## Electronics

#### Total Internal Reflection – Dielectric Interface – Boundary Conditions

• joaonizer
Subscriber

Hi,

I'm trying to observe total internal reflection in a slab interface, it quite a simple structure, but I'm not sure why I'm not able to get the proper results.

I'm setting up an HFSS simulation where I include two slabs one glass (eps_r = 5.5) and another vacuum (eps_r=1). Then I surround the structure with Lattice Pair boundary conditions and specify a phase shift of 'theta0' (incidence angle), which is the variable I'm going to sweep. Then, at the bottom face, I set a Floquet port (FP1) that touches the glass slab and at the top, I have a second Floquet port (FP2) that touches the vacuum slab.

I make sure that the A and B dimensions of the unit cell are small enough so only the fundamental modes are propagating.

For TE and TM (m=0, n=0) I do get the correct results that match with Fresnel coefficients only for the case where the wave is incident from n1=1 to n2=sqrt(5.5) (n1

• Praneeth
Ansys Employee

All the very best.
• cearl20415
Subscriber
I have the exact same question as OP. "This question is being addressed in another platform. Please check there." What other platform are you referring to? Any help would be greatly appreciated.
• cearl20415
Subscriber
,meant to tag you in my previous response. I saw that you responded to OP's original inquiry, but I cannot find the follow-up information you are referring to.
,did you ever get this problem resolved?
Thank you!
• joaonizer
Subscriber
The setup I have in the thread is correct for n1Global Material Environment is set to vacuum, thus for n1=1 the simulation was correct and we were able to observe the Brewster angle.
To observe Total Internal Reflection (TIR, n1>n2) we have to set the Global Material Environment to n1, with n1 different than 1, otherwise, the Floquet Ports will not work properly for observing Total Internal Reflection in the case of a single interface.
Select the design you are using for TIR, then go to HFSS>Boundaries>Edit Global Material Environment and select the higher index (n1) for total internal reflection.
After doing that I was able to get the TIR result that agrees with Fresnel coefficients:

• cearl20415
Subscriber
fantastic! Thank you for taking the time to respond to my post, as well as presenting your TIR results. This looks like the correct solution. Thank you so much for sharing this information!
I was going mad trying to figure this out. Classic example of how various computational techniques and simulation software have nuances in the various methods and implementations. I found this thread originally upon googling "HFSS Fresnel Coefficients". I was having the exact same problem, so I was encouraged when I found this thread. Thanks for putting together such a detailed original post. You're description was very clear and well organized. Cheers!