http://tech.yahoo.com/blogs/null/143945

Nokia, however, has taken another baby step in that direction with the invention of a cell phone that recharges itself using a unique system: It harvest ambient radio waves from the air, and turns that energy into usable power. Enough, at least, to keep a cell phone from running out of juice.


While "traditional" (if there is such a thing) wireless power systems are specifically designed with a transmitter and receiver in mind, Nokia's system isn't finicky about where it gets its wireless waves. TV, radio, other mobile phone systems -- all of this stuff just bounces around the air and most of it is wasted, absorbed into the environment or scattered into the ether. Nokia picks up all the bits and pieces of these waves and uses the collected electromagnetic energy to create electrical current, then uses that to recharge the phone's battery. A huge range of frequencies can be utilized by the system (there's no other way, really, as the energy in any given wave is infinitesimal). It's the same idea that Tesla was exploring 100 years ago, just on a tiny scale.


Mind you, harvesting ambient electromagnetic energy is never going to offer enough electricity to power your whole house or office, but it just might be enough to keep a cell phone alive and kicking. Currently Nokia is able to harvest all of 5 milliwatts from the air; the goal is to increase that to 20 milliwatts in the short term and 50 milliwatts down the line. That wouldn't be enough to keep the phone alive during an active call, but would be enough to slowly recharge the cell phone battery while it's in standby mode, theoretically offering infinite power -- provided you're not stuck deep underground where radio waves can't penetrate. Nokia says it hopes to commercialize the technology in three to five years.

What I keep wondering is how the set will know if it's 'unnecessary' EM energy, or, in other words, how do you prevent such a device becoming a radio (wifi, bluetooth, etc) jammer/sink ?

Maybe it will use the back of the phone for cell connection and front of the phone to suck EM waves... or maybe brain waves?

I'm still really not all that impressed with the wireless charging and power systems. While the concept is good, they're grossly inefficient by nature. Now an application like this however might be a better use for such a system. But then the next question arises. While there's enough EM radiation to make this work well in urban environment, what about rural areas where there's not much of any EM radiation to speak of?
Well, if they did that, it'd have the advantage of partially shielding the user from cellular radiation, while reclaiming part of the energy lost due to someone's big fat head being in the way of the signal.

the physics involved?

a jammer is a active transmitter that sends a stronger signal then the one you want to recieve.

as for it being a sink, you will need a wall of phones more or less, and stand in the direct "shadow" of that wall.

best way to envision it is like a thin piece of fabric in front of a lamp. it may produce a darker area on the opposite wall, but it will not darken out the whole room unless you basically wrap it around the lamp...

That really depends on the frequency. Even without human sources you will have SOME EM radiation everywhere. Now, if you're not near short-range pesky microwave sources, the ones who might curse you for leeching will be cellular operators, radio stations, terrestrial TV stations, wimax folks, basically anyone who does long-range wireless communications.

PS. The idea is not really lab-tech - I remember making detector/crystal radios when I was a kid, those were simple shortwave receivers that were getting both signal and power through antennas. Cool stuff (even by todays standards), but when harvesting EM waves, you want BIG ANTENNAS

Nokia try to recharge battery by wave around instead built a photovoltaic device...

that's a weird orientation lol

yah! put a big transmitter near a dam then every house having a big antenna to receive electricity so we can have wireless electricity!

Almost, although it's not related to power - it means decreasing signal to noise ratio of a signal (altough done by emission most of the time as it's the easiest way of achieving that goal). I admit being somewhat free with the terminology

No, it doesn't work that way, unfortunately Radio waves propagate differently than light - that's why you use antennae that are very different, to, say, optical telescopes. Of course, the actual difference varies with the frequency, but it's far from the lamp example -> it's a bit like a magnet drawing metallic particles, the affected area is much larger than just the actual antenna. Now, if these buggers want to harvest a consistent 50mW out of thin air, they HAVE to cover a large area, not just a 'speck' on the back of the set (either that, or we're already glowing in the dark )

heh, the devil will as always be in the details.

still, EM waves are EM waves, no?

got to confess tho, im a curious amateur when its comes to a topic like this one...