A new architecture for the implementation of force-feedback tunable mechanical monolithic horizontal sensor

This paper describes a new mechanical version of the monolithic tunable folded pendulum, developed at the University of Salerno, configurable both as seismometer and, in a force-feedback configuration, as accelerometer. Typical applications of the sensors are in the field of geophysics, including the study of seismic and newtonian noise for characterization of suitable sites for underground interferometers for gravitational waves detection. The sensor, shaped with precision machining and electric-discharge machining, is a very compact instrument, very sensitive in the low-frequency seismic noise band, with a very good immunity to environmental noises. Important characteristics are the tunable resonance frequency and the integrated laser optical readout, consisting of an optical lever and/or an interferometer. The theoretical sensitivity curves, largely improved due to a new design of the pendulum arms and of the electronics, are in a very good agreement with the measurements. The results of the monolithic sensor as accelerometer (force feed-back configuration) are also presented and discussed.