Tutorial: Scattering by a metallic sphere

This tutorial is an extension of the prior scattering by a dielectric sphere tutorial. In it, the prior tutorial will be repeated, but for a silver particle. As discussed in the prior tutorial, looking forward to later tutorials, the solution will be purposefully not converged.

You will learn:

• How to define a dispersive material in the materials file
• How to spot signs of an unconverged calculation

Note again that the geometries file will not be created for this problem. The files for this tutorial (input and expected output) can be obtained here: Tutorial2.tgz

Note also that this tutorial assumes that you are thoroughly familiar with the scattering by a dielectric sphere tutorial.

Preparing the work directory

Create a work directory, work/. Copy the input files from the scattering by a dielectric sphere tutorial, param, mat, and geom.unv, to this directory.

Geometries file

The geometries file from the scattering by a dielectric sphere tutorial, geom.unv, will be used in this tutorial.

Materials file

The primary task in this tutorial is to modify the materials file from the scattering by a dielectric sphere tutorial, replacing glass with silver. Recall that the sphere is assigned a material number 1.

Open mat in a text editor, and replace:

material 1
{
    epsr 2.25
}

with the following model for silver:

material 1
{
    epsr 3.189

    Drude
    {
        omegap 9.183
        gamma 0.0179
    }

    Lorentz
    {
        depsr 0.4323
        omegap 4.668
        delta 0.207
    }

    Lorentz
    {
        depsr 0.2237
        omegap 4.240
        delta 0.186
    }
}

Save this file.

Parameters file

The parameters file from the scattering by a dielectric sphere tutorial, param, will be used in this tutorial.

Running FDTD++

Now that the relevant files have been created, the simulation can be performed.

Open a terminal in your work directory, and since this simulation is to be run in serial, type:

FDTDxx param mat geom.unv

Output

Once the simulation has finished, the following output should exist:

• work/FDTDxx.log
• work/FDTDxx.err
• work/output/cross_sections.dat

First, check work/FDTDxx.err to ensure that no errors were generated during the simulation.

Next, check work/FDTDxx.log for any important notes. Also, double check the definition of materials and simulation parameters, as reported.

Finally, work/output/cross_sections.dat contains the cross sections, which can be plotted, etc.