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