Demonstration model, designed and built at NIKHEF

Demonstration model, designed and built at NIKHEF

Geometric Anti Spring (GAS) FilterUsed for vertical seismic isolation

Horizontal compression of blades

Fx

Finite element analysisprestressed blade

Undeformed maraging 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.

Mathematical analysis

200 mm

suspension wire

filter plate

keystone

Top view