Learning Forum

[sirazul_cenimat]

We want to study the total scattered and absorbed intensity from a periodic array of dielectric nanoparticles. Such studies require a TFSF source, and a scattering and absorbing monitor located outside and inside the TFSF source, respectively. However, we are not able to properly set the boundary and mesh conditions to obtain reliable simulation, as the Auto shutoff condition is never achieved nor it goes below 1e-3.

[Guilin Sun]

It might indicate that there are some incorrect settings.
To use TFSF for periodic structure, TFSF has to be extended outside of the periodic BCs: Tips and best practices when using the FDTD TFSF source
PML may need to have more layers. If the periodic structure has higher diffraction orders and larger diffraction angles, you may need to use Steep Angle PML. Once the PML behaves properly with minimal reflection the autoshutoff level should decay as expecgted.

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While recent trend is to quantify the scattering from periodic structure, I think it has already deviated from the original meaning of scattering, which means non-direct propagation. Actually all the diffraction orders other than the 0th order are scattering. This is just a side note to this issue and you can ignore it.