Gold nanorod pair: result of monitor different between plane and TFSF source


I am simulating a gold nanorod pair to obtain scattering spectrum and more properties such as refractive index. This rod pair geometry is known to behave as negative-index material in NIR (Drachev, V. P. et al. Laser Physics … (2006). doi:10.1002/lapl.200510062), so I use this geometry as a practice to simulate metamaterials.

However the results are different between plane source and TFSF source. The scattering spectrum obtained with plane source has many steep peaks, while the spectrum with TFSF source is smooth. This aspect affects all other calculations such as refractive index with S parameters (I have already turned “grating analysis” of S parameter on to get rid of diffractions).

I would like to know the meaning of this difference and this kind of steep peaks. Here I attach the files.

Thank you,

Au nanorod pair - plane.fsp (351.7 KB)
Au nanorod pair - tfsf.fsp (393.4 KB)

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I found periodicity caused the unusual peaks. The steep peaks doesn’t appear when BCs are all PML, but they appear with periodic BCs in both plane and TFSF sources. The steepness can mean wave doesn’t converge. It is also obvious there are interaction between neighboring rod pairs.
Now I wonder why this interaction cause this phenomenon. How should I do to simulate periodic metamaterials?


Are you sure the periodicity you need is in the x and y directions?

Dear aya_zaki,

Sorry for very late reply,
Yes, periodicity needed is x and y. Inserting glass in the gap of rods decrease the strange peaks.