Changes

As can be seen from the above criterion, a high resolution mesh requires a smaller time step. Since you need to let the fields in the computational domain fully evolve over time, a smaller time step will require a larger number of time steps to achieve convergence. EM.Cube automatically chooses a time step that satisfies the CFL condition.

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. Different methods have been used to simulate an absorbing boundary condition in FDTD simulations. The most common ones are Mur, Liao, and the perfectly match layer (PML). The Mur boundary condition calculates the boundary field values from the three dimensional scalar wave equations, while the Liao boundary condition is based on extrapolation of the fields in space and time. In 1994, Berenger proposed a new boundary condition called the perfectly matched layer (PML), which provides a much better performance than the Liao and Mur boundary conditions. The PML medium properties surrounding the computational domain are chosen to effectively absorb all the outgoing waves propagating towards the boundaries. In PML regions, an artificial conductivity is introduced such that it starts with very small values at the free space-PML interfaces and gradually increases until it reaches its maximum value at the last layer of the PML region.