The calculation of the impedance of a right-cylindrical air-core coil placed next to a flat plate of a uniform polycrystalline metal alloy is a canonical problem in quantitative eddy-current inspection. Cheng [1] and Dodd and Deeds [2] proposed a widely-used solution for a coil next to a semi-infinite half-space of metal, which agrees quantitatively with impedance measurements made for a wide variety of thick but nonmagnetic metal plates. Said plates were assumed to have a uniform and frequency-independent conductivity, σ. The same authors proposed a similar solution for ferromagnetic metals (such as iron, steel and nickel), characterized by both a uniform σ and a nontrivial uniform permeability ¼.