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dispalcement calculation???

Posted Apr 15, 2013, 7:08 a.m. EDT MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Structural Mechanics Version 4.2a 4 Replies

Prasanna Kumar
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hi,
i am designing a pressure sensor......i have got displacement of 0.28nm for applied pressure say 10000 pa...how can i know whether it's correct or not... how are pressure n displacement related to each other, i will be thankful to you if you could tell me how to calculate....
4 Replies Last Post Apr 15, 2013, 11:55 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 15, 2013, 8:37 a.m. EDT
Hi

you should always check your results, the easiest is to say you have a pressure P0 applied and than a membrane (circular flat one) of radius Radius and total thickness H gives a deflection (at beam centre = neutral line of , (cf wiki) for a clamped end:

Dz(r) = -P0/(64*D)*(Radius^2-r^2)^2

Dth(r) = P0*r/(16*D)*(Radius^2-r^2)

where plate constant D = H^3*E0/(12*(1-nu0^2)) and E0 the Young modulus and nu0 the Poisson coefficient

and Dth(r) is the rotation of the plate, in COMSOL it's expressed as -0.5*solid.curlUPHI

You will hardly see the differences ;)
My model is 4.3a
--
Good luck
Ivar
Hi you should always check your results, the easiest is to say you have a pressure P0 applied and than a membrane (circular flat one) of radius Radius and total thickness H gives a deflection (at beam centre = neutral line of , (cf wiki) for a clamped end: Dz(r) = -P0/(64*D)*(Radius^2-r^2)^2 Dth(r) = P0*r/(16*D)*(Radius^2-r^2) where plate constant D = H^3*E0/(12*(1-nu0^2)) and E0 the Young modulus and nu0 the Poisson coefficient and Dth(r) is the rotation of the plate, in COMSOL it's expressed as -0.5*solid.curlUPHI You will hardly see the differences ;) My model is 4.3a -- Good luck Ivar

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Prasanna Kumar
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Posted: 1 decade ago Apr 15, 2013, 9:04 a.m. EDT
Thank u fr the reply...but i did not understand what 'Dz(r)' and ' r ' mean in the relation, could you be more precise on that..actully i am designing a nanotube sensor of length 6 um, radius of 1 um and thickness of 50 nm...i have also attached snapshot of nanotube.
Thank u fr the reply...but i did not understand what 'Dz(r)' and ' r ' mean in the relation, could you be more precise on that..actully i am designing a nanotube sensor of length 6 um, radius of 1 um and thickness of 50 nm...i have also attached snapshot of nanotube.

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Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 15, 2013, 9:42 a.m. EDT
Hi

Dz(r) is the Z displacement asa function of r, the same for Th the rotation along the 2D-axi PHI variable, check your doc Plate physics doc

--
Good luck
Ivar
Hi Dz(r) is the Z displacement asa function of r, the same for Th the rotation along the 2D-axi PHI variable, check your doc Plate physics doc -- Good luck Ivar
Prasanna Kumar
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Posted: 1 decade ago Apr 15, 2013, 11:55 a.m. EDT
hi,
still i am in confusion, what should i put for ' r ' in the first equation??....why negative sign in first equation?? i am applying pressure onto one of the boundaries of nanotube in x -axis direction.
hi, still i am in confusion, what should i put for ' r ' in the first equation??....why negative sign in first equation?? i am applying pressure onto one of the boundaries of nanotube in x -axis direction.

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