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This demonstration model showcases the Geometric Anti-Spring (GAS) Filter, engineered at NIKHEF for vertical seismic isolation. It employs undeformed maraging steel blades to suspend a large mass (payload 4.8 kg) using three blade springs. With an initial resonance frequency (f0) of approximately 5 Hz, the filter plate is oscillated at around 10 Hz to simulate seismic motion. As the frequency exceeds f0, the mass oscillates with reduced amplitude. Horizontal compression of the blades significantly decreases stiffness, lowering f0 to approximately 0.3 Hz and enhancing attenuation. Measurements are conducted via LVDT displacement sensors.
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Geometric Anti Spring (GAS) Filter Used for vertical seismic isolation Demonstration model, designed and built at NIKHEF Undeformedmaraging steel blade • A large mass (payload 4,8kg) is suspended from 3 blade springs. • Initial resonance frequency f0 ≈ 5 Hz. • The blades are mounted on the filter plate. • The filter plate is set into oscillation with frequency f ≈ 10 Hz, using coil • springs. This mimics seismic motion. • As f is larger than f0, the mass oscillates with smaller amplitude than the plate. • By horizontal compression of the blades the stiffness strongly decreases, resulting into smaller f0 (≈ 0. 3 Hz) and a much larger attenuation. • The motion of plate and mass are measured with LVDT displacement sensors. keystone filter plate Horizontal compression of blades suspension wire Fx Top view 200 mm Finite element analysis prestressed blade Mathematical analysis
