A Stable SBP–SAT FDTD Subgridding Method for T-Junction Blocks

A stable summation-by-parts simultaneous approximation term (SBP–SAT) finite-difference time-domain (FDTD) subgridding method for electromagnetic simulations is proposed, specifically addressing computational challenges in T-junction block configurations. By integrating SBP operators and SATs into the FDTD framework, a three-block computational scheme is developed, which can be extended to a five-block configuration for regions centered within rectangular subgridding blocks. Our method employs specially designed interpolation matrices that maintain stability and accuracy across diverse grid ratios at interfaces of T-junction blocks. Numerical results validate its high efficiency, accuracy, and flexibility. Compared with traditional SBP–SAT FDTD subgridding methods for aligned blocks, our approach significantly reduces redundant SAT boundary conditions, enhancing the accuracy near boundary regions. These advantages are particularly pronounced in high dimensional and multisubgridding scenarios, establishing the proposed approach as both computationally efficient and straightforward to implement in complex applications.