Leaf-spring suspension of a vertical inertial sensor for active seismic isolation

Gravitational-wave detectors must be isolated from the Earth’s constant vibrations to be able to sense low-frequency gravitational waves. The combined performances of passive and active isolation stages allow getting close to the seismic vibration isolation requirements. A new active platform is currently designed by the Precision Mechatronics Laboratory (SILENT platform), and is aimed to be part of the E-TEST project. Its embedded inertial sensors measure the ground motion, which is then actively canceled by actuators. The inertial sensors require a large dynamic measurement range, which can be achieved by lowering the sensor resonance frequency while increasing the internal modes frequencies away from the operational range. Vertical inertial sensors need a particular suspension system to compensate for the gravitational load acting on their proof-mass. The leaf-spring suspension composing the gravity compensator system of a vertical inertial sensor, the Compact Vertical Interferometric Inertial Sensor (µVINS), is numerically and experimentally characterized. We extend the dynamic measurement range of that particular inertial sensor by evaluating the impact on its resonance frequencies of various suspension parameters. The studied parameters are the leaf-spring length, curvature, and clamping location (hor izontal, vertical and orientation). A series of design guidelines enable the suspension to be tuned into a low resonance frequency quasi-zero stiffness mechanism. The µVINS design can be modified to be competitive with the already existing sensors, while being more compact. Optimizing the leaf-spring suspension length and clamping location enabled the resonance frequency to be decreased by more than one order of magnitude (from 2.9 Hz to 0.14 Hz).