Testing of magnetic shielding system exceeding 10¹⁰ damping based on ultrasensitive atomic magnetometer

High-performance magnetic shielding systems require accurate shielding factor (SF) evaluation, yet testing ultra-high-performance systems (SF > 10⁸) remains challenging due to the need for impractically large external excitation fields. We developed a testing system specifically designed for this task, based on a portable atomic magnetometer, achieving a sensitivity better than 1 f T/Hz^1/2. By applying an order of 10⁴ nT external field via uniform coils and extracting signals via noise spectrum analysis, we achieved the capability to test SFs up to the order of 10¹⁰ at a signal-to-noise ratio of 2. Testing of 10-layer magnetic shielding cylinders revealed a pronounced frequency dependence of the SF within the 1–100 Hz band. The radial SF ranges from 1.7 × 10⁹ to 5.0 × 10¹⁰, while the axial SF varies between 4.8 × 10⁷ and 1.3 × 10¹⁰, exhibiting the characteristic of an initial increase followed by a decrease with frequency. Furthermore, the phase-frequency characteristics, which are often overlooked in previous studies, were also tested. The results revealed pronounced hysteresis, which is of great significance for practical applications involving real-time magnetic field closed-loop systems.