ee's please reply - (or those who think think they may know)

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Read the Wall Street Journal article of last week, which references a Science article of previous.
They are using MRE technology to direct a useful power across at least three meters without wires.
Damned interesting.
I don't think that is only about frequency - but it certainly inhabits the concept of specific resonant frequency.
On Fri, 15 Jun 2007 20:15:53 -0500, Tim Daneliuk

Regards,
Tom Watson
tjwatson1ATcomcastDOTnet (real email)
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Tom Watson wrote:

This is a sort of unremarkable finding. Tesla did more-or-less the same thing years ago. There are a myriad of issues here, not the least of which is the effects on human tissue that such a technique might engender when scaled sufficiently to be useful (assuming it is practical as an engineering matter). See the comments at the end of this article:
http://www.physorg.com/news100445957.html
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Tim Daneliuk wrote:

Somebody demonstrated a model helicopter flying by transmitted power in the '60s and Gerard K. O'Neill designed a system that would transmit power from orbit in gigawatt quantities.
Using it for cell phones and the like, one might be able to have a local charger in one's car or on one's desk that charges the phone without having to plug it in, but having all cell phones charged from a central power transmitter is unlikely in the extreme.
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Tom Watson wrote:

As most of those postings noted, the "skin effect" is really only of significance and high frequency (far above the 60 Hz AC). The solution of Maxwell's equations is dependent on the material and changing the core material changes the behavior as well. A combination of materials _might_ be effective, but certainly until very recently the cost differential of manufacture w/ multiple materials far outweighs the benefits. It _might_ be getting to the realm of reasonable, but while I've not investigated it as a real possibility, I really doubt even yet we're to that point on material costs relative to other costs.
The electric utilities spend a great deal on research and I spent a sizable fraction of my career in the utilities business working w/ EPRI (Electric Power Research Institute, a utility-funded R&D organization) in the I&C and Transmission & Distribution areas and if the concept was considered very high on the list, it would have received funding for at least theoretical work. To the best of my knowledge it hasn't.
Where we could _really_ make a savings would be to get practical near-room-temperature or at least not near-absolute-zero superconductors--they're making progress, but a ways to go yet.
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The problem with those who are educated is that they have been trained off the obvious.
Their predilection is to assume the veracity of the precedent, without question.
I'm asking you to revisit the fundamental assumptions.
Regards,
Tom Watson
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Tom Watson wrote:

I'm not sure where you're going with this. Skin Effect is not an "assumption" - it can be calculated and probably even measured. From http://en.wikipedia.org/wiki/Skin_effect we get this (near the end of the article):
In copper, the skin depth at various frequencies is shown below.
frequency depth
60 Hz     8.57 mm 10 kHz     0.66 mm 100 kHz     0.21 mm 1 MHz     66 m 10 MHz     21 m
In Engineering Electromagnetics, Hayt points out that in a power station a bus bar for alternating current at 60 Hz with a radius larger than 1/3rd of an inch (8 mm) is a waste of copper, and in practice bus bars for heavy AC current are rarely more than 1/2 inch (12 mm) thick except for mechanical reasons. A possible solution to this problem consists of using cables with multiple insulated conductors. A thin film of silver deposited on glass is an excellent conductor at microwave frequencies.
----------------------
Note that multi-wire transmission lines for very high power shortwave transmitters (and their attendant power supply lines) make use of this fact today. So .... where are you going, I wonder ...
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Tim:
Let's say that I admit all that you present.
The fundamental question still stands.,
Why do we insist on producing conductors composed of very expensive core materials, when we could achieve the same effect, or better, by coating the core material with a highly conductive skin?
On Fri, 15 Jun 2007 20:48:22 -0500, Tim Daneliuk

Regards,
Tom Watson
tjwatson1ATcomcastDOTnet (real email)
http://home.comcast.net/~tjwatson1 /
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Tom Watson wrote:

Several reasons leap to mind:
1) The place where you typically most care about efficient current conduction (i.e., where resistive losses matter especially) is in high power applications. These typically are in the 50-60Hz range where skin effect is negligible.
2) The complexity and cost to manufacture what you suggest was either impossible or so economically irrational that it was never pursued historically. Even today, with quite sophisticated manufacturing process technologies, is it really worth it to, say, make a better coax to go from cable converter to your TV? The currents (and losses) involved are miniscule and almost certainly pale by comparison to the costs to spin up a new wire manufacturing facility.
3) In effect, what you ask for is already taking place. In high frequency applications like VHF/UHF radios and microwave Radar, there is a technique called "microstripline" that uses the copper etching on a circuit board (thin but with appropriate area) to actually synthesize discrete components like capacitors and inductors. This has been done for years. But note: These are very high to microwave range frequencies where skin effect does indeed kick in AND the places where microstripline is used tends to be medium to low power environments - say under 500 watts or so (at least that's my last recollection - things may well have changed in the intervening eons).
4) As someone already pointed out - the Public Futilities have a deep and vested interest in reducing cost and improving reliability of their plants and transmission facilities. They have many Smarty Pants Engineers (tm) who look at exactly these questions. If/When there is a compelling economic driver to do this, you'll see it happen. Again, though, they live at 50-60Hz so it's not likely ...
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I used to work in an industry that catered to the electric utility industry, specifically in transmission and distribution. If there was ever an industry where this would matter, this would be it. The concept of, for lack of a better term, bimetallic cable is not foreign to this industry. The have a variety of cables classified as ACSR (Aluminum Conductor, Steel Reinforced). These cables contain a stranded steel core with a stranded aluminum covering. Now, the purpose of this is not for cost reduction, but in high-strength applications where aluminum or aluminum-alloy conductors would not be strong enough. My assumption would be that since the engineers are familiar with this product and its current-carrying capabilities (and how it relates to AAC and AAAC conductors), if there was an advantage to this sort of arrangement, they'd be doing it. From your other posts on this thread, it appears that you think it just hasn't occurred to them to check. That might be the case, but I doubt it.
todd
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Don't know whether they thought to check, or not.
Don't really know how someone who isn't really creative via personality might be encouraged to think outside the box created for them - that made them part of their personal cognoscenti.
If you teach a non creative person that x is true, he will think that x is true.
He may pass his whole life without questioning what x is.
I've played with drummers who are like that.
Go back to the initial question and see if you can answer it.
So far, I haven't seen any satisfactory answers.

