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Effect of sound pressure on refractive index/density

Posted 21 gen 2013, 12:43 GMT-5 RF & Microwave Engineering, Acoustics & Vibrations, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.2, Version 4.2a, Version 4.3, Version 4.3a 6 Replies

Robert Malkin
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Hello fellow Comsol users,

Most of my experience comes from structural mechanics and fracture and would like to ask a little help regarding pressure acoustics.

The presence of high and low pressure in air will change it's refractive index due to a change in the density. I would like to model this change in refractive index, but am a little lost.

Could anyone tell me how I could go about modelling/solving for a change in material property?

I am using a time dependant pressure model in air. Within the materials section I can see that the density is a function of temperature and pA [which I assume to be absolute pressure], but when I plot the change in density it says that there is no change in density even if there is a change in pressure.

I'm sorry if this question sounds a little dumb, I'm sure that I am just being stupid today.

Also, I have had a look at the forum and a little in the documentation but could not find anything to help.

Anyone have some ideas out there? I would greatly appreciate your help.

Rob
6 Replies Last Post 3 mag 2013, 08:32 GMT-4
RVN
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Posted: 1 decade ago 25 gen 2013, 05:33 GMT-5


Could anyone tell me how I could go about modelling/solving for a change in material property?

You could try to make your material property be a function of your own paramter, lets call it "pressure"


I am using a time dependant pressure model in air. [...]

I am not very good at time dependent models (yet) so you could try to do a frequency domain analysis and use your "pressure" parameter in a parametric sweep. Then you might be able to plot the change in density.

Hope this helps, I have not tried my solution in this specific case, but I have made similar solution using this technique.
--
/RVN
[QUOTE] Could anyone tell me how I could go about modelling/solving for a change in material property? [/QUOTE] You could try to make your material property be a function of your own paramter, lets call it "pressure" [QUOTE] I am using a time dependant pressure model in air. [...] [/QUOTE] I am not very good at time dependent models (yet) so you could try to do a frequency domain analysis and use your "pressure" parameter in a parametric sweep. Then you might be able to plot the change in density. Hope this helps, I have not tried my solution in this specific case, but I have made similar solution using this technique. -- /RVN
Hassanain Al-Taiy
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Posted: 1 decade ago 9 apr 2013, 09:41 GMT-4
Hi all

can you tell me how can i make my model (RF) density dependent (acoustics) through refractive index to solve the scattered wave in RF ?

Best regrads
Hi all can you tell me how can i make my model (RF) density dependent (acoustics) through refractive index to solve the scattered wave in RF ? Best regrads
Hassanain Al-Taiy
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Posted: 1 decade ago 15 apr 2013, 07:45 GMT-4
Dear RVN


please could you tell me how can i make the density of the elastic medium : time dependent to get the variation in refractive index of the medium, i tried the time dependent with the elastic mode but i get a fixed density value.


Best regards
Dear RVN please could you tell me how can i make the density of the elastic medium : time dependent to get the variation in refractive index of the medium, i tried the time dependent with the elastic mode but i get a fixed density value. Best regards
RVN
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Posted: 1 decade ago 3 mag 2013, 02:29 GMT-4

Dear RVN


please could you tell me how can i make the density of the elastic medium : time dependent to get the variation in refractive index of the medium, i tried the time dependent with the elastic mode but i get a fixed density value.


Best regards


I made a crude model for you. I am assuming you have the Acoustics module, so take a look under the Pressure Acoustics, Frequency Domain node. Go to Pressure Acoustics Model 1 and note that I choose user defined density (as opposed to "from material"). The numbers I input have no significance, you can choose what suits your needs. The same goes for the sine function I used, use whatever you need.

Hope this helps
--
/RVN
[QUOTE] Dear RVN please could you tell me how can i make the density of the elastic medium : time dependent to get the variation in refractive index of the medium, i tried the time dependent with the elastic mode but i get a fixed density value. Best regards [/QUOTE] I made a crude model for you. I am assuming you have the Acoustics module, so take a look under the Pressure Acoustics, Frequency Domain node. Go to Pressure Acoustics Model 1 and note that I choose user defined density (as opposed to "from material"). The numbers I input have no significance, you can choose what suits your needs. The same goes for the sine function I used, use whatever you need. Hope this helps -- /RVN
Robert Malkin
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Posted: 1 decade ago 3 mag 2013, 05:19 GMT-4
Hi,

Thank you very much for taking the time out to do that for me.

I very much appreciate it.

I can not however open the attached file as it says that it was created in a later version of Comsol, which is odd as I have the latest version installed.

Version, 4.3.0.233

Could you tell me if this is the same version you are using?

Rob

Hi, Thank you very much for taking the time out to do that for me. I very much appreciate it. I can not however open the attached file as it says that it was created in a later version of Comsol, which is odd as I have the latest version installed. Version, 4.3.0.233 Could you tell me if this is the same version you are using? Rob
Hassanain Al-Taiy
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Posted: 1 decade ago 3 mag 2013, 08:32 GMT-4
Dear RVN


thanks allot for your attention, i can not open the model now and when i open it i will contact with you, once again i want to appreciate your efforts to help me, i wish you all the best for you.



Best Regards

Hassanain
Dear RVN thanks allot for your attention, i can not open the model now and when i open it i will contact with you, once again i want to appreciate your efforts to help me, i wish you all the best for you. Best Regards Hassanain

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