Which 2 they are depends on your E an H-field polarization. Be careful there, however, as I found I could only model an ifinte array of unit cell devices by using 2 PEC and 2 PMC boundary conditions. It also has handy S-parameters which makes transmission, reflection, and absorption trivial.Īlso, I know you said you were using the periodic BC. The port absorbs perfectly the reflected and transmitted waves through the sample. Reflection/Transmission problems are one of the best uses of port BC. On the other hand, you can solve this problem much easier by using port BC and then still just specifying the analytic expression for a plane wave at the input port->user defined. Anything else could potentially be reflected within your sim space. What I mean to say is that the scatt BC only absorbs perfectly for PLANE waves. I say that because if the device under test scatters things at angles other than normal, then those components would not normally be absorbed by the scattering BC. If you want to do it this way by launching the wave through the scattering BC and use scatt field formulation, I think you would ideally want the PML, but I don't know if comsol is happy with PML+scattering BC. So, does anyone know whether for COMSOL, for a case using a scattering boundary condition, like here, it is required to use PML alongside the scattering boundary condition? In finite difference methods, like FDTD or FDFD, if total field/scattered field formalism is used, one will need to put PML layers outside the total/field/scattered field box. I am not sure about the mechanism of how it works in COMSOL. Currently, I only use the scattering boundary condition, and without the PML. The question I have is that do I need put PML alongside the scattering boundary condition in the top and bottom sides.
I set the excitation by explicitly defining the analytic formula for the excitation field when the thin film is not there. For the top and bottom sides, I use scattering boundary condition. The structure is periodic in the transverse plane, so I set Periodic boundary condition on the four sides, surrounding the transverse plane. I put a thin film (may have some patterning in the film) at the center, then I try to get the absorption of the thin film under normal incidence.