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ZMT zurich med tech

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  4. Homogeneity of E-filed map in plane wave simulation

Homogeneity of E-filed map in plane wave simulation

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  • S Offline
    S Offline
    Saya
    wrote on last edited by
    #1

    Hello,

    In plane wave simulation (for example tutorial 3.3.4 Heating from a Standard Active Implantable Medical Device), one source is defined such that E-field be along the length of source (or device if exists). Since the source is plane wave (without device), E-field map must be homogeneous in all 3 planes. In the plane along E-field, the E-field is homogeneous, but not in the other two planes (For example in the mentioned tutorial, the E-field is along z-axis and the E-field map is homogeneous in yz-plane, but not in xy and xz-planes). I'm wondering is there anything wrong with the simulation?

    Thanks.

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    • SylvainS Offline
      SylvainS Offline
      Sylvain
      ZMT
      wrote on last edited by
      #2

      Hello, please add a screenshot or two, comparing the E-field in each of the 3 planes (including the colorbar, so that we can see the magnitude of the field). This way, it will be clear what you mean by "not homogeneous".

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      • SylvainS Sylvain

        Hello, please add a screenshot or two, comparing the E-field in each of the 3 planes (including the colorbar, so that we can see the magnitude of the field). This way, it will be clear what you mean by "not homogeneous".

        S Offline
        S Offline
        Saya
        wrote on last edited by
        #3

        @Sylvain plane wave.png

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        • S Offline
          S Offline
          Saya
          wrote on last edited by Saya
          #4

          The pink box is plane wave source and as it could be seen the E-field is homogeneous in yz-plane but not in two others.

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          • S Saya

            The pink box is plane wave source and as it could be seen the E-field is homogeneous in yz-plane but not in two others.

            S Offline
            S Offline
            Saya
            wrote on last edited by
            #5

            @Saya 8958309f-36b6-497f-aa85-3df62c87b25b-image.png

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            • SylvainS Offline
              SylvainS Offline
              Sylvain
              ZMT
              wrote on last edited by
              #6

              One interpretation of your results could be that the wave is dissipating energy while traveling (in the x direction). Reasons for dissipation could be physical (if there is a lossy material inside the pink box), or numerial (if the grid is too coarse, or if the simulation did not run for a long enough time and did not converge).
              I would suggest to run the same simulation with a finer grid and check if there is any difference in the results.

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              • S Offline
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                Saya
                wrote on last edited by
                #7

                The material is just dielectric gel. I'll check your suggestions. Thanks.

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                • SylvainS Offline
                  SylvainS Offline
                  Sylvain
                  ZMT
                  wrote on last edited by
                  #8

                  If there is a gel, I would expect it is dissipating some power (just check the SAR, for instance...). In that case, you should expect the E field to decrease in intensity in the direction of propagation.

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                  • S Offline
                    S Offline
                    Saya
                    wrote on last edited by
                    #9

                    I'm wondering why energy dissipation does not happen in z-direction (since in yz plane E-field is homogeneous)?

                    S SylvainS 2 Replies Last reply
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                    • S Saya

                      I'm wondering why energy dissipation does not happen in z-direction (since in yz plane E-field is homogeneous)?

                      S Offline
                      S Offline
                      Saya
                      wrote on last edited by
                      #10

                      @Saya ed1dd158-ffcc-47ae-98f1-91a0a3864050-image.png

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                      • S Offline
                        S Offline
                        Saya
                        wrote on last edited by
                        #11

                        I ran the simulation with a finer grid and for a longer time, but the result is still the same.

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                        • S Saya

                          I'm wondering why energy dissipation does not happen in z-direction (since in yz plane E-field is homogeneous)?

                          SylvainS Offline
                          SylvainS Offline
                          Sylvain
                          ZMT
                          wrote on last edited by
                          #12

                          @Saya said in Homogeneity of E-filed map in plane wave simulation:

                          I'm wondering why energy dissipation does not happen in z-direction (since in yz plane E-field is homogeneous)?

                          Because your wave is propagating in the X direction.

                          Your simulation results make perfect sense: a wave is propagating through a lossy medium, dissipating some energy in the process.

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                          • S Offline
                            S Offline
                            Saya
                            wrote on last edited by Saya
                            #13

                            So you mean in the simulation with gel, because of the power loss in x direction, E-field should be non homogeneous in xz and xy planes.
                            I checked the simulation without gel(with just air) and it seems E-field is homogeneous in all planes. Great. Thanks.
                            And two more questions,

                            • Why in the tutorial, the air is considered as gel and gel is not used as an object in the simulation?
                            • Where is the starting point of the wave propagation?
                              Thanks.
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                            • SylvainS Offline
                              SylvainS Offline
                              Sylvain
                              ZMT
                              wrote on last edited by
                              #14
                              • The "air" is not considered as "gel". Rather, the background material, which is by default "air", is set to "gel" instead. The background is not an object itself: it is the space that is not occupied by any object. As such, it does not have an explicit shape, but it has material properties.
                              • For a plane wave source, the E and H fields are imposed (based on the analytical expression of a plane wave) on the face(s) "upwind" from the direction of propagation. Note that this is an idealized concept, as true plane waves don't exist in nature (https://en.wikipedia.org/wiki/Plane_wave)
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                              • S Offline
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                                Saya
                                wrote on last edited by
                                #15

                                Thanks for your explanation. But I'm still wondering why the background is set to gel? Why the gel is not used as an object?

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                                • SylvainS Offline
                                  SylvainS Offline
                                  Sylvain
                                  ZMT
                                  wrote on last edited by
                                  #16

                                  I'm not sure. Maybe because you would then have to consider the size and shape of said object, its interface with the "background", possible intersection with the sides of the computational domain (which the plane wave source may not allow), etc... All of that for zero benefit, since the medium of propagation is a gel, not air or vaccuum.

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                                  • S Offline
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                                    Saya
                                    wrote on last edited by
                                    #17

                                    Right. Thank you very much for your explanation and comments.

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