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Author Topic: Smudge proposed NMR experiment replication.  (Read 47099 times)

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Well,  if this a naked coil, than that path should be the intrawiring capacitance (parallel capacitance).
Yes but the current flowing thru the coil (modeled as a parallel LC circuit) is not the same as the current circulating in that coil (especially at resonance).

If any magnetic field is generated by this current i doubt it as that's normally done by inductance.
Actually, ANY current generates a magnetic field.
The current flowing through a capacitor, too ...albeit in a different direction.

The next question you should be asking is what is the ratio of the current flowing in the coil's wires vs. current flowing in the intrawinding capacitance ?  Before SRF, at SRF, after SRF ...
« Last Edit: 2020-07-26, 02:07:14 by verpies »
   

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well,  if current flowing in a capacitor generates a magnetic field but in a different direction, then before
SRF we have 100%  current flowing in the coil's wires, at SRF 50% in each because of these different directions and
after SRF 100%  current flowing in the intrawinding capacitance.
   
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This test is done with a large rectangular sense coil as seen in the pix below.  It matches the mean shape of the pcb coil but is slightly off center due to the bobbin spacers.

The first scope pix shows the resultant sense current at resonance and the second scope pix shows sense current at a lower frequency or off resonance.

As Verpies suggested, it must be a capacitive coupling to the sense winding and current probe that is creating the current in the loop.  Otherwise, there should be little to no current in the sense loop with the bucking coil arrangement as shown but it would be interesting to know the exact interaction going on here.

It might be worth saying that in my experiments with transmission lines and 90 degree placed coils, the toroid winding in the NMR device will appear as a single turn to the flat coils under the right conditions.

Regards,
Pm
   

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Finished attempt 2 of a weave 1 pancake coil.
Not very happy still with it, as the problem is to fixate it.

Anyway, its specifications:

OD: 119mm
ID: 87mm
Winding: 1 layer, 10 turns of 1.6mm Litz wire (120 strand), 3.5m long, antiradial weave 1.
Inductance: 17.6µH (@100kHz)
DC resistance: ~0.1Ω

itsu

Finished my 2th weave1 pancake coil.

its specifications:

OD: 119mm
ID: 87mm
Winding: 1 layer, 10 turns of 1.6mm Litz wire (120 strand), 3.5m long, antiradial weave 1.
Inductance: 17.8µH (@100kHz)
DC resistance: ~0.1Ω



When putting them in series (no matter how aiding or bucking), i have 34.7uH.

 
Itsu
   

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It might be worth saying that in my experiments with transmission lines and 90 degree placed coils, the toroid winding in the NMR device will appear as a single turn to the flat coils under the right conditions.
You're right about this, but we have a secret weapon to kill this effect.
Namely, winding the toroidal coil using the same scheme as the new pancake coils.
   

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When putting them in series (no matter how aiding or bucking), i have 34.7uH.
My coils do not behave like that. 

My combined inductance readings, when measuring them with an LCR meter @ 100kHz, are:
- 40µH when connected in series, far apart and their planes are at right angles.
- 20µH when connected in series, 10mm apart, coaxial, planes parallel and magnetically Opposing.
- 60µH when connected in series, 10mm apart, coaxial, planes parallel and magnetically Aiding.
   

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Ok,  doing it that way i have:

My combined inductance readings, when measuring them with an LCR meter @ 100kHz, are:
- 34.7µH when connected in series, far apart and their planes are at right angles.
- 14.4µH when connected in series, 10mm apart, coaxial, planes parallel and magnetically Opposing.
- 55µH when connected in series, 10mm apart, coaxial, planes parallel and magnetically Aiding.

Itsu
   

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When putting together the toroidal coil with the new pancake coils i measure 18.7uH for the opposing pancake coils.

Toroidal coil measured earlier: 242 turns of 1mm wire, measuring 31uH @ 100Khz and 0.3 Ohm.

The below diagram shows the new dimensions.


