Arbitrary-ratio-based subgrid implementations of hybrid ZT-ADI-FDTD and its applications in 3D dispersive GPR problems

In modeling and simulating ground-penetrating radar (GPR) systems, the finite-difference time-domain (FDTD) method often involves solving a large number of unknowns, which significantly increases computational cost and constrains its practical applicability. To overcome this limitation, this study proposes a hybrid subgridding ZT-ADI-FDTD method for simulating complex three-dimensional GPR scenarios characterized by dissipation, dispersion, and inhomogeneity. The method supports subgrid partitioning with both odd and even refinement ratios, thereby enhancing adaptability in electromagnetic modeling. In fine-grid regions, the unconditionally stable ADI-FDTD scheme is employed, enabling the entire computational domain to share a uniform time step and thus avoiding the complexity of temporal interpolation. For dispersive soils commonly encountered in GPR applications, the Z-transform technique is applied to convert the frequency-dependent parameters of Debye media into the time domain.