[Amps] Skin depth: silver plating of tank circuit coil feasible with

[Dr. David Kirkby]

On 10/ 4/10 09:50 PM, Steve Thompson wrote:
> I recall an article in RF Design magazine which suggested that the
> rf current moves away from high resistivity, I think there was
> some maths supporting the analysis. If the outer surface of a
> (e.g. copper) conductor oxidises, the article predicted that the
> current just moves deeper into the pure metal so the difference in
> performance is much less than might be expected.
>
> Steve

I can see some logic in that, though I agree with you it's not as simple as 
current just taking the lowest resistance path.

The only analytical equation I've seen for skin depth assumes just two materials

1) Conductor of finite conductivity
2) Vacuum surrounding the conductor.

A more realistic model would be

1) Good conductor in the centre (copper)
2) Better conductor outside of that (silver)
3) Poor conductor outside that (silver oxide)
4) Air (or for all practical purposes vacuum) outside of that.

The equations to accurately predict the current flow would I expect be very 
difficult to derrive, though perhaps someone has done it. A check with "Google 
scholar" but could not find anything very hopeful.

http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel3%2F3773%2F11022%2F00512297.pdf%3Farnumber%3D512297&authDecision=-203
http://www.jstor.org/pss/98044
http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F22%2F32085%2F01492650.pdf%3Farnumber%3D1492650&authDecision=-203
http://iopscience.iop.org/0031-9155/23/4/006

I'd still maintain it is of no practical significance at 30 MHz on good conductors.

Dave