Original URL: http://www.theregister.co.uk/2011/11/21/sound_powered/
Japanese boffins demo sound-powered vibe lights
Son et lumière, literally. Plus: The Song of e-Money
Boffins at the University of Tokyo have been demonstrating LED lights driven by directional sound waves, but reckon the technology for delivering electricity has even better applications.
The installation consists of LEDs hung on wires around a large room, each LED being accompanied by a brace of microphones which pick up sound and turn it into power, all caught on film by DigInfoTV . The demonstrator points a standard directional speaker at the wall, causing groups of LEDs to light up, but the researchers reckon it’s the ability to use human-audible sound which makes their technology useful.
Wireless delivery of power is relatively easy using an induction coil, but only at very short ranges. This receiving tech can pick up 10mW of energy from a speaker half a meter away, and a single milliwatt from 5 meters off, which is still enough to power an LED or charge up a sensor's battery.
It's certainly a lot more sensible that Orange's headline-grabbing t-shirt which was supposed to grab electricity from the guitar riffs  at Glastonbury - but that did come demonstrated by a leggy model  rather than Japanese boffins.
Energy harvesting, as the technique is properly called, is increasing in popularity, as much because of the frugal power requirements of today's (basic) tech as the ability to generate more power. Wireless light switches powered by the pressing finger are a personal favourite, but battlefields are increasingly being covered by disposable sensors which pick up power from the vibrations of passing vehicles (and use that power to report the presence of the aforementioned vehicles). Solar power is still preferred for military apps, as it produces more current, but at a cost of being visible to the enemy.
The Tokyo boffins reckons their tech could be used to power contactless credit cards, which currently use a very-short-range induction coil for power. Sound could deliver the power right to the user's pocket, and so negate the need to take out the card, with the added advantage that the user could hear when their card was being powered - making life much harder for the electronic pick-pocket. ®