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Produced in partnership with renewable energy designers GotWind, the Sound Charge t-shirt prototype's modified A4-sized panel of Piezoelectric film at the front is said to act like an oversized microphone, absorbing sound waves and converting them via the compression of interlaced quartz crystals into an electrical charge. This is then fed into a small external reservoir battery (with visuals that pulse in time with the music) and the wearer can then pop a mobile phone or smartphone into the pocket above the panel, connect it up to the reservoir and top up the device battery using sound.
The t-shirt was designed to generate up to 6 Wh of power when exposed to sound levels of around 80 dB - that's about the same noise level as a bustling city street and will not pose too much of a problem for Glastonbury Festival-goers. The reservoir hopefully gets enough energy to fully charge two standard mobile phone or one smartphone, although wearers would most likely use it for a quick top up rather than a full charge.
The video linked below gives a short developmental overview.