Mutual inductance (M) of two circular coils of radius of r₀ = 11 mm and spaced apart d = 37 mm inside a conductive medium with conductivity of σ = 10 S/m as a function of the normalised horizontal displacement Δd/r₀. (a) Modulus and (b) phase of M obtained by the multilayer solution are compared with D&D solutions [21] and CST MWS simulation results for three different sizes of the insulating boxes. The mutual inductance of two coils in free space (air) is also inlcuded.