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Piezoelectric Devices with Electrical Circuit Help

December 15, 2010, 10:56 am
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Hello -

Ive been using COMSOl for about 6 months, and working with Piezoelectric devices. I recently upgraded to the ACDC module to include SPICE models with my piezo component models. I would like to look at parameters such as output voltage some a set input force etc. But instead of purely open circuit solutions (floating potential) I want to be able to electrically load the piezo.



Mike B.
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time discrete solver

August 26, 2011, 12:38 am
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Hello,

what do you say about the time discrete solver? I use transient flow for switching on buoyancy force in a buoyancy driven flow field.

Using the BDF solver the model runs but it needs much computation time for iteration of the nonlinear couplings (mass and heat transfer -> T,c -> rho -> Fz -> flow). I have looked for a possibility to use Fz from the previous timestep for a long time.

Now I f found the COMSOL operator prev(expr,i) what evaluate prev(c,1) concentration from the previous time step f.i. The operator prev works with the time discrete solver only.

I use the orperator to calculate Fz based on results of the pervious time step. The model runs fast with a larger timestep compared with the BDF method. What are your experiences? How can I control the timestep?

Best regard
Michael
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time discrete levels

February 29, 2012, 2:27 am
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Hi,

Could anyone explain what does the "number of time discrete levels" mean?

Thanks.

Best
Lakshmi.
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Pull In Example Provided in the Model Library

June 6, 2012, 1:57 am
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Hello,

I have a question about the pull-in model in COMSOL 4.2a, which is entitled: Pull-in voltage for a biased resonator.

I understand the general approach but I have a few questions:

1. The separation between the resonator and the actuation electrode is around 200nm. However, the model specifies the 'yset' parameter to 100nm. I cannot figure out why 100nm? Why not 150nm? Why not 253nm? and what does it mean to specify the y-coordinate of the middle point of the resonator?

2. The other strange thing in the model, is that it uses this 100nm in determining the pull-in voltage in the Global Equations in the integration operator. I cannot see why or how? and why the expression (intop1(y)-yset)/yset is used? What does y stand for here? What would happen if I choose yset to be something other than 100nm?

3. The third and final strange thing is that the parametric sweep was set for 'yset' from 120nm to 140nm! Where did this range come from? Aren't we looking for pull-in? The pull-in will be somewhere between 60nm and 70nm (the resonator will move down not up). Didn't we set the y-coordinate of the middle point of the resonator to 100nm as in point 1 above. It seems that I don't understand point 1 and as such I am failing to understand the rest of the tutorial.
Any feedback will be appreciated.

Thanks.

Amro
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Piezoelectric Potential Distribution in Bent Zinc Oxide Nanowire

June 7, 2012, 12:16 am
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Hi,

I did a simulation about the piezoelectric potential distribution in a bent zinc oxide nanowire reported in a previous literature. But my result is weird, it doesn't consistent with the literature's result. In my simulation the piezoelectric potential exists only in the bottom of the nanowire, but in the literature the piezoelectric potential also exists in the rest part of that wire. I am very confused and couldn't find the reason for this discrepancy. Can anyone help me with this problem?

In my attachment is the mph file and that literature.
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Simulating a piston cylinder assembly

June 18, 2012, 6:37 am
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Hello!
I'm trying to simulate a reciprocating move of a piston cylinder assembly under Comsol in order to adapt it later to a heating transfer problem.
I am not able to start it.
I have found some information on the forum, but nothing solid.
Is there anyone who made a similar model?
Thank you :)
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how to interface a piezoelectric beam with a resistor between the two charged layer??

July 23, 2012, 1:25 am
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i have modeled a cantliever with comsol and i want now to add a resstor betwwen the two charged layers in order to calculate the power offred by the piezo! but all simulation are not working i always get an error message!

how can i do that?
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How to create a homogeneous magnetic field

September 11, 2012, 11:50 am
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Hello everyone,
my goal is to observe the magnetic flux density in an area with a homogeneous magnetic field , dependent on the relative permeability of the walls.
In the beginning i would like to simulate it in 2D, for this i need to create a homogeneous magnetic field outside the magnet itself.
The only solution i was able to produce is:
- a normal magnet defined by Amperes Law and Magnetization
- 2 Rectangles (with a high relative permeability) attached to each side of the magnet
With this a get ~homogeneous magnetic field between the two Rectangles.

So finaly my question: Is it posible to create a normal North and South pole of a magnet, without beeind attached to eachother (for getting my homogeneous magnetic field between them).

In the file attached is my model with the geometries, if i didn`t described it enought.

