Wireless Transmission of Power

[Martinmyst]

Dear Physics Forums Users,


I have a Bachelor of Science degree on Physics and Applied Mathematics, currently on the way out of a masters in EE. As a graduation project, I chose wireless power transmission as the project topic.

I found two wireless transmission schemes that got some recent traction which claim to overcome some or all of the range related problems (enabling more than charging toothbrushes):

1. WiTricity by Dr. Marin Soljacic (MIT)
2. Vortex Wireless Power Transmission by Dr. Konstantin Meyl (University of Applied Sciences at Furtwangen, Germany).

I am trying to theoretically compare systems, build and test their efficacy.

Soljacic system uses what is termed as evanescent fields, these fields much like quantum tunneling field effect penetrate physical space and die out in a somewhat exponential fashion. My question is about Meyl System, I am unable to locate any serious treatment of scalar waves in a textbook or an academic paper other than Meyl's badly translated book Scalar Transponder .

If you know of any credible references on Scalar Waves (refuting or supporting, it does not matter as long as they are robust), please let me know.

 

[berkeman]

Dear Physics Forums Users,


I have a Bachelor of Science degree on Physics and Applied Mathematics, currently on the way out of a masters in EE. As a graduation project, I chose wireless power transmission as the project topic.

I found two wireless transmission schemes that got some recent traction which claim to overcome some or all of the range related problems (enabling more than charging toothbrushes):

1. WiTricity by Dr. Marin Soljacic (MIT)
2. Vortex Wireless Power Transmission by Dr. Konstantin Meyl (University of Applied Sciences at Furtwangen, Germany).

I am trying to theoretically compare systems, build and test their efficacy.

Soljacic system uses what is termed as evanescent fields, these fields much like quantum tunneling field effect penetrate physical space and die out in a somewhat exponential fashion. My question is about Meyl System, I am unable to locate any serious treatment of scalar waves in a textbook or an academic paper other than Meyl's badly translated book Scalar Transponder .

If you know of any credible references on Scalar Waves (refuting or supporting, it does not matter as long as they are robust), please let me know.

I did a Google search for "wireless power" here at the PF, to pull up all the threads that have discussed this. Please look through these threads to see if they help.

http://www.google.com/search?hl=en&...=&as_occt=any&cr=&as_nlo=&as_nhi=&safe=images

Note that only mainstream science is discussed here in the technical forums at the PF. I'm not sure your quote qualifies as mainstream science:

Soljacic system uses what is termed as evanescent fields, these fields much like quantum tunneling field effect penetrate physical space

 

[es1]

No wonder it is so hard to search for scalar field theory. They overload some common terms. "Scalar wave" seemed a bit contradictory. Now I know why.

http://en.wikipedia.org/wiki/Scalar_field_theory_(pseudoscience)#Terminology

 

[Martinmyst]

Dear Berkeman,


Dr. Marin Soljacic's wireless power transmission system operates on the principle that slowly-evanescent electromagnetic fields can be utilized for effective/less-loss power transmission across distances without wires.

Here are a few references:
A. Karalis et al. / Annals of Physics 323 (2008) 34–48
A. Kurs et al. / Science Vol 317 (2007) 83-86

Here is a wikipedia article on Evanescent Waves / Magnetic Fields:
http://en.wikipedia.org/wiki/Evanescent_wave


So in short, it's as mainstream science as apple pie.


Cheers.

I did a Google search for "wireless power" here at the PF, to pull up all the threads that have discussed this. Please look through these threads to see if they help.

http://www.google.com/search?hl=en&...=&as_occt=any&cr=&as_nlo=&as_nhi=&safe=images

Note that only mainstream science is discussed here in the technical forums at the PF. I'm not sure your quote qualifies as mainstream science:

 

[Martinmyst]

Thanks Es,


Pseudo theory classification does not look very encouraging. Unfortunately Wikipedia article does not get into detail about how scalar field theory became a "pseudo theory".

It's best not to take anyone's word for "pseudo" or "commonly accepted" theories as not too long ago, flat Earth was moved from one to the other.


Cheers.

