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arXiv · 0709.2543

Calculation of Magnetic Field Noise from High-Permeability Magnetic Shields and Conducting Objects with Simple Geometry

S. -K. Lee·M. V. Romalis
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Abstract

High-permeability magnetic shields generate magnetic field noise that can limit the sensitivity of modern precision measurements. We show that calculations based on the fluctuation-dissipation theorem allow quantitative evaluation of magnetic field noise, either from current or magnetization fluctuations, inside enclosures made of high-permeability materials. Explicit analytical formulas for the noise are derived for a few axially symmetric geometries, which are compared with results of numerical finite element analysis. Comparison is made between noises caused by current and magnetization fluctuations inside a high-permeability shield and also between current-fluctuation-induced noises inside magnetic and non-magnetic conducting shells. A simple model is suggested to predict power-law decay of noise spectra beyond quasi-static regime. Our results can be used to assess noise from existing shields and to guide design of new shields for precision measurements.

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S. -K. Lee, M. V. Romalis. 2007-09-17. Calculation of Magnetic Field Noise from High-Permeability Magnetic Shields and Conducting Objects with Simple Geometry. https://doi.org/10.1063/1.2885711

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