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NanoComp / meep

free finite-difference time-domain (FDTD) software for electromagnetic simulations
GNU General Public License v2.0
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Anomalies in the transmission spectrum for a metal-dielectric structure #2790

Open leSemaleon opened 9 months ago

leSemaleon commented 9 months ago

Hello, I model metasurfaces and their spectral properties. There is a layer of copper, specified through epsilon (-75000) and conductivity, and a layer of polypropylene - epsilon 2.3, conductivity ~10^-4. The spectrum turns out to be jagged, which I cannot explain. Moreover, if you make the epsilon of polypropylene closer to 1, then the spectrum is smoothed out. It seems that such a change in epsilon should not affect the spectrum since the radiation comes from a metal with epsilon -75000, and compared to this, 1 or 2 makes no difference. Spectra are attached. With epsilon = 2 photo_2024-02-24_21-47-50 With epsilon = 1 photo_2024-02-24_23-14-27

oskooi commented 9 months ago

There is a layer of copper, specified through epsilon (-75000) and conductivity

Note that a frequency-independent negative $\varepsilon$ is unstable. There are two options: (1) use Cu from the materials library or (2) fit the $\varepsilon(\lambda)$ profile yourself using a Drude-Lorentzian fit.

Also, conductivity can be used to model complex $\varepsilon$ and only over a narrow bandwidth. Conductivity cannot be used to model negative $\varepsilon$ which is purely real (i.e., lossless).

leSemaleon commented 9 months ago

When I used Cu from library, fields became infinity in some step, so I begun use epsilon with conductivity