Magnetic field changes over time can have a negative effect on medical imaging methods such as MRI. To guard against this problem, shielding methods are available for sensitive equipment installed in less than ideal environments. These methods include passive and active cancellation.

Passive cancellation involves building a room around, for example, an MRI scanner, using shielding material for DC or AC fields.

Active cancellation might be required in a more severe case. This consists of an ensemble of coils generating a magnetic field opposite in direction but equal in amplitude to the disturbing field. To measure the field variations, a Mag-13 with 1000uT range is generally used, with the sensor’s output feeding in to the cancellation system. The higher the range, the closer the sensor can be to the MRI scanner.

Higher frequency sensors may also be required to reduce higher frequency signals. In this case, sensors such as the Mag639 will be more suitable.