Analysis of the electromagnetic fields inside building structure using the subgrid FDTD method

Based on the FDTD method, the subgrid technique is used is applied to analyze the distribution of electromagnetic fields inside a building structure. The whole lightning channel is calculated with the primary grid while the structure is modelled with subgrid, which would guarantee the calculation accuracy while not increase computation time. The results show that a surge occurs inside a building with peak value of a few times higher than the normal conditions. It also presents critical areas of a building when struck by lightning, and the significant influence of earth on the horizontal electric field.