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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.
In FDTD, the TFSF source divides the calculation region into two distinct regions:
TFSF sources are often used to study scattering and antenna problems. Typical applications include:
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.
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.
The Geometry tab can be used to set the geometric dimensions of a source. See the geometry settings in Source.
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 tab can be used to set the wavelength/frequency of a source. See wavelength/frequency settings in Source.
Users should follow the guidelines below when using TFSF sources to avoid common errors in TFSF source settings and ensure the accuracy and reliability of simulation results.
When adding a TFSF source, ensure the following conditions:
Below are examples of valid and invalid settings:
Valid injection: The wave vector is perpendicular to the gold and glass layers. Each side of the source "sees" the same refractive index distribution (air-gold-glass) along the propagation direction (from the incident surface to the end surface).
Invalid injection: The wave vector is not perpendicular to the substrate. The upper part of the source "sees" the refractive index of air, while the lower part "sees" the refractive index of the substrate.
The internal structure of the TFSF source can be divided into two cases:
The two cases are described in detail below:
1. For a TFSF source containing only a single medium, the TFSF source supports arbitrary incidence angles. However, for oblique incidence, uniform meshes must be used to avoid large numerical errors.
It is recommended that users disable the material structure to check whether the TFSF source settings are correct before proceeding with oblique incidence simulations. The simulation results for both cases are shown below. When the structure is disabled, the TFSF source propagates in a vacuum, and the electric field is concentrated only within the TFSF region (i.e., the total field), while the scattering field is nearly zero.
2. For multilayer material simulations, only normal incidence is currently supported. Generally, the propagation field through the substrate cannot pass through the TFSF boundary into the scattering-field region. For example, in the air-gold-glass layer simulation shown above, the incident light is reflected by the gold layer and absorbed by the TFSF boundary, and the electromagnetic field cannot enter the scattering-field region.
If a gap is introduced in the middle of the gold layer, the scattered light can pass through the gap into the scattering-field region. This gap is considered a scatterer and must be completely located within the TFSF source.
Currently, TFSF sources support non-uniform mesh simulations for normal incidence. However, to ensure simulation accuracy and stability, it is recommended to use uniform meshes (i.e., equal mesh sizes in all directions: dx, dy, dz). If anomalies or errors occur in TFSF simulations, check whether the mesh sizes are uniform.
In general, TFSF sources should not cross the boundaries of the simulation region, with the following two exceptions:
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:
