Discussion Forum

May 8, 2010 4:09am UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

Thank you for your consideration of this question, but I have just now solved both the 2D and 3D Cantilever beam models without the use of the MEMS Module, so I no longer require assistance.

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

August 18, 2010 12:03am UTC in response to Syamsul

Re: Calculating Electrostatic Force without MEMS Module

Hello Syamsul,

I would be glad to help. The model I created was similar to the 2D MEMS Cantilever beam, except I specified a slightly different geometry with different boundary constraints. That is to say, I created a device which had a top-gate grounded conductor, separated by an air gap, a substrate, then finally used a back gate conductor with applied voltage. In this model, I successfully coupled the three physics applications:

Version 3.5a

Struct. Mech> Plane Strain (smpn)
COMSOL Multiphysics> Moving Mesh (ALE)
COMSOL Multiphysics> Electrostatics (es)

I assume you have the same dilemna I had: you wish to model the 2D MEMS Cantilever beam, but you don't have the MEMS module, correct?
The trick to follow is thus: Follow all steps in described in the 2D MEMS Cantilever beam pdf file tutorial [add Plane Strain as first application, then add Moving Mesh to the Multiphysics tab (under automatically-created frame: Frame (ale) ), then make sure to add Electrostatics to frame: Frame (ale), and continue to follow the steps in tutorial accordingly].

Now, if you're using version 3.5a and do not have MEMS Module, you probably have noticed that there is no force tab under your Physics boundary settings (indeed, only the MEMS module has a force tab in Physics boundary settings for electrostatics). There is one simple step to circumvent this problem: use Maxwell's (electromagnetic) Stress tensor.

So, simply click Plane Strain application from your Multiphysics tab, and go to boundary settings and apply Maxwell's stress tensor to the appropriate boundaries that you wish to feel the Electromagnetic force, namely:

Plane Strain:
Physics>Boundary Settings>Load tab

and apply the following loads to the appropriate boundaries under the load tab:

Fx = dnTEx_es
Fy = dnTEy_es

or

Fx = unTEx_es
Fy = unTEy_es

Use dn or un if you wish for the stress tensor to point in the downward normal direction or upward normal direction, respectively.

And make sure to click the check box: Edge load is defined as Force/area.

This should be the single trick you need to circumvent the need for MEMS Module.
-------
-------

Use the above technique, and first try to get your 2D MEMS Cantilever Beam model working using Maxwell's Stress tensor. After that, try making your own specific model (where you may need to specify appropriate meshes).

When creating your own specific model, your most likely problem will be either properly specifying your Moving Mesh boundary settings, or properly specifying your mesh itself. If you're having problems with your mesh (Ex. inverted mesh elements error), then you may need to either:

Use Mapped Mesh parameters
or
Try using a swept mesh.
-------
-------

If you are interested, I've actually created a hand-written tutorial explaining Step-by-Step instructions how to compile the specific model I created [a thin membrane (graphene, for example) top gate grounded conductor, separated by air gap and substrate, then bottom gate induced voltage]. There are a few pages in there that are probably meaningless to you (I used it to present to my research group), but the tutorial will nonetheless allow you to create the model and observe deflection caused by electromagnetic forces using Maxwell's Stress tensor and coupling the aforementioned 3 physics applications.

Let me know if you're interested in this tutorial, and I will be able to probably upload it tomorrow (it is saved at student office at my University).

Good luck!

Best regards,
Kevin

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

September 4, 2010 2:52am UTC in response to Shourie Ranjana

Re: Calculating Electrostatic Force without MEMS Module

Hello Shourie,

I managed to solve the Cantilever Beam with 3.5a without the MEMS module. Attached, are 2D and 3D Cantilever beams for 3.5a as well as a self-made Tutorial documentation with model describing explicitly how to create a similar model (different geometries and boundary constraints) for version 3.5a. As I do not have version 4.0a, I will not be able to answer any explicit questions regarding that version.

Firstly, I can tell you that the Cantilever beam requires three physics applications:

Structural Mechanics
Moving Mesh (ALE)
Electrostatics

So, by not applying Moving Mesh, that would probably explain why your model is not deflecting, or bending, due to Electrostatic force. You may wish to review the online COMSOL pdf documentation explaining how to create the 2D and 3D cantilever beams, however, they only apply for verison 3.5a. You will need to make any necessary modifications for the model to solve with version 4.0a, and contact COMSOL tech support for advice, accordingly.

Basically, the key details in order to solve the Cantilever beam are (as far as version 3.5a goes):

1) Electrostatics app. must be in the frame containing Moving Mesh (ALE)
2) All app.s (Struct. Mech., moving mesh, electrostatics) must have proper Physics Properties settings
3) Boundary and subdomain settings must be properly specified in all 3 app.s.

