Re: NEC-LIST: Ferrite Loaded Loops

Winston,

I have just been doing some literature and web searching on
this subject. If you plan on designing a multi-turn loop on
a ferrite rod with close wire spacing, you hit two
limitations of NEC.

(1) NEC doesn't model the proximity effect of closely-spaced
wires.
(2) NEC doesn't inherently model finite blocks of material.

I have done some preliminary work on the second problem. My
approach is to use a 3D wire grid for the material, and load
it with LD cards of values appropriate to the permeability
or permittivity and the cell size. I've written some code
to generate the NEC wire list, but have not played with it
enough to determine the conditions for which it might
produce useful results.

The first problem is simply avoided by not spacing the wires
closer than three or four radii on center. In the July '77
issue of IEEE Trans. on Ants&Prop there are two articles on
ferrite-loaded antennas which have some potentially useful
equations. I am just now reading Glenn Smith's 1972 paper
on proximity effect (J.App. Physics vol. 43, no.5, May) with
a view to mechanizing his results. I prefer equations and
programs to graphs.

Doug Miron

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