According to the skin effect, alternating current in a conductor has the highest current density on the surface, and it drops with the distance from the surface, such that the current is conducted in a layer near the surface.
For a tube, is the inner surface a skin?
I am wondering about it because in cylindrical conductor with a radius larger than the depth of the skin, there is a part of the cylinder not part of the skin, so there should be no current. I can remove the part of the conductor that is not conducting current by creating cylindrical hole. The result is a tube.
If I removed something that was not an active part of the conductor, why does it change the current in the active part?
I can also create a tube in a different way than drilling: Bending a sheet to a tube, which can plausibly create a tube where the inner surface is a surface with conducting skin depth.
I start with a flat sheet, with the thickness more than two times the skin depth. It's length is the same as the length of the cylinder. I bend it to almost form a tube by bending its shorter side incrementally to a section of a circle, until I have a tube with a small open gap parallel to its center. There are two surfaces building the gap. As a conductor, the voltage between the sides of the gap should be the same based on the geometric symmetry of the cross section. If I close the gap to create a proper tube, the geometry changes very little, but the topology changes, the surface gets a hole. The cross section allows for a loop current now, but as the surfaces that came in contact had the same voltage, there should be no current in the loop. So it seems the inner skin should behave like the outer skin.
This means the inner surface has a skin.
The method by creating a hole seems seems to indicate it is somehow different.
Can I change a conductor by removing something not part of it?