COMSOL Multiphysics Tutorials - Akshansh

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COMSOL Multiphysics Notes, First Edition
Copyright © 2013 Akshansh
ALL RIGHTS RESERVED.
Presented by: Akshansh Chaudhary
Graduate of BITS Pilani, Dubai Campus
Batch of 2011
Course content by: Dr. Anand Kumar
Then Faculty, BITS Pilani, Dubai Campus
Layout design by: AC Creations © 2013
The course content was prepared during Spring, 2014.
More content available at: www.Akshansh.weebly.com

Point Load
Starting Interface -
Idea:
Starting with cantelever
Design a beam
Leave the second side free of the beam
COMSOL: MEMS Notes – Akshansh Chaudhary

Next, select the measurement unit and other dimensions as given

Now, rotate the model and select one of the sides of length 5. Next, click on + button on the toolbox
at the side.

This makes the diagram colored
A strip tells the amount of stress and the details on that.
Which figure has the max stress - we get to know from the figure

We find that the free end has maximum displacement

Note:
We can know the properties of material we are using. Here we are using copper. So, click on it to see
its properties.
Save the file.

Boundary LOAD

The total displacement is, as shown in the diagram.

By observation, it is lesser, as compared to point load.
Save the file again.

Changes
Now,
Change 1
Changing the values in geometry and seeing the deflection in that case.

Change 2
Now, change the thickness (height) of the model and for small values, check which is the smallest
value, giving the maximum deflection and is able to tolerate as well.

EXTRA
Displaying moving details of how the figure was getting modified

Joule Heating Method for Actuator
We want to see how the temperature varies in our work piece when it is made as per the
specifications.
Idea :
S1) Make a 3d Figure. For that, make a workplane under geometry tab. Then, add rectangles as per
the dimension. Next, go to Work plane option and click on Extrude. That makes it 3D.
S2) Add Material. Go to Material library and select Poly-Si.
MEMS>Semiconductor>Poly-Si
S3) Select Joule Heating in Physics.
Model 1 - Right Click> Add Physics
Heat Transfer> Electromagnetic Heating> Joule Heating (jh)
S4) Now, start adding the properties to the work piece.
S5) Do meshing of the object
S6) Compute
Objective - To model Joule heating of a micro actuator using COMSOL Joule heating module

Then, go to Union and click Buld all.
Next, Extrude the 2D image we made.

Analysis of Circular diaphragm in micro
pressure sensor and find the deflection
We have to make a disk (or a thin cylinder)
Now, apply pressure at its top and analyze the figure we get.
Initial steps - 3D > Solid Mechanics (solid) > Stationary
Select cylinder in Geometry and take the following dimensions -
Now,
Select the material -
Poly-Si
Next,
Click on Solid Mechanics.
Right click and add -
Fixed Constraint.

Now, once the base is set, we need to add load over the top or bottom.
For that use Boundary load option.

Next, go to Mesh and Build All.
Finally, Study 1 > Compute.

Now, to see the total displacement,
Stress> Surface
Then, Click on Plot.

Similarly, the dimensions of the disk can be changed and we can see for different values.
Done!

Making a Capacitor

Microgripper

Note: Force also has to be given only at the top and bottom. Not in the middle.

In Force calculation, the force has to be added in the specified part:

MICROGRIPPER: Scale Changing
Micro gripper was used in Micro scale.
Now, change it to different scales and measure the difference in deflection.
We see that the only change needs to be done in the scaling factor.
The scaling needs to be increased to see the same effect of gripping.
Original Scale : um
Case 1:
Changing scale to mm
Case 2:
Changing the scale to cm

Case 3:
Changing scale to inch
Note: Displacement is independent of scaling.
OBSERVATION 1:
Constant:
• Material - Si (c )
Table 1: Shows the amount of scaling that needs to be done in order to get the gripping action at the
corner.
Dimension Scaling Displacement (m)
Mm 4e12 6.0617*10^-13
Cm 4e13 6.0614*10^-14
In 9e13 2.3865*10^-14
OBSERVATION 2:
Now, keeping um as standard displacement, changing the values of voltage to get the same
displacement at other scales.
Constant:
• Material: Silicon
• Reference - um
o Scaling - 4e9
o Displacement - 6.0617*10^-10 m

Table 2: Shows the value of the voltage for each scale, giving the same displacement as in
micrometer scale.
Dimension Displacement (m) Voltage value (V)
Mm 6.0617*10^-13 5
6.0617*10^-11 50
1.3639*10^-10 75
6.053*10^-10 158
Cm 6.0614*10^-14 5
6.0617*10^-12 50
5.455*10^-11 150
6.0617*10^-10 500
In 2.3865*10^-14 5
9.546*10^-12 100
8.5914*10^-11 300
6.03333*10^-10 795
OBSERVATION 3:
Now changing the material of the micro gripper and observing the displacement.
Constant:
• Dimension: um
• Middle layer: Air
Table 3: Shows the displacement of the micro gripper with different materials.
Material Displacement (m)
Si ( c ) 6.0617*10^-10
Poly-Si 5.1787*10^-10
Glass (quartz) 1.0616*10^-9
GaAs 1.189*10^-9
SiO2 1.1665*10^-9

Scaling Problem: We have a cylinder (tube) and fluid flowing through it.
Now, when the dimensions of the tube is changed, note the pressure drop.

Surface option. (instead of Solid)

Note: In case you get the error saying, "Error: Maximum number of Newtonian Iterations
reached" change the mesh amount from NORMAL TO EXTREMEMLY COARSE.

Radius is 5um

On changing the dimensions to 10um and 20um, we have this pressure.
(it decreases, as expected)
Radius is doubled (10um now)
So, by formula, Pressure is inversely proportional to the square of radius.
So, as radius is doubled, pressure is becoming 1/4 times.

MICRO MIXER
Model - 3D
Physics - Laminar Flow
Property - Stationary
Make the model.

ONLY CREEPING FLOW

ONE FLOW LAMINAR, ONE FLOW CREEPING

USING TWO FLUIDS, WATER AND ETHANOL

COMSOL Multiphysics Tutorials - Akshansh

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