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It seems that using ferromagnetic materials is the easiest way to shield static magnetic field. But is it still working in strong field strength(up to 5T)? Another question is that are mu-metal (iron-nickle) shield under magnetic force in the field? I didn't see anyone considering this. Is it because the force is too small?

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Iron is a ferromagnetic material and it begins to saturate at 1.6 teslas so if "dipped" into a 5T static field it will be far less effective as a shield.

There will be a force on all ferromagnetic materials in a static magnetic field.

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  • \$\begingroup\$ Re "far less effective...": The shield just needs to be thicker is all. Picture a box of mu-metal in the 5T field. It shunts some lines of force around the cavity, but it can't shunt all because it saturates. So there still are field lines in the cavity, but not as many. So put another box inside the box, and another box inside that, until the innermost box is not saturated. The box inside a box inside a box structure is just the equivalent of a thicker walled box. Maybe the thicker walls will even keep it from collapsing under the tremendous strain... \$\endgroup\$ – Solomon Slow May 19 '15 at 19:11
  • \$\begingroup\$ Thanks for your explanation. From book it seems iron does begins to saturate below 1.6T. But its permeability begins to drop from 100 H/Amps per meter. Does this mean there already are field lines through the cavity way below 1.6T? It should be calculated with the permeability of air right? \$\endgroup\$ – tendo May 19 '15 at 19:38
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    \$\begingroup\$ I'm not really prepared to be specific on so general a question as originally posed. Magnetics and predicting field strengths can be very hit and miss. As for mentioning a cavity (which of course there will be) dimensions can affect the field in the cavity massively so nothing really to say other than recommend you get a student edition of an FEA tool that does magnetics. I used one a few years ago called quickfield. \$\endgroup\$ – Andy aka May 19 '15 at 20:04

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