The bifilar pancake coil at its resonant frequency

[itsu]

Trying to merge the resonance frequencies of the TBP coil with that of the pickup coil is not that easy.

The screenshot (sweeping from 10KHz to 1MHz) shows the resonance frequency (the voltage this time) of the TBP coil in yellow around 300Khz.
The resonance frequency of the pickup coil in purple is around 500Khz and also picks up the 300Khz resonance frequency of the TBP coil.
Blue is the sweep signal from the FG.

I used a combination of fixed capacitors and variable capacitors to try to merge them, but they won't really, (guess i really have to look
into TK's mentioned DRSSTC) see video: https://www.youtube.com/watch?v=hH2YvExpMm4&feature=youtu.be



Itsu

[TinselKoala]

Itsu, It looks like you are getting very close to having the same resonant frequency on both "primary" and "secondary". I don't know what the result would be when you get them perfectly matched; in DRSSTCs it results in maximum power transfer between the coils, I think.

It would be very nice to be able to look at these things with a Spectrum Analyzer. Our scopes can probably do limited FFT analysis (mine can but it really sucks) that would be helpful but my scope's FFT function, even when working well,  is a poor substitute for a genuine Spectrum Analyzer. Maybe that's why really good SAs often cost more than a house and car put together.  I wonder if anyone posting experiments here has access to a proper SA.


Mags, why is this "unflattering comparison" photo, which is nothing more than TOS violation, personal attack and childish insult, allowed to remain in view?

[gyulasun]

...
I used a combination of fixed capacitors and variable capacitors to try to merge them, but they won't really, (guess i really have to look
into TK's mentioned DRSSTC) see video: https://www.youtube.com/watch?v=hH2YvExpMm4&feature=youtu.be

Itsu

Hi Itsu,

I think you would need to make the pancake's self resonant frequency a little bit tunable by connecting a max 100 pF variable cap in parallel with it first and then approach the pickup coil near to it with its own variable cap. 
The detuning factor mutually affecting both coils resonances is the distance between them i.e. coupling between them. Any time you change the distance, you would have to retune both coils, this means you need coils to be tunable to both directions, up and down.   I do not think a  max 100  pF extra cap across the pancake would influence meaningfully any other properties of it other than its self resonant frequency.
The so called critical coupling would bring the most favorable response between the coils like in band pass filter cases.

Addition: I think any time there is a double peak created in the response then overcoupling is happening, this means you need to increase the distance between the two coils and retune their variable capacitors a little. 

Gyula

[skycollection 1]

In this video i am presenting a curious effect, the experiment consist in one big pancake coil connected to the circuit JL94 is driving a motor with a neoball inside of a plastic container, on top of the pancake coil i placed five PANCAKE COILS, (pickup coils) made of thin wire and all the pancake coils have a led bulb. The neoball turns at very high speed and when the magnet pases infront of the pickup coils "induces" a current that turn on all the bulb leds. This is the experiment....https://www.youtube.com/watch?v=hZaYpYOFvL4

[MileHigh]

I see knobody will answer my earlier questions so far, so Ill pose them again...

If we have a 100t tbf coil and we apply 100v dc, how long would it take for there to be 50v between all pairs of adjacent turns in the coil and what criteria do you consider determines the given answer, if it is ever given a shot.

Would one say that the 50v would be there between each turn only after the inductor has reached full current?

Mags

Ignoring the speed of light, it's instantaneous.  However, just because there is 50 volts between two adjacent conductors and there is a measurable transient distributed capacitance between those two conductors does not mean that there is instantly an excess negative charge on one conductor and a lack of negative charge on the other conductor.  Any charge displacement to charge this transient capacitance would still have to flow in the form of current by snaking its way through the spiral conductors, and that means you encounter an inductance to overcome again and the energy to do that has to come from somewhere.  At the same time, the electric field is starting to push current through the coil in a conventional sense and slowly energizes the inductor.  It's very complicated with multiple things going on at the same time and in the realm of supercomputer simulation.

One part of the problem is that the bulk of the electric field flux is snaking its way through the coil and is pointed in the direction of the coil.  That electric field might manifest as a measurable potential on the surface of a conductor, but it is at right angles to any electric field that would be associated with the transient distributed inter-winding capacitance.

So we put a black box around the whole thing because it's too complicated and we just make empirical measurements of the signals that we can measure with our scope and apply our models on that.

I don't know why you want to believe that there is some "hidden magic trick" associated with a bifilar pancake coil.  What Tesla says in his patent is certainly about the reactance of the capacitance cancelling out the reactance of the inductance at resonance.  There are probably about 50 YouTube clips out there that explain this with phasor diagrams.  Phasor diagrams are more intuitive than hard mathematical analysis and you should check them out.