Ultra-low frequency vertical vibration isolators for absolute gravimeters

Abstract

High-precision absolute determinations of gravitational acceleration g provide important data for many fields such as metrology, geophysics, and geological exploration. In absolute gravimetry, vibrational noise from seismic and other environmental disturbances is one of the limiting factors. Several types of ultra-low vertical vibration isolators have been developed in Tsinghua University. The first one is a passive isolator based on LaCoste spring linkage and can achieve a natural period up to 32 s. The second one is an active isolator employing a two-stage beam structure. The upper beam is suspended from the frame with a hex spring, and the lower beam is suspended from the upper one using a zero-length spring. A feedback circuit is equipped to keep the angle between the two beams at a fixed value. The isolator can achieve a natural period of 100 s. The last one is an active isolator based on a two-stage structure, in which geometric anti-springs are used to support the proof mass. The volume of the isol...