Magnetic flux continuity vs. stress: a critical trade-off in shielding performance analysis of magnetic shields

Abstract Magnetic shielding technology has been widely used in precision measurement of extremely-weak magnetic fields. For nearly static magnetic fields, the most effective shielding strategy is to divert the magnetic flux into the magnetic shields according to the Ohm’s law for magnetic circuits. These magnetic shields, particularly the large-scale ones, are typically assembled by overlapping soft magnetic materials, e.g. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> </mml:mrow> </mml:math> -metal. Previous research studies have shown that both mechanical stress and magnetic flux continuity at the joints of the shielding shells critically influence the ultimate magnetic shielding performance of magnetic shields. However, at the joints of the shielding shells, achieving an optimal balance between magnetic flux continuity and mechanical stress remains a major engineering challenge. Combining the experiments and theoretical modeling analysis, this work reveals that at the joints of the shielding shells, increased mechanical stress at the joints degrades the permeability of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> </mml:mrow> </mml:math> -metal but simultaneously enhances magnetic flux continuity. Under the investigated experimental conditions, the enhancement in magnetic shielding effectiveness associated with improved magnetic flux continuity is observed to be on the order of several times greater than the degradation resulting from stress-induced permeability reduction. Within the tested range, the best shielding performance was achieved when magnetic flux continuity was effectively ensured while the applied mechanical stress remained at the minimum level necessary to maintain joint contact. This work can proffer valuable insights into the design and construction of magnetic shields for precision measurement of extremely-weak magnetic field, notably advanced magnetic shields for biomagnetism detection.