An Investigation into the Implementation of ADI-FDTD Subgrids in FDTD GPR Modeling

The implementation of subgrids in the traditional finite-difference time-domain (FDTD) method is often required, especially when structures of fine geometry need to be modeled. Since the FDTD method is conditionally stable, different time-steps should be employed in the main grid and in the subgrid. To overcome the requirement for time interpolation at the boundary between the two grids, an unconditionally stable method, the alternating-direction-implicit (ADI-FDTD) method, has been used in the subgrid. As a result both the main FDTD grid and the subgrid use the same time-step. This paper presents an investigation into the performance of an ADI-FDTD subgrid when it is implemented into the conventional FDTD method.