1. n. [Geophysics]

The effective depth of penetration of an electromagnetic wave in a conductive medium. The skin depth is the distance in which the wave decays to 1/e (about 37%) of its value; it can be expressed as:

δ_s = (2/σμω)^1/2 = (2/σ)(ε/μ)^1/2,

where
δ_s = skin depth
σ = electrical conductivity
ω = 2πf = angular frequency in radians/s
f = frequency in Hz
μ = μ_rμ₀ = magnetic permeability
μ_r = relative magnetic permeability of the conductor
μ₀ = relative magnetic permeability of free space = 4π × 10⁻⁷ newton per ampere squared (N/A²)
ε = ε_rε₀ = dielectric permittivity
ε_r = relative dielectric permittivity of the material
ε₀ = dielectric permittivity of free space = 8.854 × 10⁻¹² farads per meter (F/m).

See related terms: electromagnetic method,  permeability