Energy question of the week: How does one turn a T-shirt into a power station?

08. February 2010, 09.02, Jan Oliver Löfken, 4 Comment/s
Whenever the battery in a mobile phone, laptop or MP3 player goes flat, the desperate search for a power socket begins. A power source that everyone can carry with them at all times will provide more independence in the future – their own shirt. That your electronic equipment could ever be recharged by a piece of fabric does sound rather like a fairy tale. But is the 'T-shirt power station' really such an impossibility?

For Zhong Lin Wang’s group of researchers at the Georgia Institute of Technology in Atlanta, special electrical fibres are actually a future source of mobile electrical power. After several years of research, over a year ago they successfully produced a robust prototype of an electrical fibre and unveiled their results in the prestigious journal 'Nature Nanotechnology'. A thin zinc oxide thread generated electricity simply from bending motions. These fibres were able to convert mechanical energy into electrical power with an efficiency of almost seven percent.

Electricity from the flexing of nanofibres

This tour-de-force was accomplished using the piezoelectric effect – whereby materials generate electrical voltages in response to mechanical movements. Electronic lighters generate their ignition spark using a piezo module of this kind and ultra-sensitive pressure sensors measure a mechanical load via the voltage generated by this process. For the electricity-generating piezo fibres, the researchers used a thread measuring just four millionths of a metre in diameter and just one fifth of a millimetre in length, with or without a number of zinc oxide fibres in a flexible film made of polyamide plastic. Whenever this module is bent, the zinc oxide fibres stretch one tenth of a percent, causing the bristles to rub against one another. This causes a current of up to eight picoamperes (million-millionths of an ampere) at a voltage of 50 millivolts (thousandths of a volt).

sThe researchers are now able to enclose zinc oxide, a material renowned for its brittleness, so effectively in a plastic sheath that the fibres do not crumble to dust straight away. Following their first tests with individual piezo fibres, researchers estimate that one square metre of this fabric, with electrical fibres woven through it, should be capable of delivering about 80 milliwatts (thousandths of a watt) of electrical power. That would be quite sufficient to power a mobile phone in standby mode.

Mobile power station for medical sensors

Wang can already imagine many applications for his tiny power stations. "Nanotechnology that can provide its own electrical power could form the basis for a new branch of industry," he says. Using implanted fibres of zinc oxide, it could become possible for muscular movements to operate medical sensors. However, he is also thinking of larger modules that could be incorporated into soles of shoes or textiles, which could continuously charge the batteries of mobile electronic devices while the owner is walking. Many of his colleagues are taking Wang’s ideas very seriously indeed.

Further reading for subject specialists: 'Power generation with laterally packaged piezoelectric fine wires', Rusen Yang et al.; Nature Nanotechnology, doi:10.1038/nnano.2008.314

Further information:
Wang’s working group

The DLR energy question of the week in 'The future of energy' Year of Science

The Federal Ministry of Education and Research (BMBF) has given the Year of Science 2010 the motto 'The future of energy'.  For this reason the science journalist Jan Oliver Löfken will this year answer a question on the subject of energy in his blog each week.  Do you have a question about how our energy supply might look in the future? Or do you want to know, for example, how a wave power plant works and how it can efficiently generate electricity? Then send us your question by email. Science journalist Jan Oliver Löfken will investigate the answers and publish them each week in this blog. 

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