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Author Topic: Ferrite Core Resonance investigation.  (Read 18804 times)

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Dear All.

It has been suggested that a new thread be started with the sole purpose of investigating the properties of Ferrite Cores in relation to the present round of experiments that various members are participating in.

Areas of investigation should be....

Composition.

Permeability.

Ferro resonance frequency.

I am sure that there many more to add to this list ?? So don't be shy, join in !!  O0

Cheers Grum.


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Is ferroresonance different from one of these?:

1) LCR resonance (what C ?)
2) Mechanical resonance between two core halves (a two masses and a spring system)
3) Electron Spin Resonance
4) Nuclear Magnetic or Nuclear Acoustic Resonance
5) Standing EM wave resonance inside the ferritee (related to its permeability and permittivity)
6) Resonance of acoustic standing waves (a.k.a. "dimensional resonance")
    a) transverse
    b) longitudinal
    c) torsional

It would be prudent to have the subject of this thread deconflated before it starts.
« Last Edit: 2014-05-19, 00:08:53 by verpies »
   

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Is ferroresonance different from one of these?:

1) LCR resonance (what C ?)
2) Electron Spin Resonance
3) Nuclear Magnetic or Nuclear Acoustic Resonance
4) Standing EM wave resonance inside the ferritee (related to its permeability and permittivity)
5) Resonance of acoustic standing waves (a.k.a. "dimensional resonance")
    a) transverse
    b) longitudinal
    c) torsional

It would be prudent to have the subject of this thread deconflated before it starts.

Dear Verpies.

Thank you for getting the "Ball rolling" .

So.  We need a "Bench mark", a basis from which our tests can be conducted. "The same hymn sheet"  I shall wait for the more erudite members to contribute !!  :)

Cheers Grum.


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In the attached paper the author suggests winding at right angles and pulsing one of the windings with pulses around 1uSec,

He does not say which of the categories of resonance is excited.

I recommend experimenters do not confuse this with normal LC resonance.

verpies has suggested that a spring material be used between the core halves.

This would convert the inductor into a parametric device, activated at the acoustic or ultrasonic level or slightly beyond.

Maybe he had something different in mind and can explain it to us.


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I welcome this initiative from Grum. It will hopefully divert us somewhat from our pre-occupation in dribbling over Akula's very unconvincing attempts to demonstrate self running devices.
   

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Verpies has suggested that a spring material be used between the core halves.
This would convert the inductor into a parametric device, activated at the acoustic or ultrasonic level or slightly beyond.
Maybe he had something different in mind and can explain it to us.
When core halves become attracted, they gain kinetic energy. This energy is lost if absorbed by a dampening spacer.
To return the core to its original position one of the three things below has to happen:
A) The halves collide and bounce back
B) A second asymmetrical winding periodically creates repulsion between the core halves.
C) A springy material pushes them back apart

I suggested a paramagnetic spring material between core halves in case the core is configured to experience resonance described in pt.2 by the method from pt.C.
   

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Dear All.

I have attached a picture of the Single pulse generator that ION posted in a PDF earlier in this thread.

Both ION and I are pretty sure that using this device into a single turn primary coil wrapped around the Ferrite under test. And a scope pick up coil also single turn and at right angles to the primary we should be able to see the ringdown. This signal would be un cluttered !!

I have tried a number of methods both acoustic and electromagnetic but have found in all cases that the received signal was very difficult to decipher !!

Thoughts ??

Cheers Grum.


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Dear All.

I have attached a picture of the Single pulse generator that ION posted in a PDF earlier in this thread.



Cheers Grum.

Good evening Grum.

Is a schematic available for the  Single pulse generator  shown in the attachment?

thanks
take care, peace
lost_bro
   

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Concerning a pulser, in the days when i was replicating the Dally circuit/nano pulser, i was pointed by verpies to
an application of a LT1073 DC2DC converter chip named:  "1.5V Powered 350ps Risetime Pulse Generator"

It can be found on page 14 of this PDF:  http://cds.linear.com/docs/en/datasheet/1073fa.pdf

I did build it and in the crude version it was still able to create 3ns pulses @5V see this video:
https://www.youtube.com/watch?v=s-Alj7gm0RA

Lateron i used it to do some coax time domain reflection measurements with it which where successfull.

I will try to use this on my ferrites to see if it will show any ringing.

Regards Itsu
   

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Ok,  some tests with the pico-pulser on my E-core ferrite.

I have some solid ringing on 22MHz (45ns), not sure if its the 5 turns coil(s) or the ferrite, but my guess its the coils.
Sometimes however it shows a frequency around 1.1MHz which in my feeling would more match the ferrite resonance frequency.

Playing with the FFT function is not really helpfull, as the massive 22MHz signal obscures the rest.

Picture of the used setup, and a screenshot of the scope, yellow = output pulser, blue is ringing pickup.
Video here:   https://www.youtube.com/watch?v=S2pBnRTGdIw&feature=youtu.be


Regards Itsu
   

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I removed some windings on the both puls and pickup coils (went from 5 to 3 turns each) and as expected, the frequency response went up from 22MHz to 30MHz, see screenshot 1.
So the ringing is from the coils, not the ferrite.

I do however see, like mentioned before, still these occasional 1MHz responses and was able to capture one, see screenshot 2.
Here you see the frequency response of the scope again mentioning 1.043MHz which my feeling is the ferrite resonance frequency.
Need a way to verify this, any suggestions?

Regards Itsu
   
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Hi Itsu,

I assume it is a mechanical resonance (=magneto-elastic resonance) for that ferrite E core around 1MHz. If it is, than perhaps suspending the E core on a piece of thread may increase the amplitude vs the amplitude you have found so far with laying the core on  the table surface (damping may be less when the core is suspended). Instead of suspending, perhaps laying the core onto a soft material like a sponge may also reduce dampening the mechanical Q of the core.

Also, if you position the other E core to face the one with the coil i.e. close the open E core with the other E core, then perhaps the 1MHz response also changes (use also a soft base for the two). I know you cannot fully close the two E cores because of the output becomes positioned in the gap.

(Sorry that I am suggesting things I have not tested personally but this is my take on this.)

You may have noticed I uploaded a Philips data sheet on the ou forum for MnZn ferrite material 3R1 and it included a formula for calculating the mechanical resonant frequency of ring cores made from that material, and the formula includes OD and ID sizes only, besides a 5700 number in the nominator.
I attached the file here too, see pdf file page #8 for the remarks. I mention this because if you happen to have a toroidal core from MnZn material then you could also test it at the frequency the formula suggests. Maybe the formula works for other ring cores you have but with less precision. Seeing some output pulses for different toroidal cores in your setup may help identify the E core responses too.

Gyula
   
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Concerning a pulser, in the days when i was replicating the Dally circuit/nano pulser, i was pointed by verpies to
an application of a LT1073 DC2DC converter chip named:  "1.5V Powered 350ps Risetime Pulse Generator"

It can be found on page 14 of this PDF:  http://cds.linear.com/docs/en/datasheet/1073fa.pdf

Regards Itsu

Thanks Itsu;  I've already ordered the LT1073 chip, will get to building it as soon as it arrives.....

take care, peace
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I removed some windings on the both puls and pickup coils (went from 5 to 3 turns each) and as expected, the frequency response went up from 22MHz to 30MHz, see screenshot 1.
So the ringing is from the coils, not the ferrite.

I do however see, like mentioned before, still these occasional 1MHz responses and was able to capture one, see screenshot 2.
Here you see the frequency response of the scope again mentioning 1.043MHz which my feeling is the ferrite resonance frequency.
Need a way to verify this, any suggestions?

Regards Itsu
Try make scope not 20 ns one division, but 50-100, then maybe you see after pulse lower frenquency.
   

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Hi Itsu,

I assume it is a mechanical resonance (=magneto-elastic resonance) for that ferrite E core around 1MHz. If it is, than perhaps suspending the E core on a piece of thread may increase the amplitude vs the amplitude you have found so far with laying the core on  the table surface (damping may be less when the core is suspended). Instead of suspending, perhaps laying the core onto a soft material like a sponge may also reduce dampening the mechanical Q of the core.