The Moving Mesh constraints may sometimes be the hardest to specify, in general, use predefined quantities: u,v, w defining x,y, z variable deformations.

Best regards,
Kevin

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

September 4, 2010 7:32am UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

Hi

Why not zip it or send it in parts on the "Community Model Exchange" then, tutorials (also from the users) are often nice courses to learn from :)

--
Good luck
Ivar

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

September 8, 2010 7:28am UTC in response to Ivar Kjelberg

Re: Calculating Electrostatic Force without MEMS Module

Wow,

in that case, thanks for all your help, Ivar.

Your efforts are appreciated on this Discussion forum.

Best regards,
Kevin

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

September 30, 2010 7:10am UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

hi kevin
your last advices was very usefull and this time i have three problems in previous work
as i said i couple solid stress strain / electrostatic /moving mesh modules
1) i want to read the all of capacity while nD_emes gives me the charge dencity on a plane ?
2)my sestem properties are 2.66(core 2 dual) 4G 6M and when my mesh element numbers exceeds from 5000 i face with memory err what can i do?
3)in all of problems which i solved from the help element type was lagrangian-quadratic and i dont know whether this element is satisfactoriness or not?

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

October 4, 2010 8:31am UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

hi kevin
thanks a lot for all helps
i could mesh with around 5000 element and solve it but i want to get the capacity after it
how can i read the total capacity of the valium?
i entered the voltage as electric potentiol in electrical boundry setting

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

October 6, 2010 9:02pm UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

hi kevin
"and then multiply by volume" what do you mean?
i inserted V as electric potential in electrostatic boundry setting

also i did what you said the consiquence was zero in a plot for all of the line

can you give me your email address to connect or chat easily?

by the way thanks a lot

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

October 7, 2010 7:31am UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

hi again kevin

there's a subdomain integration or boundry integration in postproccessing and from there i can integration of surface charge or subdomain charge

thanks for all helps

this problem has solved

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

December 23, 2010 6:15am UTC in response to milad moradi

Re: Calculating Electrostatic Force without MEMS Module

Hello Mehrdad,

I must warn you that I am an amateur COMSOL user and I struggle day by day to understand the program. With that said, take my advice with a grain of salt and cross-check it with COMSOL tech advice, etc.

It seems that you are using the MEMS application mode, presumably with Version 4.0a or 4.1. I have been using ver. 3.5a without the MEMS application mode and have been using the Maxwell Stress tensor in my Solid, Stress-Strain Physics boundary settings in order to simulate an electrostatic force, convienently circumventing my need for the MEMS application mode.

1.1 You are concerned whether Residual stress is properly being applied in your model.
1.2 You're wondering if COMSOL can calculate a spring constant.

Well, honestly I don't know the answer to either of those inquiries. I would guess that 1.1 depends on the specific solver that you are using, I assume you are solving a Parametric-valued solution. Is your solution time dependent? Regarding the spring constant, I've done a cursory inspection and cannot see how it would be calculated, you might consider the following paper discussing a MEMS device and calcluating a spring constant (although they did not explicitly mention "how" they calculated it):

cds.comsol.com/access/dl/papers/6285/Mathur.pdf


2 You're wondering if: Exterior electric Maxwell tensor (for predefined quantities ) Fes_nTEz_emes gives the electric force on a plane.

I know that the diagonal components of the Maxwell stress tensor (T_xx, T_yy, T_zz) give the pressure, or stress on a surface, while the off-diagonal components give the in-plane shear. As I mentioned previously, in my 3D models [which use the applications: solid, stress-strain (smsld); moving mesh (ale) and electrostatics (es)], I specify a downward Maxwell stress tensor (say in the x-direction) dnTEx_es on the proper boundary in the smsld application, this value has units of Pascals, or N/m^2.

So I would assume, although I'm not certain, that Fes_nTEz_emes [a solution postplot parameter for the MEMS application which I don't have] also gives units of pressure as well, and that the F which alludes to Force would be misleading. You should be able to tell by checking the units, if the solution you're given is in Newtons then you know it's a force. Have you tried using the Cross-Section Plot Parameters? Sometimes there are more variables to solve for in there than there is in just the Plot Parameters dialog box alone.

I fear that I may not have been as helpful as I wanted to be. It might help to know which COMSOL version you have, which Physics applications you are using, which solvers you use and which post plot parameters you are using (you might consider trying Cross-Section Plot Parameters or Domain Plot Parameters).

