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Entry  Mon Nov 12 22:56:10 2012, tara, Notes, NoiseBudget, Thermoelastic noise in spacer and substrate cavity_TE_v2.png
    Reply  Tue Nov 13 01:56:24 2012, tara, Notes, NoiseBudget, Thermoelastic noise in spacer and substrate 
       Reply  Wed Nov 14 00:25:48 2012, tara, Notes, NoiseBudget, ฺBrownian noise in spacer and substrate IMG_1975.jpg
       Reply  Wed Nov 14 19:46:47 2012, tara, Notes, NoiseBudget, Thermoelastic noise in spacer and substrate substrateTE_compare.pngTE_cavity_v2.mph
          Reply  Tue Nov 20 11:50:29 2012, rana, Notes, NoiseBudget, Thermoelastic noise in spacer and substrate 
             Reply  Wed Nov 21 20:16:55 2012, rana, Notes, NoiseBudget, Thermoelastic noise in spacer and substrate 
                Reply  Mon Nov 26 15:36:46 2012, rana, Notes, NoiseBudget, Thermoelastic noise in spacer and substrate 
                   Reply  Tue Nov 27 05:30:03 2012, rana, Notes, NoiseBudget, Thermoelastic noise in spacer and substrate 
          Reply  Tue Nov 27 05:38:01 2012, tara, Notes, NoiseBudget, Thermoelastic noise in spacer and substrate TE_Brownian_compare2.pngTE_Brownian_compare2.fig
Message ID: 1080     Entry time: Wed Nov 21 20:16:55 2012     In reply to: 1079     Reply to this: 1081
Author: rana 
Type: Notes 
Category: NoiseBudget 
Subject: Thermoelastic noise in spacer and substrate 

Quote:

 What is the reason for the COMSOL TE noise to diverge from the analytic one at low frequencies?

Don't you have to consider the coherent TO noise between the coatings and the substrate?

 At low frequency, the adiabatic approximation (used by BGV, Liu & Thorne) breaks down. Basically, it assumes that heat inside the material is not diffusive. The only place that heat flow must be considered is in the volume integral where gradient of expansion is non zero for the dissipation. (see Liu & Torne explanation just above eq 8). This is easier for COMSOL simulation. Since I just press the substrate with static force, and calculate the deformation of the body which, under adiabatic approximation, gives me the temperature change of the body.

 If I want to take into account the heat flow, I have to (see Cerdonio)

  • solve The stress balance with temperature dependent and
  • solve heat equation with expansion dependent (these two equations are coupled).

Then for COMSOL simulation I have to use different setting and I'm not exactly sure how to do this yet.

 

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