Current work at Nottingham Trent University

Work is concentrating on heated textiles (Figure 2), embroidered antennas (Figure 3), and fully integrated electronics. The heated textiles are made using textile-based heating elements knitted into the structure. The antennas are embroidered from silver coated yarn and are designed to work at megahertz frequencies, initially for search and rescue applications [65].

In addition, a computerised flat-bed knitting process is used for the manufacture of large-area textile structures with repeated patterns to produce periodic structures such as frequency selective and meta-material surfaces for communication systems [66,67].

The work on antennas is being undertaken in collaboration with the University of Loughborough, and research on frequency selective surface (FSS) and high impedance surfaces (HIS) is being carried out with the University of Sheffield. Work on additional application of fully integrated electronics has been undertaken with the University of Southampton.

There are a number of approaches to the production of electrical and electronic textiles. These include inserting pre-packaged electronics into pockets, stitching components to the surface, integrating functionality using conductive threads, using printing technology or integrating electronics into belts or straps. However, the ultimate aim would be to integrate electronic functionality into textiles without compromising the required textile characteristics of softness, flexibility and conformability. In addition, to minimise costs, it is essential that electronic textiles can be produced on conventional textile equipment. One approach is to encapsulate semi-conductor chips within the fibres of yarns. As a textile conforms to a shape some regions bend and some go into shear deformation. Both factors are important for drape [68] and conformability. Knitted and woven textiles are able to conform to a shape as they bend and shear. For example, paper can bend but, as it cannot shear, it buckles and crumples rather than conform to a shape.

The approach that is being developed at Nottingham Trent University, under the leadership of Professor Tilak Dias, is to connect semi-conductor chips to fine copper filaments and incorporate them within the fibres of a yarn. The chips are then protected by resin micro-pods. Free fibres between micro-pods help retain the desired textile characteristics. The yarns are then woven or knitted using conventional textile equipment. Schematic representations of the resultant yarns are shown in Figures 4 and 5.

By way of a demonstrator, light emitting diodes (LEDs) have been integrated into yarns. The LEDs are off the shelf and are 500µm in width and are shown against grains of salt in Figure 6. The chips are manipulated using a focused IR reflow and pick and place device (Figure 7).

The resultant yarn is shown in Figure 8.The yarn functions under water (Figure 9)

Woven fabrics have been produced on a hand loom (Figure 10) and on state-of-the-art flat-bed knitting machines (Figure 11).

The resultant fabric retains the ability to shear as the electronics are embedded within the yarns. A garment produced using the technique is shown in Figure 12. The fabric retains its conformability and, when the LEDs are switched off, the inclusion of electronics is not visible to the naked eye on either face of the fabric. The garment was exhibited at the Future Textiles exhibition at the Palace of Westminster in December 2012 (Figure 13).

A n important feature of the technology is that the resultant fabrics can be machine washed and tumble dried. This is made possible by the resin encapsulation of the semi-conductor chips. In addition, due to the free fibres between micro-pods, the fabrics remain soft and flexible. The ability to introduce electronics at the yarn stage has significant cost implications for the manufacture of large scale electronic assemblies.