Colloquia

Summary

The extreme sensitivity of the Einstein Telescope requires improvements to the active vibration isolation platforms of the optical elements. Particularly the development of a vertical seismometer with a high resolution at low frequencies would be beneficial to the project. The goal of this study is to make progress towards a seismometer design that has a lower self-noise than any other state-of-the-art seismometer. To minimise sources of noise, a purely passive approach is taken to the seismometer design. Many challenges that are solved in the electric and control domain in conventional seismometers have to be solved in the mechanical domain in a passive seismometer. Considering these challenges, a design architecture is set up for a passive seismometer, and three main components, the 1-DOF guide, sensor and a stiffness and gravity compensator, are identified. A highly accurate encoder is selected, and the 1-DOF guide and stiffness and gravity compensator are modelled and designed to meet requirements. Through testing, the stiffness and gravity compensator is shown have a constant stiffness within 0.8 Nm over a 1.6 mm range, and to output a tunable negative stiffness down to -1000 Nm.