The bifilar pancake coil at its resonant frequency

[itsu]

Yes, it is, and if you do the test I recommended, scanning all around the edge of the coil with the hall sensor in the plane of the coil, you will see no opposite fields, the lines will always go through the sensor in the same direction.

TK,   Mags,


its not that easy to scan the coil like you mention as the probe connected to the hall and the disk shape of the coil prevents easy access around the wires.

I will try later today, but i do not expect nice results, perhaps Mag's will be able to better show his results.


Itsu

[itsu]

Quote from: MileHigh on April 16, 2017, 04:07:28 PM

Yes it's a strange question because it was a discussion about Magluvin's mistaken belief that "since a series bifilar coil can look like the wire resistance only, then I can pulse a series bifilar coil and get an instant magnetic field without having to energize the inductor."  It wasn't about the bandwidth-limited square wave excitation that you see in Conrad's clip.

Hi MileHigh,

Well, it is true that Conrad's function generator happened to produce a distorted square wave instead of a beefy brick wall wave form at the 4 MHz frequency involved but nevertheless it was already far from a sine wave, close to "imitate" a switching waveform, do not you think?

For me, this is not an explanation,  and I do not think what Magluvin wrote is a mistaken belief, I agree with him.

Obviously, the claims have to be proved by measurements and hopefully it is taking place in this thread.

Gyula

going back to this part in the thread for a moment, as i tried a similar setup as in Conrads video to show the resonance, especially when driving with a square wave signal.
As my TBP coil has a much lower resonance frequency (307KHz compared to Conrads 8.5MHz) i had to change the 1pF cap (was blocking my signal) to 10pF.

The video here:  https://www.youtube.com/watch?v=oeHswSGwneg&t=196s

It shows various square wave signals when driving the TBP coil and the influence it has on the resonance frequency.


Itsu

[MileHigh]

TK,   Mags,

its not that easy to scan the coil like you mention as the probe connected to the hall and the disk shape of the coil prevents easy access around the wires.

I will try later today, but i do not expect nice results, perhaps Mag's will be able to better show his results.

Itsu

In looking at your "TBP coil resonance 1" clip I can see how you have access to the left and right sides of the coil sitting in the CD case with your Hall sensor so you can do the measurement there.  You don't have to scan around the full 360 degrees of the edge of the coil.  The whole thing is symmetrical so there is no need to make more than a single measurement.

[MileHigh]

going back to this part in the thread for a moment, as i tried a similar setup as in Conrads video to show the resonance, especially when driving with a square wave signal.
As my TBP coil has a much lower resonance frequency (307KHz compared to Conrads 8.5MHz) i had to change the 1pF cap (was blocking my signal) to 10pF.

The video here:  https://www.youtube.com/watch?v=oeHswSGwneg&t=196s

It shows various square wave signals when driving the TBP coil and the influence it has on the resonance frequency.

Itsu

Another great clip like usual Itsu.  The subject of breaking up a square wave into the sum of a bunch of sine waves at different frequencies is a challenging topic to understand for people with no background in this subject matter.  The short answer is that one of the sine waves in the frequency spectrum of the square wave is at the resonant frequency of the coil, and it's only that particular frequency that makes the coil resonate.

And that is why when you are looking for resonance or just to see how a circuit responds to a frequency sweep, you never use a square wave.  Multiple different square wave frequencies will make an LC resonator like the TBP coil resonate at its resonant frequency.  That can cause errors where you think the "wrong" square wave frequency is telling you the resonant frequency of the device under test.

[Magluvin]

In looking at your "TBP coil resonance 1" clip I can see how you have access to the left and right sides of the coil sitting in the CD case with your Hall sensor so you can do the measurement there.  You don't have to scan around the full 360 degrees of the edge of the coil.  The whole thing is symmetrical so there is no need to make more than a single measurement.

Agreed.  I was just thinking if he has the face of the hall on the same plain as the coil throughout the go around, then it is not showing the actual flux density at the edges as compared to the flat areas, though it does explain the red and blue differences as he went around as we have taken notice of.

Mags