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Einstein

Passive seismic attenuation Applied in gravitational wave detection. Einstein

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Einstein

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  1. Passiveseismicattenuation Applied in gravitational wave detection Einstein Albert Einstein predicted the existence of gravitational waves as ripples of space-time moving with the speed of light. They are caused when two massive objects, for example neutron stars, are orbiting closely around each other with an incredible speed. VIRGO If such a propagating wave passes the earth, it will deform space. To prove that those waves exist VIRGO has been built near Pisa. VIRGO is a detector using a Michelson interferometer to measure the length difference of its two arms. Each of these arms is 3 kilometers long. A passing gravitational wave makes one arm longer and the other shorter or vice versa. These length fluctuations are typically 10-18 meters, this is 10000 times smaller than an atomic nuclear diameter! Orbiting neutron stars emittinggravitationalwaves VIRGO gravitationalwaves detector nearPisa, Italy GAS blade Problem? Of course there is! Seismic vibrations disturb the measurements of VIRGO. NIKHEF & partners developed a seismic attenuation system. It uses an Inverted Pendulum (shown right) for the horizontal movements and a Geometric Anti Spring filter (GAS, shownleft) for the vertical movements. Ultra-low stiffness Both attenuators can support a large payload, constituting an ultra-low-frequency oscillator thanks to the application of springs and anti-springs. The graphs below show measured non-linear spring curves for different horizontal compression states of the blades in a GAS filter. Most curves cross each other at the same point. The local stiffness (k) reaches a minimum at this ‘working’ point. In this point the resonance frequency can be tuned to a very low value, which is required for an ultra-low transfer of vibrations. The bottom graph shows a transfer function with one low resonance frequency (green) and one with a higher (red). Note that, above 2 Hz, the 100 times slower oscillator is attenuating 100 times better. Stiffness curves InvertedPendulum demonstration model Geometric Anti Spring Filter demonstration model Bart Harteloh 2012

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