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Author Topic: Confirming 90deg coupling to ferromagnetic wire.  (Read 650 times)

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I think a lot of people still don't believe the 90deg coupling voodoo associated with ferromagnetic wire, so I thought I would post a brief kickstarter for those interested in replication of GK and other TPU-related works.

Few details listed here because almost every component is non-critical.  Only main aspect is:  interrupted currents in ferromagnetic wire create impulses that can be picked-up at a 90deg angle to the current, creating a transformer action based on changing permeability that is non-reciprocal to the source.

I'm looking forward to seeing others tinker around with this on the bench.

PS: Use some kind of metal shielding between yourself and the device unless you want to personally confirm the migraine headaches that can be associated with pulsing such setups. :P
« Last Edit: 2021-04-26, 23:44:24 by Reiyuki »


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It's not as complicated as it may seem...
Hi Reiyuki,

Could you please post a simple schematic?

I know it is simple, but I don't think anyone wants to assume, and I certainly don't. Didn't we tackle this way back on OU.com, or gn0sis.com one time? Or maybe here?
   

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Could you please post a simple schematic?

I know it is simple, but I don't think anyone wants to assume, and I certainly don't. Didn't we tackle this way back on OU.com, or gn0sis.com one time? Or maybe here?

Attached is simple coil driver akin to what has been posted in many variants by many people over the years.
I just didn't want to use too much detail as I didn't want someone holding off replication because they didn't have the exact MOSFET or capacitors laying around (guilty of this myself! :P)

The operating margins are quite wide, and as long as you start at a low voltage there's minimal risk of letting out the magic smoke.
Sanjev21 would probably be the best source for high-current feedback-protected MOSFET drivers, but in this case the effect shows up at very low power levels (6v 0.02a with ~4us pulses at about 20% duty for the above example that I whipped together today).


The resulting impulses we see are very likely caused by the change of inductance in the ferromagnetic wire, which explains why loading the copper output coils do not result in increased load to the supply (there is BEMF+CEMF for induced currents, but not for a changing inductance IIRC ???).

I think an ideal circuit would be as-per GK's suggestion, where ferromagnetic wire is not pulsed directly but in series with a charge-pump, so that the stored inductive energy is redirected instead of dissipated.  A buck/boost DC-DC converter would work well here, with the ferromagnetic wire in series with the inductor. :)


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It's not as complicated as it may seem...
If I understand the setup correctly, you are pulsing a straight long/narrow piece of ferromagnetic material that has a light gauge copper wire "coil" wrapped around it from end to end, correct? And it can be advantageous to load the coil with a cap to lower/dampen the frequency, correct?

Does a piece of ferromagnetic material stretched out reasonably straight have more inductance than a same length copper strip?

Does the inductance increase or decrease? I would guess decrease.

What is the current working theory as to why the inductance/permeability changes with the pulsing current?
   

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If I understand the setup correctly, you are pulsing a straight long/narrow piece of ferromagnetic material that has a light gauge copper wire "coil" wrapped around it from end to end, correct? And it can be advantageous to load the coil with a cap to lower/dampen the frequency, correct?
Yes, exactly this :)

Quote
Does a piece of ferromagnetic material stretched out reasonably straight have more inductance than a same length copper strip?
update:
0.2uH for the ~14in length of straight nickel strip
The few-foot copper coil wrapped around it reads 4uH and about ~2uH when a few small magnets are used to saturate the nickel 'core'


Quote
Does the inductance increase or decrease? I would guess decrease.
The inductance decreases as current flow increases.  It is very much akin to a magnetic amplifier, and a setup like this could indeed be used as a mag-amp / saturable reactor.  As magnetic flux increases in a permeable metal, it saturates causing permeability to decrease (inductance along with it).

Quote
What is the current working theory as to why the inductance/permeability changes with the pulsing current?
I suspect saturable reactor/magnetic amplifier formulas can directly apply here, with current through the nickel 'core' treated as a single-turn control winding.
https://www.sunpower-uk.com/glossary/what-is-magnetic-amplifier/
« Last Edit: 2021-04-27, 19:43:29 by Reiyuki »


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Does a piece of ferromagnetic material stretched out reasonably straight have more inductance than a same length copper strip?
A straight length of wire has both an internal inductance (from the field within the wire) and an external inductance (from the field outside the wire), the actual inductance value is their sum.  The internal inductance is uru0/8pi Henries per meter independent of the thickness of the wire.  That has to be added to the external inductance .  For high u wire like Fe or Ni that internal inductance can dominate the total value at low frequencies.  At higher frequencies the internal inductance is lower on account of the skin effect.

