# Converting Radio waves into D.C Electrical energy

Discussion in 'Wireless & RF Design' started by prab00, Dec 24, 2009.

1. ### prab00 Thread Starter New Member

Dec 24, 2009
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Radio waves(U.H.F) into D.C electrical energy of 800mAh 4.2V
converting it and the procedures to do it....my mail address is <snip>
am under an innovative

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Last edited by a moderator: Dec 24, 2009
2. ### Papabravo Expert

Feb 24, 2006
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The voltages and currents available at an antenna are far too small to convert into meaningful amounts of DC power. The figure that you gave, 800 mAh @ 4.2 Volts is actually a battery capacity. It means that a battery can supply 800 mA for 1 hour at 4.2V, that is 3.36 Watts for 1 hour.

Back to the antenna receiving a UHF signal, we are talking microvolts and nanoamperes. Its a fundamental proposition that you cannot convert a handfull of femtowatts on an antenna into 3.36 Watts from a battery without an external source of power.

Ain't no free lunch in this life or the next one. Sorry 'bout that, someone may have swindled you on this one.

Apr 5, 2008
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4. ### prab00 Thread Starter New Member

Dec 24, 2009
7
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but i got this idea following.......
{First detect the UHF and convert to an electrical signal. Then use a diode to rectify it to all pos. (or all neg.). Then you can use the appropriate value capacitor to smooth from half wave rectified to a solid DC. You'll need to use some sort of regulator to get the 4.1V you want.}is it Possible dude? reply me

5. ### hgmjr Retired Moderator

Jan 28, 2005
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I think you will find that the amount of power expended to recover the energy from the RF signals will always exceed the amount of RF energy you recover.

hgmjr

6. ### steveb Senior Member

Jul 3, 2008
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Very interesting article. Personally, I would be very surprised if they actally made a 50 mW energy harvester as a practical product.

If they do, it's going to open up a can of worms on regulation issues. People will be hoarding around wireless transmitters trying to steal energy, and the people who own the transmitters aren't going to like it.

I remember reading an article (I think it was Popular Mechanics) about a company claiming that flying cars would be practical soon. It was a front page article on a well-known magazine cover. It came out in the early 1990s and claimed these cars would be common in the 2000-2010 time frame. I laughed when I saw it.

Marketing people publish many pipedreams, but some of them do come true ... so we'll see.

EDIT: I couldn't resist going online to find the magazine cover (see attached). The idea itself is not crazy, but what made me laugh was that the article claimed that 1 decade was enough to get by all the technical and regulation issues that any layman would understand as extremely difficult issues.

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Last edited: Dec 24, 2009
7. ### Duane P Wetick AAC Fanatic!

Apr 23, 2009
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We still haven't come up with a usable battery design to compete with Thomas Edisons 1903 lead acid design, and it is still being put into new cars today. In spite of Interstate Battery's all out advertising campaign, its no secret!

Regards, DPW [ Everyone's knowledge is in-complete...Albert Einstein]

8. ### prab00 Thread Starter New Member

Dec 24, 2009
7
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no dude but my question is different from what u answered?

9. ### Papabravo Expert

Feb 24, 2006
12,284
2,723
No UHF signal received on an antenna is going to be anywhere near 4.1 Volts, 4.1 microvolts maybe. So amplify it you say, but an amplifier takes power from an external source and the power you get out is always going to be less than the power that you put in.

In words of as few sylables as possible:

There is no way to extract meaningful amounts of power from a UHF signal on an antenna unless you are within a very short distance (centimeters) of the transmitter. You've been scammed, and I hope all they've taken is your pride. If they've relieved you of your hard earned shekels then you have my sympathy.

10. ### beenthere Retired Moderator

Apr 20, 2004
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Well, the answer was not about energy harvesting, but did point out that not all ideas pan out.

Radio receivers typically get signal levels off the antenna in microvolts, with lower current levels. The power "available" is in the nanowatt level. RFID devices tend to be passive and use energy harvesting to make their replies, but the tranceiver is usually within a meter or two.

Expecting to get multiple volt signals at 800 ma currents is not realistic. Not at any portion of the RF spectrum, let alone UHF.

The physics building where I worked was inside the near field of a radio transmitter (89 MHz) for a couple of years. Only some optical experiments could be done, as the RF levels were very high - 1 - 2 volts. Currents were possible in the 10's of microamps. That would give a possible power of 20 microwatts. That's a long way from over 3 watts.

11. ### Papabravo Expert

Feb 24, 2006
12,284
2,723
@beenthere -- sail on
BTW when is the next TGYC regatta I'm itching to get my wetsuit on and take my Laser II out for a spin.

12. ### Duane P Wetick AAC Fanatic!

Apr 23, 2009
420
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Last edited: Dec 26, 2009
13. ### prab00 Thread Starter New Member

Dec 24, 2009
7
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is there any ways like using induction methods because radio waves are electrons right and by using transformers in the circuit can v power them up plz tell me if there is a way

Dec 24, 2009
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15. ### Papabravo Expert

Feb 24, 2006
12,284
2,723
There is no practical way to extract "free" DC power from the ambient RF energy that surrounds us all day everyday. I know that delusions are powerful and that it takes considerable effort disabuse ourselves of things we are obsessed with, but you need to channel your energies in another direction

16. ### Wendy Moderator

Mar 24, 2008
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You're hearing pretty much the same things I said in the other post before it disappeared. If there were as much radio energy as you seem to think there is I suspect we would all be dying of cancer.

Unless you live next to a powerful transmitter it isn't going to happen. I suspect the guy your stealing power from would not be happy, he went to a lot of trouble to make it, it was intended for other uses. Using it might even qualify as theft of service.

There is a form of electromagnetic radiation that is plentiful, that would be sunlight.

17. ### prab00 Thread Starter New Member

Dec 24, 2009
7
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dude..... i have head that radio waves have ionizing energy is it possible??? can we make use of that in my project suggest me........

18. ### AlexR Well-Known Member

Jan 16, 2008
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You heard wrong! Radio waves are a form of non-ionising radiation. Ionising radiation occurs at Xray energies and above.

As everyone else has been trying to tell you, unless your reciever is very very close to the transmitter you cannot get any useful power from received radio waves.

19. ### prab00 Thread Starter New Member

Dec 24, 2009
7
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ok dude i understand your quote.......but be on the logic is it possible to convert them if it is very very close to the transmitter....now we have to find out this...and then we will decide whether is it possible at long distance or not using other technologies......

20. ### Wendy Moderator

Mar 24, 2008
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We are talking very basic well understood physics, unless you are close to the transmitter taint gonna happen.