Smart textiles

July 2011

HINOW Summer 2011 (140px)According to the speaker, Professor Tilak Dias, Professor of Knitting, School of Art and Design, Nottingham Trent University, the current generation of textiles, including technical textiles, are passive.

However the next generation of textiles will have the ability to monitor their environment and interact accordingly in order to accomplish a pre-programmed functionality. Rita Arafa reports.

Environmentally aware textiles can be considered as truly smart textiles, and they would consist of three basic elements:

  1. Sensing and measuring capability
  2. Activation capability
  3. Intelligence (programming capability)

One of the solutions for incorporating the above components into a textile material is to create electrically active zones within the structure, whose electrical characteristics can change due to an environmental change or whose structural properties would change due to the application of an electrical signal; for example, change of electrical characteristics due to the deformation of the textile structure.

Generally textiles are made out of materials of very high electrical resistance and can, therefore, be considered as materials with good electrical insulating properties. However, modern fabric manufacturing machines can be used to create textile structures with localised electrically active zones, in order to create textile sensors and actuators.

Textiles: the past and the present

Professor Dias explained that textiles are fibre structures made from two types of material:

  1. Natural raw materials e.g. wool, cotton, silk etc
  2. Synthetic materials

The process that is gone through in making fabric differs according to the source of the fibre. For example cotton fibres are extracted from the cotton seeds which are a cellulosic structure, whereas wool requires the hair of an animal (sheep) to be sheared.

All fibres have the same characteristic - they are very short in length, but their thickness is negligible in comparison.

The fibres go through the following processes:

  1. Extraction
  2. Cleaning
  3. Arranging to lie in parallel
  4. Twisting together to provide strength. (Yarn manufacture or spinning)

There are two directions of twist: S and Z, (see end notes) with the former being the most common. The main characteristic of twisted fibres remains the same as individual fibres - length is much greater than thickness, but now the length is unlimited.

The twisted yarn can be bound into fabric using two main methods. The first is weaving, where two sets of yarn are interlaced. This method is the oldest and is thought to have been around for 9,000 years. The second is knitting where single yarns are interloped. This is a much newer method of producing fabric having been in existence for just 3,000 years. Examples have been found in the tombs of the Ancient Egyptians.

The next generation will be smart textiles. This is an emerging sector and it is still in its infancy, but it is an area that is fast growing. In 2008 the market was reported to be worth US$720 million.

Textiles: the future

The three core elements in smart and intelligent fibre structures are:

  1. Transducers
  2. Intelligent signal processes
  3. Actuators.

The key steps in the integration of electronic devices within apparel during the manufacturing process interface can be seen in Figure 1.

Smart textiles (Fig 1)

The first generation of smart garments had all the electrical elements attached externally to the garment, usually with a power pack strapped on the side.

The second generation has fibres that can conduct electricity which can themselves be combined with the normal fibres in a garment to create localised conductive areas and pathways.

Research in the second generation electronic textiles has produced heat-generating knitted structures, knitted transducers, and sensors and light-emitting fabrics.

The question was, 'How do you create electrically active knitted structures?' The advantage of using knitted structures, as opposed to woven ones, is that knitted structures can be fitted close to the skin.

With knitting, conductive fibres can be incorporated into the structure by using intarsia techniques (knitting techniques used to create patterns with multiple colours) to create localised conductive areas, called electro conductive areas (ECAs).

The advantage is that ECAs are fully integrated with the basic knitted structure. Electro-conductive fibres / yarn includes metal yarns (mono-filament and multi-filament), metal deposition yarns (coated), carbon fibres and yarns, and conducting polymeric yarns.

Two examples are nylon fibres with a thin coating of metal film around it, and silicon yarn that has been loaded with carbon fibres.

As part of the research, the smallest area (unit cell) that could be replaced by a resistor was identified. Mathematical models were developed to characterise the functionality of ECAs. The accuracy of the models was evaluated with experimental results. The models were used to develop a heated glove as the first product. Carbon loaded silicone yarns were used to create knitted heater elements and metal coated fibres were used to form knitted connecting leads (conductive pathways) of the heater elements.

