Re: [SI-LIST] : skin effect

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From: C Deibele (deibele@fnal.gov)
Date: Thu Aug 31 2000 - 05:38:21 PDT


Michael Khusid wrote:

> Craig,
>
> The formula Ray and you are referring to
> skin depth = sqrt(2/(omega * mu * sigma))
> indeed seems to be geometry independant, but that's where the catch is.
>
> This formula is derived from a current/electric field penetration if an
> electromagnetic wave is normally incident on the half-infinite slab of
> homogenious material (metal in this case). This would normally be a
> viewpoint of microwave textbooks.
>
> There are two gotchas going to high speed digital world. First, in the
> stripline the propagation of field is parallel to the metal, not
> perpendicular. Second, the thickness of metal comparable to field
> penetration depth changes the current distribution, and thus, the skin
> effect. What a digital designer ultimately cares for is an increased
> resistance of the stripline at high frequencies, and that can be determined
> from the current distribution.

hang on here, the problems is NOT whether the fields are incident or
circumferential or along the line of propagation. i have solved as an exercise
in grad school these problems....

the problem is identical....it is a boundary condition problem. One can come up
with nice simple results with coax....that agree completely with the plane wave
on a conductor. the problem is BOUNDARY conditions. AFAIK, boundary conditions
have nothing to do with a digital world. digital worlds just require a bit more
bandwidth.....and most "high speed digital circuits" are limited by 10 GHz or
so. The boundary conditions must be satisfied from dc to daylight.

craig

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