Also, if you position the other E core to face the one with the coil i.e. close the open E core with the other E core, then perhaps the 1MHz response also changes (use also a soft base for the two). I know you cannot fully close the two E cores because of the output becomes positioned in the gap.

(Sorry that I am suggesting things I have not tested personally but this is my take on this.)

You may have noticed I uploaded a Philips data sheet on the ou forum for MnZn ferrite material 3R1 and it included a formula for calculating the mechanical resonant frequency of ring cores made from that material, and the formula includes OD and ID sizes only, besides a 5700 number in the nominator.
I attached the file here too, see pdf file page #8 for the remarks. I mention this because if you happen to have a toroidal core from MnZn material then you could also test it at the frequency the formula suggests. Maybe the formula works for other ring cores you have but with less precision. Seeing some output pulses for different toroidal cores in your setup may help identify the E core responses too.

Gyula

Thanks Gyula,

so this specific 3R1 cores resonance point will be around 98KHz when using that formula.
This is lower then i would expect, so good to know.

Regards Itsu
   

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Try make scope not 20 ns one division, but 50-100, then maybe you see after pulse lower frenquency.

Thanks MenoGather,

normally i do check the scope at various settings but i will double check for lower frequencies.

Regards Itsu
   

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Gyula
Quote
You may have noticed I uploaded a Philips data sheet on the ou forum for MnZn ferrite material 3R1 and it included a formula for calculating the mechanical resonant frequency of ring cores made from that material, and the formula includes OD and ID sizes only, besides a 5700 number in the nominator.

That is fantastic and important information.

Thankyou for finding this  O0
   

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You may have noticed I uploaded a Philips data sheet on the ou forum for MnZn ferrite material 3R1 and it included a formula for calculating the mechanical resonant frequency of ring cores made from that material, and the formula includes OD and ID sizes only, besides a 5700 number in the nominator.
...and that 5700 number is the speed of sound in the ferrite - 5700m/s
   
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...and that 5700 number is the speed of sound in the ferrite - 5700m/s

So are we talking "shock wave" here?  Maybe resonating the speed of propagation just above and just below the Mach speed in such a way as to flip/flop the magnetic dipoles?

If that happens to be true, maybe we need to investigate frequency modulation...?
« Last Edit: 2014-05-13, 03:43:12 by Matt Watts »
   

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McFreey used the same formula to calculate resonance of his copper fuel ring, but instead of using the average of the internal and external diameter he just used the diameter as it was a thin copper wire ring, also the speed of sound in copper was lower

http://www.overunityresearch.com/index.php?topic=1526.msg33149#msg33149
Quote
fr = VL/(pi*d )

A resonant LC is run at fr/2 to bring the ring into acoustic resonance at fr, the frequency needs to be pretty exact.
The frequency is finely adjusted using a microphone which listens to the ring, the ring calculated frequency may not be precise and therefore a sweep of the ring noting any resonant sines picked up with the microphone.

For copper the speed is between 4000 - 5000m/s

but there are problems with the McFreey device, the evil skin effect stops the electrical LC sinewave from permeating the copper because copper has a small skin depth even at low frequencies.

MnZn does not suffer this evil skin effect anywhere nearly as bad and this makes MnZn ferrite a fantastic fuel for NAR.

   

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Ok, it became deafening silent overhere on this important subject, but fortunately our Russian friends still are active and via a PM i got some info on how to continue.
Not sure if he appreciate to be named, so i will call him Mr S and only forward info and links.
I got the following link to a PDF describing in Russian how to measure the resonance of ferrite, that link is here:
http://realstrannik.ru/media/kunena/attachments/6159/CE_ferrit.pdf

I have let google translate this and put it into a Word document which is attached and i will refer to this Word document in the video

This Word document info together with the following info should lead to a method on how to determine the resonance frequency of a ferrite core.

Received extra info via PM:

For exaple you want to find ferro-resonace of core from your HV flyback transformer.

