Wave equation in a rectangular duct (waveguide)

[cyrillebreard]

based on the example of helmohtz equation , i set up this case for wave equation in a rectangular duct. I can not get a correct solution, I have tried many thing like more iteration , changing between Robin and Dirichlet BC for imposing the incoming wave , which is basically a plane wave. I am sharing the code (Model1-shared.txt) and the output png files using Jupyter lab.
Any help would be welcome. thanks in advance
Model1-shared.txt

[lihangshiwo]

I'm interested in your work, but I suspect that there is a problem with the boundary conditions on your left and right, can you give some explanation.