It sounds a little sci-fi at first, but it's not: RFID tags are powered by electrical signals converted from electromagnetic waves emitted by a nearby sensor machine, which is exactly how this system is said to work. The thing is, the amount of electricity involved here is tiny, and Nokia's system won't even have a base station—it'll draw from ambient electromagnetic waves, meaning Wi-Fi, cell towers and TV antennae. Nokia hopes to harvest about 50 milliwatts—not quite enough to sustain a phone, but enough to mitigate drain, and slowly charge a handset that's been switched off.
Current prototypes only gather about 5 milliwatts, which is essentially useless, and scientists and industry experts just don't see the technology maturing to the point that Nokia wants it to, at least in the near future. But the company's researchers are standing strong:
I would say it is possible to put this into a product within three to four years.
If you believe them, this is pretty exciting: maybe not as a primary charging mechanism, but as a battery extender. [Technology Review—Image from Technology Review]