Re: surface area of wire

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 07:48 AM 9/19/2003 -0600, Tesla list wrote:
>Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net>
>The skin depth for a plane conductor where the thickness is >> the depth is:
>
>depth = sqrt(2/(w*permability*conductivity))  where w is the angular
>frequency expressed in radians per second (2*pi*f).


Note that first condition: plane conductor where thickness >> skin depth...

This is hardly ever met in RF wiring usage...
- round conductors are not plane, and if diameter is < 10*skin depth, the 
effects are significant
- There are almost always other conductors within several wavelengths (not 
skin depths!) and the current in one conductor creates a magnetic field 
which induces a current in the others which create their own magnetic 
fields; of such phenomena are inductors born. (particularly a problem when 
considering Litz wire...)
- Use the idealized skin depth as a guideline to determine when you need to 
start worrying.. (i.e. if skin depth is 1 micron, and you're working with 
dimensions of meters, skin depth is irrelevant, even if it's miscalculated 
by an order of magnitude)




>Maybe this will help
>
>Gerry R
>Ft. Collins
>
> >
> > I'm considering winding a small test coil with litz wire. I would like to
> > know if theres a chart which states the skin depth of wire at high
>frequency
> > in mm. Ive seen a chart in inches floating around though I can only get to
> > grips with mm. From what ive found 200khz is around 0.15mm skin depth. It
> > would be useful to have exact figures.
> >
> > Many thanks,
> > Chris
> >
> >