We are going to have small tip-tilt suspensions as the folding mirrors in the 40m recycling cavities. Presently, these are designed to be passive suspensions with eddy-current damping. Strong eddy current damping ties the suspended optic to the frame of the suspension somewhat and spoils the seismic isolation. Instead of a 1/f^2 frequency repsonse, the eddy current damped suspension only has 1/f

This project is to redesign the tip-tilt suspensions to have soft (suspended) dampers.

To do this we have to make a Simulink model to calculate the frequency response of the system and the work with the SolidWorks model to come up with a design and then actually build the new system and test it.

Current design

The current design of the tip tilt suspension is here: TipTiltDrawings.zip (actually this one is with BOSEMS)

Eddy current damping

If you move a conductive object against a magnet, eddy current will be induced by the changing magnet field inside the conductor. This eddy current will eventually dissipated to heat thus taking away the kinetic energy of the moving conductor. In this way, you can damp the motion of a harmonic oscillator (such as a pendulum) using a magnet and a conductor. The more the conductivity of the object is, the better the damping.

Soft suspension for the eddy current damper

In the current tip-tilt stage design, rod shaped magnets are attached to the mirror and metal rings are placed around the magnets. Since this ring is rigidly mounted to the frame of the suspension, the frequency response of the mirror to the ground motion will be degraded to 1/f. By softly suspending the metal rings, we can recover the 1/f^2 response at frequencies above the resonant frequency of the ring support structure.