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Steve Conner

Sat Jun 09 2007, 04:50PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

+1 on what Firkragg said. He just more or less described Tesla's original plan for wireless power, and I believe this thing works the same way.

I don't know how to model the radiation characteristics either. But I think, given that the antenna structure doesn't have any dimension larger than 60cm, and the wavelength of 10MHz is 30m, it's a fairly safe bet that it will suck completely as a radiator. That is only 1/50 of a wavelength so the radiation efficiency would be a few %. The measured Q factor of 950 also suggests that it is a lousy radiator.

I know this is just a new spin by some university PR department on Tesla's original ideas. But maybe the time really is right for "Witricity" now... Anyway, it looks like something that many board members here could lashup in an afternoon and I encourage you all to try it

Replicating the experiment could get 4hv some good publicity if nothing else.

DrZoidberg

Sat Jun 09 2007, 05:31PM

Registered Member #350 Joined: Mon Mar 27 2006, 05:14PM
Location:
Posts: 106

I don't think filling an entire room with an em field is a good idea. Why not just have a box, drawer, locker, whatever. You put a coil in the wall of that box and any device you put in there gets charged. Sure you will have to go through the inconvinience of taking your cell phone out of your pocket and putting it in the box but still I think it's a much more practical approach, also you can put several devices in there at once and the field can be stronger too and you get a higher efficiency.
I personally would prefer clothing that can convert sunlight to electricity but looks perfectly normal. Then your phone gets charged all the time.

ragnar

Sat Jun 09 2007, 11:39PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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Posts: 1425

I don't mind standing in a big lowish-frequency EM field all day. No tinfoil hats for me =)

Coronafix

Sun Jun 10 2007, 02:17AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

From my understanding of what Tesla was on about, he was using the GROUND as the transmitting medium, not radiating it out like we are talking about here. This is how he could transmit such a long distance to Pikes Peak.
He specifically said that when it starts radiating out in EM waves, it's wasting power.
This is why he went to such trouble to create a GOOD ground for Wardenclyffe.

Marko

Sun Jun 10 2007, 09:50AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Sure, for a capacitively coupled system ground between two resoantors is essential.
Displacement current closes one part of circuit, ground is return path.

Magnetic coupling like MIT system doesn't require ground but has other disadvantages like directionality of coils and possible heavy dissipation in metal objects, especially high remanence iron.
What they built looks somewhat like a large paralell resonant induction heater.

Steve Conner

Sun Jun 10 2007, 10:05AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes, the difference is that Tesla didn't believe in the need for displacement current to close the circuit, he thought that only the ground connection was required. We now understand EM theory much better and know that he was wrong: the displacement currents exist and act to cancel the ground currents in the far field, which severely limits the range of a Tesla wireless power system.

Note that displacement current and EM radiation are not the same thing. You can transmit power by displacement currents in the near field while radiating hardly any of it to the far field, and conversely, a good antenna can radiate strongly to the far field without giving people RF burns and striking corona off things in the near field.

Marko

Sun Jun 10 2007, 12:37PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi Steve, all,

Yeah, goldsphere and other guys, don't confuse displacement currents with EM radiation! There's actually no need to mention EM radiation in this whole story.

The thing is actually very simple. I'l try to draw a simplified schematic if it can make things any more clear.

Yes, the difference is that Tesla didn't believe in the need for displacement current to close the circuit, he thought that only the ground connection was required. We now understand EM theory much better and know that he was wrong: the displacement currents exist and act to cancel the ground currents in the far field, which severely limits the range of a Tesla wireless power system.

I don't know how much can I comment on there, but all the time I tought that use of displacement current was his initial idea.
Some of his former patents utilize no ground connection at all. And wasn't that what he called ''non-hertzian'' wawes after all?

As much as tesla coils may be fooling to someone I really think tesla was brillant enough to realize that all electric circuits still need to always be closed.
But meh.

I would say that what truly limits the range of such system is solely efficiency of resonators.
All the loss occurs as ohmic loss on resonators themselves. The small amount of radiation produced is also considered as a loss.
And tesla coils as we have them are eally poor on that part!

