Recharging via radio waves?

OAQfirst

I'm not knowledgeable about these things, with all the free energy nonsense I frequently see. So what do you think?

http://tech.yahoo.com/blogs/null/143945
Does this sound right? If so, it looks like exciting news. Even for stand-by charging, that's still a good thing.

mgb_phys

You have to assume Nokia have done their sums.
But assuming the signal is a couple of milliwatts and you leave it on continually.
My phone battery is 700mAh x 3.6V so stores around 2.5Wh, charging with 1mW would take 3months! It's difficult to believe it's even enough to overcome the leakage in the charging circuit.

OAQfirst

It reports their goal is 50 milliwatts. Would that be substantial enough?

mgb_phys

My phone lasts a week on standby with a 2500mWh battery so around 15-20mW - if they can pull 50mW out of the air that would certainly help.
I suppose if they didn't just use the phone antenna they could also use the power form lots of other transmitter sources, TV/radio/wifi etc.

OAQfirst

Hmm. Well, here's to hoping!

Thanks.

Greg Bernhardt

Would this phone technology be useful only to those in major cities?

russ_watters

Presumably. I wonder if anyone has actually calculated how dense the radio energy is in various places.

[edit] calculation deleted. I guess you'd want to do a calculation based on surface area....

Ivan Seeking

...and over what range of frequencies?

flatmaster

I immagine you would want to make your windings as large as possible to contain the maximum amount of magnetic flux. Probabilly the entire surface area of the phone. Also, if the phone wasn't sitting in the correct orientation with the source, you wouldn't get anything.

russ_watters

The surface area of a 1"x2"x4" phone is 8 square inches. At 50mw, that's 900 mw/sq ft. The side surface area of my 19x14x8' living room is 528 square feet, which would mean if I wrapped it with antennas, could generate 475 w. My house is 20'x40'x20', or 2400 square feet side surface area. That's 2.1 kW, which (with storage), would be more than enough to supply all my energy needs.

I find that hard to swallow.

Moonbear

Over what time frame?

When would this be most useful? I'd think if you were stranded out in the wilderness without a charger is when you'd need something like this...one would hope the charge would happen fast enough to call for help before you die of dehydration or exposure to the elements. Otherwise, it's nothing more than a gimmick.

russ_watters

miliwatts is power, Moonbear - it's got a timeframe in it (seconds).

Blenton

Isnt it illegal to 'harvest' energy from radio waves? I could imagine those who live near the transmitters putting up huge coils on their houses to sap up the free kilowatts.

Moonbear

D'oh. Sorry, I made the classic mistake of mixing up power and energy. Thanks for the correction.

Pengwuino

What transmitter?

Blenton

Radio station transmitters.

Pengwuino

I would think that's somtehing you could do right now. I was thinking he meant that Nokia was planning on building transmitters specifically for recharging cell phones.