# Wireless transmission of electric power

Joined Sep 26, 2006
8
1. What impediments are involved in the transmission of electric power through wireless means (just like the transmission of information signals)? Is the idea even practicable? Are there any hazards involved? or is it costly to realize the idea? Can someone explain in detail? Thanks!

#### bloguetronica

Joined Apr 27, 2007
1,424
It is not practicable, because of the implied efficiency and losses. A good cable in the right conditions has 99.9% efficiency when transmitting power. In the wrong conditions has only 99%. It is difficult to beat.

#### beenthere

Joined Apr 20, 2004
15,819
Google "tesla" and "wireless power transmission". No practical means beyond very short distances have been demonstrated yet. The current Scientific American has an article (no details) about an experimenter who has managed to transmit AC over a distance of about 3 meters and light a 60 watt bulb. The effect is magnetic resonance, per the article.

Anytime you work with large amounts of power, there will be dangers.

#### bloguetronica

Joined Apr 27, 2007
1,424
Google "tesla" and "wireless power transmission". No practical means beyond very short distances have been demonstrated yet. The current Scientific American has an article (no details) about an experimenter who has managed to transmit AC over a distance of about 3 meters and light a 60 watt bulb. The effect is magnetic resonance, per the article.

Anytime you work with large amounts of power, there will be dangers.
That looks like induction by the means of microwave energy.

#### Mike M.

Joined Oct 9, 2007
104
From everything that I know, it doesn't seem practical unless scalar waves in scalar interferometry are used, if such a thing really does exist, due to the losses sustained at all frequencies through interation, and thus losses, by surrounding matter. Don't quote me on that because there may very well be an undicovered very narrow band that only interacts with very rare forms of matter, at least on Earth. If you go to another planet you may have to rediscover a new frequency window for transmission based on the materials and quantities of those materials present. I think it will be a few decades before that even begins to get funding though because the lobbying copper industry wouldn't appreciate it that much if transmission lines became obsolete, just as the oil companies have their grip on the subject matter funded by the government in our schools and Universities. If you don't follow the current established framework, you don't see any \$. It is almost like there is a reluctance to advance in this country and that reluctance is powered by those with lots of cash that want more cash. They will do anything they can to reduce efficiency while simultaneously running alternative energy propaganda commercials.

#### Dave

Joined Nov 17, 2003
6,970
In the context of the OP, what do we think of Microwave Power Transmission (MPT)?

Dave

#### recca02

Joined Apr 2, 2007
1,214
i read once that wireless power transmission is aimed at transmitting power to planes to reduce pollution.
IIRC US has made some progress in that area.

#### Mike M.

Joined Oct 9, 2007
104
In the context of the OP, what do we think of Microwave Power Transmission (MPT)?

Dave
I don't know what "OP" is but microwaves seem like a bad idea because the large microscopic cross-section for absorbtion that the water molecule has in that frequency band.........hence the high efficiency of a microwave oven to heat food and not readily other material due to the high water content in food but not other materials. From what I remember, the water molecule diameter is the same as, or very close to, the microwave wavelength.

#### recca02

Joined Apr 2, 2007
1,214
In more detail, a microwave-powered helicopter with a six-foot rotor has been flown at an altitude of fifty feet for ten continuous hours.
interesting article that,
now the question is was it a manned helicopter?

#### Dave

Joined Nov 17, 2003
6,970
interesting article that,
now the question is was it a manned helicopter?
They would have to be very small!

That early publication was a proof of concept...there is much more literature on MPT.

Dave

#### Dave

Joined Nov 17, 2003
6,970
I don't know what "OP" is but microwaves seem like a bad idea because the large microscopic cross-section for absorbtion that the water molecule has in that frequency band.........hence the high efficiency of a microwave oven to heat food and not readily other material due to the high water content in food but not other materials. From what I remember, the water molecule diameter is the same as, or very close to, the microwave wavelength.
OP stands for "Opening Poster/Post"

Indeed microwave energy has always lent itself to electro-heat technologies, however I must stress that microwave energy will have an impact on the majority of dipolar dielectric materials - it just so happens that the primary dipolar constituent in food is water.

The wavelength of microwave fields at 2.45GHz (the standard ISM microwave frequency, although not the only one), which translates to a wavelength of 12.24cm is substantially larger than the diameter of a water molecule.

As for MPT, the power levels are not much more than that for leakage from a microwave oven, IIRC ~5mW/cm^2, so the impact on heating or indeed other health issues are negated thus far as possible.

