Abstract
Magnetic shielding made from permalloy is frequently used to provide a time-stable magnetic field environment. A low magnetic field and low field gradients inside the shield can be obtained by using demagnetization coils through the walls, encircling edges of the shield. We first introduce and test the computational models to calculate magnetic properties of large size shields with thin shielding walls. We then vary the size, location and shape of the openings for the demagnetization coils at the corners of a cubic shield. It turns out that the effect on the shielding factor and the expected influence on the residual magnetic field homogeneity in the vicinity of the center of the shield is negligible. Thus, a low-cost version for the openings can be chosen and their size could be enlarged to allow for additional cables and easier handling. A construction of a shield with beveled edges and open corners turned out to substantially improve the shielding factor.
Highlights
Magnetic shields made from permalloy are commonly used to protect measuring equipment and experiments against environmental magnetic field changes
A low magnetic field and low field gradients inside the shield can be obtained by using demagnetization coils through the walls, encircling edges of the shield
A low-cost version for the openings can be chosen and their size could be enlarged to allow for additional cables and easier handling
Summary
Magnetic shields made from permalloy are commonly used to protect measuring equipment and experiments against environmental magnetic field changes. Their size varies from a few cm[3] for speedometers in cars to magnetically shielded rooms (MSRs) to measure e.g. the magnetic field created by a human. A low magnetic field and low field gradients inside the shield can be obtained by demagnetization (degaussing) with a decreasing alternating current through demagnetization coils. The magnetization coil has to be wound through the walls, encircling edges of the shield. For the best residual field achieved so far, the demagnetization coils encircle every edge of the cubical shield.
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