Core material for high power high frequency coil/solenoid

[artis]

I'm not trying to blindly believe the idea is 100% practical, but I'm not willing to throw it away before I have fully understood the results of it, if not for anything else then at least for learning sake.

What do you mean by "cannot buy these on the web" , what is meant by "these" ?

Well laminating and cutting slits in copper sheet is indeed not a problem these days, in fact it's rather cheap.
On a second thought those rivets can't be made of conducting material because then they would electrically join the multiple isolated discs creating one large and so eddy currents would form again, but that can be solved.

So the skin depth at any frequency is determined by eddy current strength , so the weaker the currents the more into the material the flux can penetrate right? I wonder realistically how thick each sheet/disc could be made practically and how many of them can I stack together.
A stupid question maybe but say I stack one or two discs too many and the flux can't penetrate those last discs, where then does the flux go? Obviously the field lines must loop somewhere and enter back into the magnet that created them so if the area is blocked do they then go sideways parallel to the sheet of metal and then loop around or how?10% cuts for a disc that would be 360/10=36, so a slit after each 36 degrees or so, and one or two of them go deeper

 

[artis]

Ps. Since at high frequencies eddy currents form on the surface of the material then would stacking multiple isolated discs together be any more beneficial than simply taking one thicker disc and machining slits on the surface of the disc with some given depth while leaving the inner disc untouched?

 

[Baluncore]

What do you mean by "cannot buy these on the web" , what is meant by "these" ?

The device you are imagining does not now exist. That could be because it is impractical or impossible. You have not explained what you are really trying to do. I use the laws of physics to avoid wasted effort. You should study the field and do the same. Until then you are dreaming.

Obviously the field lines must loop somewhere and enter back into the magnet that created them so if the area is blocked do they then go sideways parallel to the sheet of metal and then loop around or how?

The field lines initially run at the speed of light past the edge of the disc, or through the slots, then quickly pull into follow the entire surface. With time they diffuse into the conductor but only at about 100 m/sec. Any line that is still penetrating when the field reverses represents a waste of energy as the investment cannot be recovered. If material cannot be reached in the time available it represents a material, energy and a financial burden.

10% cuts for a disc that would be 360/10=36, so a slit after each 36 degrees or so, and one or two of them go deeper

No. If the Wire EDM cuts were 0.25 mm wide then they would be separated by 0.25 mm * 10 = 2.5 mm. The maximum frequency is then determined by the penetration depth of 2.5 mm / 2 = 1.25 mm. For copper that will be about 5 kHz. Closer cuts reduce the skin depth and raise the possible operating frequency.

I don't think you understand the complexity of the field you are trying to enter. You are certainly not the first.

 

[artis]

trust me @Baluncore I do understand the complexity, just that I'm not so good at maths but nowhere am I blind to the multiple setbacks and dead-ends, I just like to figure things out, I have spent quite some time thinking this one through, right now the biggest problems are the field magnets and this one.

Those slits then are very close even at 5Khz , the disc rim would turn into a saw blade rather than a rim, I wonder how long radially those cuts would have to be measuring from the rim.

judging by what you said if I ever wanted to get above 1 Mhz and have low eddy's, my disc would have to be so thin and so slotted that it would resemble a piece of paper shot up by a shotgun , because conductive metals are not among the strongest ones and making them so thin and then slotting them would essentially render their mechanical properties useless I guess.

 

[artis]

I found a simulation here
https://www.cst.com/academia/examples/eddy-currents-on-copper-disc

it seems that this simulation shows accurately how a disc within a changing homogeneous B field would look like from the standpoint of eddy currents?

a stupid question maybe but still , how about instead of slotting the disc letting it have a larger radius so that the return flux from the magnet partly crosses the very outer part (circumference of the disc) since these return flux lines would have opposite direction through the disc they should impose eddy's that run in opposite direction within the circumference and the two currents running in opposite directions should cancel at least partly cancel one another?
Well we can have fewer slots in order to greatly save the mechanical integrity of the device and let the radius be longer so the return flux induces opposite eddy currents that cancel the original eddy current in each part or segment.

What do you think about this?

 

[Baluncore]

That simulation is for a 4mm diameter Cu disc at 50 Hz, so the current has time to enter the material.

What do you think about this?

Until I know what you are trying to do I can't really help you.

 

[artis]

I have a question, see this is a slotted disc but the circumference is solid (shown by the green) the B field lines penetrate only the slotted part of the disc, (shown by the blue dots) if the flux does not go through the small circumferential solid circle only through the larger portion of the disc that is slotted would then there be circumferential currents in the circumference?
I ask this because it would make the disc structurally better if I could keep the disc solid at center and circumference and only make slots in the main part of the disc where the flux will pass through,

 

[Baluncore]

... if the flux does not go through the small circumferential solid circle only through the larger portion of the disc that is slotted would then there be circumferential currents in the circumference?

Yes, a circumferential current will flow whenever there is a change to the magnetic flux passing through the shorted turn.

 

[artis]

Ok I see, no matter the geometry as long as there is a closed loop around a bunch of field lines there will be induced currents. I guess I could use this slotted geometry with a circumferential solid ending but I would then need atleast one break in the circumference also in order to destroy the loop.

Ok another question then, since the B field always goes both directions i wonder if the flux cuts the disc in one direction I could make the disc diameter larger and at least half of the return flux would cut the outer part of the disc in the opposite direction , now this should then induce eddy's in opposite directions canceling each other and the net result would be no or very little circumferential current, is this reasoning sound?

 

[Baluncore]

... now this should then induce eddy's in opposite directions canceling each other and the net result would be no or very little circumferential current, ...

Correct; but why have the disc if the lines loop back so effectively they do not pass through the disc.

 

[artis]

I'm not sure I understood your remark, well the field lines are going to loop back anyway whether there is a disc or isn't one I was just thinking that maybe I can put them to good use, although on a second thought if they experience another disc in their path that would in total lessen the strength of the field and I'm not sure whether the effect of cancelling circumferential currents would outweigh the extra mechanical complexity and other factors, probably not.
If I make a slotted disc I would have to use some low permeability (the same as air) composite material disc on which to attach the multiple thin and slotted copper fragments that join at the center for more structural integrity, this way I could sandwich the thin copper plate between the non-conductive discs to make one larger rotating structure.

 

[Baluncore]

You need to specify exactly what you are trying to do. Many things are provably impossible. The design of magnetic machines is well defined. You need to shorten the magnetic field lines and you need to minimise the air gaps. You cannot get away with breaking the laws of physics by negotiating with the devil, or by getting a more expensive lawyer. Are you dreaming or engineering?