Measurement of inline-component of gravity gradient by three-position method based on superconductor

Based on superconducting perfect diamagnetism and flux quantum effect, the superconducting coil converts the proof mass displacement into an inductance, further into a current by superconducting circuit. Different currents on three positions can be used to deduce inline-component of the gravity gradient. Measuring principle has been analyzed, and the inline-component can be measured by detecting the relative specific force along the inline direction and the angular velocity components on the other two directions. The specific force acting on the proof mass consists of the mechanical spring force and the magnetic force, which is related to the current of superconducting circuit, whereas the current is changed with the inductance of the coil and the trapped flux in the circuit loop. On condition that the left limit and right limit on the middle position are approximately equal, the specific force gradient can be derived by currents on three different positions. The parameters of measurement system have been designed, and it is predicted that the precision is 1E.