Magnetic signature measurements using the NPL low magnetic field facility
NPL’s low magnetic field facility includes a cancellation system in which the ambient magnetic field can be reduced to sub-nT levels at the centre of a 3 m diameter tri-axial Helmholtz coil system. The tri-axial cancellation system can then be used to measure the magnetic signature of materials, components and systems.
In space and defence applications, it is important that the magnetic moment of items are at levels that do not compromise a larger system or safety critical situation. When the items have large dimensions it is not possible to use a detection coil method and measuring the magnetic flux density at a distance is used to determine the magnetic moment.
A calibrated three-axis fluxgate magnetometer used to establish the zero of the cancellation system can be used for magnetic signature measurements. For items under test, measurements can be made at a known distance for each of its three geometric axis and the magnetic flux density measured. From these the magnetic moment can be calculated.
Either of these quantities can be compared with the customer requirements to see if the item passes for magnetic signature. For space applications, we have experience in handling flight-ready components, can develop bespoke calibration programmes, including de-perming, and have measured the magnetic signature of items including battery banks, on-board computers, motors and various mission critical components.
Certain measurements, such as the exploration of the ambient magnetic fields or calibrations of coil systems, can also be made on site.