Re: Skin Effect
For surface impedance of a line of thickness t, see eq. 5 in my paper:
J. C. Rautio and V. Demir, "Microstrip Conductor Loss Models for Electromagnetic Analysis," IEEE Tran. Microwave Theory Tech., Vol. 51, No. 3, pp. 915–921, Mar. 2003.
This equation is for current flowing on only one side of the conductor. This is pretty close for microstrip because current typically flows mostly on the bottom side. If you have stripline, where current flows equally on both sides, you have to cut Rrf in half.
If you do not have access to IEEE Xplore, email me at rautio((at))sonnetsoftware.com and I will email you a copy. I am not posting the paper here because it is copyrighted. The IEEE copyright agreement, however, does allow me to personally send copies of the paper to anyone I like.