Lenzless resonant transformer

[itsu]

...and anything below the X-axis means, that the DUT is returning energy to the signal generator.

like negative resistance, a negistor?

Or do we have here a severe case of reactive power versus real power?
Guess that the returning energy never will be more then half of the total energy

Thanks,  regards itsu

[verpies]

like negative resistance, a negistor?

No, no ...more like a charged capacitor discharging itself back into the signal generator.
Inductors can do it, too.

[Magluvin]

If this large 3^rd coil was physically rotated 90º so it would be encompassing both the primary and the secondary windings, then you would be able to detect the induction caused by the leakage flux spilling out of the core.  The more current flows in secondary, the more voltage is induced in this 3^rd winding. 
It is just a neat trick to detect how much flux leaks out of a transformer's core.  It has a large educational value.

P.S.
As always, the even number of layers of back&forth winding rule designed for pitch-current nullification, applies to all windings.

I think a better way to measure the field leakage of a toroid core in operation would be to us a coil that I added to the pic you posted above.  It should not be in direct physical contact with the toroid windings or core.   

Mags

[dieter]

So, Verpies, let me get this straight, the scope shot says "OU"?

[verpies]

I think a better way to measure the field leakage of a toroid core in operation would be to us a coil that I added to the pic you posted above.  It should not be in direct physical contact with the toroid windings or core.   

Yes, this will work. too and it will avoid capacitive coupling.

Alternatively, such leakage detecting coil can be placed inside the toroid's hole (please make a pic of that configuration, too, for completeness and for the future).