Smudge
   

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It's not as complicated as it may seem...
Thanks smudge.

For non-fwerromagnetic materials, is u1 * u0 = 1?
« Last Edit: 2021-04-28, 02:02:56 by poynt99 »
   

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It's not as complicated as it may seem...
update:
0.2uH for the ~14in length of straight nickel strip
The few-foot copper coil wrapped around it reads 4uH and about ~2uH when a few small magnets are used to saturate the nickel 'core'
Rei, what would the inductance be of a straight 14in strip of copper (not wound on the nickel strip)? We want an equal comparison don't we?

What are you using to make the inductance measurements?
   

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Quote from: poynt99
Rei, what would the inductance be of a straight 14in strip of copper (not wound on the nickel strip)? We want an equal comparison don't we?
Indeed :P,
I *think* I can find a strip of copper long enough, and/or use aluminum foil/strip to do a quantitative comparison.  But I also have several types of wire onhand from when these tests were first done a few years ago.  Copper, aluminum, soft iron, steel, nickel, nitinol, and craft wire which I believe was a tin alloy were all tested, with all non-magnetic materials behaving similar to copper.  Of the ferromagnetic materials, nickel had the strongest results, followed by soft iron, followed by high-carbon steel wire in the audio freq range.
Also bear in mind that flat strip wire will perform a bit differently vs round.

Quote
What are you using to make the inductance measurements?
I'm using a B&K Precision 878/879 LCR Meter.


When replicators begin experimenting with ferromagnetic wire, you will likely find it difficult to model+predict the behavior of any given setup, since the core material and transformer windings are the same element. ;)


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It's not as complicated as it may seem...
0.02uH must be close to the capability of your meter I would think (smallest FSV of 40uH). When you measure only the meter leads, is it 0uH?

Yes, I think it is important to measure one of your non-ferrous strips or wires to compare.
   

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I think it is important to measure one of your non-ferrous strips or wires to compare.
Agreed.
I'll update this post with the relevant results when the opportunity arises.  And yes, such short lengths of wire are indeed close to bottom-scale for the meter I'm using.

I hope others are picking up some nickel strip so they can tinker around themselves as well  :P


     Update 4/28:
(Meter short-circuit calibrated before each measurement)
Test using 100in nickel strip:
2.7uH  (@1k)
.257 ohm measured resistance
.254 ohm measured impedance @1k

Test using 100in paired copper speaker wire (~14awg)
2.6uH  (@1k)
0.033 ohm measured resistance
0.023 ohm measured impedance @1k

Note: measuring permeability, specifically change in permeability requires a different setup entirely.
« Last Edit: 2021-04-28, 17:39:09 by Reiyuki »


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Thanks smudge.

For non-fwerromagnetic materials, is u1 * u0 = 1?
No.  u1 = 1 and u0 = 4*pi*10-7 so u1 * u0 = 4*pi*10-7
(In my post I used the subscript r for relative u and not the subscript 1)

Smudge
   

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Adding GK's post from a little while back:


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Reiyuki

I find it really strange that there are still people who believe 90 degree coupling or longitudinal forces cannot occur.

For example, if we build a tesla coil of any size it will light a neon/fluorescent or vacuum tube/LED at any angle from the source within it's sphere of influence. If we connect a coil to said devices it will produce the same effect and become more effective with a ground connection. So we should be clear that offset coupling and longitudinal forces are the norm in nature, any voltage over 500v, high frequency and almost anything in a hard vacuum. It is only in man-made low voltage, low current and low frequency systems that limited coupling occurs.

Here's another strange concept, the space between particles at the atomic level is a hard vacuum like outer space because there is no air or other atoms/molecules present on that level. So we are surrounded by a universe filled with the vacuum of space and all matter we know of also contains a hard vacuum. It is only on our peculiar, often superficial level of existence that things appear to be something there not or more than they actually are in reality. In fact everything we call "material" is only 1% particles immersed in 99% hard vacuum full of EM waves.

That's a real mind bender isn't it?, only within the very limited scope of our reality within a pressurized environment here on Earth does this supposed limited and directional energy coupling occur yet many consider it ... normal.

I beg to differ...

Regards
AC



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It's not as complicated as it may seem...
Thanks Rei.

