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Cable Asylum Interconnects, speaker wire, power cords. Ask the Cable Guys. |
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In Reply to: The $64,000 question posted by Jon Risch on November 8, 2004 at 20:44:10:
JR: ""The signal is actually carried in the space between the wires, more in the insulation than in the wires. If the conductors were perfect, and had zero resistance, then technically, the signal would not be inside the wires at all, but would exist only on the surface, and in between the two wires. Since we have a less than perfect conductor, some of the signal 'leaks into' the conductor. ""
In reality, the two models can be applied equally, as you stated..but that only works when the transmission line (wires) is being used at the exact characteristic impedance of the load.When the wires are used at an impedance lower than their characteristic Zcable, the current is in excess of what the distributed model requires...and for loads higher than the Zcable, the voltage is in excess..so for unmatched cases, a very large part of the signal is indeed, not travelling as a TEM wave down the line. And the "leakage", as you mentioned, will result in a storage of inductive energy within the surface of any normal conductor (as opposed to a super, which will only store inductive energy within the conduction zone.).
For wire pairs or t-lines, where the impedance is not matched, there is an energy storage which presents as a lagging mechanism..this efefct is minimized at match..
JR:
""Note that for a true superconductor, the surface of the wire would be of paramount importance for high performance audio use, as it is where almost ALL the current flow would be, and where all of the AC audio signal would traverse.""
Actually, that's not quite correct..For supers, the surface is actually entirely unimportant...because it is a super.
"Almost" all the current flow is not quite right..a superconductor does not care in the least what frequency it is transporting when it comes to depth of penetration..it works entirely at a constant current density mode...a parameter called JC, the critical current density. Expressed as Kiloamps per mm2, currently running in the 2 to 3 Kiloamp/mm2. This is not an engineering value, of course, as these conductors require a copper stabilizer in parallel, for preventing motion, and providing a current bypass in the event a quench occurs. So, actual magnet use is more like 1 Kilo to 1.5 Kiloamp/mm2.
In use, the depth of penetration is independent of frequency, and entirely dependent on the current being carried.
And, flux penetration does indeed occur..many super vendors are using dislocations in the conductor lattice, by impurities or ion implantation, to provide sites that pin the flux into place..it is the flux movement that causes quenching..
Course, that's just my experience.. :-)
JR: ""It could be argued equally well that the signal actually IS the EM field, and that the current flow is merely a side effect""
Correct for matched impedance systems...partially correct for unmatched..Cheers, John
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Follow Ups
- Re: The $64,000 question - jneutron 09:45:44 11/09/04 (2)
- Re: The $64,000 question - Jon Risch 20:09:01 11/09/04 (1)
- Re: The $64,000 question - jneutron 06:36:23 11/10/04 (0)
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