Schematic drawing (not to scale) of the vacuum box supported by three spacers: in the interior, the first stage of the suspension is shown. The positions of the three accelerometers used in the measurement of the vertical transfer function discussed in Sec. IV are also shown: number 1 accelerometer is fixed to the vacuum box while numbers 2 and 3 are fixed to the load mass. Right: top view to show the positions of the accelerometers with respect to the springs, indicated as black thick lines.
Schematic cross sections of (a) shape A load mass; (b) shape B load mass (hatched) and payload (gray fill). Dimensions are shown in millimeters.
Drawing of the single stage assembly (bottom view): three C-shaped springs are connected in parallel to the same load mass and are displaced by 120°. The parts in aluminum are shown in lighter gray with respect to darker gray used for the steel mass. (a) Any of the two bottom single stages with shape A load mass. Total height of the single stage is 94 mm; (b) the top single stage with shape B load mass and the payload. Total height of the top single stage, with no payload, is 84 mm.
(a) Photograph of the full assembly of the suspension without payload. The photograph shows also the cables fixed to the load mass flats to carry signals to and from the payload. Total height of the suspension (in absence of gravity) without payload is 232 mm. (b) Cross section of the full assembly with the payload: the oscillator inserted in the load masses coaxially is clearly visible, as well as the empty space for housing the readout electronics in the top flange.
Vertical transfer function of a single stage of the suspension. Circle points are the average of the experimental measurements of the transfer function obtained at two different positions on the load mass. Solid line is prediction from Eq. (1) with .
Vertical transfer function of the full suspension, consisting of a cascade of three stages each resonating at 38 Hz. Black line: experimental measurements; gray line: prediction from the coupling in cascade of three oscillators of masses, respectively, 17.4, 17.4, and 19.8 kg and with . In order to also drive the nonaxial modes, the excitation was eccentric.
Power spectral density of the amplified output of the capacitive sensor which senses the vibrations of the suspended mechanical oscillator hanging from the aluminum flange [see Fig. 3(b)]. The oscillator longitudinal resonance at about 1.63 kHz can be appreciated, along with a pattern of resonances above 2 kHz. The inset shows the zoom in the low-frequency region: suspension and oscillator modes cause the pattern of resonances up to about 100 Hz.
Power spectral density of the amplified output of the capacitive sensor which senses the vibrations of the suspended mechanical oscillator hanging from the aluminum flange [see Fig. 3(b)]. Solid gray line (red online) is a fit of the experimental data in the range with the thermal noise model; from the fit we determine the oscillator noise temperature .
Histogram of the square amplitude of a lock-in set at recorded during seven continuous hours. Line is exponential fit of the data which gives the oscillator noise temperature .
Main figures of the elements forming the suspension and the payload. For each element, the material is listed along with mass and estimated resonant frequency of the first acoustic mode (see Sec. III). For the oscillator assembly, the first resonant frequency is given which is not proper of the oscillator itself.
Resonant frequency in Hertz of the first modes of the single stages. The second column lists the FEM estimated (see Sec. III) frequencies for any of the first two bottom stages shown in Fig. 3(a); the third column lists the room temperature experimental measurement (see Sec. IV) for the third, bottom stage. Suspension modes are those listed in the rows 1–4.
Experimental values of the resonant frequency (in Hertz) of the first acoustic modes of the full suspension which have vertical component.
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