Re: Skin Effect Re: [TCML] Q,,question

["Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>]

David N. Van Doren wrote:
> I believe that ac current seeks the path of least magnetic field 
> encircling it.
> For tubes and solid conductors that is the outer most skin.
> For coax with a return current in the center conductor,
> it's the inside of the outer conductor, because of field cancellations.
> from the inner return current.
> Terman argues that in a flat strip the max current is at the outer
> edges leaving the middle less current dense. how ever I've
> read arguments to the contrary.
I think that Terman is correct, and the other distributions that you 
mention too.
I am uncomfortable with what I wrote in the last post, about the 
magnetic field
being null inside the tube being the cause of no current at the inner 
surface.
This doesn't work at DC. And also, it's known that if a wire is passed 
trough
the interior of a tube carrying AC current, a voltage is induced on it.
Skin effect can probably be analyzed by decomposing a conductor in a 
number of
parallel filamental conductors, all with identical resistances and 
inductances
per unit of length, but mutual inductances among them determined by the 
distances
between each pair of filaments. The whole circuit can then be described 
by a
system of equations V=[Z]I, and for a given voltage V the currents I can be
calculated by solving the system. The analysis can be done in sinusoidal 
steady
state, what will give the usual skin effect as function of the frequency.
Transient analysis is also possible. For simple shapes as cylinders and 
tubes,
the exact solution is known, I believe.

Antonio Carlos M. de Queiroz

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