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    Rotor shaft within AC solenoid question

    Imagine there is a rotating shaft, most likely made of some stainless steel or some other metal that rotor shafts are made of, but I have a solenoid mounted on the rotor shaft, the diameter of the solenoid is much larger than that of the shaft and it is an air core solenoid, the solenoid produces a B field along the Z axis of the rotor shaft.

    the problem here is the solenoid is powered by high frequency AC, so my magnetic flux in the axial direction is time varying, would this flux impact the rotor shaft similarly to an induction heating coil? (most likely)
    what remedies could I use to shield the rotor from the flux, because the flux is not intended for the rotor but for other things mounted on the rotor it just happens to be in the same direction as the longitudinal direction of the rotor.

    thanks.

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    Re: Rotor shaft within AC solenoid question

    Is the Stainless Steel shaft magnetic?



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    Re: Rotor shaft within AC solenoid question

    Well as of now nothing is realized this is just a thought so I don't know , but I assume that all metals more or less will get heated with high frequency AC fields, I am planning on going up to 1Mhz and higher so the metal shaft in the center might be a problem, I wonder mostly about two things , firstly can I shield it by using some thin copper around it and how would all of this influence by axial B field,


    the coil diameter is much larger than the shaft diameter so in theory the flux should have plenty of air to travel through but since the shaft sits in the center I'm not sure how that will turn out.



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    Re: Rotor shaft within AC solenoid question

    Is it a rotary solenoid? They are usually operated by DC or mains frequency AC, is this type specifically designed for high frequency AC drive? If not, are you sure that high frequent AC current produces sufficient torque?

    Shielding should be possible, are you sure that there's an actual problem with AC field?



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    Re: Rotor shaft within AC solenoid question

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    It's not a motor, torque here isn't relevant, it is a thought experiment that Ii want to try out, but before that I am making sure it will work in theory at least.
    so I have a rotor shaft made of some ferrous metal probably or stainless, and I will have a couple of things on the rotor as well as planar type solenoids , multiple ones one after another to produce a B field that is axial in direction. In theory I could make the coils stationary but for the question at hand it would make no difference as the rotor would still be in the same axis as the B field.

    My worry here is that the flux which I would need to be rather strong at high frequency will influence the rotor by creating eddy currents in it and heating it up, much like in an induction oven.
    I would like to somehow isolate the rotor from the flux both for the longevity and performance of the rotor as well as for higher efficiency of my B field because the rotor might extract alot of energy out of the field if it will absorb the field and heat itself up.



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    Re: Rotor shaft within AC solenoid question

    Thanks for clarifying the setup.

    Whatever the purpose is, I fear it's effectively impossible to shield the shaft from the field. Theoretically an embedding ferrite tube can partly isolate the shaft, but depending on the frequency and field strength, its losses may be already too much. Why not use a plastic or ceramic shaft?

    Stainless steel will surely produce eddy currents, ferro magnetic steel additional hysteresis losses, think of induction cookers.



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    Re: Rotor shaft within AC solenoid question

    But in theory since the field is time varying (AC) shouldn't I be able to put some thin foil around the rotor and the field couldn't penetrate because if the foil would have no holes in it, the eddy currents would produce currents that would set up opposite fields that would block the original field from entering further?
    at least I know this to be the case if a high frequency flux is introduced at 90 degrees to a conducting sheet of metal it produces a strong current in the sheet that creates an opposing field.
    Also the flux has plenty of free space to travel through and loop around the outside so would it do much harm to the flux if it was "denied" the very middle of the solenoid where the rotor is located?

    I don't know much about composite materials and shafts and their torque strength to be honest but I believe a composite material shaft that has the same torque rating would have a large diameter than a stainless steel one?
    I thought to say there is no torque on the magnets themselves but there would be torque on the rotor shaft, depending on the power and size it might be quite strong.

    https://quickfield.com/advanced/iron..._shielding.htm

    In this link they show a sphere , I wonder can a cylindrical enclosure would do the same trick, also they seem to show that as the frequency increases the B flux shielding becomes better, which kind of seems sound, your thoughts?


    thanks.



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    Re: Rotor shaft within AC solenoid question

    A conducting as well as a ferromagnetic cylinder can shield an AC field. The practical question is if you can accept the losses. This has to be discussed referring to actual parameters (H, frequency, material properties).

    The Quickfield example is apparently focussed on the shielding effect as such, not discussing losses. You can model your setup with Quickfield or other EM tools to explore the actual behavior.



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    Re: Rotor shaft within AC solenoid question

    I suppose you mean losses with respect to the solenoid when there would be this block introduced in the very middle of the flux path? But since there still would be a significant space between the middle where the rotor is and the outer parts of the solenoid there should be plenty of room for the flux to pass.

    what would be the best flux simulation software that are also easy to use that you would recommend ?



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