Changes

===The FDTD Solution Domain===

You may occasionally want to use [[EM.Cube]]'s FDTD simulator to model planar structures. Although [[EM.Cube]] provides the more computationally efficient [[Planar Module]] for this very purpose, there are many cases when an FDTD simulation might prove advantageous over a 2.5-D MoM simulation. To model a laterally infinite dielectric substrate, you must assign a PML boundary condition to the four lateral sides of the domain box and set the lateral domain offset values along the ±X and ±Y directions all equal to zero. If the planar structure ends in an infinite dielectric half-space from the bottom, you must assign a PML boundary condition to the bottom side of the domain box and set the -Z offset equal to zero.

[[EM.Tempo]]'s FDTD mesh is a rectangular Yee mesh that extends to the entire computational domain. It is primarily constructed from three mesh grid profiles along the XY, YZ and ZX principal planes. These projections together create a 3D rectangular (voxel) mesh space. You have the option to choose one of the three FDTD mesh types:

{{Note|When choosing a mesh type for your FDTD simulation, keep in mind that adaptive and regular mesh types are frequency-dependent and their density varies with the highest frequency of your specified bandwidth, while the uniform mesh type is always fixed and independent of your project's frequency settings.}}

Because a full 3D FDTD mesh is difficult to visualize everywhere in the computational domain, only the discretized objects are displayed in [[EM.Cube]]'s "'''Mesh View'''" mode. In particular, only the outer boundary cells on the surface of [[Solid Objects|solid objects]] are shown. However, you can view the mesh grid planes across the domain. You can even step these planes back and forth inside the domain and view different mesh profiles of your physical structure.

In certain cases, you may wish to exert some level of local mesh control. For example, you may want to increase the mesh density at a very particular area of your structure. Or you may want to increase or decrease the mesh resolution inside certain types of materials independent of their permittivity and permeability. [[EM.Cube]] provides two additional mechanisms for local control of the FDTD mesh: locking mesh of object groups and user defined fixed grid points.

==Excitation Sources==

# Sinusoidal

# Gaussian Pulse

# Modulated Gaussian Pulse

A sinusoidal waveform is single-tone and periodic. Its spectrum is concentrated around a single frequency, which is equal to your project's center frequency. A sinusoidal source does not have a finite energy and it does not decay as t → ∞. A Gaussian pulse decays exponentially as t → ∞, but it has a lowpass frequency spectrum which is concentrated around f = 0. A modulated Gaussian pulse decays exponentially as t → ∞, and it does have a bandpass frequency spectrum concentrated around your project's center frequency. For most practical problems, a modulated Gaussian pulse waveform provides an adequate performance. That is why this type of waveform is chosen by [[EM.Cube]] as your project's default waveform.