1. Remove the core from Flyback
2. It has quadratic form. Now wind 2 test coils X and Y coil with smae number of turns and same wire diammeter. For example 10 turns in X axis than continue winding 10 turns in a Y-axis. As you will see it is in fact one coil electricaly but not magneticaly. 1/2 coil is positioning in X-axis and 1/2 in Y-axis.
3. Use generator from 50 Hz- up to 1..2 MHz for square wave impulses. You can try your generator on TL494.
4. Main goal here is time for opening MOSFET must be shortest as possible. Also time for closing them must be shortest as possible. You need 10ns to open output transistor and not higher 50ns for closing him. Both parameters for ezxample on 200kHz or upper (it's better).
5. Put 75 oms (non-inductive) resistor at output of MOSFET and measure turn-off time on your 3054C. For example MOSFET has gave 50ns turn-off time which is what you need.
6. Remove resistor and conect coil to MOSFET between VPlus supply rail and Drain of your MOSFET.
7. Wind 1/2 winding on your core for connecting your 3054C. Winding should be placed farther away from your excitation coil. So put it on the opposite corner of your quadratic core. Opposite side is maximum longer from your excitation coil.
8. One channel probe on Gate of MOSFET - (if you have signal ringing from TL494 generator put a several small ferrite beads in your gate terminal)/
9. Second channel signal from 1/2 winding.
10. Sweep frequency and stretch the time base to get nice big oscillogram. For example you get 400ns from excitation pulse-width 10ns....200ns.  Now you have got impulse resonse of your ferrite core. As you carefully look at oscillogram you will see how ferrite is establishing self-oscillations on exactly one frequency but strictly at the moment after turn-off your MOSFET. Read pulse width response and check it on spectral analyser. You should get nice big peak eactly on Resonant frequency of your ferrite core. As shortest excitation impulse is better. If you have prfessional signal generator try excitation from 1nS up to 200 ns. Just turn on peak detector and sweep generator. Very simple if you have equipment.

I did follow the instructions in the Word document together with the above info, but the result is not as mentioned in the Word document.
The pickup signal is a nice copy of the input frequency, so a nice square wave.

See the video here:  https://www.youtube.com/watch?v=muC-UlyDBcw&feature=youtu.be     

Not sure what went wrong as i also sweeped a large frequency range (so not only at 173KHz) and varied the duty cycle between 10 and 90%.

Any comments are appreciated,  regards Itsu
   
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@Itsu

Seems to me the first procedure of using one coil then a pickup coil wound over the first coil is not right for finding ferrite resonance, since the pickup will be corrupted by the main coil impulses being imparted directly from wire to wire.

The second Russian procedure you just posted is a good start but again not complete.

Seems to me working with a single pick up is not the right method since the pickup coil will show two potential resonance types on the scope depending on how high your FG will go, you will see many resonance points, so how do you know if the resonance is engendered by the ferrite resonance or the pick up coils inherent resonance points.

Seems to me the only way to really find ferrite resonance by using a secondary medium like a pick up coil is to use several pick up coils all having a different number of turns located anywhere on the ferrite as long as they are not one over the other.

So you put one drive coil of let's say 5 turns, then you add let's say three pickup coils of 4, 7, 11 turns (the number is not important as long as each are different).

Then you drive the drive coil with the FG at 10% duty sweeping the frequency and scoping the first 4 turns pick up coil. Each time you see a rise in the waveform you jot down that frequency, then repeat the same procedure with the other two pick up coils.

Since each have different turns, their own internal resonance point should not be the same. By going over your three lists of frequencies, the frequency that is the same in all three will be the ferrite resonance since this is not dependant on any turn ratios. So ferrite resonance, since you cannot connect your scope to the ferrite itself, can only be done with a secondary pick up coil that itself may be misleading. So you need several pick ups to then arrive at a common resonance point.

wattsup



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@Itsu

Seems to me the first procedure of using one coil then a pickup coil wound over the first coil is not right for finding ferrite resonance, since the pickup will be corrupted by the main coil impulses being imparted directly from wire to wire.

I agree, it shows nicely the resonancepoints of the used coils,  not of the ferrite, as also confirmed by Grumage.

Quote
The second Russian procedure you just posted is a good start but again not complete.

Seems to me working with a single pick up is not the right method since the pickup coil will show two potential resonance types on the scope depending on how high your FG will go, you will see many resonance points, so how do you know if the resonance is engendered by the ferrite resonance or the pick up coils inherent resonance points.

