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High H field shielded inductors?

Discussion in 'Electronic Design' started by Fred Bartoli, Jul 1, 2008.

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  1. Fred Bartoli

    Fred Bartoli Guest

    I'm working on a sensor that'll include bucks and LF passive signal
    filters that have to withstand high H field, possibly up to 50kA/m (DC).
    Shielding the whole box is a last resort possibility.

    So, anyone knowing of inductors that'll withstand this kind of
    environment or manufacturers of these?
  2. Mark

    Mark Guest

    Can you elaborate why a DC magnetic field is an issue?

  3. Might saturate the cores of the inductors?
  4. Wimpie

    Wimpie Guest


    A uniform field of 50kA/m causes about 63mT (Vs/m2) in air. Depending
    on the shape of the ferrite (for example le/D ratio ) and the
    orientation to the field, the flux density inside the material may
    increase significantly (factor 10 is not uncommon).

    The AM ferrite antenna oriented parallel to the field is an example of
    where the flux in the core material is far higher then the undistorted
    flux density. Such a ferrite stick will definitely show saturation.

    Even a sphere will "attract" field lines, so your 50kA/m field will
    bias your ferrite material certainly above 100mT. When you use "open"
    coils (bobbin style inductors), inductance variation because of the DC
    field will not be that high as most wanted field already goes through
    the air.

    You may notice more distortion in your analog circuit because of
    asymmetric behavior of DC biased core material. You can compensate for
    that by using two coils in series or parallel with opposite polarity

    You will probably have to measure it yourself.

    Hopes this help you a bit,

    when you remove abc the address is correct.
  5. Leon

    Leon Guest

    How about mu metal shielding?

  6. whit3rd

    whit3rd Guest

    If it's just LF filtering, would switched capacitor filters do
    the trick? Magnetic flux at low frequency is hard to shield,
    and sensitivity to ambient field isn't usually spelled out
    in the inductor data sheet.

    If it's bucking converters that are an issue, simply using
    overrated units will probably work. Power component
    saturation isn't likely to do anything but tickle the
    overcurrent shutdown in any case. Filters that change
    character according to uncontrolled B-field, though,
    are a nuisance. I remember a friend trying to match
    capacitors who said the bridge was giving him different
    values every time... and the problem turned out to be
    BX type ceramic capacitors being altered by his body
    heat as he held them to attach the bridge probes.

    Nonlinear inductors aren't any more tractable than
    those nonlinear capacitors were...
  7. Tim Williams

    Tim Williams Guest

    Heyyy, if that DC field is in the same direction all the time, you could use
    some of those magnetized inductors. :)

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