On 6/30/11 4:40 AM, Brian Hall wrote:
I am looking for formulas to calculate the inductance of an elliptical coil, for use as a primary or secondary, in the shape of a flat spiral, or vertical helix, or conical spiral. Google showed me something about elliptigal integrals but I was never that good at calculus (that and 15+ years between being taught calc and not having used it since). Does anyone know of such formulas, to determine inductance in henries or microhenries, and would be willing to share?
I think you're going to have a tough time finding an analytical expression for this. What I would do is calculate the inductance for a circular coil with the diameter = major axis, and then for diameter = minor axis. You know the elliptical coil will be somewhere in between.
The good analytical inductance equations were all developed early in the 20th century by E.B.Rosa at what became the NBS. If you google "rosa inductance" you'll get plenty of hits for the (not copyrighted) document. The units used are a bit weird (inductance in centimeters, eh?) because back then, there were 4 or 5 different systems of units used (abamperes, statcoulombs, etc. in addition to cgs vs mks, and SI was only a gleam in the eye of future metrological hegemony at BIPM)
There are also tables and equations from Grover ( who worked at NBS, for Rosa, as it happens). Grover's book is available in softcover from Dover for about $10. (it might also be out of copyright.. original date was 1947)
A bit of googling shows that elliptical coils might be used in MRI, but that same googling says that the coils are designed using Finite Element methods, not analytical expressions..
_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla