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Re: Lumped vs. T-line - You be the judge...
Tesla List wrote:
>
> Original Poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
>
> Tesla List wrote:
> >
> > Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> >...
> > No doubt about it, the waveform is distorted much like the T-line model
> > would predict but far from exact. Hardly a clean sine wave. However,
> > there is definitely a rise in the wave before the 720nS a T-line model
> > would predict which the lumped model does predict.
> >
> > So we see the fast output rise of the lumped model but distortions similar
> > to the T-line model... So the fast rise is definte proof of the lumped
> > model and the distortions are proof of the T-line model...
>
> The differences from the ideal transmission line are due to the fact
> that a coil is not a TEM transmission line (a line where the electric
> and magnetic fields are perpendicular to the direction of the line).
> The magnetic coupling along the coil, predicted in the lumped model,
> causes that initial rise. The transmission lines incorporated in
> simulators, and treated in usual books, are all TEM models. They model
> very well cables, but don't work very well for coils. Maybe a waveguide
> model can be a better approximation.
>
> Antonio Carlos M. de Queiroz
Terry, Bob, Antonio, and all,
Excellent stuff - I think you've really nailed it down! BTW, the Corums
suggested that a waveguide model is a very close relative to a TC
resonator, even though their helical resonator theory was actually
derived from a TEM transmission-line model. The MicroSim T-L model
predicts voltage peaks that are significantly higher for the T-L model
than for the lumped model, and actual measurements appear to bear this
out. However, the addition of any significant topload C would tend to
attenuate these higher-frequency T-L effects, driving the system towards
virtually "pure" lumped behavior.
For practical, toploaded coils, lumped apparently wins out (though T-L
is always lurking in the background...).
Great work!!
-- Bert --
--
Bert Hickman
Stoneridge Engineering
http://www.teslamania-dot-com