Coil/Antenna Design for Energy Harvesting?

[bklein]

I came across this article today:
http://www.electronicproducts.com/Po...A_battery.aspx
So new that it looks like their server is overloaded and I can't see the video.
I am going to ask dumb naive questions here...
For energy harvesting purposes, where would the applicativity of a coil suffer in favor of a yagi antenna? (Given the size can be larger than the hand-held thing he has built) Perhaps a coil could be less obtrusive than a pointy yagi.
I've seen things like coffee cans used for 2.4Ghz beams. But for energy harvesting perhaps an omni-directional antenna would be better? (several ambient signal sources)
Feel free to just discuss energy harvesting experiences (but I know all about joule thief things - keep the main topic on ambient rf energy reception).

Barry

[Qiaozhi]

I came across this article today:
http://www.electronicproducts.com/Po...A_battery.aspx
So new that it looks like their server is overloaded and I can't see the video.
I am going to ask dumb naive questions here...
For energy harvesting purposes, where would the applicativity of a coil suffer in favor of a yagi antenna? (Given the size can be larger than the hand-held thing he has built) Perhaps a coil could be less obtrusive than a pointy yagi.
I've seen things like coffee cans used for 2.4Ghz beams. But for energy harvesting perhaps an omni-directional antenna would be better? (several ambient signal sources)
Feel free to just discuss energy harvesting experiences (but I know all about joule thief things - keep the main topic on ambient rf energy reception).

Barry

He could harvest even more energy if he removed the LED. A small meter would be a better alternative.

If we assume the single AA battery has a capacity between 1700 and 2000mAh, then it would need a constant charge rate of approximately 70 to 80 mA for 24 hours to fully charge from empty. The website doesn't state where he positioned the charger in order to achieve this, but we can safely assume that it wasn't done by hanging over a wall and leaching energy from a mobile phone. Doesn't sound too diffcult a task.

[ODM]

Ambient RF in tens to hundreds of mW - and losses? ... Honestly? With a loop or antenna the size of an alarm clock housing?

Did he hang it from an AM station's feed line?

[Overtheedge]

Ever build a crystal radio? It only worked if the headphones were high impedance. This means extremely small amperage. Physically short antennas didn't work so well either.
eric

[Midas]

I'm willing to bet this thing will never harvest enough energy in dollar terms to pay for its components. Its certainly not going to beat other 'free energy' technologies (PV,wind, hydro,wave, etc.) in terms on dollars invested per watt of generating capacity. Unless as ODM suggests its stuck to a very high power RF source or an AC power line in which case its probably reducing the transmission efficiency by more than the energy it harvests. So really its an energy stealing device, it will only operate effectively when someone else is suffering the consequences. I can't believe he won second prize...

Midas

[moodz]

..what a load of B$ ... the power density would be way in excess of safety standards to light a led like that from such a small box ...let alone charge a battery.
you will believe this also then ... http://www.youtube.com/watch?v=3NrfOt0PJdc

[bklein]

Ok but even if it is BS...
What about my questions?

[Qiaozhi]

So really its an energy stealing device, it will only operate effectively when someone else is suffering the consequences.

I completely agree. That's why I referred to it as "leaching".
The term "energy harvesting" implies that this is energy being recovered which would otherwise have been lost. But this is not the case, as it will load the transmitter and "steal" energy.

Maybe it's not even a "real" device, as I notice that Dennis Siegel is a student at the University of the Arts. So, is he an engineering student? Seems odd.

[mikebg]

PASSIVE METAL DETECTORS

For energy harvesting can be used not only crystal radio and battery charge. There are passive VLF metal detectors that do not contain their own transmitter. The principle is described in patent US3500175

http://www.geotech1.com/forums/showt...335#post108335

A simple and primitive use of this principle have metal detectors GOLD GUN (AL707 and AL71:

http://www.qudamaa.com/vb/f93/gold-g...tml#post167866.

[ODM]

Energy "harvesting" from the motion when using a MD will likely not reach high enough a fraction to be feasible. Near field energy leaching is an option - though there was already a thread about using a search coil assembly for charging detector batteries, and I don't remember if any viable options for that were proposed.

But yes, it seems the fellow is a design student and this might be some kind of portfolio eye catcher, or a viral advertising project he's doing.

[golfnut]

Im impressed it charged up AA in a day.

It would be practical to use a wall of these around a power distribution substation like those photographed - rather than waste it.


"In fact, it took Siegel’s device a full day to charge a single AA battery."


S

[Aziz]

*LOL*
Forget this stuff. Get your own ZPM and destroy or freeze other universes.
Aziz

[bklein]

Wow, this thread went directions I didn't expect.
I'm not really thinking of using the detector coil as an energy harvesting component to charge the detector batteries.
I don't mind charging an extra battery pack or two.
Here's what I'm curious about. Say you are in a large room full of 2.4Ghz transmitters, like an Apple conference or something. What type reception device would best collect energy from them that would fit in/on a reasonable size box? It is an omni vs directional antenna question I guess. Do coil solutions become relatively ineffective at some frequency?

[bbsailor]

All,

Check out this patent number from the 1920s: 1540998. The most practical and efficient transfer of energy through induction is when the TX and RX antennas are tuned to the same frequency. I believe the referenced patent attempts to extract static electricity potential differences to make use of that power.

bbsailor