from mechanical, thermal, chemical, electrical, magnetic or other sources.'

An obvious anomaly here is that the word 'textile' does not appear anywhere in this definition - and herein lies the dilemma. The problem with smart textiles is that they are mainly being developed by electrical and materials engineers. Therefore, smart textiles are usually designed with a strong emphasis on the 'smart' aspects and less with a focus on retaining the truly textile properties of the material.

It is my belief that the development of smart textiles requires an interdisciplinary approach in which knowledge of circuit design, micro- and optoelectronics is married to an in-depth understanding of textile fabrication and characterisation techniques.

Textile feel

Important, yet often overlooked, textile properties include the textile 'handle', breathability and drapability - that is, how the textile feels when it is worn by a person. The body of smart textile literature available makes it clear that these issues require more consideration, particularly during the design phase.

Current smart textiles can be roughly divided into three categories:

- Structures in which commercial electronic devices are attached or laminated to textiles substrates, such as in the STELLA project;
- Textiles in which functionalised fibres - for instance conductive or optical fibers - are integrated with standard textile fibres during textile fabrication (e.g. by weaving or knitting); and
- Hybrid structures, in which the textile itself becomes part of the sensing device, and is integral to its functionality.

Of these categories, the first clearly does not result in a 'true' smart textile, since commercial components inherently stiffen the material and reduce textile comfort and breathability. Smart textiles from the second and third categories are true smart textiles - but their sensing properties are limited due to a lack of high-level electronic/optical fibers.

Advanced sensing

Therefore, real progress will only occur within the smart textile field when scientists develop textile fibres with advanced sensing and signal processing capabilities. A key to the success of this approach will be to integrate such advanced fibres directly into textiles. This will involve using commercial fabrication processes, such as weaving, in which several square metres of a textile are produced per second.

Groups that have taken the first steps towards this goal include the Lumalive Technology Incubator from Phillips and research groups at Princeton University and the University of Berkeley. At the Wearable Computing Laboratory at ETH Zürich we are also engaged in pushing the boundary of this field further within the TecInTex Nanotera project. Here we develop thin-film transistors and sensors directly on weavable plastic fibres. Our first weaving tests have shown that it is possible to integrate thin-film devices, fabricated using conventional microelectronics, directly into textiles during weaving without degrading the textile properties.

However, there are key challenges that all advanced textile fibre projects share before they become industrially viable. Scientists need to resolve the issue of interconnects between different sensor fibers inside the textile and protect sensitive device layers and fibres from excessive bending, flexing and moisture damage, to allow the textile to be washed.

Power

Most importantly, it is critical to develop and integrate a textile power source so that smart textiles can be self-powering. This would allow designers to remove the heavy battery pack that is usually inserted into clothing tailored from smart textiles. Current energy harvesting and flexible battery technologies are not yet mature enough to supply sufficient power for smart textiles.

To put matters into perspective, energy harvesting technologies proposed for textile applications, such as integrating piezoelectric nanowires at the fibre level, generate very low powers per unit area - to adapt these wires for smart textiles, we would need textile surface areas that could cover football stadiums to generate the same power as is supplied by a single conventional AAA lithium ion battery! However, new breakthroughs are being made every day, and it is within the field of energy harvesting that I expect the most exciting developments over the next few years.

I believe that smart textiles will become an integral part of everyday life in the future - but that the smart textiles of the future will have little resemblance to the smart textiles of today. Currently, there is little consensus on the structure and implementation of smart textile fabrication, but in my opinion the most promising approach is to integrate advanced electronic and optical fibres directly into the textile during commercial fabrication.