Seems to me the only way to really find ferrite resonance by using a secondary medium like a pick up coil is to use several pick up coils all having a different number of turns located anywhere on the ferrite as long as they are not one over the other.

So you put one drive coil of let's say 5 turns, then you add let's say three pickup coils of 4, 7, 11 turns (the number is not important as long as each are different).

Then you drive the drive coil with the FG at 10% duty sweeping the frequency and scoping the first 4 turns pick up coil. Each time you see a rise in the waveform you jot down that frequency, then repeat the same procedure with the other two pick up coils.

Since each have different turns, their own internal resonance point should not be the same. By going over your three lists of frequencies, the frequency that is the same in all three will be the ferrite resonance since this is not dependant on any turn ratios. So ferrite resonance, since you cannot connect your scope to the ferrite itself, can only be done with a secondary pick up coil that itself may be misleading. So you need several pick ups to then arrive at a common resonance point.

wattsup



Ok,  i am trying to follow that second procedure first with comments coming in which i will post here.
If it still not works i will continue to follow up with your approach,  thanks.


Regards Itsu
   

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I got the following feedback on the above video (my answers between brackets):

The pickup coil needs to be at a right angle to the ferrite
(Which indeed was not 100 correct, so i changed this on 2 separate U-cores, but no improvement was seen)

Try to increase pulse width (average pulse power fro excitatio)!! Start from 1microsek and lower down to 500ns.
Amplitude of your Rigol DG4102 12V or higher 18-20V.
If this doesn't help try to wind bucking coil configuartion.
(pulse width was increased (duty cycle) from 1% to 99%, FG was driven at max (20V pp) amplitude, on a new bigger U-core,
the excitation coil was wound in bucking configuration, see also next comment).

Responded pulse width of ferrite shoud not depend any how from excitation pulse width not from number of truns.
Try simetrical configuartion on X axis 5 turns and Y axis also 5 truns (same wire diameter). Also try X axis 5 turns left winding - y Axis 5 turns right winding. Conect serially.
For oscillograph loop coil (output) try 2.5-5 turns on other side of core.
And don't put nothing in air gap. Both halves need to be fasten very hardly.
(I used a new bigger U-core (see picture) and used bucking mode (cc/ccw) symmetrical (2x 13 turns) configuration. U-cores have/had no air gap and are clamped together).

ps: One thinh more how to know you are finding Resonant frequency of ferrite. Both halves will be attracted so hard just like you using
neodimium magnets when you hit Main resonant peak. This is also confirmed by Avalon and some more people.
(never did i found a spot where there was ANY attraction (with core half's loosely together) noticeable)

Aleksandr and Vitaly were measured resonance on Russian Ferrite-Cores !!
Does the methnod work wit american ferrites i don't know !! It;s a different technolgy !!
(i have some Russian toroid cores which i could try, not sure yet how to setup the excitation and pickup coil on a toroid)



So i tested another evening on these U-cores, but never did i found a conclusive resonance point fixed to the ferrite.
It could be indeed that the Russian ferrite behaves differently in which case we in Europe/America have a problem.

I will try to test these Russian toroid's i have to see if any resonance can be found there.

Regards Itsu
   

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As promised i tested one of my in Russia bought ferrite cores (no idea of this is really made from Russian ferrite).
I used the same setup as used on the earlier U-cores, meaning a coil of magnet wire consisting of 2 coils in series wound 90° apart of 15 turns each.
I used them in cw/cw and later on (video) in cw/ccw (bucking mode) setup.

Input signal via a bipolar cap (10uF) from by FG in pulse mode, 10V pp all positive pulse 50% duty cycle at about 173KHz leading edge of
the pulse set to 200ns, trailing edge to 10ns.

But i also swept across a broad range of frequencies, duty cycles and leading/trailing edge settings.

Pickup coil was half a turn squarely to the ferrite core.

The pickup waveform is a close copy of the input waveform, and never did i see that the leading edge of the pulse got missing like
showed in the ferrite Word document attached in one of my earlier posts.

Video here:  https://www.youtube.com/watch?v=x9sdscgys7E&feature=youtu.be

So still no successful way to determine the used ferrite resonance frequency.


Regards Itsu
   
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