John,

I couldn't get your link to work ... error 404.

 

Here is a little teaser of an article - http://www.newswireless.net/index.cfm/article/6853

Notice that no reason is postulated for why the power transfer mechanism might escape inverse-square attenuation.

One hit from Google sez that this outfit - http://www.lightninglab.org/concept/index.html transmitted 800 watts across 5 meters, but the site has nothing about the feat.

Another "source" hints of the power transfer being a near field effect, thus ducking the inverse-square law. Every other article turned up (at least the non free energy ones) by "wireless power transmission + inverse square law" spoke of the problem of attenuation over distance.

 

@Joe Jester: Fixed URL, there was a misplaced colon at the end.

As for the inverse square thing, I suspect the field strength follows the inverse square law, as stated above. However, this is a non-radiative device. Unlike a radio transmitter, transfer of energy occurs with magnetic coupling. In the absence of a receiving device, the amount of power used is probably (?) quite small, just like a transformer with an open secondary. Hence, efficiency would not be expected to follow the radiative inverse square law. I would love to see data on the power consumption while not coupled. The authors refer to it as a midrange device. That is, longer range than one gets with a transformer, but not as far as a radiative device.

I suspect a lot of that is explained in detail in the other papers, such as the one in Science. Unfortunately, I no longer have access through the university here, and I don't want to pay the $30+ to Elsevier just to see a single pdf.

John

 

Beenthere,

According to http://www.osha.gov/SLTC/radiofrequencyradiation/electromagnetic_fieldmemo/electromagnetic.html

NEAR-FIELD: The region located less than one wavelength from the source is called the "Near-field". Here, the relationship between E and H becomes very complex, and it requires measurement of both E and H to determine the power density. Also, unlike the far-field where EM waves are usually characterized by a single polarization type (horizontal, vertical, circular, or elliptical), all four polarization types can be present in the near-field.

Since both the E field and the H field components of electromagnetic waves are absorbed by living tissue, and since the relationship between E and H is complicated in the near-field, we must measure both E and H when evaluating near-field hazards. This includes all low frequency sources, such as RF heat sealers.

With E and H both contributing might be the reason for the basic observation of "fooling" the inverse square law. However, they do not talk of the contribution from each polarization mentioned.

The question would become, how is the "receiving" coil treating the E and H fields. A vertical coil (horizontal windings) must have some E field energy induced.

 

The intented target is to unbalance the E and H in the receiving end. Ofcourse, you will be getting some Electric Field, but majority will be H from magnetic coupling. Also, this experiment avoids the radiative properties of RF radiation. It is done through magnetic coupling, and the only downside to magnetic coupling is that you lose "strength" of the coupling with inverse cube of the distance, not the actual power sent by the transmitter or efficiencies associated with that matter. However, this is the intended use of the device because the magnetic field set up by the transmitter should be able to cover a small room in which all devices within its vicinity may be powered. That was the work by MIT. The transmitter is using very minimal current input to create a big current through a large magnetic field. At all times this "minimal" current will be consumed, even when there are no coupled devices to it, unless the transmitter is shut off that is.

When I have the time to actually build this device I will post a video and my notes on this forum. It will be the first place where I share my knowledge and credits to those that have contributed to materialize it.

For the time being, I am still doing research on materials and a few other concepts related to wireless power transmission.

 

JoeJester,

The near field info is right on, especially that part that talks of absorption by living tissues. The MIT pix from their demo of some years ago shows a person standing between the coils while a 60 W bulb is being powered.

That makes me think that near field is not a correct way to describe the power transfer mechanism. Or that the student was photoshopped into the pic.

If it turns out to be some resonance effect that is reliably tuned into, it opens up the avenue for - drum roll, please - power snarfing. Let the guy in the next door apartment power your lights.

 

The intented target is to unbalance the E and H in the receiving end.The intented target is to unbalance the E and H in the receiving end.

We've been doing that since the days of Marconi ... polarization of the transmitting and receiving antennas.

Also, this experiment avoids the radiative properties of RF radiation.

Not going to happen. You will be irradiated with non-ionizing radiation from the E field as well as the H field. Both have OSHA standards for workers and public. Workers, meaning they had the training on the hazzards, has a higher threshold of uT exposure than the public.

You can't get from point A to point B without wires and not have radiation. You have radiation from wires also.

The only way to avoid being irradiated, is to have your experiement in a Faraday cage with you on the outside of the cage.

Just sitting here typing this message, I've been irradiated by non-ionizing radiation ... it's everywhere. Only the level is so minute it's immaterial.

And to further the inquiry on the near field ....

From STANAG Number 2345 Nato Standardization Agreement:
Evaluation and Control of Personnel Exposure to Radio Frequency Fields - 3 kHz to 200 GHz.

18. Near-Field Region. A region generally in close proximity to an antenna or other
radiating structure in which the electric and magnetic fields do not exhibit a plane-wave relationship, and the field strength does not decrease proportionally with the distance from the source but varies considerably from point to point. The near-field region is further subdivided into the reactive near field, which is closest to the radiating structure and contains most or nearly all of the stored energy, and the radiating near-field region where the radiating field predominates over the reactive field, but is not a plane wave and has complex field characteristics.

Beenthere,

I agree. If the student wasn't photoshoped ... oh well, the price one pay's.

I tend to think of it more like two coil's, mutual inductance, and coupling coefficient. After all, those are some pretty intense coils.

 

Well, yes. You can't avoid radiation, but the objective is to minimize it to such levels comparable to what cellphones or radio/TV stations currently have on us. The near-field phenomena is extremely complicated, and although this device can be built fast and without even doing any reading, my objective is to really understand the theory and concepts behind it. Building or replicating the device is easy. You just need to go out and buy some parts and watch a couple youtube videos and you can build one. The theory is whats really interesting. We could develop new devices by exploiting near-field reactive regions of a transmitter antenna. That being said, a lot more needs to be done in terms of research. This phenomena has been in existence since the days of Tesla, but it has only been revisited since 2006 when MIT power the lightbulb 2 meters way. Pretty new yet pretty old.

 

The first half-wave is what they are describing as the reactive near-field.

MIT chose 10 MHz ... interfering with WWV's time transmission on that same frequency. Granted, the interference was local, probably not outside the lab, and hence no complaints from serious users, those that extrapolate their clocks with WWV.

10 MHz is 30 meters with a halfwave length of 15 meters. At best, that will be the distance. Did MIT do any non-ionizing radiation measurements? Probably not as that was beyond the scope of their project. Witricity can be inefficient and yet practical, IF, and that's a BIG IF, there is no harmful effects from the transmission of such power.

 

Well, in their supplement paper they did some measurements in terms of efficiencies and power radiation, and they concluded that the amount of power radiated @ 10MHz from the transmitter is 3.3 Watts, which is about how much a cellphone radiates, maybe a bit more. Check out page 2 of this file. It says it there.

In regards to the harmful part, there is no harm in wireless transferring powering via magnetic coupling. Magnetic fields have very weak interaction with living organisms. It is only the radiative E field part they were concerned with, and they radiated 3.3 Watts @ 10 MHz, which was below the FCC regulations for safety.

 

I'm sorry, you can not light a 60 W lamp using a transmitter of 3.3 W. I've yet to see documentation on the power consumed by the emitter to light that 60W bulb.

Did you double check their power density figures?

Here are a couple of documents concerning RADHAZ.

Happy reading.

 

i have selected this as my project of last year and hence need to complete in 3 months so is a bit of urgent kinda thing

 

i have selected this as my this sem's project so need to complete in 3 months thts why a bit urgent

 

Pick one article from a reputable source. The first one I linked to, for example. Follow the procedure there.

It sounds like you are just beginning in this area. Why try to change what is known to work?

Yes, it is good to review prior art, but your first post indicates you have been doing that for months:



What is your sudden urgency?

John

i have selected this as my this sem's project so need to complete in 3 months thts why a bit urgent

 

Well, you need not post 3 times first of all. And second of all, you can't do this in just 3 months unless you are just doing a simple research paper and not a project that involves experimentation.

@ JoeJester: The document I linked in my previous message stated that @ 10 MHz the MIT's proposed design emitted/radiated 3.3 Watts. Those are the facts. It's not about what's possible or not possible. That's what they reported in that documentation. A fake? Maybe, but I doubt it.

 

It is supposed to be non-radiative. From that perspective, 3.3W is relatively insignificant compared to the radiative power that would be needed to light a 60W bulb at 2 meters.

John

 

I like how this thread is entirely repeating itself, even including some of the same people... we already had this discussion on inverse square law and radiative vs near field...

Just to try to drive it home again - yes it still gets severely attenuated over distance but that is locally stored field, it is not energy that is being sent to space. Like was mentioned by Joe this is a pair of coils with mutual inductance over a larger than usual distance.
Yes, some energy still radiates and is lost.
Yes, there is plenty of energy loss in setting up the fields.

I think the efficiency they claimed was about 60%, I'm sure zero_coke has the number handy somewhere. Just divide 60W by efficiency to get the input power...

 

Yep. Maybe I was not clear enough in my last post. I meant that they radiated 3.3 Watts of power in the form of RF while trying to "magnetically induce" power into a light bulb 2 meters away at 40% efficiency.

You can't have a system that is purely magnetically coupled, especially this one that MIT had built. This is not the conventional transformer with 0.1 mm spacing where little is lost in the form of RF. This is essentially a transformer but with 2 meters spacing. You will lose some of it in the form of RF radiation due to the huge spacing and the construction of the magnetic fields and collapse and etc. In fact if you look at the numbers the majority of the un-induced energy has been lost to other forms and not RF. Only a mere 3.3 Watts of the 150 W input was lost to RF radiation. They designed it to be this way so it would comply with FCC standards. They didn't really care about the efficiency of the magnetic coupling, but more in regards with the safety and radiative (RF) issues. Now they have this figured out, they can go on improving the efficiencies with better materials and better design.

In summary, that means they input 150 Watts to induce 60 Watts successfully to a 60 Watt light bulb 2 meters away, while radiating 3.3 Watts in the form of Radio Frequency.

 

This is not the conventional transformer with 0.1 mm spacing where little is lost in the form of RF.

0.1 mm spacing would only have a higher mutual inductance, as compared to the MIT transformer.

Only a mere 3.3 Watts of the 150 W input was lost to RF radiation. They designed it to be this way so it would comply with FCC standards

RF, Radio Frequency, is both the H and the E Fields.

In summary, that means they input 150 Watts to induce 60 Watts successfully to a 60 Watt light bulb 2 meters away, while radiating 3.3 Watts in the form of Radio Frequency.

So what is it? You said the lost 3.3 W to RF radiation and then stated they only radiated 3.3 W? I'm having a difficult time accepting your premise that only 3.3 W was radiated.

 

The other energy is just contained in the field and and the light bulb's coil is not able to tap into it. The strength of the magnetic field decreases with cube of the distance, and at 2 meters I suppose it can only obtain 60 Watts. At 3 meters it would probably be only half of that. Remember, we're talking about magnetic fields here. They decrease in strength with cube of the distance. The reason it required 150 watts to induce 60 watts into a lightbulb is because it is 2 meters far away. It can only tap into enough strength to take 60 watts out at that distance. Bring the light bulb closer and it can tap into more power. The closer you bring the better it becomes like a conventional transformer. The radiation by the source is 3.3 Watts.