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Re: Induction heating in toroid / short circuit of secondary



David Trimmell wrote:

> Every *Toroid* I have ever used is not a "true" donut shape. I have always
> used *conductive* Al tape or some other metal material in the **center** of
> the Toroid, as it assisted with support, etc. Now IF I am using a Toroid as
> a wheal type shape, then how does the *circuit* SEE it as a "shorted" turn?
> It should "see" it as a lumped capacitance, no? I think I am missing
> something here...

At RF frequencies, most of the current ciculates in the outer layer of
conductors, so there is not great difference if a toroid is solid or
just a thin skin. A tube ring is equivalent to a ring of very thick
wire. It also behaves (with more significant role) as a distributed
capacitor, that for most purposes may be modeled as a lumped 
grounded capacitor. The lumped circuit model for the toroid would
then be a grounded capacitor connected to a floating inductor short-
circuited by a very low resistance, with weak coupling to the secondary
coil, and maybe weaker coupling to the primary coil too.

Antonio Carlos M. de Queiroz