In order to evaluate the displacement of the outer structure of the CryoTraps (where the baffle are anchored) a sensitive accelerometer (PCB 393B12) will be attached along the z direction by means of a aluminum cube.

To evaluate the stiffness of the cube, especially of the screws used to clamp the accelerometer and to connect the cube to the surface to be sure that the cube does not introduce resonances, its mechanical TF has been measured in the Optics Lab.

The TF has been measured by attaching the PCB 393B12 to the cube orthogonal to the excitation surface, as it will be connected in situ, and with the PCB 356B18, gold colored cube figure 1, connected to the ground.

At first the two piezo accelerometers have been cross calibrated, see figure 2, placing both on the granite bench and measuring the TF(z/z) (along the vertical direction in that case).

The result is shown in figure 3.

Then the three TFs from the three ground excitation directions and the z direction of the cube have been measured both placing the aluminum cube on the granite bench and both placing the cube on a metallic breadboard which laid on the ground, see figure 1.

The  TFs obtained in the measurements done on the granite bench show low frequency structures (starting from 15 Hz green circle in figure 4) which are due to the bench resonances, indeed these resonances disappears in the measurement performed on the floor. Figure 4 is on the granite bench and Figure 5 is on the breadboard.

The first resonaces visible in the measurement performed on the floor, apart from a very low frequency one due to the breadboard itself, start from 300 Hz. This means that the cube stiffness is enough for our purposes.

Moreover we checked how the TFs change if some washers are inserted between the attaching surface and the cube, see figure 6, and as it is visible on figure 7 the effect is very strong thus the use of washers has to be avoided.