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[ESC] Two views of wireless power harvesting

Catwell
Power harvesting is indeed a major trend as of late. Many companies at the ESC expo were showing off their offering in this vein. Heat conversion using Peltier junction blocks used in reverse, was very common. Vibration energy absorption using piezoelectric devices on everything from cars to shoes were present. And of course wind turbines were fluttering everywhere. But the most discussed and inspiring of all were the wireless energy harvesting concepts (related article). Wifi, cellular, and other radio signals were analysed for their energy potential by many groups.


One speaker, replying to a question of whether power could be harvested from wifi and such signals said without hesitation, "It ain't going to work." And a little later followed that up with a confident, "can not work." I am skeptical. I believe it's possible. If Tesla could do wireless power transfer 70 years ago, why can't it be done today?


At another lecture a different speaker had the complete opposite view on wireless power transfer. He said that wireless power options were yielding results in the uW ranges in his experience. However, he didn't discuss how the results were achieved.  Very dichotomous views, I thought.
 

I want to know, since I have not attempted such a feat, is wireless power harvesting a viable option? Has anyone tried this, or have experience in such things?
 

Cabe
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    This isn't of course what you had in mind, but power transfer by wireless means is accomplished, often very efficiently, by transformers.

     

    Power transfer by radio signals is undoubtedly less efficient. I can remember some years ago lighting a 4 foot fluorescent tube by holding it near a VHF transmitter. Input power to the transmitter maybe 60W, effective radiated power around 25W, light output at around 18 inches was enough to show that the tube did light up, though not too brightly.  I was also told it worked nicely near big transmitters like the UK's `BBC Crystal Palace Transmitter' .. but then that's several megawatts.

     

    Energy harvesting from cellular, WiFi, etc. is probably feasible if you can get by on microwatts.

     

    I did see an article a while back about using MEMs techology to build `massive arrays' of dipoles in the Infra-Red band to receive energy from the heat of the sun. The idea was that it might be more efficient than PV cells, though I know not yet whether it was. A dipole for infra-red is around 0.5 micometers long and the electrical signal still needs converting to a useable frequency or DC. My guess is that this would use a fractal technique, but that's very much a guess on my part.

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    This isn't of course what you had in mind, but power transfer by wireless means is accomplished, often very efficiently, by transformers.

     

    Power transfer by radio signals is undoubtedly less efficient. I can remember some years ago lighting a 4 foot fluorescent tube by holding it near a VHF transmitter. Input power to the transmitter maybe 60W, effective radiated power around 25W, light output at around 18 inches was enough to show that the tube did light up, though not too brightly.  I was also told it worked nicely near big transmitters like the UK's `BBC Crystal Palace Transmitter' .. but then that's several megawatts.

     

    Energy harvesting from cellular, WiFi, etc. is probably feasible if you can get by on microwatts.

     

    I did see an article a while back about using MEMs techology to build `massive arrays' of dipoles in the Infra-Red band to receive energy from the heat of the sun. The idea was that it might be more efficient than PV cells, though I know not yet whether it was. A dipole for infra-red is around 0.5 micometers long and the electrical signal still needs converting to a useable frequency or DC. My guess is that this would use a fractal technique, but that's very much a guess on my part.

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