Attend XDA's Second Annual Developer Conference, XDA:DevCon 2014!
5,804,462 Members 43,428 Now Online
XDA Developers Android and Mobile Development Forum

NFC Antenna (Back Cover) can be magnetized and will affect compass

Tip us?
 
chadrockey
Old
#1  
Junior Member - OP
Thanks Meter 4
Posts: 28
Join Date: Apr 2009
Location: Cleveland
Default NFC Antenna (Back Cover) can be magnetized and will affect compass

So I've been noticing that my compass would always misbehave (in terms of accuracy, not stability a la Sky Maps). I would get a pretty large static error (30 to 40 degrees obviously not declination); rotations would not be consistent (IE, a 180 degree turn would yield 100 degrees change.); and the magnitude of raw measurements was not like that of the magnetometer I got from Sparkfun.

Turns out the neodymium magnets I had near my desk actually latched onto my phone and magnetized the NFC antenna. I tested this by removing the cover and putting the magnet near the antenna and it sticks. :P Without the cover on, the compass worked much better.

I've mostly demagnetized my NFC antenna now by doing some magnet sweeps and leaving it near the heater, but I've learned to keep the magnets away.

If anyone is having problems with the compass overall accuracy, removing the back cover may help.
Attached Thumbnails
Click image for larger version

Name:	IMG_20110108_163323.jpg
Views:	514
Size:	102.7 KB
ID:	484233  
The Following 2 Users Say Thank You to chadrockey For This Useful Post: [ Click to Expand ]
 
Jonathon Grigg
Old
#2  
Senior Member
Thanks Meter 254
Posts: 1,223
Join Date: Dec 2010
Location: Perth, WA

 
DONATE TO ME
Quote:
Originally Posted by chadrockey View Post
Turns out the neodymium magnets I had near my desk actually latched onto my phone and magnetized the NFC antenna. I tested this by removing the cover and putting the magnet near the antenna and it sticks. :P Without the cover on, the compass worked much better.

I've mostly demagnetized my NFC antenna now by doing some magnet sweeps and leaving it near the heater, but I've learned to keep the magnets away.
Why did you have such strong magnets near your desk? lol

Quote:
Originally Posted by chadrockey View Post
I've mostly demagnetized my NFC antenna now by doing some magnet sweeps and leaving it near the heater, but I've learned to keep the magnets away.
Phones + magnets = bad same as with hard drives, but I guess at least you don't loose files with magnets and phones that would suck...
 
chadrockey
Old
#3  
Junior Member - OP
Thanks Meter 4
Posts: 28
Join Date: Apr 2009
Location: Cleveland
I use them to test various things, such as magnetic interference on magnetometers in phones/compasses/inertial measurement systems. :P The magnets used to hold doors closed are very powerful and affect compass heading. Rare earth magnets are also extremely cool.

That's mostly a myth with the hard drives. Floppy disks/cassette tapes sure. I think it takes something like .2 to .5 Telsa to actually start affect hard drives. My largest magnet is only something like .1. In large spinning drives, they all contain a neodymium magnet in the center.

Mostly I was surprised that the NFC antenna could be imprinted by a magnetic field. I was getting a pretty significant field too. The change was something like 10 uT.

Sources:
http://www.pcworld.com/article/11657..._pc_myths.html
http://en.wikipedia.org/wiki/Neodymium_magnet
 
Jonathon Grigg
Old
#4  
Senior Member
Thanks Meter 254
Posts: 1,223
Join Date: Dec 2010
Location: Perth, WA

 
DONATE TO ME
Quote:
Originally Posted by chadrockey View Post
I use them to test various things, such as magnetic interference on magnetometers in phones/compasses/inertial measurement systems. :P The magnets used to hold doors closed are very powerful and affect compass heading. Rare earth magnets are also extremely cool.

That's mostly a myth with the hard drives. Floppy disks/cassette tapes sure. I think it takes something like .2 to .5 Telsa to actually start affect hard drives. My largest magnet is only something like .1. In large spinning drives, they all contain a neodymium magnet in the center.
I took apart several old hard drives and found those magnets, so I knew about it but they are exceptionally strong! the two magnets are near impossible to pull away from each other when stuck, you have to slide them I have since lost them though
 
treesurf
Old
#5  
Senior Member
Thanks Meter 124
Posts: 581
Join Date: Sep 2010
Thanks for the tip here! Removing the back cover does indeed bring my compass back to sanity. However, I have no idea how to demagnetize the NFC antenna. What are magnet sweeps? Any suggestions?
 
evcz
Old
#6  
Senior Member
Thanks Meter 75
Posts: 621
Join Date: May 2010
Didn't saw this thread either.

Thanks will check it later if compass works fine without the back cover
 
evcz
Old
#7  
Senior Member
Thanks Meter 75
Posts: 621
Join Date: May 2010
Tried without cover and it works ok!

Now need to find a way to de-magnetize thus damn cover :-\
 
treesurf
Old
#8  
Senior Member
Thanks Meter 124
Posts: 581
Join Date: Sep 2010
If you figure out how please let us know.
 
jeremy112683
Old
#9  
jeremy112683's Avatar
Senior Member
Thanks Meter 32
Posts: 488
Join Date: Jan 2011
Google how to demagnetize metal...


Sent from my Nexus S 4G using xda app-developers app

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes