Learning Forum

[jmnolan]

Hi Ansys Learning Community, 

I am trying to simulate an air water boundary using Plane Waves as a source. What would be the correct boundary settings to simulate this properly?

I've used floquet ports and the results match Snell's law however, eventually I want to insert objects at the water/air boundary to see the impact. Can I still use floquet ports in this scenario?

I've set the Global Material Environment to Water or Air and the results dont make much sense. I should see the plane wave refract towards the angle calulcated by Snell's Law. 

I used PML boundaries around the water region, and Radiation Boundaries around the air region since the global variable is set to air. The image below is using a waveguide probe instead of a plane wave. I was thinking that would be more accurate, but the results are still strange.

 

Any pointers or suggestions would be much appreciated. 

 

Thanks

[DMARATHE]

Hi jmnolan, 

Thanks for posting your query on Ansys learning forum.

The floquet ports and coupled lattice pair boundaries, would simulate the plane wave effect. You can use these setup and also insert objects at the water/air boundary to see the impact. I don't see any concern in modelling such setup.

From another query, I can understand that you are trying to simulate a parallel plane waveguide setup. If that is the case, you need not have to use PML or radiation boundary assignment. To create a parralel plane waveguide using boundaries, you can assign PEC boundary to the top and bottom face of airbox (along longest dimesion) and PMC boundary to the other side faces of the airbox. For excitation, you can use waveports at other two ends of the airbox where wave is emanating. To create a two different medium, you can insert two separate boxes in airbox and assign respective medium properties. Any intersection error if any, you can override by using options HFSS > Design Settings > Validations > Enable material override.

Thanks.

 

[jmnolan]

Hi D. Marathe , 

Thanks for your reply. Using the floquet/lattice setup I am able to simulate unit cells with no problem. However, it doesnt seem to work when I try and simulate a larger structure like a Frequency Selective Surface for example. I think the problem I am facing is that the global material variable doesnt allow me to inject a plane wave from a floquet port assuming 1 material and then measure the far fields assuming another material. 

For example in the image above, if I set the global variable to water the plane wave enters the bottom water box as expected. It then refracts (I am assuming) correctly into the air box , but then once it leaves the air box into the "infinite" environment, the far fields are calculated using the global variable as water where I want it to be air. 

Is there a way to adjust this? 

 

Thanks,

[jmnolan]

Is it possible to use dielectric half spaces with a floquet / lattice pair setup? Since the structure is all dielectric I figured IE regions wouldnt apply which is required for half spaces, but is there a way around this? 

 

Thanks 

[DMARATHE]

Hi jmnolan, 

I would suggest you to keep 'Global Material Enviornment' as Vaccum. It is not possible to use floquet ports/lattice pairs with half dielectric space. I suggest you to create a single full size box and assign material as 'Air'. You can assign lattice pairs and floquete ports to this 'Air' box. Now to create a interface of two different medium (Air and Water), insert two boxes having size half of the earlier created 'Air' box. Assign this boxes 'Air' and 'Water' medium respectively. Intersection errors if any, you can override by using options HFSS > Design Settings > Validations > Enable material override.

Could you please check results with this method ? Thanks.

 

[jmnolan]

Hi D. Marathe, 

Thanks for the reply. The issue with setting the Global material as air is that the floquet port plane wave will not enter the water as expected due to snells law. For example if I want the water plane wave to arrive at 40 degrees, it will refract from the beginning and appear to enter at 4 or 5 degrees. If I set the global material to water however, the plane wave arrives correctly but then I cant view the far fields assuming an air medium. 

[DMARATHE]

Hi jmnolan,

Thanks for your reply !

Looks like you are working on solving specific engineering problem. Unfortunately, this question is the beyond the scope for ANSYS employees to answer on a public forum, so hopefully other community users can chime in.

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