Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Magnets and Smartphones

  1. Sep 13, 2015 #1
    So I've been looking at information at how magnets interact with things like credit cards, smartphones, etc. and I've noticed that there's an endless debate as to how magnets affect smartphones.
    I realize that it has to do with the size of the magnet and exposure, so for the sake of example,
    What if I have a standard neodymium magnet (size 1 cubic centimeter) next to the smartphone 24/7? What will happen? Is it big/powerful enough to do anything?
    I know phones use neodymium magnets for various purposes themselves, but there seem to be conflicting evidence for both sides. Can someone give me a conclusive explanation of what would happen?
    Thanks
     
  2. jcsd
  3. Sep 13, 2015 #2

    berkeman

    User Avatar

    Staff: Mentor

    The biggest issue would the saturation effects on the inductors and transformers in the smartphone circuitry. Are you familiar with saturation and inductance? :smile:
     
  4. Sep 13, 2015 #3
    Unfortunately, no. Could you please elaborate?
     
  5. Sep 13, 2015 #4

    berkeman

    User Avatar

    Staff: Mentor

    Where are you in your learning about electronics, Josh? High school, starting undergrad, etc? That will help us to target replies to help you the most. Are you familiar with this for example?

    https://en.wikipedia.org/wiki/Saturation_(magnetic)

    :smile:
     
  6. Sep 13, 2015 #5

    berkeman

    User Avatar

    Staff: Mentor

    Also, have you read the pinned thread about inductors at the top of the EE forum? That would be good background info for you to understand to help in our explanations of inductor saturation. :smile:
     
  7. Sep 13, 2015 #6

    meBigGuy

    User Avatar
    Gold Member

    I am not aware of anything in a smartphone that would be damaged by a magnet. Does anyone have any experience or opinion to the contrary?
    For example, would a strong magnetic field cause a switching supply inductor to saturate and cause phone damage?

    I'm certainly not going to run an experiment.
     
  8. Sep 13, 2015 #7

    berkeman

    User Avatar

    Staff: Mentor

    Saturation is a potential problem...
     
  9. Sep 13, 2015 #8

    meBigGuy

    User Avatar
    Gold Member

    I guess the magnet might affect the compass? Magnetize internal components?

    I couldn't find any reliable information on the internet. People say yes, people say no, people say reasonable things, and people say stupid things.

    But, the trend is that there is no obvious serious issue between powerful magnets and smartphones. If they caused serious damage there would be lots of anecdotal reports of such.
     
  10. Sep 13, 2015 #9
    I'm as confused as bigguy is on this one, I'm concerned about things like the compass but I'm not sure. There's lots of people on the internet that are on either side so I came here to resolve it. As far as experience goes, I'm in high school right now and I'll be reading through the saturation information as I type this. I don't mean to come across as rude or anything, but I'm more interested with the practical application of it than the explanation :P
     
  11. Sep 13, 2015 #10

    russ_watters

    User Avatar

    Staff: Mentor

    I use a strong magnet as a dashboard mount and I'm pretty sure that's why my compass is hosed.
     
  12. Sep 13, 2015 #11
    Like I said, I'm not really sure what "strong magnet" means...
    As per the example I stated earlier, would a 1 cubic centimeter neodymium magnet (under 24/7 contact with the phone) be enough to create such problems?
     
  13. Sep 13, 2015 #12

    russ_watters

    User Avatar

    Staff: Mentor

    I'm not sure either, but it uses a steel disk taped to the inside of the case and holds it to the dash with surprising force.
     
  14. Sep 13, 2015 #13

    rbelli1

    User Avatar
    Gold Member

    A common type of magnetometer used in portable devices utilizes permalloy. This has an extremely low (but nonzero) coercivity. Presumably a strong enough magnetic field could magnetize it. That said, many types of cell phone cases use strong magnets in their design. Is it a fair assumption that this common type of case will not break the phone?

    I just did a test with my cell phone. I could not get the magnet in its case to change the compass reading. However the reading looked to be about +-180 degrees at best at startup. (Samsung S5 sport)

    BoB
     
  15. Sep 14, 2015 #14

    meBigGuy

    User Avatar
    Gold Member

    My only concern might be the effect on the inductors of internal switching regulators. If you could cause those to saturate, or induce currents, it could cause power supply spikes. But, I don't know if such a thing is even possible. I have some neodymium magnets at work, and some boards with switching regulators. Maybe I can run an experiment (but, finding a junk/spare board with a good switcher may be a problem). I hate even taking those things into the lab. The only reason I have them is to show people how slowly they fall through copper pipes.
     
  16. Sep 14, 2015 #15
    I'd be interested to know if such a magnet could cause such large problems, or even affect the compass (in a more specific fashion than rbelli1 tested).
     
  17. Sep 14, 2015 #16

    berkeman

    User Avatar

    Staff: Mentor

    The radio and power supply circuits in the phone use inductors along with other components. When a strong magnet is brought close to those inductors, they can saturate, which changes their inductance value (lowers it). This detunes the radio circuitry and interferes with the power supply DC-DC circuitry. The detuning of the radio can make the phone stop working while the magnet is over the radio components. The saturating of the DC-DC inductors will likely cause the output voltage to drop, until the magnet is removed, when the output voltage will likely overshoot, and possibly damage some of the phone circuitry. Not a great experiment to try on a phone that you care about. And not a good idea to try it on somebody else's phone either -- you may end up having to replace their phone.
     
  18. Sep 15, 2015 #17
    Fascinating. What about something not so large/extreme, but different like alternating north and south-orientation magnets? (For the sake of example, a cubic centimeter or so)
     
  19. Sep 15, 2015 #18

    berkeman

    User Avatar

    Staff: Mentor

    Why are you asking these questions? It's starting to sound like you want to come up with a way to jam cell phone communication, which is generally illegal...
     
  20. Sep 15, 2015 #19
    Is that what it does..? That wasn't my intention, i'm just wondering how various magnets might affect my phones/credit cards...I read that north and south orientation magnets were found in refrigerator magnets...
     
  21. Sep 15, 2015 #20

    berkeman

    User Avatar

    Staff: Mentor

    Bad idea.....
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook