[SI-LIST] Re: Internal Inductance
- From: Ege Engin <engin@xxxxxxxxxx>
- To: scott@xxxxxxxxxxxxx
- Date: Fri, 06 Aug 2004 11:10:23 +0200
Craig,
The internal inductance is frequency dependent, and simulations at
multiple frequency points are necessary as Scott explained. L.J.
Giacoletto; "Frequency- and Time-Domain Analysis of Skin Effects", IEEE
Tran. Mag., Jan. 1996, gives some analytical formulas for rectangular
conductors.
I assume you want to obtain the internal inductance at dc. The method
that we apply to extract the dc internal inductance of conductors is to
simulate at a very high and a very low frequency (if you have an
eddy-current solver such as Ansoft Maxwell 2D). The difference in the
inductances gives the dc internal inductance. Though, I think it is
difficult to obtain a definite internal inductance value for conductors
in the presence of planes. The reason is that if the planes are assumed
to be infinite in extent, the current should distribute itself
uniformly in the planes at dc. But this should also mean that the
inductance goes to infinity! Although I could not find a supporting
statement in the literature, it seems obvious, and simulations have also
shown this divergent behavior. As a result, this method gives a definite
internal inductance value only if the planes have a finite (and known)
width.
Regards,
Ege
Scott McMorrow schrieb:
>Craig,
>
>I don't believe there is a straightforward analytical formula for
>non-round conductors. When you start getting into internal inductance
>for trace geometries in the presence of a plane, then it will definitely
>depend on the shape and proximity to the other conductors. However,
>this problem is easily solved by several different field solvers.
>
>Commercially, Ansoft Maxwell 2D does a very good job of extracting
>inductance at multiple frequency points. You just have to be sure to
>use the impedance matrix.
>
>Academic codes such as FastHenry from MIT and Simian from Dean Neikirk
>at the University of Texas can correctly solve for frequency dependent
>inductance and resistance of arbitrary shapes. Links to these can be
>found at http://www.fastfieldsolvers.com/links.htm
>
>Or, if you are dealing with stripline traces, you can use a boundary
>element method or method of moments field solver to run two problems.
>
>Problem 1) your rectangular trace at the normal thickness centered
>between the planes.
>
>Problem 2) a very very thin trace centered between the planes.
>
>
>
>regards,
>
>scott
>
>
>Craig Clewell wrote:
>
>
>
>>Greetings,
>>
>>Does anybody out there have an equation handy to calculate the internal
>>inductance of a square, rectangle, or any other object that is not
>>round? I already know that the internal L of a round wire is (u*length)
>>/ (8*pi), but I'm not looking at using a round wire. I've read that it
>>should be about 20% of the external inductance, however I want to dial
>>it in better than that. I'm so used to neglecting this, that I know
>>find myself at a "loss".....ok...that wasn't funny :>)
>>
>>Thanks for sharing....
>>
>>Craig
>>
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