With ideal resonators of infinite Q you could transfer any amount of power trough any distance (as long as you have ''ground connection'' though).

With real, but still superrealistically efficient resonators you could indeed transmit power over great distances with little loss.

As such the transmitter would give enormous voltages on it's topload for a little power input, and as receiver would also represent extremely high impedance voltage drop across capacitive resistance betwen them would be almost negligible.

In reality something as such is nearly impossible to acheive considering all the problems one would run into. I've done some math on this.

One can increase the efficiency of a helical resonator by increasing it's L/C ratio and decreasing ohmic resistance.
Once resistance is low enough it implies that we will have really massive base current flowing trough earth. Effect would presist even if we make the resonator superconducting, making the earth itself biggest disipator.

Breakout from the topload would be very hard to stop considering we want hundreds of megavolts on our 'tower'. And etc.

Coronafix

Sun Jun 10 2007, 12:39PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

So is it right to say that this device 'displaces the aether' in the near field and radiates in the far, but because of its design, it radiates poorly, therefore making it "efficient"?
I use the term aether because that is what Maxwell thought was happening concerning
displacement currents, that the aether was being displaced when an AC signal traveled between two
plates of a capacitor.

Terry Fritz

Sun Jun 10 2007, 10:36PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

Thanks Bert for providing some reliable details. The news accounts and such contain no solid useful information.

The coupling between the two coils calculates to k = 0.0026 at 29.26uH each. To get to 9.9MHz, they would have about 14pF of stray capacitance from the driver coils, light bulb, and such to add to the 34.72pF of natural capacitance of the coils. The Q calculates to 1010 with a Z of 654 ohms and Rac = 0.6 ohms (they are using heavy "stranded" wire if you look really close).

The efficiency seems real good, but I'll wait until someone gets some real power meters before trusting the numbers much. 15% at about 7 feet with 2 foot diameter short antennas is not too hard to believe. The real killer is turn one of the antenna 90 degrees and see what you get then.

Before anyone gets too excited ("we" all seem to knowledgeable here though for that), lets compare this to a helical plane antenna:

Hmmmm

Looks they they have reinvented it...

I am sure John Kraus wishes he would have thought of it

They are transformer coupling the drive to the antenna and light bulb since their impedances are all screwed up so they can't drive it directly. The drive coil also acts as a ground plane which is sort of cute. Of course, they could have gone out and simply bought two 10MHz commercial helical antennas, a 50 ohm transmitter, and a 50 ohm resistor and done much better. But that would have been too conventional with too much real proven 100+ year old science behind it... It is odd since their setup seems to have needed some "electrical engineering help" to get it to work - they should have "seen thought it" right away...

The patent office just hired 1200 new examiners and the patent rate has suddenly dropped from 72% to 49% as a result, so they might have trouble getting it patented now unless that 100 year old prior art is too dusty to go check anymore

Of course, every antenna company on Earth will jump their case if they make a penny off it...

This is all a bit hard since these guys are optical physicists and not electrical guys. Thus, they don't know the proper names for anything or the usual physics behind it. They should talk to a few good antenna engineers:

Like I said before, it is all just a high profile scientific train wreck in slow motion... Fortunately, "Tesla's name" is not getting mentioned much now, so it will be less of an embarrassment there...

Is it useful? Considering that is is simple to do, has been done many times before, and it is pretty easy and obvious to make. But unless some new modern application needs it, it will just be a curiosity just as it has always been. The size, efficiency, highly directional, etc. problems just limit it terribly along with the considerable stray RF it pumps out. It will be interesting to see if anyone bothers to write up and "good" papers on it... Most in the science community will have something better to do and won't want to risk "getting it on them" too.

I wonder how many popular science writers will proclaim the end of electrical wires, free energy for all, unlimited energy... I have a bunch of old magazine articles they could simply copy

Cheers,

Terry

Carbon_Rod

Mon Jun 11 2007, 03:14AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Yes, it's always a shame when Tesla gets mentioned in anything that happens to be somewhat questionable. Unfortunately the media always chooses the stories that are more entertaining... not the ones that happen to be scientifically plausible. <rolls eyes>

I would think the high-powered laser guided lightning strike experiment would draw a more of a crowd. ;P

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