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I've just bought this case for my mobile phone. It has three credit card slots, which isn't strange at all, but in combination with a strong magnet closure, it almost seems a bit stupid, because, who would want their credit cards demagnetized?

However, the the manufacturer states that it has an

Extra strong magnetic closure which will not demagnetize your credit cards

I find this interesting. From what I've heard, all kinds of magnets (though, not for example the magnetic field caused by the phone itself) demagnetizes credit cards, so I wonder what is so special with this magnet, and how it can even be extra strong.

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    $\begingroup$ A likely explanation is that most magnets have very limited range: experiment with a fridge magnet to experience that. That means that any magnetised strips would only be in danger if they sat right on top of the closure magnet. $\endgroup$ – Gert Oct 29 '15 at 15:05
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    $\begingroup$ Please do not try dissuading votes by putting irrelevant disclaimers, people will vote how they want based on the content of your question and are not at all obligated to explain their vote in either direction. $\endgroup$ – Kyle Kanos Oct 29 '15 at 16:36
  • $\begingroup$ I have my doubts about the statement you’ve heard. It isn’t that easy to demagnetize a credit card… $\endgroup$ – Holger Oct 29 '15 at 20:30
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    $\begingroup$ I have my credit card demagnetized and use it still all the time. How that? We use the much more secure (relatively) chip&pin here always anyways. How did I demagnetize it? With a strong degauss field. A small magnet did not do anything. I think there is even a mythbusters about it. $\endgroup$ – PlasmaHH Oct 30 '15 at 9:40
  • $\begingroup$ @PlasmaHH I'm from Sweden. Here it isn't as common to use the chip – most people don't use it very often – however, most shops have the option to do it. $\endgroup$ – Daniel Kvist Oct 30 '15 at 10:07
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Sounds like a Halbach Array - a specific configuration that maximizes flux on one side and minimizes it on the other

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  • $\begingroup$ I will mark this answer as the correct one because it points out the specific technique (which sounds likely to be te used one). $\endgroup$ – Daniel Kvist Oct 29 '15 at 16:02
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    $\begingroup$ It might also undermine their patent as "prior art" $\endgroup$ – user56903 Oct 29 '15 at 16:26
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    $\begingroup$ so, Ask Patents? $\endgroup$ – Braiam Oct 30 '15 at 14:18
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One possible way (and I've no idea if this is what they are using here) is to use alternating magnetic strips with opposite polarities.

A magnet has two poles: north and south. Put two bar magnets next to each other, so their fields are in opposite directions

N------------S

S------------N

If you are roughly the same distance from each magnet, the fields cancel out, giving no magnetic field. If you are close to one or the other, you get nearly the full effect of the magnetic field of that magnet.

So you make a 'magnet' that actually consists, in essence, of lots of strips of alterating N-S and S-N bar magnets. If you are very close to the magnets (such as the metal clasp of the phone case that is attracted to the magnet to hold it closed), you get the full effect of each magnet, because each point of the metal is very close to one magnet.

As you get further away from the surface, the magnetic field drops off very rapidly because the alternating magnets cancel out. The field becomes negligible on a distance comparable to the width of the magnetic strips.

Many fridge magnets are usually made the same way (if you are familiar with fridge magnets). You can test with them and see how close you have to hold them to a metal surface for them to start to feel a noticable force. They can be pretty strong very close in, such as when you try to pull them off the fridge, and do absolutely nothing just 5mm away from the surface.

So if this is the situation with you phone case, then the magnetic field can be very strong when holding the case closed, and virtually nothing except with a few mm of the magnets. Sticking your card magnetic strip right on the magnet is still going to be bad for it, but as long as you avoid physical contact between the card and the magnet, everything should be fine.

