Anyone who has received an electric shock from a colleague after walking across a synthetic carpet knows that even the most mundane of activities can generate energy. But is there any way that this energy can be harnessed? Yong Qin and colleagues suggest it could (Nature 451, 809–813; 2008), using fabrics made of specially coated fibres that produce electricity through the piezoelectric effect.

The authors' fibres consist of two intertwined strands of Kevlar. On one of the strands they grow a forest of radially aligned bare zinc-oxide nanowires, and on the other a similar coverage but of gold-coated nanowires (pictured). Stretching one of the strands back and forth along the length of the second strand causes the nanowires to rub against each other. This rubbing causes the bare zinc-oxide nanowires to bend, which, owing to the piezoelectric characteristics of the oxide, causes a separation of charge to develop across the diameter of each wire. As this happens, the rectifying metal–semiconductor junctions that form at the points of contact between the opposing sets of nanowires allow only negative charge to pass from the bare nanowires to the gold-coated nanowires. This, in turn, generates a voltage across the two strands.

From a single double-stranded fibre, the authors generate peak closed-circuit currents of around 5 pA. By entangling multiple strands together — which increases the area of contact between opposing nanowires — this current can be increased by a factor of up to 50, to an average output current of 200 pA for a six-stranded bundle. And by reducing the core resistance of the strands by depositing a conducting layer before the nanowires, they improve the output of their double-stranded fibres by three orders of magnitude.

One of the advantages of Qin and colleagues' fibre-based generators — compared with previously reported schemes for generating electricity with piezoelectric nanowires — is that they operate at low frequency, which means they can produce power from a wider range of sources of mechanical vibration, such as that generated by someone's physical movement. The flexibility and low-temperature growth conditions of the system are other advantages. By weaving these fibres into a 'power shirt', the authors estimate that up to 20–80 mW of power could be generated by one square metre of fabric — comparable to the power used by a personal music player.