On the Cabling Seismic Isolation for the Microwave Transducers of the Schenberg Detector

Abstract

Schenberg is a resonant-mass gravitational wave detector developed by the Brazilian Graviton group that is sensitive to a central frequency near 3200 Hz with bandwidth around 200 Hz. Its spherical antenna weighs 1150 kg and it is connected to the outer environment by a suspension system designed to attenuate local noise, both seismic and non-seismic. During the passage of a gravitational wave the antenna is expected to vibrate and such motion will be monitored by six parametric transducers whose electronic signal will be digitally analyzed. For the microwaves to reach the transducers, coaxial cables are needed, which are also connected to the outer environment and may be a source of seismic noise. Using the finite elements method, this work shows that the proper addition of masses along these cables reduces such seismic noise to levels below the detector’s thermal noise when it operates at 50 mK, thus avoiding the decrease of the expected sensitivity of the detector.