Re: NEC-LIST: About the speed of wave

Chuck Counselman wrote:
>
> At 5:12 AM -0400 6/12/98, Maciek_Walkowiak wrote:
> >On Wed, 10 Jun 1998, Chuck Counselman wrote:
> >
> >.......
> >> (1) If the conductor is perfect, then wave propagation along it
> >> is at the speed of light in vacuuo.
> >.......
> >>
> >> Best regards -Chuck.
> >
> >The statement about the speed of wave along a perfect conductor is
> >not true. Pocklington (18..) wrote that for a perfectly conducting
> >and infinitely long wire the speed of electromagnetic wave along
> >athe wire has gone to the speed of lights only if the wire radius
> >has gone to zero. I get from above that the speed of EM wave along
> >wires is less than the speed of lights in free space because of an
> >nonzero radius and not because of ends phenomena.
> >
> >With infinitely :-))
> >
> >Maciek Walkowiak
>
> If end effects don't matter, then why does the length of the perfectly
> conducting wire matter? I.e., why "infinitely long"?
>
> I believe we need to know the context of the statement you attribute
> to Pocklington, and precisely what he said, before we can understand
> it. By any chance do you have his book or his paper at hand so you
> can give us more info.?
>
> -C. (whose v<<c)

If we are talking about the propagation of a surface wave along a
single wire then I believe the mode (a TM mode) only exists for finite
conductivity and is loosely bound to the surface. The velocity of
propagation is less than c. E.g for a copper wire at 3GHz and wire
radius of 1mm there is something like a 0.004% reduction in
velocity. I think this reduction goes to zero as the wire radius goes
to zero but I'd have to check.

References:

[1] Field Theory of Guided Waves, R E Collins, 2nd ed, IEEE Press,
    1991, p 718.
[2] Electromagnetic Theory, J A Stratton, McGraw Hill, 1941
[3] Surface Waves and their applications to transmission lines, G
    Gaubau, J. Appl. Phys., Vol. 21, pp 1119-1128, Nov 1950.

-- 
Dr Ian David Flintoft           Email:      idf1_at_ohm.york.ac.uk
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