Research On Modulation Device In The Superconducting Gravity Instruments

Airborne gravity gradiometer have being developed as one of the most efficient and powerful exploration tool. However, the notorious working conditions imposes exceedingly rigor requirement on the common-mode rejection rate for the instrument. To adjust the instrument parameters to reach the best common-mode rejection rate, a vibration exciter is needed to provide a common-mode acceleration with a given bandwidth and amplitude for the instrument test and adjustment. In this thesis,a vibration exciter has been developed for the superconducting gravity gradiometer(SGG).To be compatible with the Dewar structure, in which the SGG is installed, the vibration exciter is designed as a build-in spring oscillator. The oscillator uses rubber rods as spring. The SGG is suspended in the Dewar by a composite wire and acts as the mass. The suspending wire consists of three parts: the rubber spring, a permanent magnet and a stainless steel wire. The permanent magnet is upwards connected to rubber rod and to the stainless steel wire downwards. The SGG is finally suspended by the stainless steel wire. An exciting force is exerted through the magnetic between the permanent magnet and the solenoid. Driven by the alternating current in the coil, a forced vibration is obtained for the SGG.According to the theoretic model for spring oscillator,the natural frequency and the exciting force have been determined to provide required test acceleration. Subsequently, the magnetic force between the magnet and the coil has been calculated. Based on the calculations, the parameters of the driving coil and the magnet have been optimized.Using a copper cylinder as simulated SGG, the fabricated vibration exciter has been tested. It found that when the current is sinusoidal signal with amplitude of 1A and frequency of 1Hz, the acceleration is sinusoidal signal with amplitude of 0.1m / s2 at the same frequency. Changing the amplitude and frequency of the current, acceleration with other amplitude and frequency would be got.