Eddy Current Loss in Laminations

For a thin lamination of thickness d, the eddy-current loss per unit volume is P = π² · B² · d² · f² ÷ (6ρ), with resistivity ρ (≈ 4.7×10⁻⁷ Ω·m for silicon steel). Thinner laminations cut the loss with the square of thickness, which is why cores are stacked from insulated sheets.