magnetic shielding

Discussion in 'General Electronics Chat' started by piracyer, Jul 25, 2012.

  1. piracyer

    Thread Starter Member

    Jun 9, 2012
    I encountered a question about magnetic shielding in the website's worksheet.

    The question is:
    "Suppose we needed to shield a sensitive electronic instrument from external magnetic fields. How would you suggest we do such a thing? How can we keep stray magnetic fields away from this instrument? "

    And It gives the answer:
    "Magnetic shielding requires that the instrument be completely surrounded by a high-permeability enclosure, such that the enclosure will 'conduct' any and all magnetic lines of flux away from the instrument."

    However, I was thinking about an enclosure made up of material with high reluctance so that it can block any magnetic force. Should this also be a valid answer?

    Also, regarding the answer that's given, doesn't an enclosure of high-permeability "conduct" the magnetic force toward the sensitive electronic instrument?

    Here's the link to the question (Question 9):

    jwilk13 likes this.
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    You shield magnetic fields using a material that is good for shielding: the stuff called "mu metal" is specifically designed for mag shielding.

    Steel is also good, aluminum is weak. There are tables listing the relative shielding strength of various materials.

    Magnetic shield ability is proportional to thickness of the material, unlike shielding for E-field interference.
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Think about this: Air has VERY high reluctance. If this scheme would work, you wouldn't need a shield.;)
  4. piracyer

    Thread Starter Member

    Jun 9, 2012
    That makes sense.
    But whats the difference between reluctance to magnetic flux and resistance to electrical current?
  5. crutschow


    Mar 14, 2008
    They are unrelated. One is is the resistance to magnetic field flow and the other is the resistance to electricity flow.
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
    It doesn't actullay need to be completely surrounded. Depends on how strong the disturbing magnetic field is.

    Example: Zero Gauss chamber

    There are other zero Gauss chambers with multiple layers of MU-metal.

    If, for example, you take the magnetic field line concept imagine that they are concentrated in the material of high permeability. So they are actually diverted from where you don't want them. This is different from the common idea of "shielding".