Research On Three-dimension Active Vibration Isolation In Atom Interferometry Gravimeters

Precision measurement of gravity acceleration has both important scientific significance and wide application value. Cold atom interferometry gravimeters are high-precision absolute gravimeters developed in recent years. Because of its high precision and the capability of long-term continuous measurements, atom gravimeter is one of the development directions about absolute gravimeters.The atom interferometry gravimeter uses free falling cold atoms as test mass in gravitational field, and measuring the acceleration relative to Raman mirror to acquire real-time local gravity acceleration g. According to the equivalence principle, the gravity acceleration g and vibration acceleration a of the Raman mirror can’t distinguished by experiments. Therefore vibration noise of platform will limit the resolution of atom interferometry gravimeters. The vibration isolation has become a key technical problem in absolute gravimeters.The main work during my master includes designing and building a three-dimensional active vibration isolator on the basis of our preliminary works. This thesis describes the principle of our isolator, including mechanical design and feedback filter design. We also show the basic principle of the constituent parts of the systems. This isolator uses a combination of active and passive vibration isolation technology and can suppress three-dimensional vibration noise simultaneously. The equivalent natural period of the isolator is 100 s and 12 s for vertical and horizontal direction, respectively. The residual vibration noise after active vibration isolation in the vertical direction is about 50 times reduced during 0.2 and 2Hz, and 5 times reduced in other two orthogonal directions in the same frequency range.In order to estimate the noise floor of our isolator, we test and analyze the noise floor of the seismometer, signal amplification circuit, data acquisition card(DAQ), voltage controlled current sources(V.C.C.S), and voice coil actuators used in our isolator. The results show that the vertical direction vibration noise almost reaches the noise floor of the seismometer, and the horizontal direction has great potential space to improve. The sensor noise inside the seismometer limits the vertical vibration noise, and the vibration coupling from vertical to horizontal direction is a major factor restricting the feedback gain in the horizontal direction.