Progress in the development of a spherical superconducting gravimeter based on SQUID detection

This study presents the design, development, and evaluation of a spherical superconducting gravimeter employing superconducting quantum interference device (SQUID) detection, with the objective of achieving ultrahigh sensitivity and a lower noise level in gravity measurements. To this end, a novel multi-coil levitation system was developed to reduce the system's intrinsic frequency, thereby enhancing low-frequency sensitivity and noise suppression. Comprehensive noise analysis, encompassing mechanical thermal noise and SQUID noise, reveals that the system theoretically achieves a noise level below the new low noise model (NLNM) across the entire frequency spectrum. We conducted a five-day solid tide observation experiment and performed a linear fitting analysis between the experimental and GWR tidal data. The results revealed a transfer function of 55.974 ± 0.053 μGal/V, which surpassed the design expectations. Furthermore, the experimental data showed excellent agreement with the theoretical solid tide, validating the theoretical model and confirming the feasibility of the prototype design.