Settings for TFSF Sources

This section describes the settings for TFSF sources.

When studying scattering field problems, Total-Field Scattered-Field (TFSF) sources can be employed to directly acquire the scattering fields.

Select the TFSF in the solver tab and create a TFSF source in the Composite viewer, then set further parameters in the Edit properties interface that automatically pops up.

TFSF Sources

In FDTD, the TFSF source divides the calculation region into two distinct regions:

• Total field $\boldsymbol{E}_{total} = \boldsymbol{E}_{inc} + \boldsymbol{E}_{scat}$, i.e., the total field $\boldsymbol{E}_{total}$ is equal to the sum of the incident field $\boldsymbol{E}_{inc}$ and the scattering field $\boldsymbol{E}_{scat}$;
• The scattering-field region includes the scattering field $\boldsymbol{E}_{scat}$ only.

TFSF sources are often used to study scattering and antenna problems. Typical applications include:

• Particles in homogeneous media (which may be lossy or anisotropic), such as triple scattering;
• Aperiodic structures in multilayer substrates, which may be lossy or anisotropic;
• Periodic structures in multilayer substrates, when used with the periodic or Bloch boundary condition.

The option of TFSF source is an advanced feature. Users should determine the appropriate source settings according to these instructions to ensure accurate results. Otherwise, incorrect settings may lead to inaccurate results.

Settings for TFSF Sources

General Settings

The General tab can be used to set the incident axis, amplitude, and other parameters related to a source.

Name	Description
Incident axis	Select the desired incident axis for a TFSF source from the drop-down list.
Direction	The propagation direction of a TFSF source, specifically selected as Forward (forward propagation) or Backward (backward propagation).

For the settings related to the amplitude, phase shift, and rotation of TFSF sources, see the general settings in Source.

Geometry

The Geometry tab can be used to set the geometric dimensions of a source. See the geometry settings in Source.

Polarization

The Polarization tab can be used to set the polarization of a source.

Name	Description
Linear polarization(θ)	The polarization angle for linear polarization.

Wavelength/Frequency

Wavelength/Frequency tab can be used to set the wavelength/frequency of a source. See wavelength/frequency settings in Source.

Advanced

When a TFSF source is added into a project, make sure the following conditions are met:

• The scatterer must be completely located within the TFSF source, and the scatterer can't be extended through the source span;
• The wave-vector of the source must be perpendicular to the substrate. In other words, all sides of the TFSF source must undergo the same refractive index distribution along the propagation direction. The following examples show valid and invalid settings respectively.

Valid injection: The wave-vector is perpendicular to the gold and glass layers. Each side of the source undergoes the same refractive index distribution (air-gold-glass) along the propagation direction (from the incident surface to the end surface).

Invalid injection: The incident axis is not perpendicular to the substrate. The upper part of the source is exposed to the air, while the lower part is exposed to the substrate.

Case: Mie Scattering

TFSF sources are used to study Mie scattering in this case. For related information, see Mie Scattering. The project is shown as below:

Once the simulation is completed, the scattered field (i.e., the field outside the space surrounded by the TFSF source) is extracted, and the far-field analysis is used to obtain the following polar plot and radiation pattern: