SAW gas sensor piezoelectric material properties

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Hi,

In the example "saw gas sensor" present in the comsol application library, the piezoelectric material is a YZ lithium niobate. The material properties are taken from (https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1426375)

I have few questions:

1) For example c33 = 242 GPa but why in the matrix (see file attached pag4) is in the position of c11 value. I don't understand the order.

2) Why in the piezoelectric material interface, under coordinate systems, "Material XZ plane system" is selected? If the properties are already related to the YZ LiNbO3, I think that "global coordinates" has to selected, or I am wrong?

3) Why "Material XZ plane system" and not "Material YZ plane system" is selected?



3 Replies Last Post Feb 23, 2021, 11:12 AM EST
Dave Greve Certified Consultant

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Posted: 2 weeks ago Feb 22, 2021, 12:58 PM EST

Interesting question. It appears that the posted model uses a custom set of parameters for lithium niobate. If you look at the Comsol built-in parameters for lithium niobate you will see that c11 = c22 < c33 as expected.

This helps explain the choice of the plane system.

By the way, when using the built-in LiNbO3 parameters, I think you want to use the ZY plane system to get what you want (YZ means Y-face, Z-propagating). You can sort this out by looking at the definitions of the coordinate systems and it is advisable to verify that you get the right velocities.

Interesting question. It appears that the posted model uses a custom set of parameters for lithium niobate. If you look at the Comsol built-in parameters for lithium niobate you will see that c11 = c22 < c33 as expected. This helps explain the choice of the plane system. By the way, when using the built-in LiNbO3 parameters, I think you want to use the ZY plane system to get what you want (YZ means Y-face, Z-propagating). You can sort this out by looking at the definitions of the coordinate systems and it is advisable to verify that you get the right velocities.

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Posted: 2 weeks ago Feb 22, 2021, 4:29 PM EST

Thanks for the help.

I want to model SAW device for acoustophoresis and the piezoelectric material is YZ lithium niobate. I notice that because the "saw gas sensor model" and the article (from which I have to reproduced the example) take the material properties from the same reference that I indicated in the first post.

So I use the same setup present in the "saw gas sensor model", and I don't think that I can use the built-in comsol parameters for lithium niobate. I thought to use "global coordinates" under the coordinate selection section, but maybe I am wrong.

How I can verify that I get the right velocity?

Thanks for the help. I want to model SAW device for acoustophoresis and the piezoelectric material is YZ lithium niobate. I notice that because the "saw gas sensor model" and the article (from which I have to reproduced the example) take the material properties from the same reference that I indicated in the first post. So I use the same setup present in the "saw gas sensor model", and I don't think that I can use the built-in comsol parameters for lithium niobate. I thought to use "global coordinates" under the coordinate selection section, but maybe I am wrong. How I can verify that I get the right velocity?

Dave Greve Certified Consultant

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Posted: 2 weeks ago Feb 23, 2021, 11:12 AM EST

The Eigenfrequency calculation gives you the frequency corresponding to a particular wavelength, so c = f*lambda.

Working out the orientations for anisotropic materials gets tricky. There's no alternative to thinking carefully about what you are doing and checking...twice...or more. It gets worse for multiply rotated orientations.

The Eigenfrequency calculation gives you the frequency corresponding to a particular wavelength, so c = f*lambda. Working out the orientations for anisotropic materials gets tricky. There's no alternative to thinking carefully about what you are doing and checking...twice...or more. It gets worse for multiply rotated orientations.

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