MEMS-based differential gravity gradiometer (MBDG)

• Applicants: Professorin Dr.-Ing. Karla Hiller; Dr. Christian Rothleitner
• Subject Area: Measurement Systems
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 562637951

Often only local or temporal gravitational changes are relevant for investigations of very sensitive gravity measurements (e.g. for the determination of density distributions), but not the absolute gravitational acceleration. However, as this force is extremely small and cannot be shielded, special requirements are placed on the measurement sensors. The project aims to develop a novel MEMS gradiometer for determining relative changes in gravity based on a novel differential gradiometer concept, to manufacture it as a demonstrator and to investigate the achievable resolution. This novel concept (patent has already been granted) is intended to eliminate the absolute (earth) acceleration from the measurement signal and thus enable highly sensitive detection of the relative changes in gravity. Compared to the state of the art in terms of MEMS, the aim is to achieve an improvement of at least one order of magnitude (target: resolution of the gravity gradient with 0.1 E/√Hz). In the field of MEMS development, suitable spring-mass arrangements are being designed and analysed for this purpose and an extension of the already patented BDRIE-HS* technology is being researched in order to be able to produce even larger seismic masses, but still achieve very sensitive capacitive detection of the tiny movements in the pm range. The measurement results can be validated using known gravity inhomogeneities (with defined bodies, so-called field masses). One procedure for validation will be to install the gradiometer on a coordinate measuring machine (CMM) at a fixed position. Furthermore, the body generating the density inhomogeneity (e.g. sphere or cylinder) is attached to the CMM at different positions and the relative position to the test mass of the gradiometer is determined in each case using the CMM. The exact shapes and densities or masses of the field masses can be traced back to national standards, as can the distance measurements using the CMM. In the course of digitalisation and to evaluate the measurement uncertainties, a digital twin is created for the gradiometer. This also makes it possible to optimise the parameters.

• DFG Programme: Research Grants