Ansys Employee
nThis topic is discussed in the post here: is the relevant section:nSimulation spannThe span of the FDTD region should be set such that PML boundaries are a half wavelength away from the sides of any geometry objects in the simulation. “Wavelength” here refers to the longest wavelength in the source spectrum, taking into account the refractive index of the material between the object and the boundary. Exceptions to this rule include substrates, cladding, or any other objects that are supposed to extend beyond the simulation region (for example, the ends of input/output waveguides). For example, in a simulation of a simple straight waveguide in the Z direction:nXY cross-sectionn• Substrate extends through the X max/min and Y min boundaries.n• X max/min and Y max PML boundaries are at least a half wavelength away from the sides of the waveguides.nnnXZ cross-sectionn• The ends of the waveguides extend through the Z max/min boundaries.nnTo answer your questions:n1) You should consider the longest wavelength in the spectrum when setting the simulation span.n2) The rule of thumb for metal boundaries should be the same as the rule for PML boundaries.nAlso, note that these are just guidelines. The final simulation spans should be determined using convergence testing.n