Low frequency - high sensitivity horizontal monolithic Folded-Pendulum as sensor in the automatic control of ground-based and space telescopes

We describe a new mechanical implementation of a monolithic inertial sensor and its application to the control of the top stage of a multi-stage mechanical suspension for seismic attenuation. In particular, we discuss the sensor theoretical model and the experimental results in connection with a new control strategy that can be applied to the control of mechanical suspensions (seismic attenuators), inertial platforms and low frequency monitoring and control of the mechanics of earth-based and space telescopes. The monolithic inertial sensor is a compact, light, fully scalable, tunable in frequency (< 100 mHz), with large measurement band (10−6 Hz ÷ 10 Hz) and high quality factor (Q > 1500 in air) instrument, with immunity to environmental noises guaranteed by an integrated laser optical readout. The measured sensitivity curve is in very good agreement with the theoretical one (10−12 m/sqrt(Hz)) in the band (0.1 ÷ 10 Hz). Although its natural application is in the fields of earthquake engineering and geophysics, its performances make it suitable also for applications as sensor in the control of mechanical suspensions and inertial platforms of interferometric detectors of gravitational waves, where a residual horizontal motion better than 10−15 m/sqrt(Hz) in the band 0.01 ÷ 100 Hz is a requirement, and in the control of the mechanics of ground-based or space telescopes.