Energy harvesting textiles
For Professor Steve Beeby, the idea to generate electrical energy from vibrations began in 1995. Piezoelectrical materials generate energy if you squash them or move them and that became the obvious way to develop energy harvesting. Now his team at the School of Electronics and Computer Science, University of Southampton are developing a method of printing piezoelectric circuits on textiles to generate a power supply for local applications such as medical sensors on the wearer’s body.

Their study of the electronic functionality of textiles is part of an EU funded project called Microflex, whose 13 partners include other research institutions and textile manufacturing partners.  One area they are looking at creating is smart fabrics, which can sense stimuli and adapt to them. However, sensors on fabrics need power so combining piezoelectric films with the sensors makes more sense than using external batteries.

Screen printed circuitry
Beeby points out that ‘the piezoelectric material that goes on to the textile has to be flexible and comfortable for the wearer, survive washing and all the rigours of use in a textile application. We are developing these materials that we can easily and cheaply print on to the textiles, so it’s a printable piezoelectric material.’

Using a piezoelectric powder they can mix it with polymers to get a viscose paste and screen print it. Screen printing has been used for hundreds of years to pattern textiles, their idea is simply to screen print with active materials.

Battery free health monitors
Like a printed circuit board, the conductive tracks are printed on the fabric then a capacitor is used to store the energy. The power only appears when force is applied to the textile. The energy is stored and when there is sufficient energy the other electronics wake up, do some sensing and go back to sleep when the job is done. As textiles are potentially large surface areas, there’s the advantage of printing pretty big patterns with the potential to harvest more energy.

Beeby foresees that the circuitry will vary according to its application. Medical applications are an obvious area of need. If you can sense a patient’s well being or their recovery after an operation, using sensors in the clothes they are wearing and the wearer just puts on the vest, that would be a very useful application to achieve.