No wonder it is so hard to search for scalar field theory. They overload some common terms. "Scalar wave" seemed a bit contradictory. Now I know why.

http://en.wikipedia.org/wiki/Scalar_field_theory_(pseudoscience)#Terminology

 

[berkeman]

Hmm. So in the context of EM, "evanescent" means near-field, it looks like. Okay.

So are there practical applications here, or not really practical until you get to field strengths that are not good for human tissue? Technical people are not stupid. If there were practical applications that were safe, it seems like there would be things coming to market, no?

 

[Martinmyst]

Hello Berkeman,


I should have mentioned that INTEL already bought this technology (Evanescent version, not the second one I mentioned).

Here is their demonstration video:

http://www.mefeedia.com/entry/wireless-resonant-energy-link-efficient-wireless-power-research-intel-day/19736570

Human Tissue absorption... Their model and empirical evidence suggests it's not a problem.

Real issue is something like this, in antenna theory it's well known that a certain portion of the electron gas passing through an antenna causes an EM reflection into near field and re-absorbed back. Through impedance matching etc. virtually all operators try to minimize that leeching part. So in a sense, a problem became a solution here (near field effect which was undesirable from communications theory point of view). Much like the concept of Cavitation, we knew certain frequency of sound can cause cavitation effect (and destroy submarine propellers for example) but it took nearly a century 'til we figure out that we can use the same effect for transferring energy to liquids (Which spawned the field of Sonochemistry).


However my primary question remains about the second (Dr. Konstantin Meyl invention) wireless power transmission system. He is not doing a rigorous proof of his theory nor could I find anything seriously supporting/refuting what he is demonstrating... weird?


Cheers.

Hmm. So in the context of EM, "evanescent" means near-field, it looks like. Okay.

So are there practical applications here, or not really practical until you get to field strengths that are not good for human tissue? Technical people are not stupid. If there were practical applications that were safe, it seems like there would be things coming to market, no?

 

[Pumblechook]

It is nonsense. Don't waste your time with it.

Absolutely nothing new in resonant coupled coils. It is 1920s technology.

It is just near field which was what Hertz used rather than the far field which is the normal mode for radio transmission over much greater distances.

I gather they have acheived a 45% coupling over two metres with whopping 60cm coils. The size of the aerials tend to a significant proportion of the gap you are trying to bridge. They use more wire in the coils than if they just ran a simple power wire from A to B. The overall efficiency will always be poor. You have to convert AC to DC then to RF then back to DC.. Overall you get less than 20% efficiency.

You won't get much more than 2 metres. The efficiency will be pretty poor further apart and there is a limit to how big you can make resonant coils at a given frequency.

The bit about energy won't be be dissipated in other surrounding wiring/objects is particularly nonsense.

I thought it was an April Fool joke at first sight.

Don't be surprised if it is all quietly forgotten.

 

[agrocadabra]

OP I suggest you look into tesla's work on this.

 

[negitron]

Tesla's work on wireless power was garbage.

 

[agrocadabra]

Tesla's work on wireless power was garbage.

How so?

 

[negitron]

It was completely impractical and highly inefficient, for openers. Not to mention dangerous. Wireless power is fine for near-field, low-power applications but a practical impossibility for high-power far-field transmission.

 

[agrocadabra]

Perhaps if he had been given a decent chance he might have got somewhere.

 

[negitron]

No. Even with today's technology we cannot create a global wireless power system such as he envisioned, even if we wanted to.

 

[agrocadabra]

ok no point arguing you win.

 

[berkeman]

ok no point arguing you win.

Good choice. Note, however, that there were some proposals for microwave beaming of power from orbital solar arrays back down to receiving stations on the Earth. But the cost-to-orbit was quite high, and as you can imagine, pilots weren't too keen on the idea.

 

[negitron]

Good choice. Note, however, that there were some proposals for microwave beaming of power from orbital solar arrays back down to receiving stations on the Earth. But the cost-to-orbit was quite high, and as you can imagine, pilots weren't too keen on the idea.

Some of these are still viable; if the bean is spread over a wide area, say, an acre or two, the power density becomes low enough that it's safe for anything passing through it even in the gigawatt range. Cost is the single largest obstacle here.

 

[berkeman]

Some of these are still viable; if the bean is spread over a wide area, say, an acre or two, the power density becomes low enough that it's safe for anything passing through it even in the gigawatt range. Cost is the single largest obstacle here.

