Piezoelectric transducer model accuracy in Ansys Workbench 19.1

[RaphaelR]

Hi,

I have been modeling piezoelectric acoustic transducers in Ansys Workbench 19.1 to determine the frequency response spectrum in water.

The specific transducer types I am modeling are monopole ring and dipole bender bar transducers. They are to be operated in a pulse mode: a single sine differential voltage pulse is applied. The frequencies I am modeling are between 500 Hz and 20 kHz.

I have been using a harmonic analysis in workbench 19.1 with both the acoustic and piezoelectric extensions. Materials are modeled as isotropic as a simplification.

My models (for both ring and bender transducers) all suffer from the same issues:

(1) The model shows a much higher response than the experiment at resonance
(2) The model shows a lower response than the experiment at both higher and lower frequencies than resonance
(3) The location of the peaks in the model vs. experiment is substantially different
(4) Typically the difference in response for the model between two designs is much greater than reality

I have attached the response of two different ring transducers for the model vs. experiment to illustrate the problem.

What's wrong and what could be used to improve the fidelity of the model (and be able to use it to predict the behavior of the actual part)?

Much higher mesh densities?
Adding damping to the transducer? If so what is the best method?
Modeling via fluent rather the acoustic extension in workbench?
Doing a transient analysis rather than a harmonic analysis to more closely match the experiment?
Or am I expecting too much from this type of model?

Any help or insights would be much appreciated as I have very little experience with Ansys and acoustic/piezoelectric modeling and don't know where to start.

Thanks,

Raphael

 

[scheah]

Raphael,

It sounds like an interesting project. Perhaps a way forward is to fine tune your parameters with narrowly focused experiments. For example, you could try calibrating the piezoelectric properties by testing it in air with a laser vibrometer orienting it in multiple directions.


Kind regards,
Jason

 

[btrueblood]

What are the acoustic b.c.'s in the model, and what are they in the experiment?

Is an isotropic model suitable for your piezo material?

Yes to your suggestions, and the steps you are suggesting sound like the right approach (start with mesh refinement, especially at the acoustic interface). It sounds like your model is not considering damping, which would reduce the peak response at resonance (and slightly shift the resonant frequency, do you see this in the model vs. experiment?) as well as increase the response at other frequencies.