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I have an air core inductor.

Since its magnetic field will be large, and it will turn on and off rapidly, I assume it will make a lot of noise.

I don't want that noise to disturb the PCB's nearby, so I want to encase the inductor in mu metal.

Here is my question:

I don't want the magnetic field inside the inductor to change noticeably. Magnitude and direction should be unchanged inside the bore of the coil. (A 1% change is tolerable, but less is better.) How far away does mu metal need to be from the coil?

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  • \$\begingroup\$ What frequency range? Do you care about DC shielding? \$\endgroup\$
    – Tim Williams
    Commented Sep 12, 2023 at 16:14
  • \$\begingroup\$ @TimWilliams Not sure of the exact frequency yet, but the fundamental will be in the range of 100 Hz to 1 kHz. DC - no. \$\endgroup\$
    – James Strieter
    Commented Sep 14, 2023 at 0:28
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    \$\begingroup\$ 1kHz, so "rapidly" is some fractions of a millisecond? Or are there edge rates / harmonics that matter? What would be the "victim": what are the PCBs nearby, what can they tolerate? Do you know that your situation is problematic at all? \$\endgroup\$
    – Tim Williams
    Commented Sep 14, 2023 at 0:40

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It is not an answer to the distance question, but when using mu metal, it can often be worth using a soft iron inner shield near the interfering component, with an outer mu metal shield. This is because the soft iron has a higher saturation limit and will divert most of the field, whilst the mu metal will divert the remaining field.

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