Reluctance of a conical magnetic pole
= Reluctance of a conical magnetic pole
{title2=$\mathcal R_{\rm taper}=s/(\mu\pi Rr)$}
For a linear-radius taper from $R$ to $r$ over <length> $s$, constant absolute permeability $\mu$, and a common approximately axial flux, integrate $dx/[\mu\pi\{R-(R-r)x/s\}^2]$ to obtain the displayed reluctance. Leakage, fringing, nonuniform transverse fields and saturation limit this one-dimensional magnetic-circuit approximation.