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.

To increase the amount of power that can be harvested and the range at which it works, Nokia is focusing on harvesting many different frequencies. “It needs a wideband receiver,” says Rouvala, to capture signals from between 500 megahertz and 10 gigahertz–a range that encompasses many different radio communication signals.

Historically, energy-harvesting technologies have only been found in niche markets, powering wireless sensors and RFID tags in particular. If Nokia’s claims stand up, then it could push energy harvesting into mainstream consumer devices.

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.

Smith says that 50 milliwatts could require around 1,000 strong signals and that an antenna capable of picking up such a wide range of frequencies would cause efficiency losses along the way.

“To get 50 milliwatts seems like a lot,” adds Harry Ostaffe, head of marketing for Pittsburgh-based company Powercast, which sells a system for recharging sensors from about 15 meters away with a dedicated radio signal.

Formula 1:
After Filipe Massa’s nearly fatal accident (luckily, he will fully recover from it) a few months ago, a new safety device came to my mind today. It’s simple but due to the speed of a F1 car tricky to implement. Like the rollbar of the Mercedes SL it would pop up in front of the driver’s helmet and protect from severe injuries. The question is just: “How do you activate it?”

Nice equipment!

The Nokia N96 is coming soon!

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Stainless steel knob (diameter approx. 50 mm).
Occupied all 12 stations of the turret for this first operation:
Bar stop
O.D rough and finish
I.D. rough and finish
Center Drill
Drill
O.D thread
Tapped hole
Milled square inside
Milled flutes on O.D.
Part off