Seismic isolation by mechanical filters at very low frequencies

The VIRGO SuperAttenuator is a complex six-degrees of freedom remote-controlled mechanism that isolates a 80 kg payload from environmental perturbations, such as the seismic noise. It consists of a Pre-Isolator stage, a chain of mechanical filters and a last stage, holding the payload. The Pre-Isolator and the filters are essentially harmonic oscillators with a low resonant frequency. The filters are designed to work below 500 mHz in all degrees of freedom. During the last year, a Pre-Isolator with resonant frequencies of 30 mHz in three degrees of freedom has been engineered and built. Intensive studies on the long-term spring behaviour have been performed to find a metal suitable to be stressed up to 1 kN/mm2 with no evidence of creep.