A cell phone that never needs recharging might sound too good to be true, but Nokia says it's developing technology that could draw enough power from ambient radio waves to keep a cell-phone handset topped up.via Technology Review via Engadget
Ambient electromagnetic radiation--emitted from Wi-Fi transmitters, cell-phone antennas, TV masts, and other sources--could be converted into enough electrical current to keep a battery topped up, says Markku Rouvala, a researcher from the Nokia Research Centre, in Cambridge, U.K.
Rouvala says that his group is working towards a prototype that could harvest up to 50 milliwatts of power--enough to slowly recharge a phone that is switched off. He says current prototypes can harvest 3 to 5 milliwatts.
The Nokia device will work on the same principles as a crystal radio set or radio frequency identification (RFID) tag: by converting electromagnetic waves into an electrical signal. This requires two passive circuits. "Even if you are only getting microwatts, you can still harvest energy, provided your circuit is not using more power than it's receiving," Rouvala says.
Earlier this year, Joshua Smith at Intel and Alanson Sample at the University of Washington, in Seattle, developed a temperature-and-humidity sensor that draws its power from the signal emitted by a 1.0-megawatt TV antenna 4.1 kilometers away. This only involved generating 60 microwatts, however.