Abstract
Ferrites are promising nonmetallic materials used for the fabrication of low-noise magnetic shields because they possess high permeability and high electrical resistivity. However, large-sized ferrite components are difficult to fabricate or machine. In this study, we develop a cylindrical ferrite shield that consists of five annuli and two lids with an inner volume of φ11.2 cm × 22.5 cm. Although this structure contains gaps between different components, it eases considerably the fabrication and machining process as compared to the entire module. The magnetic noise is measured by a spin-exchange relaxation-free atomic magnetometer, and the detrimental effects of the gaps are analyzed quantificationally using the finite element method. Our research results indicate that compared with the ferrite shield without gaps, the magnetization noise increases by 34.1%. Nonetheless, the magnetic noise at the center of the ferrite shield achieves 5.5f -1/2 fT, which is much lower than that of μ-metal shields with a similar size. If the gap width can be reduced to be smaller than 0.01 mm, the increase of the magnetization noise will be less than 4.9%, which can be negligible in practical applications. Our study provides a low-cost, readily available, and low-noise ferrite shield structure.
Highlights
Modern atomic sensors, such as atomic magnetometers, atomic gyroscopes, and atomic clocks, are highly sensitive to magnetic fields [1]–[3]
If the gap width can be reduced to be smaller than 0.01 mm, the increase of the magnetization noise will be less than 4.9%, which can be negligible in practical applications
In this study, we developed a cylindrical ferrite shield that consisted of multiple ferrite annuli and lids
Summary
Modern atomic sensors, such as atomic magnetometers, atomic gyroscopes, and atomic clocks, are highly sensitive to magnetic fields [1]–[3]. The innermost layer of μ-metal shields generates magnetic noise in the range of 1–10 fT Hz−1/2 at the center of the shield attributed to Johnson noise (its electrical resistivity ρ∼10−6 m) [9]–[12]. This level of magnetic noise limits the performance of high-precision atomic sensors [13]. Ferrites have been studied as ideal materials for magnetic shields owing to their high permeability
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