Dave

#### bloguetronica

Joined Apr 27, 2007
1,424
I don't know what "OP" is but microwaves seem like a bad idea because the large microscopic cross-section for absorbtion that the water molecule has in that frequency band.........hence the high efficiency of a microwave oven to heat food and not readily other material due to the high water content in food but not other materials. From what I remember, the water molecule diameter is the same as, or very close to, the microwave wavelength.
It depends on the frequency of the microwave. The microwaves have a broad spectrum (wavelength from 1mm to 1m). If you use coherent microwave radiation, you avoid the problem because you are using a pure light wave with a defined frequency. There is some research around MASERs (Microwave LASER).

P.S.: Only visible light has the same wavelength of the same size of some coloured macromolecules. That is why those molecules absorb light, therefore having colour (the water would absorb U.V. that way). The microwave ovens work because water absorbs microwaves, but is is not a resonating phenomenom. It is because water molecules are dipoles, having more charge on the oxigen atom and an assimetrical configuration. This makes them have dipolar moment. Thus, they "vibrate" when this electromagnetic field is present, like tiny magnets. The frequency of the microwave is sufficiently small to physically turn water molecules on themselves. Higher frequencies are to rapid to induce such movement. That explains why frozen water and other solids are not heated (the molecules are trapped and cannot rotate). Liquid substances having no dipolar moment are not heated as well.

#### Mike M.

Joined Oct 9, 2007
104
It depends on the frequency of the microwave. The microwaves have a broad spectrum (wavelength from 1nm to 1m). The microwave used for cooking has a wavelength of about the same size of a water molecule, thus making water molecules vibrate. If you use coherent microwave radiation, you avoid the problem because you are using a pure light wave with a defined frequency. There is some research around MASERs (Microwave LASER).
I read an article somewhere where they were experimenting with MASERs on the exhaust of vehicles. Exhaust would be MASERed and it would raise the energy levels of particles from medium to high. Then the particles emit photons of a much shorter wavelength than infrared. Then they had some photovoltaic plates arranged to capture those photons that are now capable of producing a photoelectric effect.

The exhaust comes out cold and the energy produced by the cells gets regulated back into the battery to reduce the loading on the alternator and ultimately save gas.

Edit: DAMN that's a large range of wavelengths for one segment of the spectrum!!!!!! I need to brush up on the basics like that because I can tell it has been way to long since I have known them.

#### beenthere

Joined Apr 20, 2004
15,819
The Scientific American article did not mention frequencies, but it was definitely not microwave. The term "magnetic resonance" was used, and the visible coils were almost 1 meter in diameter, and about 5 - 6 turns. There were 4 or 5 people standing between the transmitting coil and the receiver. The energising apparatus was just off-picture.

Induction was conspicuously not used to describe the effect. Thinking about it, resonance is about the only way to be able to transmit power, although inverse square losses make it iffy for any distance.

I seem to recall the work being done at MIT, so we're not as likely to be dealing with another true believer here.

Joined Sep 26, 2006
8
Thanks for the detailed replies! Though some posts went above my head , I have got a sufficient understanding of the topic from your replies. And yes I googled the website about Tesla and wireless transmission. Found it helpful too. Thanks once again!

#### Mike M.

Joined Oct 9, 2007
104
P.S.: Only visible light has the same wavelength of the same size of some coloured macromolecules. That is why those molecules absorb light, therefore having colour (the water would absorb U.V. that way). The microwave ovens work because water absorbs microwaves, but is is not a resonating phenomenom. It is because water molecules are dipoles, having more charge on the oxigen atom and an assimetrical configuration. This makes them have dipolar moment. Thus, they "vibrate" when this electromagnetic field is present, like tiny magnets. The frequency of the microwave is sufficiently small to physically turn water molecules on themselves. Higher frequencies are to rapid to induce such movement. That explains why frozen water and other solids are not heated (the molecules are trapped and cannot rotate). Liquid substances having no dipolar moment are not heated as well.
Thanks for a bunch of information that I wasn't even specifically looking for but I have always wanted to know.

#### bloguetronica

Joined Apr 27, 2007
1,424
Thanks for the detailed replies! Though some posts went above my head , I have got a sufficient understanding of the topic from your replies. And yes I googled the website about Tesla and wireless transmission. Found it helpful too. Thanks once again!
What can I say. I don't know about the others but I went a bit off the topic.

#### thingmaker3

Joined May 16, 2005
5,084
From the article cited in the previous post: "With such a design, power transfer has a limited range, and the range would be shorter for smaller-size receivers. Still, for laptop-sized coils, power levels more than sufficient to run a laptop can be transferred over room-sized distances"

Sounds like the same 3 meter barrier cited by Beenthere in post #3 of this thread. R^2 is still r^2, no matter how resonant one makes the coils.