Best wishes,
Andreas Schneider
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comsol solve this kind of moving mesh

September 12, 2012, 4:03 am
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hi,

i have one doubt about moving mesh (ALE). i want to pass the laser beam on rectangular plate. i want to use mesh density around the laser beam only,not full laser path. so i would like to move beam with fine mesh(both are moving together).this is possible.comsol can solve this problem?
please help me
please look my attached file.
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Importing/Specifying your own voltage signals

September 12, 2012, 6:47 am
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Hi there,

I am new to COMSOL, very new, so there is every chance I am barking up the wrong tree with this. However, I have been able to construct a 2D model:

5 x 0.5mm radius HV electrodes arranged in a line, equi-spaced. Around these is a rectangular array of ground electrodes so that the HV and grounds are mostly equal distance apart.

In the gap between the HV and GND's there is a dielectric material. I have all this sat in a big box of air.

Now I used the Electrostatics module, and was able to define the edges of the HV's as voltage potentials and set them to 20kV, like wise I defined the edges of the grounds as grounds. I was also able to define the materials for all the regions and I assume thats all you need to do there (just define the material, then leave it floating in space).

COMSOL can calculate the resulting electric field and to me at least, it looks reasonable. It certainly matches what I have managed with equivalent circuits in a SPICE program.

What I want to try now is applying a voltage signal. I have actual oscilloscope data I would like to use of a fast rise time HV signal (0-20kV in 100 ns). Failing that, I have approximate forms generated by single wiebe functions (these at least present nice smooth curves).

How do I actually get such signals into COMSOL? Can I do that with the electrostatics module? Or do I need use a different module - one of the RF modules? - ( I have full access here). Any help is much appreciated.
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Angular resolution in line plot export

September 12, 2012, 7:35 am
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Hi,

I am looking to be able to control the angular resolution of 2D line plots. Specifically for when I export the line plot data.

Background:

I am doing polar acoustic pressure studies and am beginning to investigate the effects of data resolution.
In the line plot, for x-axis data, I can select either 'Arc Length' or expression.
I currently have defined a cylindrical coordinate system so that I can choose 'cylindrical system'.phi as the x-axis data for my line plot.

But I would like to take this a step further in terms of customizing the x-axis data.

I had some ideas:

1. Use range( ) to create my own set of discrete angle points and use this set as input for the x-axis data field in the line plot. Unfortunately I could not figure out how to get this to work as range( ) does not seem to evaluate in the plot expression entry field.
2. Use range( ) somewhere up in the parameter definitions and feed the plot field this identifier. That didn't work either as range( ) refused to evaluate in Global Parameters also.


Has anyone else worked through this already?
Or is there a flaw in my thinking of how to get my desired outcome?

Thanks,

Will
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COMSOL in IBM AIX

September 12, 2012, 9:02 am
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Can COMSOL be run in AIX?

http://en.wikipedia.org/wiki/IBM_AIX

A quick search both here and in google couldn't answer this.
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Piezoelectric coupled with a shunt circuit for vibration damping

September 12, 2012, 11:42 am
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Hi, everyone! I am simulating the effect of a shunt circuit on the vibration of a piezoelectric device. Theoretically, with a shunt circuit connected (a resistor and a inductor in parallel with the pzt), the vibration of the device will be further damped. This is because the mechanical energy generated by the vibration of the pzt will be converted to electric energy and further consumed by the shunt circuit in the form of Joule heating. However, when I connect a shunt circuit to the two electrodes of the pzt, the vibration amplitude is unchanged. I bet the circuit and the pzt is not coupled well and the circuit does not back-affect the pzt module.

To make the problem clearer, I list the main boundary setup of my model:

For the PZD module: 1. one end of the pzt beam is fixed and a harmonic loading is applied on the other end;
2. the lower face of the beam is grounded; the upper face is set as floating potential; the other faces are set as zero charge;

For the electric circuit module:
1. ground node is 0;
2. a resistor node is added between 1 and 0;
3. a inductor is added between 1 and 0;
4 "External I vs.U" is added between 1 and 0 and is connected the PZD module and the voltage is the floating potential on the upper face of the pzt beam.


So the question is: 1. will the "electric circuit " module response back to the pzd module?
2. will the "electric circuit" module consider the conservation of energy and thus can consume the mechanical energy in the form of joule heating?
3. any comment on this model and any suggestions?

Thank you in advance for any comment and help!!

Rock
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missing internal contact bounderies when convert to solid

September 12, 2012, 2:37 pm
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Hi,

I have problem with introducing internal contact boundaries. A model consists with two glass plate and two cylindrical objects (model-glass plate contact with cylinders). The cylindrical objects are transversally loaded by the upper glass plate. The cylindrical objects have different material properties so the assembly method was used. To introduce contact behaviour in between glass plate and cylinder, points were used following cylinder_roller_contact example (Structural mechanical module -verification model). When I convert all the objects into the solid internal contact in between two cylinders are disappearing. I tried several ways to get that boundaries as contact pair but couldn’t.

Any comment is greatly appreciated

Thanks
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Contact problem at large Indentation

September 12, 2012, 2:41 pm
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Hello,

I am trying to simulate the case that one hard solid object is being pushed "into" another soft solid object under a large force. The two objects are in contact throughout the process.

