What's BETD3D ?
It's an implementation of the fast time-domain boundary element method for 3D electromagnetic scattering problems proposed in the following paper:
``Beyond FDTD''
Because BETD3D is a boundary element method, it can deal with exterior domain or free space without any artificial/fictitious absorbing boundaries. In addition, the surfaces of objects, which are currently assumed to be perfectly electric conductors (PECs), can be modeled arbitrarily with a set of plane triangles, that is, triangular mesh. Further, BETD3D employs the fast algorithm based on a time-domain version of the fast multipole method. Therefore, BETD3D can be a competitive of the finite-difference time-domain (FDTD) method. In particular, the BETD method can outperform the FDTD method if the aforementioned conditions are met.