I used COMSOL to estimated thermoelastic noise in 1.45" spacer.  The noise is not significant for our coating Brownian measurement. I still need to verify the model with some analytical estimation.

• The model is 1/8 of the spacer with symmetry boundary condition on each cut surface.
• The applied force is a quarter of an annulus, 2 mm width. This annulus represents the contact area between the substrate and the spacer.
• The deformation is simulated, and its gradient is calculated by COMSOL and integrated over the volume (1/8 of the cavity).
• I followed the calculation on Liu and Thorne, 2000, and get thermoelastic noise from spacer. It is lower than coating's Brownian noise at least 1 order of magnitude and will not be a limiting source for us. The plot below show spacer' TE in black dashed line.

Note:

• I should compare the simulation result with an analytical result, but I'll do that later in parallel with other work. This is not an urgent one. I'll also try to reproduce the result reported by Kessler et al. about Brownian noise in spacer as well. Then calculate the Brownian noise in our cavity.
• I'll check the spacer's TE noise for our previous 8" cavity to make sure that there is consistent with the result.