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 nonmagnetic conducting shells. A simple model is suggested to predict power-law decay of noise spectra beyond a quasi-static regime. Our results can be used to assess noise from existing shields and to guide design of new shields for precision measurements.
Original language | English (US) |
---|---|
Article number | 084904 |
Journal | Journal of Applied Physics |
Volume | 103 |
Issue number | 8 |
DOIs | |
State | Published - 2008 |
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)