{{Twoimg|FDTD93.png|A Dielectric Object...|FDTD94.png|...and its Yee mesh.}}
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The FDTD simulation time depends directly on the size of the computational domain. For free space radiation or scattering problems, the computational domain must be extended to infinity, which means an infinite number of cells in the computational domain. The solution to this problem is to truncate the domain by a set of artificial boundaries at a certain distance from the objects in the computational domain. The absorbing boundaries should be such that the field propagates through them without any back reflection.
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Learn more about EM.Tempo's [[Perfectly Matched Layer Termination]].
The FDTD method provides a wideband simulation of your physical structure. In order to produce sufficient spectral information, an appropriate wideband temporal waveform is needed to excite the physical structure. The choice of the waveform, its bandwidth and time delay are important for the convergence behavior of the FDTD time marching loop. By default, EM.Tempo uses a modulated Gaussian waveform with optimal [[parameters]]: t = 0.966/Δf and t<sub>0</sub> = 4.5t, where Δf is the specified bandwidth of the simulation. The time delay t<sub>0</sub> is chosen so that the temporal waveform has an almost zero value at t = 0.
For more detailed information, see [[Waveform, Bandwidth, Stability]].
===Perfectly Matched Layer Termination===The FDTD simulation time depends directly on the size of the computational domain. For free space radiation or scattering problems, the computational domain must be extended to infinity, which means an infinite number of cells in the computational domain. The solution to this problem is to truncate the domain by a set of artificial boundaries at a certain distance from the objects in the computational domain. The absorbing boundaries should be such that the field propagates through them without any back reflection.  See more about EM.Tempo's [[Perfectly Matched Layer Termination]]. ===Time Domain Simulation Of Periodic Structures=== [[Image:fdtd_perdiag_tn.png|thumb|250px|Diagram of a periodic structure illuminated by an obliquely incident plane wave in [[FDTD Module]]]] A periodic structure is one that repeats itself infinitely in one, two or three directions. [[EM.Cube]]'s [[FDTD Module]] allows you to simulate doubly periodic structures with periodicities along the X and Y directions. Many interesting structures such as frequency selective surfaces (FSS), electromagnetic band-gap (EBG) structures and metamaterial structures can be modeled using periodic geometries. In the case of an infinitely extended periodic structure, it is sufficient to analyze only a unit cell. In the FDTD method, this is accomplished by applying periodic boundary conditions (PBC) at the side walls of the computational domain.
The details of the periodic boundary condition used in EM.Temp are described in Click here to learn more about[[Time Domain Simulation of Periodic Structures]].
==Defining The Physical Structure==