The Economist:
For obvious reasons, surgeons do not like opening heads up unless it is strictly necessary. Sometimes, therefore, the battery packs that power head implants are put in the wearer’s chest. But this means running a wire up through the patient’s neck, from the one to the other, which is scarcely satisfactory either. A way to power such implants without replacing their batteries at all would thus be welcome. And Hyuck Choo of the California Institute of Technology and his colleagues think they have one. They plan to scavenge the necessary energy from the vibrations of the vocal cords that occur when someone is talking