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mass loading on quartz resonator

Posted 29.03.2017, 13:54 GMT-4 Version 4.3a 3 Replies

SVSS Sumanth
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hi
i am working on the modelling of sensor for detection of fuel adulteration based on the shift in the eigen frequency for that i am trying to employ TSM based quartz resonator, the main problem i am having is that the fuel sample should be having interaction with the resonator with density of the sample acting on the resonator as mass on it. but i amnot getting how to add the mass in the model. i will be grateful if anyone tell me how to add mass on the resonator model
3 Replies Last Post 30.03.2017, 13:58 GMT-4
SVSS Sumanth
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Posted: 8 years ago 29.03.2017, 13:54 GMT-4
resonator model is using piezoelectrics module
resonator model is using piezoelectrics module
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 8 years ago 30.03.2017, 02:03 GMT-4
Hi

adding a mass in the newer V5 versions is probably far easier as these are now defined as "nodes" with the equations already made up, it's really worth to be able to follow the new releases of COMSOL, but I do understand that this is not always possible given your institutions finances.

For your case you probably want to add some "surface mass", this is added as a "surface load" = Force density [N/m^2] and force being mass * acceleration you need to get the acceleration from your model which is simply (utt,vtt,wtt) (I believe these names have not changed) for a time domain solver.

This boils up to : an added mass "m" over a surface "A" = intop1(1) over the selected surface which is "dF_x,y,z"=m/A*(utt,vtt,wtt) with the added weak condition "-dF_x,y,z*(test(u),test(v),test(w))" = 0

As COMSOL still does not allow tensor notation, you must develop these equations fully in scalar notations, then it should work. Test it with a dummy model you can hand calculate.

if you are in the frequency domain replace "(utt,vtt,wtt)" by the frequency development "(2*pi*freq)^2*(u,v,w)"


Be aware that as you solve for "u", the fields "ut" and "utt" are often quite coarse and non continuous (step shaped). To get smoother results, it could be worth considering increasing the discretization level to 3rd or 4th order, but that will slow down the solving time and increase the RAM requirement, one gets nothing for free ;)

--
Good luck
Ivar
Hi adding a mass in the newer V5 versions is probably far easier as these are now defined as "nodes" with the equations already made up, it's really worth to be able to follow the new releases of COMSOL, but I do understand that this is not always possible given your institutions finances. For your case you probably want to add some "surface mass", this is added as a "surface load" = Force density [N/m^2] and force being mass * acceleration you need to get the acceleration from your model which is simply (utt,vtt,wtt) (I believe these names have not changed) for a time domain solver. This boils up to : an added mass "m" over a surface "A" = intop1(1) over the selected surface which is "dF_x,y,z"=m/A*(utt,vtt,wtt) with the added weak condition "-dF_x,y,z*(test(u),test(v),test(w))" = 0 As COMSOL still does not allow tensor notation, you must develop these equations fully in scalar notations, then it should work. Test it with a dummy model you can hand calculate. if you are in the frequency domain replace "(utt,vtt,wtt)" by the frequency development "(2*pi*freq)^2*(u,v,w)" Be aware that as you solve for "u", the fields "ut" and "utt" are often quite coarse and non continuous (step shaped). To get smoother results, it could be worth considering increasing the discretization level to 3rd or 4th order, but that will slow down the solving time and increase the RAM requirement, one gets nothing for free ;) -- Good luck Ivar
SVSS Sumanth
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Posted: 8 years ago 30.03.2017, 13:58 GMT-4
hi ivar

i am not able to understand what you are saying, actually i am working on designing of TSM resonator to detect fuel adulteration based on the shift in the eigen frequency once the adulterated fuel sample comes into contact with the resonator,for that i have the density values of the adulterated fuel samples and i want to see how this mass is added onto the resonator so that the addition of mass results in the shift in eigen frequency, would you please send me any link or pdf on how to add mass on the resonator surface and how to solve for eigen frequencies as when i try to do that it is showing error as failed to evaluate variable jacobian

thanks and regards
sumanth
hi ivar i am not able to understand what you are saying, actually i am working on designing of TSM resonator to detect fuel adulteration based on the shift in the eigen frequency once the adulterated fuel sample comes into contact with the resonator,for that i have the density values of the adulterated fuel samples and i want to see how this mass is added onto the resonator so that the addition of mass results in the shift in eigen frequency, would you please send me any link or pdf on how to add mass on the resonator surface and how to solve for eigen frequencies as when i try to do that it is showing error as failed to evaluate variable jacobian thanks and regards sumanth

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