magnetic shielding

Discussion in 'Shop Talk' started by Ross, Sep 16, 2005.

  1. Ross

    Ross Moderator Staff Member Supporter

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    OK I'm sick of my credit/memebership cards getting messed up by too many close encounters with magnetic childrens toys, is there anything that blocks a magnetic field?
     
  2. John Hill

    John Hill Grand Master

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    Soft iron blocks magnetic force, I think what really happens is the magnetic lines of force take the line of least resistance via the soft iron.

    I dont know how you could make a practical shield for your cards etc, maybe an old tobacco or other flat type tin or perhaps fold a piece and keep the cards between them?

    If the iron or steel you use is hard enough to retain magnetism it will itself effect the cards.
     

  3. mtman

    mtman Well-Known Member

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    i dont understand how your cards can be that close to a childs toy unless you cary toys in your back pocket :shrug:
     
  4. Ross

    Ross Moderator Staff Member Supporter

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    Perhaps there's some other magnet voiding the cards however the problem remains the same. I'm assuming my boys magnetic building set is to blame and I know at least once he balanced my wallet (when it wasn't in my pocket which is normal as i hate the wretched thing) and the outer most cards were voided. It just crossed my mind to ask but if it requires me lugging around 10 pounds of soft iron then I'll just put up with the occasional problem. Thanks for the input though.
     
  5. mtman

    mtman Well-Known Member

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    ok mwell then maybee the problum is that you are scratching the strip it will act the same way put a piece of paper around the card or they do have little envolopes just for card for this perpose
     
  6. moopups

    moopups In Remembrance

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    Any card that gets close to the 'cancel system' of the thieft deturment system of stores ( the ones that add security sensor packs) can be cancled, same as they can be affected by exotic leather wallets. Reptile skin wallets are very hard on cards, electrical system also. Because the reptile skin has large amounts of iron within them - they are the most often disruptive reasons.
     
  7. John Hill

    John Hill Grand Master

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    Yes, of course it may not be the toys. Any magnetic field, especially a pulsating one, may cause the damage.

    Some likely culprits include:
    The store systems that Moopups mentions.
    Computer and TV CRT screens.
    Any grunty power transformer including your arc welder.
    Loud speakers.
    Microwave ovens (not really sure about these because I think they are magnetically well shielded)
    That handy magnet torch (sorry flashlight ;) ) you got last Fathers' Day
    Any electric motor especially power tools with mostly plastic case.
    And of course that big electro magnet they use for lifting cars at your local junk yard.

    There is a slight, but quite unlikely, risk that one card can scramble the data on an adjacent one but this gets to be much greater if the two cards are left in the one holder in the presence of even a slight pulsating magnetic field.
     
  8. Ross

    Ross Moderator Staff Member Supporter

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    I was hoping somethign like a card sized sheet of brass or what ever I could slip in the outside pockets would do it but I guess not. Great invention for some enterprising soul.
     
  9. John Hill

    John Hill Grand Master

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    Ross, if you find some junk floppy disk drives etc you may find they have various bits of soft grey sheet steel. I have never tested these but I assume the material has been chosen for its magnetic shielding properties.

    Cutting card sized pieces to put at the top and bottom of your stack of magnetic cards might have some desirable effect.

    Of course this might be the absolutely wrong thing to do but I dont think so.
     
  10. Explorer

    Explorer Well-Known Member Supporter

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    Don't know if this is scientifically true or not, but it has worked for me. I was told by a banker many, many years ago that carrying cards NEXT to each other in your billfold can affect the magnetic strip on cards (make them have errors). Put a couple business cards or something like that between the magnetic cards. I have been doing this religiously and no more problems. However, as cards get old, say 18-20 months, they seem to start having read problems.
     
  11. Hip_Shot_Hanna

    Hip_Shot_Hanna Well-Known Member

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    shove em in an old metal cigerette case it stops them geting wiped or the chip type read by thieves
     
  12. Farmer Willy

    Farmer Willy Well-Known Member Supporter

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    You might look into fabricating a small credit card sized envelope out of mylar. It's thin, light, metal coated. If wrapped around a normal card protective envelope it may perform similarly to a farady cage.
     
  13. georger

    georger Well-Known Member

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    But a Farady shield only blocks electrostatic inteference, not EM inteference.

    Sorry, but to diminish/block EM you need either:

    -counteracting field of same phase and strength
    -shielding material
    -distance, since magnetic flux alters by the inverse square of the distance.

    The most compact solution is the shielding material. And it's not usually the lightest solution.

    And eddy currents in the shielding material, induced by the EM field they are blocking may induce their own flux, which will also put your c.cards at risk too.