Re: Computer Modeling

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Josh Johnson wrote:
 > I was thinking about approximating the TC as a stack of small
 > loop antennas but the antenna software that I have come across
 > doesn't do a very good job modeling them.

Yes, antenna software will struggle with this structure.  Lots of
turns, close together - almost a worst case scenario for a software
package which is trying to evaluate the full set of Maxwell's
equations.

Since the coil is very small compared with the free space wavelength,
you can model the near field by just calculating the magnetostatic
field around a solenoid, which just takes a few lines of code.
The far field radiation can be calculated by just treating the coil
as a Hertzian current loop with the same magnetic moment as the
real coil - again an easy calculation.

I did this for my coil and found that the far field radiation, which
is very small, was dominated by the field from the electric dipole
formed by the topload and earth.  The contribution to the far field
from the magnetic dipole of the coil was tiny.   Short fat coils, or
flat spirals may be a little different in this respect.

These comments apply to radiation at the normal sort of operating
frequency of the TC, and its lower overtones.  HF and VHF radiation
would be a different matter, and could be quite tricky to model.

It's a case of horses for courses and to say more I think we'd need
to know a little more about the application - assuming it isn't the
old wireless power transmission meme.
--
Paul Nicholson
--