MEMS - Latest Discussions - COMSOL Forums

3db coupler

Mon, 21 May 2012 12:22:43 +0000

How to design 3db directional coupler.

Directional coupler

Mon, 21 May 2012 12:21:54 +0000

How to design directional coupler with 0.5 coupling coefficient using COMSOL softeare.

How can I avoid the interference between the deflected structures

Sun, 20 May 2012 02:23:15 +0000

I'm using comsol to do static analysis for a cantilever beam. I used a relatively large force to press the beam toward the substrate, I expected the deformation of the beam tip would stop at the substrate, but according to the value I got, it already penetrated the substrate.
Has anybody had this problem before?
How can I avoid it?

The attached picture shows another structure. A load is added at the upper surface in the middle, the deflection will cause the upper inner surface of the channel touch the bottom when the force is large enough, but in my simulation, it goes beyond the bottom, how can I solve this problem?

Please help: 3D model of an elastic (collapsible) thin walled tube with fluid flow (3.5a)

Sun, 20 May 2012 02:08:19 +0000

Hi Everyone,

I am working with with two other engineering students trying to create this model for some of our school faculty.

Our final goal is to output a output a force - displacement curve. The model should show the deformation of the vessel walls as the fluid flows through it.

Our variables are internal flow rate ( affecting internal pressure in the tube ) and external pressure.

We created the internal flow rate just by doing boundary conditions of high pressure in ( 2989.0 [N/m^2] ) and zero pressure out. Our fluid is just water (density = 995.7 [kg/m^3] , viscosity = 0.789 Pa*s)

The dimensions of our tube are 6.35E-3m inner (lumen) diameter, 7.32374E-3m outer diameter, (wall thickness = 3.96875E-4 m)

Modulus of the tube wall is 0.8MPa, Poisson's ratio = 0.5.

Our model is for some reason saved as a .m file and we cannot figure out how to open it in COMSOL. I attached the .m code if that will help anyone understand our model, if not please ignore it.

We could only get a velocity profile to show up, but couldn't get any stress values to appear on the walls.

any help would be very appreciated. We need help with every aspect of it, including which physics to use, how to model the fluid flow, and the vessel deformation, and how to couple the two.

Thank you everyone

Thin Film BAW Composite Resonator simulation in COMOSL 3.5a

Sat, 19 May 2012 18:22:40 +0000

I'm currently engaged in the simulation of FBAR device in COMSOL 3.5a, and want to use this model.

However, "in the model library", I find that the admittance of electrode is defined as "0.5[mm]*nJs_smppn/1[V]", where 0.5[mm] is the width of the electrode, and "nJs_smppn" is the surface current density, which I don't know why, because we use the integration coupling variables, and the width of the electrode is the variable.

Then why we use the "0.5[mm]*nJs_smppn/1[V]", but not the "1.7[mm]*nJs_smppn/1[V]", where 1.7[mm] is the thickness of the 2D scheme of FBAR device.

Stationary study failed to converge

Fri, 18 May 2012 18:06:45 +0000

Hello, I am trying to do a stationary of a MEMS device, but Comsol keeps failing to converge.

Some background on the model:
The model is a MEMS consisting of a plate attached to 4 thin cantilever beam springs, which are in turn attached to a fixed substrate. The plate is also attached to a set of combs whose teeth act as capacitors with a set of corresponding combs attached to the fixed substrate (see attached image. Everything not in purple is attached to the plate and should be free to move). A voltage is applied to the fixed combson one side of the device, while the plate itself is grounded. This causes the plate to be displaced until the capacitive force from the comb capacitors is balanced by the restorative force of the springs.

Comsol Physics setup:
I am using the Electromechanics physics node in Comsol 4.2a to do a stationary study on how much the plate is displaced. I placed all domains in Linear Elastic material model, fixed the boundaries shown in purple in the image, applied a voltage to the three fixed combs in the right of the image, and grounded the center plate. I then created a stationary study and computed. Unfortunately, the solver fails to converge. Is there something wrong with the way I have set everything up? Does anyone have suggestions about what may be going wrong?

Josh

error 2100

Mon, 14 May 2012 13:50:11 +0000

Hi,
I'm a comsol 3.5a user.I want analyse a cantilever composed of several layers.I draw 4 layers on my system and,when I add an other layer, error 2100 :'internal error in geometry decomposition' appears. I don't know why!
If someone can help me.

Thanks

piezoresistance

Wed, 09 May 2012 19:08:43 +0000

dear all,

how can i simulate the change of resistance caused by structural deformation of the piezoresistive structure under acceleration field?

thanks in advance

Temperature Sensor Model

Wed, 09 May 2012 03:11:51 +0000

Hello,

I am designing a temperature sensor using an interdigitated capacitor. Using the electrostatics modules, I was successfully able to design the sensor with the starting capacitance value I wanted. However, regarding changing capacitance with temperature is where I run into problems. Thus far, I have been using the joule heating and thermal expansion module. Can anyone tell me if this is the correct module for my goal?

I have had some measure of success using it. However I find that when I remove the surrounding rectangle with air associated with it in the positive z direction and silicon in the negative z direction, the study completes, but with that rectangle, I get an error of singular matrix/solution does not converge and cannot complete the study. Why is this?

Also, without the surrounding rectangle, and without the proper dielectric in place, it seems that I cannot calculate capacitance correctly, and the values are all very small, approaching zero.

I have attached my model.

I would greatly appreciate help understanding this, thank you.

Piezoelectric transformer interfaced with electrical circuit.

Tue, 08 May 2012 03:31:43 +0000

Hello,

I have made a piezo transformer model and wish to drive it using an external electrical circuit interface.
I have made connections to the electrical circuit elements using a voltage source, a small input resistor and a load at the output terminal.
It is basically a 3-terminal device, wherein the input and output electrodes have a common ground.

After doing a frequency domain study, I get the following error:

Failed to find a solution for the initial parameter.
Maximum number of segregated iterations reached.
Returned solution is not converged.

I'm not sure if the error is with the electrical circuit interface or something to do with the meshing/tolerance/solver since the model simulated fine before addition of the electrical circuit interface, plotting susceptance and electrical potential.

Anyone who would be able to throw some light, it would be of great help to me. I have attached the model and the diagrammatic representation of the entire model.
Thanks!

Sneha

VOLTAGE AND CHARGE SENSITIVITY of PZT

Mon, 07 May 2012 21:24:27 +0000

Hello everyone,

For quite some time I have been trying to simulate the voltage and charge sensitivity of a piezoelectric resonator. Can anyone advise me as to what should be approach for simulating these two parameters?

Thanks for helping.

-Sankha

Moving membrane with FSI

Mon, 07 May 2012 19:25:07 +0000

Hi all,
I've got a problem simulating my developed sensor. In principle it is this:
A membrane covers a cell filled with liquid, for example water. On the membrane there is a kind of bumper. A force acts on this bumper in the direction of the cell. What I expect is this:
Because of the flexibility of the membrane it will bend in the water. The water should be incompressible and therefore need to move somewhere. All walls of the cell are fixed and undeformable, thus the only deformation option is again the membrane. Also the membrane gets "down" in the middle, where the force acts and goes "up" circular around this point so that the volume stays constant.
However I cannot teach COMSOL to do the right simulation. I've tried it with the solid mechanics physics. The membrane goes down where the force acts, but the volume is compressed respectively it does't go up in the same amount around the middle.

I hope you understand what I mean, and that someone is able to give me a hint on solving this problem.

Attached is the model as it is

Kind regards

Frank

loss factor

Sat, 05 May 2012 12:29:29 +0000

Hi,

Is the loss factor in COMSOl the same with the viscosity factor?
I got the viscosity factor of silicon( as in the attachment) . And i want to use thest datas to calculate the Q factor of a MEMS resonator.

How can I do it? Can I directly consider the datas as loss factor in comsol?
Thanks!

Jun

Resonant damping problem

Fri, 04 May 2012 23:14:28 +0000

Dear all,
I am working on a simple torsional micro paddle resonator model, and I was able to model this in COMSOL 4.2a in order to see the natural frequency of the device.
However, the displacement of this tiny paddle with dimensions of 8 by 10 micro meter square gives a displacement of about 5 meter !
I realised in order to have a correct displacement value I have to include damping characteristics. I found "models.mems.biased_resonator_2d_freq" model quite informative on how to add Rayleigh Damping into a system. Rayleigh damping parameters for my model are 1292.5422 [Hz] and 4.98363e-11[s] for alpha and beta respectively. I followed the same instructions in order to see the correct values of the displacement in displacement vs. frequency graph, but I was not successful. The maximum displacement of the paddle is still about 5 meter at its first natural frequency. I attached my model here and would really appreciate if anyone can help me with this problem.
Sahand

can comsol support multilayer shell?

Thu, 03 May 2012 11:31:22 +0000

Dear all,

I am trying to model a membrane using shell element because thickness is quite thin compared to length and width. But the membrane is lamated with three to five different materials and thickness at different location. It seems impossible to use 3D solid model that will lead too many mesh elements. Do anyone know how to do multilayer shell in comsol?

