Inductance Formula 2

L=[(permeability of core mu) x (number of turns)**2 x (thickness of ring/2)**2]/[(external diameter + internal diameter)/2]
use m (meter) instead of mm (milimeter) to obtain correct value
where:
L is self-inductance of single-layer spaced toroidal coil (circular cross-sectional area)
mu = mu of air x relative mu of the material
mu of air = 4 (PI) 10E(-7)
mu of material is in per unit
valid for:
thickness of ring << internal diameter
close-winding
References:
1. &quot;Electronic Products&quot; - The Engineer's Magazine of Product Technology, July 2000, page 37
2. Giacoletto L.J. &quot;Electronics Designers' Handbook,&quot; Second Edition, McGraw-Hill, 1977, page 3-46 Table 3.8 (there is a little error in formula, namely, (thickness of ring/2) is not squared)
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