So from your test results in post #10, the copper and nickel measured the same inductance. Was that the expectation?

Not questioning the effect, but have you performed a similar "sanity check" test using copper in place of the nickel to see if there is signal on the outer coil?
   

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Thanks Rei.

So from your test results in post #10, the copper and nickel measured the same inductance. Was that the expectation?

Not questioning the effect, but have you performed a similar "sanity check" test using copper in place of the nickel to see if there is signal on the outer coil?

Thanks for the response,

It was not expected, but then again it had been a couple years since I last experimented with ferromagnetic wire.  I think I had mentally conflated 'permeability' with 'inductance' leading to the mistaken prediction.C.C

The 'sanity checks' were also performed back then, and IIRC it resulted in an extremely weak 'transformer' that acted by primarily dielectric coupling.  I predict a purely copper wire equivalent circuit would also be symmetric and not 'ring down' when current flow is interrupted.


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AC said
Quote
the space between particles at the atomic level is a hard vacuum like outer space because there is no air or other atoms/molecules present on that level
I have been making that point for years in respect of ferromagnetic material, which makes the concept of magnetization M (as dipole moment per unit volume) nonsense, there are no dipoles in that vacuum space except for itinerant conduction electrons.  That is why the incremental relative permeability of hard magnets or saturated soft magnets is that of free space.  So for conductive materials like Fe or Ni we should consider that inner space as a sort of plasma.  And electrons within a magnetized plasma will follow cyclotron curvature.  So I do wonder whether a current carrying Cu coil wound around a Fe wire giving the Fe longitudinal magnetization can make electron current along the Fe tend to follow a spiral path.  If so that will make the inductance of the Fe wire greater.  Is that worth an experiment?

Smudge
   

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AC said I have been making that point for years in respect of ferromagnetic material, which makes the concept of magnetization M (as dipole moment per unit volume) nonsense, there are no dipoles in that vacuum space except for itinerant conduction electrons.  That is why the incremental relative permeability of hard magnets or saturated soft magnets is that of free space.  So for conductive materials like Fe or Ni we should consider that inner space as a sort of plasma.  And electrons within a magnetized plasma will follow cyclotron curvature.  So I do wonder whether a current carrying Cu coil wound around a Fe wire giving the Fe longitudinal magnetization can make electron current along the Fe tend to follow a spiral path.  If so that will make the inductance of the Fe wire greater.  Is that worth an experiment?

Smudge

Thanks Smudge, I really like the cyclotron analogy. ;D

BTW the coupling does not HAVE to be 90deg to get an effect.  You can have a straight strip of insulated copper and insulated nickel back-to-back, and they will interact similarly to the first post.

Attached is a simple addendum to the previous test, demonstrating the difference in inductance winding simple coils of the two different materials.
As you can see, the nickel coil has a higher inductance, likely because the conductor is also the core material. :P


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So for conductive materials like Fe or Ni we should consider that inner space as a sort of plasma.  And electrons within a magnetized plasma will follow cyclotron curvature.
reminded me of this C.C


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Hi Reiyuki,

Where did that iron wire cyclotron image come from, I am intrigued.

Smudge
   

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It is interesting that the Cyclotron and the Magnetron are very similar in their manner of operation.

Accelerated charged particles whether they be electrons or ions follow a predictable path of motion under the influence of a magnetic field.


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Where did that iron wire cyclotron image come from, I am intrigued.


Our friendly neighborhood Iron Man ;)
https://www.youtube.com/watch?v=2KCwYSxcpjU


I believe this is the soft iron wire being used:
https://www.homedepot.com/p/Vigoro-50-ft-Heavy-Duty-Coated-Wire-T025BVG/203894420


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Adding some basic inductance measurements of some various iron+copper wire configurations.  Going for simple diagrams over text as I think it conveys the setups a bit more elegantly.
It's not directly related to 90deg coupling, but might be useful if anyone is 'anomaly hunting'. C.C


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It's not as complicated as it may seem...
Thanks Rei.

Any surprises, interesting observations, or conclusions?
   

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Any surprises, interesting observations, or conclusions?

Based on above data, the most unique observation would be that iron wire appears to have about the same inductance-per-turn as copper on a core, even though it is only about 15% as conductive.
Which helps explain its common use in early electronics as 'magnet' wire (ie: 'magnetic' wire).  Many pre-1900's inventors constructing coils that do not explicitly mention copper may in fact be referring to iron-wound coils.


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