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    Simple Questions about Plane Wave Excitation in HFSS

    Hello,

    I have a very simple questions about plane wave excitation in HFSS. My question is more about using radiation boundary and plane wave excitation, and I need someone's approve.

    In the model, I create a box which is air box, and I assign radiation boundary for all surfaces of the box. Then, I select one of the surfaces and I do Assign Excitation>Incident Wave>Plane Wave... Then, I analyse the model and I find very nice plane wave propagation.

    My questions are:

    1) I read a lot about radiation boundary on the web, they say that the nearest distance between radiation boundary and the simulation structure should be λ/4. However, in my case it is not λ/4. It is even on the radiation boundary.
    Also, when I created another structure (box, plane, sphere...) inside of the air box and assigned it to Plane wave excitation in the same way, HFSS gives me error, it says 'Adaptive solution, process hf3d error: Failure in mesh verification'. I make the air box bigger and played with mesh, and I got the same result.
    Do you have any idea what causes this problem or does my first model seems right?

    2) When there is nothing inside of my air box, why do I still get some scattered field? (Excitation>Edit Sources>Scattered Field) even the box is vacuum. That is quite strange for me. Because there is nothing comparable with the wavelength. Can it be because of the radiation boundary condition?

    Thanks
    filarmonik

    •   Alt29th September 2017, 14:34

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  2. #2
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    Re: Simple Questions about Plane Wave Excitation in HFSS

    Quote Originally Posted by filarmonik View Post
    Hello,
    1) I read a lot about radiation boundary on the web, they say that the nearest distance between radiation boundary and the simulation structure should be λ/4. However, in my case it is not λ/4. It is even on the radiation boundary.
    Also, when I created another structure (box, plane, sphere...) inside of the air box and assigned it to Plane wave excitation in the same way, HFSS gives me error, it says 'Adaptive solution, process hf3d error: Failure in mesh verification'. I make the air box bigger and played with mesh, and I got the same result.
    Do you have any idea what causes this problem or does my first model seems right?
    Many things could cause this error, I'd make sure that all of your objects are aligned properly. If you can, the radiation box should indeed be λ/4 away from any radiating edges of your structure.

    Quote Originally Posted by filarmonik View Post
    2) When there is nothing inside of my air box, why do I still get some scattered field? (Excitation>Edit Sources>Scattered Field) even the box is vacuum. That is quite strange for me. Because there is nothing comparable with the wavelength. Can it be because of the radiation boundary condition?
    It could be because of the corners of the box, which will usually be fairly inaccurate. Do you see the largest scattered fields here, or in the center of the box?



    •   Alt2nd October 2017, 15:41

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  3. #3
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    Re: Simple Questions about Plane Wave Excitation in HFSS

    Thank you for your comments.

    What do you mean by saying alignment? Alignment of mesh?

    I have largest scattering field at the edges of box. Do you think because the light reflects at the edges when I use radiation boundary?



    •   Alt3rd October 2017, 12:29

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    Re: Simple Questions about Plane Wave Excitation in HFSS

    Quote Originally Posted by filarmonik View Post
    What do you mean by saying alignment? Alignment of mesh?
    Alignment of your structural objects. Make sure there are no very small gaps between them.

    Quote Originally Posted by filarmonik View Post
    I have largest scattering field at the edges of box. Do you think because the light reflects at the edges when I use radiation boundary?
    Yes, most likely. I imagine the magnitude is small with respect to the incident wave? I also suspect this affect would decrease with increased mesh density in the corners.



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    Re: Simple Questions about Plane Wave Excitation in HFSS

    The structure of my project is very simple, I want to find the scattering cross section of a metal sphere. I have a sphere at the center of my air box. I assigned the incident plane wave excitation to one of the faces of the air box. The other surfaces is the radiation boundary. But I am really confused about the meaning of 'λ/4'. Is it the distance between the excitation location of the incident plane wave and the radiation boundary surface or the distance between the surface of the incident plane wave excitation and the radiation boundary surface? Because in my case, the radiation boundary is just next to the plane wave excitation surface.

    Do you know any example I can find on the web or ANYS web page how to use the incident plane wave? There is no example on HFSS guide of course. I find things about FSS but I am not interested in them.

    Quote Originally Posted by PlanarMetamaterials View Post
    Yes, most likely. I imagine the magnitude is small with respect to the incident wave? I also suspect this affect would decrease with increased mesh density in the corners.
    Yes, the magnitude is 100 times smaller than the incident wave without any sphere at the center. I consider changing the radiation boundary to PML or maybe putting better meshes in the corners.



    •   Alt4th October 2017, 08:59

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  6. #6
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    Re: Simple Questions about Plane Wave Excitation in HFSS

    Quote Originally Posted by filarmonik View Post
    But I am really confused about the meaning of 'λ/4'. Is it the distance between the excitation location of the incident plane wave and the radiation boundary surface or the distance between the surface of the incident plane wave excitation and the radiation boundary surface?
    It's the smallest distance between any scatterer (e.g., the outer radius of your sphere), and the applied radiation boundary.

    Quote Originally Posted by filarmonik View Post
    Do you know any example I can find on the web or ANYS web page how to use the incident plane wave? There is no example on HFSS guide of course. I find things about FSS but I am not interested in them.
    I think the RCS example in the HFSS help uses this excitation.


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