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Shield rooms are meant to protect precision equipment from the influence of external magnetic fields, so they have to be an enclosed space that implements special processing in the walls that blocks magnetic flux. The effects of external magnetic fields inside the shield room depend on how they are generated, where the precision equipment is located, and the position of the shield room’s opening and supply cable.
A magnetic field analysis using the finite element method is necessary to perform an evaluation that deals with three dimensional and temporal variations to figure out how magnetic flux enters the shield room when several external magnetic fields have been applied.
This Application Note explains how to handle the magnetic shielding phenomena used by the shield room when an external magnetic field is applied, and from there how to confirm the magnetic flux density distribution.
Magnetic Flux Density Distribution
The shield room and magnetic flux density distribution surrounding air region are shown in fig. 1. The external magnetic field is applied in the direction of the arrows in the figures. The magnetic flux from this field flows along the wall surface of the shield room, reducing the magnetic flux density inside of the room itself. The external field that is uniform in the Z-direction in the figures also tries to flow with the wall in the vicinity of the shield room, so the parts outlined in red are where the magnetic flux concentrates and gets more dense. The parts outlined in blue are where the magnetic flux density is less dense.
Magnetic Flux Density Waveform
The magnetic flux density waveforms for each evaluation axis are shown in figures 2 and 3. The shield room is between the positions of 12 m and 15 m, so the magnetic flux density is lower in that region compared to the outside because of the room’s magnetic shielding qualities. For an external magnetic field of 50 μT the magnetic flux density inside of the shield room is 0.9 μT, meaning that the magnetic shielding effect blocks out approximately 98%.
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