I think that thinking in terms of skin depth, is causing a lot of the
confusion here. Skin depth is a consequence of how the fields
representing the electromagnetic pulse propagate in the electron plasma
of the metal, so is a secondary effect, not a primary one.
This whole thing is better addressed assuming a perfect conductor, so no
wave penetration, and therefore no skin depth at all.
Far from the tube, the magnetic field is circular. Immediately outside,
it parallel to the surface. Transiting between the two, that means
field is compressed at the ends of the major axis. The field density is
proportional to the current, so the current will be concentrated near
the major axes end points.
--
David Woolley
Owner K2 06123
On 27/04/18 23:47, Alan B wrote:
My thinking is the current density is uniform in the outer surface of a round
tube falling according to skin depth at that frequency. At higher frequencies
there is no current on the inner surface so whether they touch when squashed is
immaterial, no current there anyway.
What is relevant is the shape of the magnetic field as the tube is
progressively squashed. As it gets flatter the current distribution moves
closer and closer to that of a strip. There are no sudden effects.
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