# Re: [SI-LIST] : Inductance vs. frequency

Raghu ([email protected])
Tue, 21 Apr 1998 09:10:17 -0700

It seems reasonable. I am assuming you have two conductors which
together form something like a transmission line. At high frequencies,
the current is mainly on the outer edges of the conductor and there is
very little flux inside the conductor. So the internal inductance term
is essentially absent and the inductance decreases. For a circular
conductor the internal inductance is u0/(8*PI) H/m where u0 is
4*PI*10e-7 H/m where PI=3.1416, etc.

For conductors of other crosssections, the internal inductance is close
for square condutors and decreases as one dimension becomes different
from the other.

Typically, the variation in inductance is not much, as in your case. An
exception is when you have a plane. For a microstrip,for example, the
inductance at low frequencies (1 Khz or less) can be several orders of
magnitude greater from the high frequency inductance. This is because
the current distribution is determined more by the resistance and less
by the inductance and spreads all over the plane of the microstrip.
Fortunately, in this frequency range, one need not worry about SI
effects.

The variation in resistance with frequency is considerable most of the
time.

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Raj Raghuram                                      Home