Assessment of a potentially serious EMI Threat to sensitive TEM/SEM Microscopes

FMS was engaged to conduct a thorough assessment of a potentially serious EMI Threat to sensitive TEM/SEM Microscopes located in Imaging Suites immediately adjacent to a planned new research lab with two high field, 9 Tesla super conducting magnets. Several of the microscopes had stray field EMI stray field specifications of < 0.1 mG for optimum operation.

Fringe field conditions present in areas adjacent to the two 9 Tesla super conducting research magnets.

Computer simulations were generated to provide a view of fringe field conditions likely to be present in areas adjacent to the two 9 Tesla super conducting research magnets. The computer models indicated that fringe field magnitudes ranging from 1 to > 100 mG could be present in the adjacent Imaging Suites with the research magnets energized. As a consequence, all instruments planned for use in the adjacent Imaging Suites were confirmed to be at substantial EMI threat risk from operation of the 9T research magnets.

Novel magnetic dipole compensation design feature

To reduce research magnet’s fringe field magnitudes to levels sufficient to eliminate EMI threat conditions to sensitive TEM & SEM instruments in adjacent Imaging Suites, FMS collaborated with the super conducting magnet manufacturer to integrate a novel magnetic dipole compensation design feature. The full dipole compensation feature along with active cancellation shim coils, dramatically reduced fringe field levels at incremental distances.

Robust passive shielding scheme reduced remaining fringe field

As a further and supplemental measure, a robust passive shielding scheme was developed by FMS to ensure that remaining fringe field levels from the two compensated research magnets were sufficiently reduced to eliminate EMI threat potential to adjacent TEM and SEM microscopes.

Boundary Element (BE) modeling software used to develop a passive shielding scheme

FMS utilized Boundary Element (BE) modeling software to develop a passive shielding scheme sufficient to further reduce residual fringe fields from the two compensated 9T research magnets.

BE computer simulation studies used to develop a highly optimized passive shielding scheme

Successive iterations of BE computer simulation studies, allowed FMS to develop a highly optimized passive shielding scheme for installation of high permeability shielding materials on selected wall and floor surfaces in each 9 Tesla super conducting magnet room.

Before and after shielding plots of the two 9 Tesla super conducting research magnet’s fringe fields

Plots of the two 9 Tesla super conducting research magnets fringe fields prior to and after incorporation of full dipole compensation and use of passive shielding measures, demonstrate substantial reductions sufficient to ensure that operation of the research magnets will not present an EMI threat concern to TEM and SEM microscopes in adjacent Imaging Rooms.