Then an electric current was passed through the conductive pathways to activate the heater elements of the glove. The glove can remain heated for up to four hours using a 3.6 volt battery. Three dimensional (3D) knitted technology is used for creating heating elements, and an electrical circuit with conductive pathways. Heating products are being used commercially in heated gloves for skiing and back-warming belts.

Other garments that have been made are a seamless knitted vest with integrated electrodes with conductive pathways to be used for ECGs and respiratory monitoring, and knitted resistive stretch sensors in a sensor-sock used for monitoring 3D orientation in the foot of people who are recovering from a minor stroke.

Another application of electronically active textiles is in knitted switch technology using skin resistance to operate switches in fabrics by touch (KSwitch). This seems to work more consistently when a female touches it and is not so successful when touched by a male or an older person. This difference in the level of conductivity has been found to vary dependent on age, the amount of moisture in the skin, and gender.

This application has been used for prototype switches in the fabric on the inside of car doors e.g. to operate electric windows. The advantages of this technology are easy and reliable manufacture, higher degree of design capability, cost effective manufacture, higher durability, and straightforward integration of K-Switches for different applications. The limitations are switch characteristics dependent on skin resistance, and they are ineffective to other materials so they do not work when the operator is wearing gloves.

The next stage is to develop fibres and yarns that have sensors and transducers, actuators and data processors in them, but that look just like normal fabrics.

The key steps in the integration of electronic devices with apparel during the manufacturing process interface can be seen in figure 2. If the sensors and micro processors are integrated into the yarn itself they will not interfere with the normal manufacturing process of the garment. The technology is based on the encapsulated area not exceeding 110 per cent of the threaded thickness.

Smart textiles (Fig 2)

The vision is the development of novel technology for fabricating electronically active and sensor fibres, which will be the basic building blocks of the next generation of smart fibrous materials. In the future your shirt could monitor your ECG, be your iPod, and talk to you!

It is possible to incorporate electronic chips, optical and thermal devices, into yarn. But this has not been done by anyone before so there is nothing to build on - it is necessary to start from scratch. Yarns were created with LEDs in them so that the functionality could be easily demonstrated. Hitachi is the first company to produce a chip small enough to be embedded with textile fibres, called the Mu-chip. It is 0.4mm x 0.4 mm x 0.15mm.

Work is now being carried out on light emitting yarns, ones that will measure stresses and strains on fabrics and that will sense fluids and liquids.

Professor Dias went on to show two videos that demonstrated knitted switches in a waistcoat and in gloves that could be used for stroke rehabilitation, in people with a disability, or for game playing.

The speaker said that textiles are important parts of our lives from cradle to grave. The fastest area of growth for the use of electronically active smart textiles is in the sports industry. There is no need for clinical evaluation before they can be used and there is a significant market.

However, the NHS will need convincing of the benefit and may not be willing to fund the clinical evaluation. Use of smart textiles in the NHS will need to be driven by the patient - as suggested in the government's information revolution document.

Questions & Answers

How far away are you to sending a message to an external receiver e.g. about a patient that needs help?

Technically it is possible; you can create a garment to monitor a patient's ECG, but you cannot ensure that the patient will wear it.

Ryan Giggs of Manchester United Football Club said that sports scientists monitor them e.g. to check how stressed they are. Could this technology be used to monitor things like sweating?

Top athletes don't sweat that much, it would be difficult to measure. Also there isn't a database of information to compare against. But it has been used for people going to the Arctic to help keep them warm.

 
Further notes on S & Z Twists

The direction in which the yarn is spun is called twist. Yarns are characterised as S-twist or Z-twist according to the direction of spinning. Two or more spun yarns may be twisted together or plied to form a thicker yarn.

This article also appears in the book Health Informatics.

Comments (2)

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  • 1
    saremi wrote on 14th Jul 2016

    hello I study technical textile engineering in master level. I want if it is possible have more article about smart textile that can heatable . can you help me or give me more information or more article that you have studied befor, thanks alot

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  • 2
    Rita wrote on 30th Aug 2016

    Hi Saremi, I would suggest that you contact Professor Tilak Dias directly. You can find him by searching for his name in LinkedIn.

    Regards
    Rita

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