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  • $\begingroup$ I don't know if that's what they use, but either way, it sounds like a smart solution. Thanks for the great explaination! $\endgroup$ – Daniel Kvist Oct 29 '15 at 14:51
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There is a new Magnetic patented technology from Correlated Magnetics Research. They basically design different magnetic matrixes composed of smaller point magnets in various N-S designs to refine the resultant magnetic fields. They do offer such a product as you describe.

enter image description here

http://www.polymagnet.com/about/

This is a fairly new development in architecting Magnetic fields. "There are two simple principles of magnetics to explain Polymagnets. The first is that magnets always form a circuit between the north to south poles. Magnetic flux leaves one pole and seeks the opposite pole. The second principle is that flux lines seeks the lowest energy path from north to south. By creating patterns of north and south poles on the surface of magnet, CMR controls the shape of the circuit and the path of the magnetic flux. We’ve created a series of magnetic patterns that focus magnetic energy to produce greater holding forces and direct magnetic energy to create entirely new magnets with alignment, spring or latch features."

"Polymagnets focus the energy already in a magnet to increase holding strength. Normal magnet to metal connections waste a tremendous amount of magnetic energy due to leakage of magnetic flux. By focusing the energy into the metal, Polymagnets hold with much more strength."

What is a Polymagnet? Polymagnets start as regular rare earth magnets. However, CMR uses their magnet system technology to create something entirely different from conventional magnets, which have one north and one south pole. Polymagnets contain patterns of north and south poles on a single piece of magnetic material. The fields coming off of these patterns of north and south poles in turn define the feel and function of the Polymagnet. On the Polymagnet field scan shown at right in the graph below, north is red and blue is south. And on the left is the fieldscan of a standard magnet. Turning a Magnet Into a Polymagnet Magnet Polymagnet® This particular Polymagnet has a checkerboard pattern of north and south poles. The field from this Polymagnet contrasts with the field coming off of a standard magnet, which has one north and south. Conventional magnets are limited in their function because they are limited to a basic, convention

enter image description here

enter image description here

enter image description here

http://www.polymagnet.com/media/Polymagnet-White-Paper-1-Differentiate-Your-Product-Design-with-Polymagnets.pdf

http://www.polymagnet.com/media/Polymagnet-White-Paper-2-Smart-Magnets-for-Smart-Product-Design.pdf

http://www.polymagnet.com/media/Polymagnet-White-Paper-3-Smart-Magnets-for-Precision-Alignment.pdf

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  • $\begingroup$ To me this seems likely to be what is used in the phone case. Great explaination! $\endgroup$ – Daniel Kvist Oct 29 '15 at 15:39
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    $\begingroup$ Thanks I am pretty interested in the different matrixes that can be printed with a 3D printer. I understand they may also be able to drive some of the design down to a nano level. But I think a lot of thought and work is needed in this area before it is practical. But I can imagine combining this technology with quantum dots to design custom molecules with new properties. {Maybe antigravity, invisibility aren't that far off } $\endgroup$ – StarDrop9 Oct 29 '15 at 15:51
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    $\begingroup$ Antigravity and invisibility are impossible, as any physicist knows. Also this "polymagnet" is nothing more than freshman physics as misunderstood by a company that never heard of multipole expansions. $\endgroup$ – user10851 Oct 29 '15 at 17:38
  • $\begingroup$ "Antigravity and invisibility are impossible" well I certainly disagree with you along with a number of leading physicists. And look forward to a time in the not too distant future when we master them. And I assume you don't believe in magnetic monopoles and tachyons. Expand your horizons... look harder and deeper. $\endgroup$ – StarDrop9 Oct 29 '15 at 17:50
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    $\begingroup$ @ChrisWhite You are slightly incorrect. The "polymagnet" is nothing more than freshman physics coupled with a functioning corporation that has developed a business model around custom tailoring the behaviors of these magnetic arrays to the whims of product designers. Never underestimate the leap from physics class to production and the marketing of said product. $\endgroup$ – Cort Ammon Oct 29 '15 at 19:40

protected by Qmechanic Oct 30 '15 at 22:35

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