Converting Radio waves into D.C Electrical energy

maxpower097

Joined Feb 20, 2009
816
Just for curiosity would it be possible to use some sort of laser to transmit power over LOS distances? I'm not asking if I could do it, but could MIT do it? Or someone with millions of dollars behind them do it?
 

steveb

Joined Jul 3, 2008
2,436
Just for curiosity would it be possible to use some sort of laser to transmit power over LOS distances? I'm not asking if I could do it, but could MIT do it? Or someone with millions of dollars behind them do it?
Yes, that is something you could do, and it doesn't take millions of dollars. The problem would be eye-safety. Any laser with power over 1 mW is a serious hazzard and can blind people. There are eye-safe wavelengths that could be used, but then the cost of the laser and the optical detector goes up, and these wavelengths may be attenuated more by the atmosphere.
 

Papabravo

Joined Feb 24, 2006
21,159
The problem is not the generation of large amounts of optical power. The problem is to find a non-disipative method of converting the optical power back into something useable. A clean lens is invisible to a laser, but a dirty lens will heat up rapidly if not smoke profusely.
 

steveb

Joined Jul 3, 2008
2,436
A clean lens is invisible to a laser, but a dirty lens will heat up rapidly if not smoke profusely.
The solution here is to create a wide colimated beam for transmission. This is better for eye-safety and relieves the type of power density problems you are mentioning here. A 10-100 cm diameter beam would need to exceed 100 kW before light intensity begins burning dust and debris on a lens. Still, a clean lens is needed for good transmission. This implies a vertical orientation and/or a shroud, along with routine maintainance.

Note that a 10-100 cm beam cannot fully interact with the human eye, hence it is safer than a 1-10 mm beam. But, still the beam should not be located or directed where unsuspecting people might be hit.

Basically, the idea can work for power levels that are not too high, but it only makes sense for very specialized applications, and even then only when people will not be near the transmission path (or an accidental reflection path).

I view this method of providing system power to be a case where practical implementation constraints are even more important than the technical and cost limitations of the technology itself. Issues like weather (rain, snow, fog), safety (injuring people or animals), maintainance (cleaning lenses, reflectors and detector surfaces), really limit the cases where this approach would be preferred over more typical approaches.
 

Pavlo138

Joined Feb 26, 2009
28
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
I think I might understand were you are going with this project, and it's called wireless power transmission. However, any usable forms of power transmission have occured using magnetic coupling and not through electrical fields,(since magnetic and electrical fields are 90° out of phase with each other, one does not necessarily effect the other.) But according to Lenz's law when a conductor passes through the lines of flux of a magnetic field; a current is induced. So I'm not sure of the internal dynamic of such wireless power transmission systems, but I'm sure Lenz's law is a good start as any. Also, all forms of natural/ analog energy are recipricol in nature, not descrete as DC levels are. And yes you would end up expending more enrgy powering your amplifier circuits then what you would be generating,(law of the conservation of energy; cannot get out more then what I put in!)

Heres a good example: http://electronics.howstuffworks.com/wireless-power1.htm

and: http://www.tfcbooks.com/articles/tws8c.htm

and this one is really cool!
http://www.osti.gov/bridge/purl.cov...6ED43813357FA7EA54B168F5?purl=/934452-6FyoCS/
 

Pavlo138

Joined Feb 26, 2009
28
and yes, radio waves are made of electrons that behave in a wave-like pattern, like light. Light is not a wave yet photons that behave in wave-like pattern.
 

Wendy

Joined Mar 24, 2008
23,415
and yes, radio waves are made of electrons that behave in a wave-like pattern, like light. Light is not a wave yet photons that behave in wave-like pattern.
Radio and light are both photons, the frequency of which is different, nothing else. Radio is not composed of electrons.
 

Pavlo138

Joined Feb 26, 2009
28
Radio and light are both photons, the frequency of which is different, nothing else. Radio is not composed of electrons.
That makes sense, since a lot of optical laws also apply to RF wave propagation. Should have known better, since light is part of the electromagnetic spectrum anyway. Thanks Bill.
 

steveb

Joined Jul 3, 2008
2,436
... Should have known better, since light is part of the electromagnetic spectrum anyway...
You would have been correct if you said that radio waves can be created by the accelleration of electrons. This is basically how a transmitting radio antenna works. Electrons are accellerated in the conductors of the antenna, which gives rise to EM radiation.

