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What will block damage to mag stripes?

  1. May 3, 2005 #1
    Seems like an epidemic lately of "demagnetized" credit cards, transit cards, etc. - apparently due to the card's proximity to cell phones and/or those magnetic closures on briefcases and purses...

    If I were to attempt to protect my cards from any such damage, what material could I use which would also be reasonably lightweight and durable?

    (in other words, what blocks the mag-stripe-altering magnetic field frequency generated by low-power simple magnets or by cell phones? - and a related question is whether this material would also cause any communication issues for the cell phone)

    Any ideas are appreciated.
    Thank you,
  2. jcsd
  3. May 3, 2005 #2
    Goggle for NU metal. It can be had in thin sheets. Cut it to a suitable size, fold it in half and put the cards inside. You'll have to do something about the sharp edges and corners. It won't affect a cell phone unless you cover the antenna if thats the question.
  4. May 3, 2005 #3

    Claude Bile

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    There was recently an episode of the show 'Myth Busters' that aired sometime this month in Australia on this very topic (For those that have never seen this show, it basically consists of two guys that go around scientifically testing urban myths).

    These guys put several credit cards under all kinds of grief from cellphones, money clips etc, and the credit cards still worked without a hitch. These guys even got a decent sized electromagnet and still could not cause the cards to malfunction.

    So it would seem, from the experiments these guys were doing, the magnetic fields produced from cellphones and fridge magnets are simply not strong enough to damage the infromation on a credit card.

  5. May 3, 2005 #4


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    Yet the cards do seem to loose the ability to communicate... What is it? I am pretty sure that several of mine died after leaving my wallet on the car seat in the sun on a +100F (~35C) summer day. The cards all took the curve of the wallet, and would never again lay flat or work. So apparently heat can do the job.
  6. May 3, 2005 #5


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    That would be "Mu" metal; it comes from [itex]\mu[/itex] being the symbol for permeability. NU metal is a type of music :smile:
  7. May 3, 2005 #6
    Well I hope the OP found some decent NU music sites! :blushing:
    Last edited by a moderator: May 3, 2005
  8. May 4, 2005 #7
    Thanks for the info; I'll investigate further (both the Mu metals and whether the damage is as extensive as it sometimes seems...)
  9. May 6, 2005 #8
    Little trick, somewhat related: Sometimes when a card reader is having trouble reading, you might see someone enclose a card loosely in a plastic bag before swiping it again. I've seen it work several times, even with my own cards. I'm assuming that it's using contact electrification/electrostatics to amplify the field on the mag strip (please correct me if I'm wrong).
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