inductance calculator, by
Serge Stroobandt, ON4AA
Round wire coil with dimensions and its current-sheet approximation D
mm Mean diameter of the air core coil, measured from wire centre to wire centre N
Number of turns ℓ
mm Lenght of the coil,
measured from the connecting wires centre to centre
d
mm Wire or tubing diameter
Cu, annealed
Cu, hard-drawn
Ag
Al
Plating material ρ
nΩ·m Plating conductivity μ
r
Plating permeability f
MHz Design frequency
INTERMEDIATE RESULTS: p
mm Winding pitch Φ
Proximity factor according to empirical Medhurst data
[2,3]
D
eff
mm Effective coil diameter according to Stroobandt (see below) Correction factors: k
L
Field non-uniformity correction factor according to Lundin
[2,4]
k
s
Round wire self-inductance correction factor according to Rosa
[2,5,6]
k
m
Round wire mutual-inductance correction factor according to Grover and Knight
[2,7]
Wire: ℓ
wire, phys
mm Physical wire length ℓ
wire, eff
mm Effective wire length δ
i
µm Skin depth at design frequency Sheath helix waveguide mode ψ
° Effective pitch angle β
rad/m Axial propagation factor of n=0 sheath helix waveguide mode at design frequency
[1,8]
Z
c
Ω Characteristic impedance of n=0 sheath helix waveguide mode at design frequency
[1]
Effective circuit equivalent at design frequency
L
eff,s
µH Effective series inductance
at design frequency
from Corum & Corum's sheath helix
waveguide formula,
corrected for field non-uniformity and round wire
[1,2,4-7]
X
eff,s
Ω Effective series reactance of round wire coil at design frequency R
eff,s
Ω Effective series AC resistance of round wire coil at design frequency Q
eff,ul
Effective unloaded quality factor of round wire coil at design frequency Lumped circuit equivalent at design frequency
L
s
µH
Frequency-independent
series inductance from the current-sheet coil
geometrical formula,
corrected for field non-uniformity and round wire
[2,4-7]
X
L,s
Ω Series reactance of round wire coil R
L,s
Ω Series AC resistance of round wire coil at design frequency Q
L,ul
Unloaded quality factor of round wire coil at design frequency C
L,p
pF Parallel stray capacitance at design frequency
[1]
Self-resonant frequency: f
res,L
MHz λ/4 (parallel) self-resonant frequency of n=0 sheath helix mode
[1,8]