Define skin depth

Skin depth (often denoted by δ) is a measure of how far an electromagnetic wave can penetrate into a conductive material before its amplitude decays significantly. It's defined as the depth at which the electric field strength (or current density) of the wave has decreased to 1/e (approximately 37%) of its value at the surface of the conductor.

The formula for skin depth is:
δ = √(2 / (ωμσ))

where:
ω is the angular frequency of the electromagnetic wave (ω = 2πf, where f is the frequency).
μ is the magnetic permeability of the conductor.
σ is the electrical conductivity of the conductor.