Itsu
   

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Toroidal coil measured earlier: 242 turns of 1mm wire, measuring 31uH @ 100Khz and 0.3 Ohm.
How many layers does the toroidal coil have?
How is it wound?
   

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1 layer,  spaced closely together (inside touching, outside some space)

But i see a problem with the pancake coils inductance, the selfresonance is already below 4Mhz, so if we need 4.2Mhz as NMR frequency thats not going to work.
   

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1 layer,  spaced closely together (inside touching, outside some space)
What weave ?

But i see a problem with the pancake coils inductance, the selfresonance is already below 4Mhz, so if we need 4.2Mhz as NMR frequency that's not going to work.
I'll get back to that.
« Last Edit: 2020-07-26, 10:49:17 by verpies »
   

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well,  if current flowing in a capacitor generates a magnetic field but in a different direction, then before
SRF we have 100%  current flowing in the coil's wires, at SRF 50% in each because of these different directions and
after SRF 100%  current flowing in the intrawinding capacitance.
I agree that at resonance, the currents in both branches of an ideal parallel LC circuit are equal and that means 50% current ratio.

However, keep in mind that the current "transmitted" THROUGH this coil is not the same as the reactive current circulating IN that coil *.
This is because of the phenomenon known as "Current Magnification" in parallel LCR circuits**.

The ratio of the current circulating IN the coil vs. the current "transmitted" THROUGH the coil is simply known as the Quality Factor of the coil ...or just Q.

* You once asked me: "Where does the energy of this circulating current come from? " Answer: From the past, when the power supply/generator was first switched on. It was during that initial moment, when the circulating current has been built up.
** ...and "Voltage Magnification" in series LCR circuits.
« Last Edit: 2020-07-26, 10:08:26 by verpies »
   

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What wave ?
I'll get back to that.

See picture:

   

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See picture:
So with this weave, the following Partzman's comment applies:

...the toroid winding in the NMR device will appear as a single turn to the flat coils under the right conditions.
   

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That "under the right conditions" sounds like that it is a good thing that the toroid winding in the NMR device will appear as a single turn to the flat coils, but i guess its not.


So we need a weave 1 like scheme for the toriodal coil too to kill that effect.

I have received the water tube .STL file from Conrad, so looking for a 3D printer to print some tubes.


Itsu
   

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Some pictures from the setup using the new weave 1 pancake coils.
   

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That "under the right conditions" sounds like that it is a good thing that the toroid winding in the NMR device will appear as a single turn to the flat coils, but i guess its not.
It isn't. This resultant single turn forms a loop that will pick up the signal from the pancake coils - not from the innards of the toroidal coil.

I suggest a simple experiment with a circular loop of wire* of the same diameter as the mean diameter of the water tube (100mm) and placed between the pancake coils in place of the water tube and toroidal coil.
Scope how much voltage that loop picks up when the pancake cols are driven as they are supposed to be.  That induced voltage signal will compete with the NMR signal :(

* If you are very ambitious, use a piece of coaxial cable to make this loop.  This way you can experiment how much difference the shield of the coax makes, when it is used as the E-field shield - just like in that video ...but bigger.

So we need a weave 1 like scheme for the toriodal coil too to kill that effect.
Yes, the weave1 scheme can be flattened to a single layer solenoidal coil or single layer toroidal coil. The wire crossings should be at the ID and OD as not to force the increase of the distance between pancakes and magnets.
In other applications where the symmetry and thickness of the winding is not critical (e.g. in transformers, chokes...) a two layer winding coming back on itself would be an option.
« Last Edit: 2020-07-26, 16:10:30 by verpies »
   

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Some pictures from the setup using the new weave 1 pancake coils.
I think Smudge is eagerly waiting for a video of NMR hunting with this setup.
I really want him to see the crosstalk and the tuned LC circuits ringing "louder" and longer than the protons ...at the same frequency  >:-)
Because of this, I don't think any NMR signal can be discerned without further coil optimization and E-field shielding, but seeing these problems with his own eyes might elicit some useful feedback from him.
« Last Edit: 2020-07-26, 18:30:05 by verpies »
   
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Well, I did not intend to post any more on this subject but after sleeping on it overnight, I realized what was really going.  So I re-assembled the test set and cleaned it up a bit as seen in the pix below.  The difference now is that there are two sense coils, one is a 58T solenoid and the other is the 1T rectangular both positioned as shown. 

