FDTD simulations - Why Smooth Turn-on of Source is Needed?

In Finite-Difference Time-Domain (FDTD) simulations, source injection needs to be smoothly done in order to suppress the undesired high frequency components excited during turn on. To visualize this problem, we provide two cases with and without turn-on source injection. On the right simulation, total field/scattered field injection is done using the cosine excitation without any smooth turn-on which effectively mimics the step function operation. This results in the injection of high frequency components creating the ripples and fluctuations in the signal propagating in the domain. On the contrary, the left simulation has a smooth turn of by using a half Hanning window ramp-up which effectively acts as low pass filter for the injected source. As a result, the signal propagating in the domain is free of high frequency components, hence no ripples and fluctuations.

Total Field / Scattered Field (TF/SF) Implementation in FDTD

Here, the plane wave excitation using the total field / scattered field (TF/SF) formulation in finite-difference time-domain (FDTD) algorithm is demonstrated. The interface between the "total" and "scattered" field regions is shown using the square box. The plane wave polarized in the -z direction (with respect to screen surface) is injected into the medium along the -y direction and then the scattering phenomena from two different scatterers (one metallic triangular wedge and another circular dielectric scatterer) are animated. The reflected wavefronts from the scatterers can explicitly be observed in the scattered field regions, whereas total field is observed within the box.




Keywords: Scattering from prism, 三角柱, Prisme triangulaire, 삼각기둥,முப்பட்டகம், Триъгълна призма