It is similar to the example "Cylinder Roller Contact" problem. However, in the example the displacement is very small compared with the size of the object. What I want to see is that the cylinder is pushed almost completely (80%) into the bottom foundation, under the condition that the top is hard (such as diamond) and the bottom is malleable (such as Lithium). In extreme case, the cylinder completely goes into the foundation and leaves its shape.

I have included elastoplastic properties of the materials and the hardening function into the modal. I set Prescribed Displacement for the top cylinder to control its position. It works well at small displacements. However, when I increased the displacement larger and larger (more than 10% of the top cylinder size), the solution cannot converge.

I tried to adjust the contact settings (Penalty Factor, Contact Pressure etc.), but not much success.

Am I missing something?

Thanks for any suggestions.



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Oblique incident of EM wave

September 12, 2012, 4:34 pm
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HI,

I need to simulate one RF module structure where incident wave is oblique.
I don't know how to configure it in RF module. Would anyone please help me .

Thank you
Sanjay
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Export animation/image sequence via Matlab Livelink

March 25, 2011, 5:47 am
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Hi,

I'm have a HT problem which I solve time dependently via the Matlab Livelink. Since I have a lot of models to solve this way, I would like to export the image sequence of the solution automatically to e.g. pic1.png, pic2.png, ...,picx.png.

I have created the following m-code, however it does NOT produce any warning/error, NOR it produces my wanted .png files:
(plotgroup2 is set-up properly)
model.result.export.create('anim1', 'Animation');
model.result.export('anim1').set('plotgroup', 'pg2');
model.result.export('anim1').set('type', 'imageseq');
model.result.export('anim1').set('sweeptype', 'solutions');
model.result.export('anim1').set('imagefilename', 'C:\files\pic.png');
model.result('pg2').set('window', 'graphics');
model.result('pg2').set('windowtitle', 'Plot of HT');
model.result('pg2').run;
model.result.export('anim1').run;

If I open my .mph file afterwards and click the export button, everything works fine and my files are created, but somehow the Livelink won't produce the images.

Who knows why this is?


Regards,

Peter.

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Thermal losses from RF Electromagnetic Waves

March 19, 2012, 12:52 am
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Dear all,
my problem is the coupling between an RF probelm and a thermal problem, do to the test I made 2 "attached" Blocks
and I solve before an RF problem on block1 with the calculation of the Eigenfrequency modes as "study1" and after I solve as "study2" in the near Block 2 the problem of Heat Transfer in Solid, what I get is 2 independ solutions without
any connections. If I try to include the Heat Flux from the study1 to the study2 I get the following error:
Failed to evaluate variable.
- Variable: freq
- Geometry: 1
- Boundary: 6
Failed to evaluate variable.
- Variable: mod1.emw.freq
- Defined as: freq
Failed to evaluate variable.
- Variable: mod1.emw.omega
- Defined as: (mod1.emw.freq*(pi*2))
Failed to evaluate variable.
- Variable: mod1.emw.iomega
- Defined as: (mod1.emw.omega*i)
Failed to evaluate variable.
- Variable: mod1.emw.Jsz
- Defined as: ((sqrt((epsilon0_const/mu0_const))*mod1.tEz)*sqrt((((mod1.emw.sigmabnd/(epsilon0_const*mod1.emw.iomega))+mod1.emw.epsilonrbnd)/mod1.emw.murbnd)))
Failed to evaluate expression.
- Expression: realdot(mod1.emw.Jsz,mod1.tEz)
Failed to evaluate expression.
- Expression: realdot(mod1.emw.Jsz,mod1.tEz)
Failed to evaluate variable.
- Variable: mod1.emw.Qsrh
- Defined as: (0.5*(realdot(mod1.emw.Jsz,mod1.tEz)+(realdot(mod1.emw.Jsy,mod1.tEy)+realdot(mod1.emw.Jsx,mod1.tEx))))
Failed to evaluate variable.
- Variable: mod1.ht.q0_hf1
- Defined as: mod1.emw.Qsrh
Failed to evaluate expression.
- Expression: d((mod1.ht.q0_hf1*test(mod1.T))*(dvol),{test@4})

What can be the way to connect the two problems?
Thank you very much,
Michele Comunian
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Trouble coupling heat transfer physics for both fluids and solids

April 24, 2012, 8:19 pm
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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.
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Extremely thin geometries

September 9, 2012, 11:13 pm
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I created a cylinder with radius 1e-6 m and thickness 9e-10 m in 3D to make a continuum simulation of graphene. I have initial radial stress, an uniform body load along the thickness of the cylinder and use fully clamped boundary conditions on the radial edge. When I try to mesh it the process never finishes, and earlier when I had a mesh on a similar geometry the simulation didn't converge.

Question: What do I need to consider while trying to simulate extremely thin geometries?
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