This Small Business Innovation Research Phase II project continues development of a highly sensitive and portable vertical gravity gradiometer. This is based on using two GWR Superconducting Gravity Sensors (SGS) mounted with their sensitive axes co-linear and configured in a differencing signal mode. The SGS uses a 1/2" diameter niobium sphere levitated in a magnetic field produced by superconducting coils. The goal of this research is to shock harden the instruments during transport and field measurements. The technical approach uses a mechanical constraint and a clamp to immobilize the sphere. Investigation includes: the engineering of small structures and specific materials to minimize mechanical creep, fatigue and hysteresis; and propose replacing the Nb sphere with Nb compounds to increase pinning forces of magnetic flux in the sphere's surface. Remote detection an characterization of underground targets is of great importance in environmental, geologic, mining, engineering, law enforcement, and strategic arms treaty applications. Using gravity gradients to determine underground density is a far superior technique than present day gravity techniques which are time consuming and expensive. The proposed gravity gradiometer will make measurements more rapidly, will not require a precise elevation survey for interpretation, and will provide sharper resolution of underground density features. The portable gravity gradiometer would have many engineering, environmental and military applications. Examples include: monitoring fluid leakage from waste storage area or underground tanks into the soil; locating abandoned mine workings, natural voids, tunnels or underground bunkers: monitoring natural geologic hazards such as volcanoes; and reservoir monitoring of petroleum, gas, groundwater or geothermal.
