Magnetic media (e.g. your credit card) may be affected at field strengths of 3 millitesla (mT). For comparison, this magnetic field strength is about 100 to 200 times stronger than the normal magnetic field on the surface of the Earth (depending where you are on the planet). The 3 mT field line around a typical shielded 1.5 T MRI magnet is about 2 metres from the side of the magnet, and less than 3 metres from the ends of the magnet.
Notice that the magnetic field around an MRI magnet is 500 times smaller than the strength at the isocentre at just 2 to 3 metres distance!
I wonder how the magnetic field affects the newer chip-and-pin microchip which is embedded in credit cards. Anyone care to comment?
Over a period of 15 years of repeated testing, I’ve found that magnetic strips on credit cards are in peril of being wiped in fields greater than 5 mT (50G). RFID chips appear to be immune to large magnetic fields. Over the past 3 years I’ve tested a number of RFID laden cards in fields up to 7T. The Chip and PIN cards (SmartCards), I’ve tested (by accident since it was my subway pass) in a 10 mT (100G) field with no ill effects.
August 14th, 2006, at 8:23 pm #I have come across a pre-installation manual from one manufacturer which advises a limit of 1mT (10G) for credit cards, floppy disks, watches, clocks, and a number of other interesting items such as telephone switching stations and water-cooling equipment. I expect this limit is conservative. A number of levels are advised for various equipment and devices. For example, large moving metallic objects (elevators, escalators, traffic etc) are limited to 0.3mT (3G).
October 29th, 2007, at 9:45 am #