Interesing, I didn't know that development. Thanks.

 

[Mike_In_Plano]

Well, from all of this, I can only say that I'm surprised that Intel is making a deal of induction coupling. Took them 100 years to catch on

Most any engineer who's worked with the design of induction heaters has seen the trick with the coil and a small light bulb. We also did the same trick in high school physics class.

I used to work on trans-dermal power transfer for medical implants - the same thing.

 

[Pumblechook]

How can anybody seriously believe that Tesla could do things over 100 years ago that nobody has been able to repeat?

Tesla is the patron saint of crackpots.

 

[TurtleMeister]

Tesla is the patron saint of crackpots.

He devised a way to produce a rotating magnetic field and invented the AC induction motor in 1883. Not bad for a patron saint of crackpots. However, I can agree that his ideas involving wireless power transmission were just wrong. But at least he had the excuse of not knowing what we know today. We are the beneficiaries of people like Tesla who devoted their lives to exploring new ideas.

 

[negitron]

His early work was wonderful; he was a brilliant inventor. It was only in his later years that he devolved into crackpottery.

 

[Pumblechook]

3 Phase AC and rotating fields were pioneered by John Hopkinson in Britain.

I would rate Tesla as a minor figure in science and engineering. Most of his 'things' were done before by other people. Folks were producing huge sparks with Nicholas Callan's induction coil when Tesla was a baby.

 

[TurtleMeister]

3 Phase AC and rotating fields were pioneered by John Hopkinson in Britain.

That's interesting. According to Wikipedia Hopkinson invented the 3-phase system of power distribution, not the electric motor. And I can find no reference to link Hopkinson to the rotating magnetic field motor. But it seems odd that someone would invent 3-phase power without a motor to run on it. Is there some other advantage to 3-phase power, other than powering 3-phase motors? In any event, Wikipedia dates Tesla's invention of the induction motor to 1882, the same year that Hopkinson invented the 3-phase power system. However, Tesla did not receive a patent until 1888. I guess the works of these two men are so close together in time that it's impossible to know who conceived of the idea first. But the fact remains that it is Tesla who is credited with inventing the rotating field induction motor.

Edit: It appears that Hopkinson's work involved the synchronous electric motor, which also makes use of a rotating magnetic field.

 

[Pumblechook]

Microwave beaming of power from space is a complete non-starter on many grounds.

 

[negitron]

Microwave beaming of power from space is a complete non-starter on many grounds.

You're wrong. But please, enlighten us if you feel otherwise.

 

[Pumblechook]

The proposal I saw was for 1GW of steerable solar panels which would cover an enormous area. The DC would be converted to about 2.4 GHz using thousands of magnetrons and then beamed to Earth with a 2 Km diameter dish. The dish would have a beamwidth of a tiny fraction of degree and therefore very difficult to keep on target. It would have to be constructed to within about 3mm (ideally 1mm) of the correct shape over the entire surface. With the finite efficiency of magnetrons and the efficiency of conversion back to DC and then to AC you end up with about 400MW or less. A major problem is the lack of cooling air required to cool the magnetrons. It is a major problem on even low power satellites. You would have to circulate cooling water to huge radiators in space.

The cost would be literally out of this world involving thousands of rocket/shuttle launches. And all for a relatively small amount of power.

You still think it is possible?

 

[mgb_phys]

Is there some other advantage to 3-phase power, other than powering 3-phase motors?

It's the simplest balanced distribution system (one that doesn't need a return wire)

 

[mgb_phys]

if the bean is spread over a wide area, say, an acre or two, the power density becomes low enough that it's safe for anything passing through it even in the gigawatt range.

1gW / acre = 250kW/m^2 = 25W/cm^2
At 900Mhz the FCC limit is 0.5mW/cm^2 rising to 1mW/cm^2 at 2000 Mhz

Doesn't mean 25,000mW/cm^2 isn't safe - but you are going to have a job getting permission.

In addition to get all the beam power into an acre (spot size 60m) from 36,000km up you are going to need a rather large transmitter dish = approx 1million wavelengths in diameter

 

[Pumblechook]

And the feed to this dish would just melt or at least flash over at those powers.

Utterly impractical.