Magnetic noise analysis for small magnetically shielded room in different environmental magnetic fields

Abstract

The compact high-performance magnetically shielded room (MSR) provides near-zero magnetic field environment for low-cost magnetoencephalography (MEG) measurements. Predicting the level of magnetic noise in the MSR under different magnetic field holds significant importance for the deployment of MEG systems. In this paper, the magnetic noise of MSR in different operational conditions is studied. The magnetic noise in MSR is modeled as residual environmental noise, material one, and additional one. A quantitative model for magnetic noise calculation is established, leading to the definition of the Weak Shielding Factor (WSF), which establishes a relationship between the environment magnetic noise and MSR one. Verification experiments are conducted using a compact MSR, a magnetically shielded box, and a cylindrical magnetically shielded bucket. The average magnetic noise error between calculated and measured values in 1–100 Hz range for the three shielding structures are 8.29%, 12.33%, and 7.50%, respectively, which shows the effectiveness of the proposed method.