Free Precession Bell–Bloom Atomic Magnetometer: A New-Type High-Sensitivity Magnetic Sensor for Geomagnetic Background

High-sensitivity magnetic field measurements are crucial in modern geoscience exploration. This study introduces an innovative free precession Bell-Bloom atomic magnetometer (FPBBAM) that exhibits a wide range of applications in geomagnetic monitoring and seismic disaster early warning due to its outstanding measurement sensitivity and low environmental requirements. The article details this magnetometer’s design principles, performance characteristics, and practical applications. It also explores how its internal mechanisms, particularly the behavior of the alkali-metal atoms (AMAs), contribute to geoscience and remote sensing applications. Extensive testing revealed that the magnetometer’s noise tolerance in a geomagnetic background exceeds <inline-formula> <tex-math notation="LaTeX">$300\mathrm {pT/}(\mathrm {Hz})^{1/2}$ </tex-math></inline-formula>. However, the noise sensitivity surpasses <inline-formula> <tex-math notation="LaTeX">$70~\mathrm {pT/}(\mathrm {Hz})^{1/2}$ </tex-math></inline-formula> in a shielded indoor environment. In a magnetic measurement environment with a background noise of 350 nT, the magnetic field measurement results’ root mean square error (RMSE) is better than 77.6 nT. Moreover, the magnetometer demonstrated the ability to operate stably over an extended period under challenging working conditions. This study validates the device’s real-world geoscience applications by monitoring urban spatial magnetic fields.