Skin effect: definition · Chip Field Guide

Beginner

At high speeds, electricity crowds into the thin outer skin of a wire, so the wire acts thinner and wastes more signal.

Novice

At high frequencies current flows only in a thin layer near a conductor’s surface. The layer gets thinner as frequency rises, so resistance, and loss, grow roughly with the square root of frequency.

Expert

Skin depth $\delta = \sqrt{\rho / (\pi f \mu)}$ ; conductor loss $\propto \sqrt{f}$ . Together with dielectric loss ( $\propto f \tan\delta$ ) it sets copper channel loss; surface roughness adds more above ~10 GHz.