Prestressed Harmonic Analysis

dardhruvdardhruv Member Posts: 16

Hello ,

@BenjaminStarling and @peteroznewman

I am doing my Master thesis related to Designing of Capacitive Micromachined Ultrasonic Transducer. In that, I have tasked related to prestressed harmonic analysis of Capacitive micromachined ultrasonic transducer. For that, I have to apply trans126 element (or EM Transducer load) in static structural analysis. Using that, I got a collapse voltage around 230 Volt. I am planning to do a conventional mode. As per many research paper, I have to apply voltage below collapse voltage around 80% of collapse voltage so I have applied 180 volts. Now, In a prestressed harmonic analysis, I have to apply small-signal AC Voltage. For that, I have applied 50 V using Command snippet.

Note: To use command snippet, I have checked ds.dat file so I can check EM Transducer command and using that I can modify that command.

Now, My Question is I am not sure Whether I have applied right command or not.

Then, later on, I have used Harmonic Acoustic Analysis part.

Basically, I have to apply DC and AC voltage on Membrane. DC voltage is used for making prestressed condition so we can get good pressure. Then, I have to apply AC Voltage.

Could Anyone please check my Model and let me Know, Whether I am doing right during Harmonic Part (especially command snippet window) or not?

One More question, When I use MSUP instead of Full Harmonic, I always got an error. For that, I use Reduced damped because I am not sure about damping. Should I use small damping value like 0.2 or something?

Thanks and Regards,



  • BenjaminStarlingBenjaminStarling AustraliaPosts: 101Member

    Hi @dardhruv

    Your model looks good.

    Regarding the modal solver you should be using the undamped solver. Your current Harmonic Response does not have any damping applied therefore this will be consistent between the two. If you are to apply damping, and want to use MSUP, then damping can still be applied at the harmonic response stage. The damped modal solver is technically challenging to say the least. An advantage of doing an MSUP is that damping can then be input in the Harmonic Response as a percentage of critical damping.

    Typical damping values exist around 0.01 to 0.1, percent of critical damping, for many structures. But for a MEMs device this may not hold true. To really know the correct damping you should seek out some literature or perform experiments.

    Also make sure that if you are using MSUP, you are creating another Modal analysis environment that is pre-stressed by the existing Static Structural environment.

    Your command snippet also looks fine.

    I saw in another post you were looking at performing FSI. Are you happy with the current Harmonic Acoustic analysis? or is there still a need for fluid coupling? My interpretation from your earlier posts is that you are primarily looking for energy loss, which Harmonic Acoustic is a suitable analysis for. I don't see the need for FSI in this analysis.

  • dardhruvdardhruv Posts: 32Member

    Hello @BenjaminStarling ,

    Thank you so much for your reply.

    Regarding Damping, I don't have damping data so I have used Full Harmonic Analysis. Is it ok?

    In FSI, My Aim is to find out acoustic pressure at a different location in air and water. I am following the attached paper for analysis. I am not sure, Should I have to use Two-way FSI or One Way FSI. In the paper, It shows FSI present between structure and acoustic part.

    For Acoustic part, I am referring following video made by @peteroznewman

    My model's acoustic part is correct?

    Thanks and Regards,


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