You may have no choice but to ask COMSOL tech support these questions and wait the associated 2-3 business days that follow, and hopefully 1/3 or 2/3 of your questions will be answered (or addressed in a general sense).

Good Luck!

Best regards,
Kevin

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

January 14, 2011 10:27pm UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

Hello kevin,


I have a question to you. I am simulating a particle in a micro channel and there is AC electric field in the channel. I want to calculate the forces acting on the particle. The problem is my Potential is AC and it depends on frequency . I use the coupling variables and integrate

unTEyav_emqvw+dnTEyav_emqvw

to find the force acting on it however this formulation doesnt depend on the frequency . Do you know about the frequency effect?

Thanks

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

January 15, 2011 9:37am UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

Hi

check also the version there were some sign errors in the first v4.0 and 4.0a "mef" but it might not be your case, repaired in last patched 4.1.0.112

--
Good luck
Ivar

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

January 15, 2011 5:38pm UTC in response to Kadir Gökhan Güler

Re: Calculating Electrostatic Force without MEMS Module

In addition i am using 3.5a and the answers of your questions are my frequency is constant which are 100Mhz or 10Khz

and i cheked the equation system there are no relation between the frequency and maxwell stress tensor equations


Thanks

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

January 16, 2011 8:39pm UTC in response to Jean-Marc Dedulle

Re: Calculating Electrostatic Force without MEMS Module

Hi

do not forget that variables names and content are physics dependent, so it's not "just" to copy, but its a good starting point

--
Good luck
Ivar

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

January 17, 2011 5:51am UTC in response to Kadir Gökhan Güler

Re: Calculating Electrostatic Force without MEMS Module

Hi

in frequency sweep or time harmonic, normally the forces are the amplitudes & phases and not the full oscillation detail. The latter is the output of a transient time simulation. That could be the confusion. In Time harmonic COMSOL gives mostly the average values "...ave..."

--
Good luck
Ivar

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

January 21, 2011 6:48am UTC in response to ranjit george

Re: to find out electric field distribution

Hi

that looks as a capacitor, no ?, then you ave models in the COMSOL internal model library, and on the community model exchange and elsewhere in on the website of COMSOL. Start simple and you will soon manage to make a more complex case as you want

--
Good luck
Ivar

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

July 3, 2011 3:24am UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

hi!
I would like to see the tutorial ....I think it will be very helpful for me...how can I access it...????

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

August 2, 2011 9:37am UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

sir ,
I am facing the same problem that u faced , so kindly help me

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

September 3, 2011 12:43pm UTC in response to Kevin Myhro

Re: Calculating Electrostatic Force without MEMS Module

Hi members

Problem has just been solved

--
^_^

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

September 9, 2011 9:46am UTC in response to Ivar Kjelberg

Re: Calculating Electrostatic Force without MEMS Module

Hi Ivar
At first , I applied very high voltage (200V), then I got that error ( I think the deformation of the plate is too much)
But I applied lower voltage ( about 30V) I dont get the error :))
I am not quite sure that the deformation of the plate relates to the preconditioner ( relative residual or relative tolerance)

--
^_^

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

April 1, 2012 10:13am UTC in response to Katie Girl

Re: Calculating Electrostatic Force without MEMS Module

Can you please upload your model?

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

October 19, 2012 7:07pm UTC in response to Britt Newell

Re: Calculating Electrostatic Force without MEMS Module

Is there a generic nomenclature to use when defining forces? I cannot find the dnTEx_es and dnTEy_es forces either.

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

October 22, 2012 4:27pm UTC in response to Ivar Kjelberg

Re: Calculating Electrostatic Force without MEMS Module

Ivar, thanks I found what you were talking about.

I am doing most of my work in 3.5a for now since I understand it a little better.

I've attached my model, where I'm applying a voltage to a pzt_nbp material (it's the built in pzt material that i've modified just minutely).

I just want to see the mechanical properties change (displacement, etc) of the material.

I haven't included the constitutive relations yet because what i've tried to do input isn't working.

i am using a DC voltage on the entire boundary since it is easier, for now.


I am using plane strain (pn), electrostatics (es) and moving mesh (ale)

update:

i've figured out the force error only to learn that i don't have a converging solution.

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

January 19, 2013 11:19am UTC in response to Don Domat

Re: Calculating Electrostatic Force without MEMS Module

I have uploaded my modification. Please note that there is also a significant deviation between the solution calculated by Kevin with 3.5 (stored in the model) and the solution with 4.1. How can that be?

rapidshare.com/files/1449448277/3DCantileverBeam_mod.mph

(Unfortunately I couldn't upload the file in the forum because of the size limitation.)

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse