Passive, Nonlinear, Mechanical Structures for Seismic Attenuation

Gravitational wave detectors aim to detect strain perturbations of space-time on the order of $10−21–10−22$ at frequencies between $1Hz$ and a few kHz. This space-time strain, integrated over kilometer scale interferometers, will induce movements of suspended mirrors on the order of $10−18–10−19m$⁠. Seismic motion in this frequency band varies between $10−6m$ and $10−12m$⁠. Required seismic attenuation factors, as large as $10−12$⁠, by far exceed the performance of motion sensors, and are only obtained by means of a chain of passive attenuators. High quality springs in configurations yielding nonlinear response are used to generate attenuation at low frequency. Similarly, nonlinear mechanisms are used in the horizontal direction. A description of some of these systems and some of the technical challenges that they involve is presented.