The Material Explorer is used to check the material fits that will be used in the simulation. This is most important when using the Sampled data material type, although it can be used to check material properties for all material types. If the fit for a Sampled data material is not good enough, the Tolerance and Max coefficient properties and the wavelength range of the source can be edited in the Material Explorer.

## Material settings

Property | Description |
---|---|

Material |
Select the material to check. |

Axis |
If the material is anisotropic, select the axis to check. |

Fit Tolerance |
The Tolerance setting of the material. Only applies to fitted materials. |

Max Coefficients |
The Max coefficients setting of the material. Only applies to fitted materials. |

Show/Hide Advanced |
Show or hide the advanced options. |

Imaginary weight |
Increasing the weight increases the importance of the imaginary part of the permittivity when calculating a fit. A weight of 1 gives equal weight to the imaginary and real parts of the permittivity. |

Make fit passive |
Check to prevent the material fit from having gain at any frequency. By default this is checked in order to prevent diverging simulations. |

Improve stability |
Check to restrict the range of coefficients in the material fit in order to reduce numerical instabilities which cause simulations to diverge. |

Specify fit range |
Decouple the bandwidth used to generate the material fit and the source bandwidth. |

Bandwidth range of fit |
The frequency/wavelength range used for the fit if specify fit range is selected. The bandwidth of the fit should cover the simulation bandwidth. |

Save fit parameters |
Update the Material Database with the new Tolerance and Max coefficients values. |

## Simulation bandwidth settings

Property | Description |
---|---|

Bandwidth units |
Specify range in units of wavelength or frequency. Specify range by Min/Max or Center/Span. |

Bandwidth range |
The frequency/wavelength range of interest. By default, this is the source limits. |

Save source bandwidth |
Update the source limits with these values. |

## View Settings

Property | Description |
---|---|

Vertical axis |
Plot permittivity or index |

Show material data |
Show the experimental data on the plot windows |

Standard view |
Plot the fit over the specified bandwidth range |

Extended view range |
Plot the fit over a wider bandwidth range |

Specify view range |
Specify the range to plot the fit |

Plot in new window |
Plots fit and data in a new window |

## Fit and plot buttons

Property | Description |
---|---|

Plot in new window |
Plot data in a new window |

Fit and Plot |
Calculate and plot the material fit |

## Fit analysis

Property | Description |
---|---|

Standard RMS error |
The RMS error of the fit. The fitting algorithm will use the minimum number of coefficients required to achieve an RMS error less than the value specified by the Tolerance property of that material. If Imaginary Weight =1, then Standard RMS = Weighted RMS. If Imaginary Weight ≠ 1, then refer to the Weighted RMS error below. |

Weighted RMS error |
The weighted RMS error of the fit, calculated using the Imaginary Weight property of the material. The fitting algorithm will use the minimum number of coefficients required to achieve a weighted RMS error less than the value specified by the Tolerance property of the material. |

Number of coefficients |
The number of coefficients used in the fit. |

## Using the Material Explorer with varFDTD

When using the varFDTD solver, the Material Explorer will show the material properties of all the generated effective materials (ie. the core material as well as all of the test materials).

The effective materials are generated using the methods described in 2.5D varFDTD Physics. If BROADBAND is selected for the simulation bandwidth (under the Effective index tab), a sampled dataset of effective material data will be generated over the specified bandwidth (ie. the "Material data" shown above), which will then be fitted using the multi-coefficient material model (ie. the "Propagator model" shown above). Alternatively, if NARROWBAND is selected, an (n,k) material will be generated for each at the specified frequency. Note that the effective material properties shown here include both contributions from the original material dispersion of the 3D structure, as well as the waveguide dispersion. This is important for obtaining accurate broadband simulation results.

Unlike the Material Explorer for other types of solvers, the SPECIFY FIT RANGE section is not available for the Propagator. This is because the slab mode data is always generated for the full bandwidth range of the source, and not outside this range.