Scientists have implanted a tiny pacemaker in a rabbit and wirelessly powered it to regulate the animal's heart beat. It's the first time such a device has been powered this way in a living animal, suggesting that the same technique could run pacemakers or other devices in humans. This would be huge, because now pacemakers and other devices have to be removed and re-installed when they run out of batteries, involving risky surgeries.
Without needing bulky batteries, the devices could also become much smaller--the size of a grain of rice, as in the case of this pacemaker. It's further described in a video below from Stanford University, where study author Ada Poon hails.
The pacemaker was powered by a cellphone battery within a metal plate, held about an inch above the animal's chest. It works by inducing power, with electromagnetic waves, in an energy harvesting coil in the pacemaker, as New Scientist explains:
Such "near-field energy transmission" was previously considered too weak to power devices that are small or placed deeply in the body. To get around this problem, Poon's team designed the plate to emit electromagnetic radiation in a directed beam towards the implant. They also used the rabbit's own body tissue to help deliver the signal: the radiation is of a high frequency that propagates particularly well in animal tissue, allowing it to pass further into the body without losing much energy into the tissue or causing damage.
It remains to be seen if this would be feasible or healthy for larger devices (which would presumably require more powerful transmitters), or for use in humans, although the scientists claim the electromagnetic waves don't harm the animals--and they are bullish about human applications in the near future.