gbugh
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how do people usually create an area of more concentrated flux inside a coil?
These eddy currents result in a physical force which resists moving magnetic fields, including the very magnetic field which created them. Of course there are gaps in my knowledge.
I agree with c_mitra.I do not know any practical application of this device.
I am an electronic and magnetic designer that works in the field of physics research, and this device really pricked my interest, firstly because I had not seen this idea before so it took me a while to figure out if and exactly how it works, and secondly because I wondered what application it might have in my field of physics research, where I spend much time designing coils and devices to generate all manner of magnetic fields.I came across a patent for a thick wall copper tube with an electrical gap in its side so there won't be current flow. Does this type of design actually work for concentrating flux? Like this: https://patents.google.com/patent/US6720855B2/en
If it does work, how does it work when no current flows in the thick copper tube?
So far, so good, but there is a question that begs to be asked. If the induced eddy currents are prevented from completing a loop around the circumference due to the longitudinal cut, then just what the heck does the distribution of eddy currents in the tube look like??
After considerable thought I think I know the answer, and the answer sheds light on exactly what this device does and what it does not do, and how useful it actually is.
So at this stage, what do others think about the shape of the eddy current loops in the copper tube, given the presence of the longitudinal cut?
It's surely interesting to know how the current distribution looks like.
Skin effect requires that at higher frequencies the current flows only near the surface. Respectively I expect that it's circulating under the surface, e.g. outside forward, inside backward.
I'm talking about this current flow
**broken link removed**
You can use a 3D solver to verify it.
With sufficient conduit conductance and field frequency, the field is completely displaced from the metal ...
That depends on the size and placement of the exciting coil. If there is an axial gap between the exciting coil and the end of the conduit, then I'm very certain that not all of the flux will enter or exist in the conduit opening. Likewise if the exciting coil diameter is greater than that of the conduit.It (the magnetic flux) can only exist in the conduit opening.
There is no argument that the eddy currents that you have sketched will exist. But I don't believe that these eddy currents are major players in the operation of the "conduit". And, as a fact, it is not true that continuity demands that the eddy loops that you sketched are the only possibility. I carefully described another loop structure that I suspect (but did not prove) is the main player in the operation of the conduit.The sketched eddy currents must exist at the inner surface to compensate the field. Continuity demands that the current flows back along the the gap and at the outside.
Of course this is pure conclusion. But unless you show me an alternative solution, I'll stay with it for the time being.
I do not have a 3D solver that can solve for (predict) the shape and magnitude of the eddy currents. However, for any proposed distribution of eddy currents, my magnetostatic solver can show the resultant flux density at all points in space, from which we know if the proposed distribution of eddy currents is correct. I predict that your proposed eddy currents cannot correctly predict the known behaviour of this "conduit", where no flux escapes from the tube. I can model the field produced by your proposed eddy currents if you like.
Instead of lengthy explanations, can you simply sketch which form of eddy currents you expect?
I presume you agree that there must be eddy currents at the metal surface if a field is passing along the conduit.
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