NANOTECHNOLOGY FEATURE Additive nano metal deposition enables smart textiles
Chris Hunt Head of the Electronics Interconnection team at NPL explores overcoming challenges in wearable technology
S
mart textiles have tremendous potential to shape the world of the
future, with exciting applications in sectors ranging from healthcare and sport to fashion and the military. By the end of next year the global market for smart fibres and interactive textiles alone is predicted to reach £1.7 billion, up £530 million on 2015. Such a rapid rate of growth is hardly surprising, but imposes ever greater technical challenges to ensure that supply can keep pace with demand. Many technologies used at present for
the manufacture of conductive textiles, ranging from the direct weaving of metallic threads to the deposition of plasma on the textile’s surface, perform very poorly when the underlying fabric is stretched or twisted. In order to meet the requirements of the sector, what is needed is a conductive medium that can follow the fibres, ideally without affecting their ability to deform, allowing for electrical current to flow unimpeded in any direction and on any textile. Making such lightweight electrical circuits requires new and creative advances in micro engineering technology, a key area of focus for the Electronics Interconnection group at the National Physical Laboratory (NPL). In recent years, the team at NPL has
developed a unique technique to coat individual textile fibres with a metallic layer approximately 20 nanometres thick. Experiments have shown that while silver and palladium are particularly well suited to this technique, it may also be possible to use other metals. The process relies on a solution of dispersed nanoparticles, into which a chemically treated fabric is completely immersed. Alternatively, the nanoparticles can also be formed in situ on the fabric surface. A thin and uniform coating results that remains attached to the surface by a chemical bonding process. This nano-metal layer represents a step change in manufacturing, allowing for the production of fabric which is flexible, stretchable, lightweight, and has excellent conductive properties. With a metal layer wrapped around each individual fibre, the resulting network is capable of achieving 100% coverage with good adhesion and
flexibility. Excellent resistivity has been assured by a 1µm deposition of electroless copper and has already been achieved across textile samples including polyester, linen and lycra, with values of 0.2 Ω/sq well within our reach. Given that the conductive path is applied by an additive method and can be patterned to form circuits, this technique will also enable lightweight electronics to be printed directly onto finished items of all kinds. Multiple electronic circuitry patterns can
easily be placed on a garment in a simple set-up without interfering with the characteristic feel and wearability of the fabric. This also allows for the incorporation of more complex systems such as wireless wearable sensors, which will be capable of efficiently monitoring a patient’s condition. Such domestic recording of physiological data could overcome shortcomings inherent in currently available technology and significantly improve the diagnosis and treatment of cardiovascular diseases. Sensors of this type could also be used
Figure 1:
Zigzag conductive patterning on material
to assist patients with motor disorders such as Parkinson’s disease, where the monitoring of physiological movement could facilitate the titration of medication as the disease progresses. The new additive manufacturing processes we have developed allow us to overcome a number of additional challenges hampering the development of electronic textiles for medical purposes. The ability to build devices or sensors directly into the fabric, for example, allows for an entirely new method for capturing and transmitting information within the garment. Since the conductive pattern is incorporated within the textile, we can therefore ensure that sensors are accurately and consistently placed on the same locations of the body, enabling improved sensor performance and preventing misplacement. Nano-coated fabrics equipped with the correct electronic components could also be used as highly effective personal heaters. The delivery of heat at critical times is vitally important for patients in trauma and shock as well as sportsmen, the elderly and military operatives. Wearing a heated undergarment in intimate body contact is an ideal way of ensuring temperature monitoring and control. Other important areas of application have also emerged from the choice of metal used to coat the underlying threads. Given the well-known antibacterial properties of silver, for example, nanosilver coatings can be used in the fabrication of face masks, surgical gloves and military uniforms where infection of the wound can have serious consequences. Whichever materials are used, tests have
Figure 2:
Example of a conductive circuit
shown that the metallisation process does not unduly impact on the flexibility of the fabric, and allows it to retain its electrical properties across multiple standard washes. Over the coming years, we are likely to see a rapid increase in demand for wearable electronics from industries such as sport and fitness, consumer electronics, medical and healthcare, and defence applications. Implementation of nano- coatings such as those produced at NPL could meet these needs in the near future, allowing for the manufacture of flexible and complex electronic circuitry patterns for use in intelligent clothing.
National Physical Laboratory
www.npl.co.uk 020 8977 3222
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