Photonics

Photonics

Inconsistency of intrinsic impedance

    • Jeon
      Subscriber

      Hi,

      I am trying to compare Poynting vector (P) with the value calculated using E and H.

      First, I found that the results of the two expressions below are different.

      (light traveling in the z direction, monitor located in free space)

    • Guilin Sun
      Ansys Employee
      You would not be able to get Ex/Hy=eta0 =377 since this value is valid for plane wave only in vacuum. Now you are simulating a nano scale structure, the fields you obtained are not plane wave. Please think it over. I would suggest that you simulate vacuum only by disabling the nano structure, and verify this value. Please note that when the textbook gives 120Pi, it is for real valued plane wave E and H fields.
    • Jeon
      Subscriber
      Thanks for the reply.
      However, my simulation results were sufficiently uniform plane waves. Sorry for not giving you enough information before.

      Even when a film of the same height as the nanostructure was placed instead of the nanostructure array, the same result was obtained.

      Fortunately, in the process of checking it, I think I found the reason. Increasing the mesh auto accuracy level made the difference significantly smaller.

      Even when the level is low, Ez at that point (or plane) is almost zero and it is a sufficiently uniform plane wave (compared to the error). So I don't think I've found a clear reason yet, but I found a solution anyway.
      Thanks again for your reply, and any additional comments would be appreciated.

    • Guilin Sun
      Ansys Employee
      You are right that with higher mesh accuracy the result can converge.
      For the field profile from monitor, although it seems uniform, it is not as only two digits are shown. if you use min and max, it can show you the difference.
      It seems your result has imaginary part of the impedance, than it means E and H are not phase matched, eg, not a simple plane wave. If you test a free space, you may find more info.
      I did a test with mesh accuracy 2, and using the following script:
      E=getresult("monitor","E");
      H=getresult("monitor","H");
      eta=E.Ex/H.Hy;
      ?min(eta)/(120*pi);
      ?max(eta)/(120*pi);
      The E and H fields are much more uniform:
      but the min and max are
      1.01535
      1.0508
      The error is mainly from discrete mesh: E and H are not located at the same position in Yee cell internally. The output is the result of interpolation, which can introduce additional error also.




    • Jeon
      Subscriber
      Now I have a clear understanding of the reason for the difference.
      Thank you so much for your reply.
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