Not having good results when trying to predict inductance of a multi layerThe equation that I have in my notes I got from http://home.earthlink.net/~jimlux/hv/wheeler.htm
solenoid coil.
dimensions are
inside radius 0.25 in
length 1 in
thickness of coil 0.44 in
Did femm analysis using asymetric style in a 10 inch diameter sphere with
over 14k nodes. Then assuming that inductance is 2 times the magnetic field
energy divided by the total current squared resulted in an inductance
prediction of 7.638 nH per turn squared.
However using the formula to predict the inductance of a multilayer solenoid
from ITT Reference Handbook for Radio Engineers 6th ed which is
L = 0.8 *(r*N)*r*N)/(6*r+9*length+10*thick)
produces a prediction of 3.356 nH per turn squared
This is the same thing as your equation, except that a is the average radius of the coil, not the inner radius. When I plug your numbers into this equation, I get 10.895 nH.L (uH) = 0.8 * a^2 * n^2 / (6*a + 9*b + 10*c )
where
a = average radius of windings
b = length of the coil
c = difference between the outer and inner radii of the coil.
all dimensions in inches.It states that it is accurate to 1% when the terms in the denominator are
about equal. This is also an equation by Wheeler. It applies as long as the
coil has a rectangular cross section.
-- David Meeker dmeeker@xxxxxxxx http://femm.berlios.de/dmeeker
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