# Re: Using skin effect

```Subject:  Re: Using skin effect
Date:   Sat, 3 May 1997 22:34:17 +0500
From:   "Alfred A. Skrocki" <alfred.skrocki-at-cybernetworking-dot-com>
To:   Tesla List <tesla-at-pupman-dot-com>

On Mon, 28 Apr 1997 20:18:06 -0700 Bert Hickman
<bert.hickman-at-aquila-dot-com> wrote;

> All,
>
> Alas, the perils of an early morning post! The above gives the factor
> (x) of AC resistance divided by DC resistance, not skin depth! Sorry
> 'bout that!
>
> Skin depth = 1/SQRT(Pi*f*Uo*a) for a cylindrical conductor (meters)
>    where f = Hertz
>          Uo = 4*pi*10-7 Henry/meter
>          a = 5.80x10^7 mho/m (conductivity of copper)
>            = 6.17x10^7 mho/m (conductivity of silver)
>
>    Copper skin depth = 66.1/SQRT(f) millimeters
>                      = 2602/SQRT(f) mils
>
>    Silver skin depth = 64.1/SQRT(f) millimeters
>                      = 2523/SQRT(f) mils
>
> Comparing skin depths (in mils = 0.001") of the two metals at various
> frequencies:
>                   Skin Depth (mils)
>            f      Silver     Copper
>         ======    ======     ======
>         10 kHz     25.2       26.0
>         50 kHz     11.3       11.6
>         75 kHz      9.2        9.5
>        100 kHz      8.0        8.2
>        200 kHz      5.6        5.8
>        300 kHz      4.6        4.8
>        400 kHz      4.0        4.1
>        500 kHz      3.6        3.7
>        750 kHz      2.9        3.0
>       1000 kHz      2.5        2.6
>
> As can be seen, copper tubing is very hard to beat! At typical Tesla
> Coil frequencies, smooth copper tubing is almost as good as it gets!
> Only pure silver or relatively thick silver plating can beat it.

Interesting equation Bert, where did you get it from?

Sincerely

\\\|///
\\  ~ ~  //
(  -at- -at-  )
-----o00o-(_)-o00o-----
Alfred A. Skrocki
alfred.skrocki-at-cybernetworking-dot-com
.ooo0   0ooo.
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\_)   (_/

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