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Is it possible to generate a small DC power from Radio waves?If yes then how?

clabacchio
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Atom
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    How much power? – Leon Heller Jun 21 '13 at 07:04
  • I noticed this a while ago that's worth a read about a company that produces RF energy harvesting components: http://au.mouser.com/applications/rf_energy_harvesting/ – PeterJ Jun 21 '13 at 07:07
  • @LeonHeller I just want to know that is it possible or not?If it is possible then what should i do – Atom Jun 21 '13 at 07:13
  • It's possible but it wont yield useful amounts of power. I'm sure this Q has been answered elsewhere (perhaps on physics.SE) – RedGrittyBrick Jun 21 '13 at 07:56
  • It is possible http://en.wikipedia.org/wiki/Energy_harvesting#Ambient-radiation_sources – travisbartley Jun 21 '13 at 08:59
  • @trav1s sounds like a good topic ENERGY HARVESTING thanxxx – Atom Jun 21 '13 at 09:01
  • Yes, energy harvesting is especially important for small sensor nodes that cannot be connected to an external power source or battery. But if they can draw energy from their environment they can be used to collect and transmit data, e.g. temperature, acceleration, etc. – travisbartley Jun 21 '13 at 09:06
  • look at http://en.wikipedia.org/wiki/Space-based_solar_power – JIm Dearden Jun 21 '13 at 11:02
  • @JImDearden what about Energy harvesting??? – Atom Jun 21 '13 at 11:04
  • @SHASWAT Basically the amount of radio wave power in the 'ether' is very small compared to say solar power. (Solar power being a form of electromagnetic radiation anyway). Indirectly there is wind and water. If you are going to harvest energy it makes sense to harvest the largest sources first. Radio waves just don't cut it. – JIm Dearden Jun 21 '13 at 11:09
  • @JImDearden sounds like a uneconomical project??? – Atom Jun 21 '13 at 11:13
  • to get an idea of how much power there is available to be harvested, see http://electronics.stackexchange.com/questions/72498/electromagnetic-charging/72509#72509 – Phil Frost Jun 21 '13 at 14:53
  • A reprint of an article in "Popular Electronics" from 1951. http://www.rfcafe.com/references/popular-electronics/high-power-crystal-set-august-1960-popular-electronics.htm and yet another link http://www.ke3ij.com/nopower.htm – Optionparty Jan 08 '14 at 13:55

1 Answers1

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Yes, it is possible. In fact, crystal radios work on this basis. With a reasonable antenna and a powerful enough AM station, they can drive a high impedance headphone to well-audible volume using only the power received by the antenna.

The basic trick is to us a transformer to step up the low RF voltage picked up by the antenna. Antennas tend to be rather low impedance, like 75-300 Ω. The output of the transformer would be at a higher voltage, although also at a higher impedance. The higher voltage is important so that the forward drop of a diode is small compared to the voltage, and therefore doesn't loose too much power when rectified.

In a crystal radio, the secondary of this transformer had a capacitor accross it to form a tuned circuit that resonated at the desired radio station's frequency. This capacitor was adjustable so that different radio stations could be received.

Olin Lathrop
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  • When I was in the 10..12 years range I made crystal radios for all my friends. I always used a single coil (not a transformer). A good (long) antenna, a good earth, and a high impedance headset were critical. A tuning variable capacitor was not that critical: you could hear a few stations simultaneously anyway :) – Wouter van Ooijen Jun 21 '13 at 15:34
  • I made a crystal radio about a year ago, but it didn't generate DC as far as I know. Here is the circuit. Are you talking about another crystal radio circuit, that does generate DC? Or am I wrong, and does my circuit generate DC? –  Jun 21 '13 at 16:51
  • @Camil: Note the diode in your schematic. That means the output will be positive. In this case is will have a pulse for each carrier cycle. Bascially it's a half-wave rectifier circuit without the output filter cap. If you add the cap, then you will get a more steady voltage. – Olin Lathrop Jun 21 '13 at 23:38