Regards,
Tom Watson
tjwatson1ATcomcastDOTnet (real email)
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I think you're making a fundamentally mistaken assumption here, that engineers are people "who aren't really creative via personality." If nothing else, the thousands of patents granted every year would suggest otherwise. Creativity occurs in other areas besides the fine arts, you know.
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Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

Imagine my surprise.....
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On Sat, 16 Jun 2007 13:35:31 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

Excellent point.
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Tom Watson wrote:

Copper clad steel ground rods are common.
HF tank circuits using silver plated copper are common.
Nothing novel about what you are saying. As the table of skin depths shows, the value is very dependent on the frequency of use. For DC or normal house wiring there is no benefit.
John
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Tom Watson wrote:

Because it's cheaper? I used to work, many eons ago, for American Steel and Wire in North Chicago. Plain old drawn copper or aluminum or whatever was cheap to produce. Plating was expensive. I don't know if that's still the case or not, but I'd guess it is.
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Wading in very late on this discussion, but the answer to virtually every question of the general form "why don't they do ..." is very simple. "Money".
And, in the specific instance you raise, Tom, the answer is "In the situations where it makes economic sense to do so, they *do*, and have, for _many_ years."
One of the more common examples is 'hollow tubes' used at RF frequencies. One can't get much cheaper than air for a 'core material'. <grin> It's amazing how much RF energy at even AM radio frequencies that, say 1/2" copper water tubing can carry.
Most high-power microwave waveguides -- which are nothing more than a thin layer metal surrounding an air core -- *are* _GOLD_ plated. Have been, for *decades*. For exactly the reasons you the designers of _not_ considering.
'Solid' conductors made of dissimilar materials introduce a raft of other engineering issues. Differing 'coefficient of expansion' in the materials can introduce _major_ stresses, contributing to *GREATLY* reduced life-span. If you reduce the 'cost' by 20%, but the life-span is reduced by 50% you _are_ at a net loss.
In addition, 'bi-metallic' conductors are *MUCH* more expensive to manufacture than ones of monolithic construction. There is a lot more to building wire than just the 'cost of materials'.
And, the fact remains, that at 'power line' frequencies, the 'skin effect' is minimal, except on _very_ large cables.
The _killer_ is that "very large" cables are a _bad_choice_ *economically*. One can move the same amount of energy over a *smaller* cable, by simply using a higher voltage. Which is more efficient for other reasons as well.
In short, the question you raise is a "solved problem". The physics haven't changed in the last 50 years, although manufacturing techniques have. And folks like the E.P.I. _do_ keep an eye on developments in the manufacturing arts. If a 'solution' comes along that is _cheaper_ than present methodologies, they *WILL* jump on it.
Example: substations and switchyards use a lot of rigid hollow-tube 'wiring'. For *short* runs, where you don't have 'parabolic sag' issues, it is more effective than conventional wire. Over longer spans, however, conventional 'solid core' wire strands "win", because of the 'adaptability' and consequent less frequent need for support structures.
Summary: Your 'bright idea' is *well-known* in the industry, and has been used for many _decades_ in contexts where it makes economic sense to do so. You don't see much about it, because it is such _common_practice_ in the areas where it is economically viable that nobody bothers to talk about it -- it *is* just the way 'everybody does it'.
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Robert Bonomi wrote:
Yes he did!
Have I not been paying attention or have you been away?
If away, then welcome back!
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto /
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On Fri, 15 Jun 2007 20:48:22 -0500, Tim Daneliuk

At the Boston Museum of Science, there is a live demo where an operator in a metal cage is hit by lightning while his or her hands are against the inside of the cage. The lightning travels down the outside of the cage.
<http://www.mos.org/sln/toe/cage.html
Well worth the trip if in Boston!
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B A R R Y wrote:

Just bear in mind that lightning is an electroSTATIC phenomenon not electroMAGNETIC one. It's been way to many years since I actually had to know anything about this stuff, but IIRC, the behaviors of electrostatics are governed by rather different mathematics than electromagnetics (which are described by Maxwell's Equations). So ... what you see at the museum is not exactly the same thing under discussion here. It's still fun to watch though :)
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On Sat, 16 Jun 2007 15:24:42 -0500, Tim Daneliuk

It is, and thanks for the clarification.
Maxwell's equations wouldn't mean much to me, but I'm currently reading:
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