The schematic is next showing the fields as I propose them to exist.  There are two simultaneous H fields present according to the experimental results IMO. 

The last pix is the scope shot of the resulting waveforms.  CH1(yel) is the input from the 50 ohm source Rigol SG, CH2(blu) is the ocv across the solenoid winding and CH4(grn) is the current in the 1T rectangular winding.

The H1 field is produced by the conventional current flow in L1 and L2 and with these coils in a buck configuration, an open circuit voltage of 13.11v rms is produced in the solenoid winding.  L1 and L2 are 33T each.

The measured L1 buck L2 = 83.6uH and the measured L1 to L2 inter-winding capacitance = 7.0-7.5pfd assembled.  The resonant frequency is 6.388MHz so the required capacitance to series resonate with 83.6uH would
be C = 1/w^2*L = 7.4pfd which is close to the measured value. 

So, H2 is therefore produced by the series resonance of L1buckL2 and the inter-winding capacitance Ciw with the H2 field flowing between L1 and L2 as shown in the schematic.

If this is correct, there may be possibilities for some interesting field interactions.

Also, in the present proposed NMR configuration, the H2 field will exist when L1 and L2 are bucking and tuned for resonance IMO.

Regards,
Pm
   

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The schematic is next showing the fields as I propose them to exist.  There are two simultaneous H fields present according to the experimental results IMO. 
Yes, a current flowing through capacitance will generate a second H-field.
There is capacitance between the turns of one coil (intrawinding capacitance*) as well as capacitance between the coils themselves (interwinding capacitance). All of them generate their own H-fields.

Could you amend your drawing to depict the entire electric circuit, which is made by the current flowing through that interwinding capacitance ?


* If there weren't, a single coil would not exhibit a self-resonance frequency.
   

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The schematic is next showing the fields as I propose them to exist.  There are two simultaneous H fields present according to the experimental results IMO.
If you denoted the H2 field as flowing into or out of the screen then that would fit with the field from displacement current through the capacitor, and would be detected by the solenoid coil.  The single turn shorted coil looks to be slightly tilted from vertical, and that would then see some through flux from the H1 field.  Does tilting that coil either side of vertical cause the induced current to go through zero?

Smudge
   
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Yes, a current flowing through capacitance will generate a second H-field.
There is capacitance between the turns of one coil (intrawinding capacitance*) as well as capacitance between the coils themselves (interwinding capacitance). All of them generate their own H-fields.

Could you amend your drawing to depict the entire electric circuit, which is made by the current flowing through that interwinding capacitance ?


* If there weren't, a single coil would not exhibit a self-resonance frequency.

You mean like this?

Pm
   

Group: Professor
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You mean like this?
No, no. Complete the Ciw1 electric path all the way to signal generator.

These interwinding capacitances you've added, are correct, btw.
   

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If you denoted the H2 field as flowing into or out of the screen then that would fit with the field from displacement current through the capacitor, and would be detected by the solenoid coil.
Yes, the magnetic flux should be perpendicular to the current loop's plane. That's why I asked Partzman to draw that current loop including Ciw1 and SigGen.
What do you think of this current's path and the direction of the magnetic flux generated by it, after the toroidal coil is surrounded by a grounded Litz cloth ?

   
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If you denoted the H2 field as flowing into or out of the screen then that would fit with the field from displacement current through the capacitor, and would be detected by the solenoid coil.

I'm not sure I understand you here but I will try to figure it out with perhaps more testing.

Quote
The single turn shorted coil looks to be slightly tilted from vertical, and that would then see some through flux from the H1 field.  Does tilting that coil either side of vertical cause the induced current to go through zero?
Smudge

No, the current reduces slightly due to a slight change in frequency due to the very small change in parasitic capacitance.

Pm

 
   
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