Even light is created by electrons changing energy levels in atoms.

Anyway, electrons are worth mentioning with regards to both light and radio, but Bill is correct to point out that photons are the elementary "stuff" of electromagnetic radiation, at any frequency.
 

Papabravo

Joined Feb 24, 2006
21,159
There are particles in baseball. Does this mean that there is crying in radio? ;)
All the time when you can't break a pileup.
When Sporadic-E becomes just that
When a 10:1 SWR smokes your finals
You bet there is crying in radio!

RF is created by moving electrons in a conductor, but once the wave leaves the antenna there are no electrons and no photons either, until the wave arrives at the receiving antenna and makes the electrons in the receiving antenna start moving back and forth.
 

Pavlo138

Joined Feb 26, 2009
28
All the time when you can't break a pileup.
When Sporadic-E becomes just that
When a 10:1 SWR smokes your finals
You bet there is crying in radio!

RF is created by moving electrons in a conductor, but once the wave leaves the antenna there are no electrons and no photons either, until the wave arrives at the receiving antenna and makes the electrons in the receiving antenna start moving back and forth.
This is just the discussion I had today with a fellow at work, exactly how and why radio wave propagation and antennas work the way they do. And in his conclusion was that nobody really knows exactly how or why it works, but there are few models out there to help conceptualize the dynamics of it all. I was trying to better understand how RF waves are converted into electrical energy to produce an intelligence signal. My idea was that the magnetic component in the wave, the moving lines of flux, induced a current into the antenna as it passed through. But his quick and dirty answer was that the antenna could be thought of as a transducer,as you said, converting one form of energy to another. It's really interesting stuff.
 

Pavlo138

Joined Feb 26, 2009
28
You would have been correct if you said that radio waves can be created by the accelleration of electrons. This is basically how a transmitting radio antenna works. Electrons are accellerated in the conductors of the antenna, which gives rise to EM radiation.

Even light is created by electrons changing energy levels in atoms.

Anyway, electrons are worth mentioning with regards to both light and radio, but Bill is correct to point out that photons are the elementary "stuff" of electromagnetic radiation, at any frequency.
True, such as the luster or glint from the sun hitting a pice of metal... electrons moving between energy levels in the atom, giving off photons as they go.
 

hgmjr

Joined Jan 28, 2005
9,027
I too hold that harvesting the RF energy that is present all around us for use in doing useful work is impractical.

The most effective use of the RF energy around us is to turn on our radios and tune them to the stations that broadcast the content we most enjoy.

hgmjr
 

Pavlo138

Joined Feb 26, 2009
28
This bit of misinformation is erroneous, wrong, and most unfortuneate. I think there are quite a number of people who will agree with me.
“I think it is safe to say that no one understands quantum mechanics.”
Physicist Richard P. Feynman

I believe this was along the same lines of the point that my coworker was trying to get at. We have models to help us understand physical phenomena, such as RF, but no one really, truly understands, exactly why it works the way it does.
 

beenthere

Joined Apr 20, 2004
15,819
“I think it is safe to say that no one understands quantum mechanics.”
Physicist Richard P. Feynman

I believe this was along the same lines of the point that my coworker was trying to get at. We have models to help us understand physical phenomena, such as RF, but no one really, truly understands, exactly why it works the way it does.
The framework for radio (and all of electromagnetism) was developed by a British physicist in the 1860's - http://en.wikipedia.org/wiki/James_Clerk_Maxwell

Some people might disagree with you about the level of understanding we have about RF.
 

Papabravo

Joined Feb 24, 2006
21,159
“I think it is safe to say that no one understands quantum mechanics.”
Physicist Richard P. Feynman

I believe this was along the same lines of the point that my coworker was trying to get at. We have models to help us understand physical phenomena, such as RF, but no one really, truly understands, exactly why it works the way it does.
If you think he was serious, then you know nothing of the man or his contributions.
 
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