# Discussion Forum

## How to define the material properities for the specific mesh element

Hello,all. I want to give specific material properties to specific mesh element. For example, create a cirlce in COMSOL, create material and mesh. Set the permittivity as 1 in material for the whole circle. Now, I want to set the permittivity as 27 for a certain mesh element of the circle, and the rest mesh elements is still 1. BUT the mesh is not a geometric entity, so I don't know how to set it. Matlab&COMSOL can be used. If anyone knows how to set it, please contact me. Looking forward to your reply. Thanks.

2 Replies Last Post Mar 27, 2020, 2:07 AM EDT

Posted: 2 weeks ago
Updated: 2 weeks ago

In COMSOL, materials, and more generally, physics, are set on the geometry level, not on the mesh level. This is both more logical (since meshes are artefacts of the numerical procedures and have no physical meaning) and more convenient (It makes trying multiple meshes straightforward).

Can you explain what you are ultimately trying to do? I have an inkling that it can be done in some other way in COMSOL.

Best,

Jeff

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Jeff Hiller

Posted: 2 weeks ago

In COMSOL, materials, and more generally, physics, are set on the geometry, not on mesh. This is both more logical (since meshes are atefacts of the numerical procedures and have no physical meaning) and more convenient (It makes trying multiple meshes straight forward).

Can you explain what you are ultimately tring to do? I have an inkling that it can be done in some other way in COMSOL.

Best,

Jeff

Thanks Jeff.

I want to reconstruct an image using capacitance tomography. The principle is that permittivity distribution of object in the detection zone will lead to changes of detection capacitance. To realize this method, I need to obtain a sensitive map.

The sensitive map consists of several mesh elements. Each mesh element corresponds to a specific ΔC (capacitance). To calculate the ΔC of a certain mesh element (label as Mi), the permittivity of Mi (i=1,2,....N) should be set as 27, and the rest of mesh elements are 1. Then calculate the case in 'es' physics. Every mesh elements should be in loop and done as above . In this way, ΔC corresponding to N mesh elements can form the sensitive map.

That is what I want to do. I think there are two ways to realize it. One is to define specific material property for mesh elements. The other is to make mesh become geometry. But I can't find the convinient way to complete it. If you have any good idea, please let me know. Anything is OK as long as it helps. Thanks again.

Shirley Chen