Skin Effect and Skin Depth Difference

Hi everyone,

I am having trouble understanding the difference between skin effect and skin depth.
I know what they are; that:

Skin effect is when there is more current flow nearer to the conductor surface as frequency increases, rather than utilizing the whole cross sectional conductor area.

Skin depth is 1/e or 37% of the outer surface current density value (the maximum current boundary at the perimeter of a wire).

I know that skin depth is different for every conductor,
However I can't understand how skin depth is different for different frequencies.

If the skin depth is 1/e or 37% of the outer surface current density value, and
this outer surface current density value is the same/constant for all frequencies,
hence 37% of this value will be the same too for all frequencies??

Or is there a problem with my reasoning?

Hi,

Skin depth or skin penetration definitely depends on frequency.

With high frequency there will be more current at the outer diameter of a wire than in it's center.
The current is decreasing continously from surface to center.
Let's say at the surface is 100%, decreasing to 90%..80%...50%...37%..20%...
At the 37% point the skin depth is defined. But it may be 0.1mm with high frequency and 0.3 mm with lower frequency.

--> The 37% is just the point of where the depth is defined. But the depth itself differs.
The curve is steeper with higher frequencies.

Klaus

See :- https://en.wikipedia.org/wiki/Skin_effect
Frank

skin depth = 0.066 / SQRT(MHz) in mm, (for copper) so thinner with rising frequency...

as you say the skin depth tells the distance at which the current density falls to 37% of that at the surface....