Trouble coupling heat transfer physics for both fluids and solids

Wed, 25 Apr 2012 09:19:20 +0000

Hey all,

So I'm getting stuck with my model where I try to couple three different physics. The three physics are: Electric Currents, Heat transfer in Solids, and Heat transfer in Fluids. Basically what I'm trying to model is a silicon microbridge which is doped, which makes it so that it has a temperature gradient accross it when heated. I am able to couple and run the electric currents and heat transfer in solids physics, where the power dissipated from the ec physics is inputed into the ht physics as the heat source, and then the temperature that is calculated is used to calculate a new resistivity value for the silicon, until the model converges to a value for the temperature at the given voltage.

The problem arises when I try to incorporate the ht2 physics to mimic the effects of natural convection from the sorrounding gases. I set a temperature boundary condition within the ht2 physics which tells the program that the temperature of the microbridge is given by T, which is calculated in the ht physics. However, when I run this, I get the following error:

"Constraing found for variables in different Segregated groups. Try to merge these groups.
-Feature: Stationary Solver 1 (sol1/s1)
-Error: Constraint found for variables in different Segragated groups. Try to merge these groups."

Any ideas? Attached you will find my model. Thanks.

Circuit terminal question

Mon, 09 Apr 2012 07:37:00 +0000

Hi, All,

I'm trying to build a model four terminal nodes. Two of them are COMSOL voltage (terminal 1) and ground (terminal 0), another two is connected to 'external' resistor which is not defined as part of the multiphysics model.

Should I name the two terminal as type 'circuit', and name them 2,3? Then choose the nodes in electric circuit (cir) to be 2 and 3? What else should I do? I'm have an error says The DAE is structurally inconsistent .

Thanks!

beam vibration by a shaker

Sat, 27 Aug 2011 15:25:50 +0000

Hello, eneryone.

I am doing a project simulating a simple beam structure vibrated by a shaker. The left end of the beam is fixed with the shaker. If I want to set the beam vibration acceleration at 10 m/s^2, how can deal with this boundary condition?

Thank you all in advance!
Yuan Xue

128° YX Lithium Niobate

Tue, 22 Mar 2011 23:58:45 +0000

Hi,

I´m interested in doing and eigenfrequency analisis of a SAW based on the model "SAW GAS SENSOR" available for COMSOL 4.1 an 3.5a. Mi interest is to obtain free velocity. If I simulate with YZ-Lithium Niobate, I get a velocity of 3425 and the reported one is 3488. This result is acceptable. But, when I try to simulate 128° YX Lithium Niobate, I shuould get a velocity of 3996 and Im not even close.

For the simulation I've used a rotated system, based on Euler Angles (0,38°,0). I've calculted the elasticity matrix, coupling matrix and permitivitty matrix taking into account the transformation available in the COMSOL userguide (Page 158). I include the matrixes obtained:

{2.02897e+011[Pa], 6.99850e+010[Pa], 1.93975e+011[Pa], 5.78425e+010[Pa], 9.03296e+010[Pa], 2.21158e+011[Pa], 1.28464e+010[Pa], 9.31243e+009[Pa], 8.00285e+009[Pa], 7.53232e+010[Pa], 0[Pa], 0[Pa], 0[Pa], 0[Pa], 5.68597e+010[Pa], 0[Pa], 0[Pa], 0[Pa], 0[Pa], -5.09155e+009[Pa], 7.79193e+010[Pa]}

{0[C/m^2], -1.88047[C/m^2], 1.71492[C/m^2], 0[C/m^2], 4.44672[C/m^2], -2.69210[C/m^2], 0[C/m^2], -1.52214[C/m^2], 2.31358[C/m^2], 0[C/m^2], 0.06738[C/m^2], 0.63381[C/m^2], 4.47243[C/m^2], 0[C/m^2], 0[C/m^2], 0.27875[C/m^2], 0[C/m^2], 0[C/m^2]}

{43.6, 0, 38.1267, 0, -7.0055, 34.63333}

My question is, do I have to include any additional consideration besides a rotated coordinate system so I can have an adequate result for this material? Does anyone know where can I get the real matrixes for this rotated material?

How to calculate the differential capacitors using 3D comb drive model

Tue, 22 Feb 2011 17:36:21 +0000

Hi

I'm a beginner for using COMSOL3.5 software.
What I'm doing is similar with the comb drive 3d in model library.
The difference is in my model, for the moving mass, it has both sides fingers. So there are totally two fixed part at each side of the proof moving mass.
With one side of the capacitance increased, the other side capacitance is decreasing.

I totally followed the tutorial of "comb drive 3d" to do the simulation, except the model was draw according my own design.
Now the problem is, in the model documentation, after give the Expression: C11_emes, then one capacitance value of this model is calculated by the software.(e.g. 0.021 pF—appears in the message log at the bottom of the screen).

However, in my model, I should get two capacitance values. So what should I do? what kind of the expressions should I give.
By the way, what's mean of C11_emes. I know that "emes" is the model name, but what about C11?

Your help is very important to a beginner.
Thanks a lot.

Regards