Acceleration of Trimmed MLFMA Using the PO Method for Large-Scale Scattering Problems

The physical optics (PO) method is used to improve the convergence and the computational efficiency of the multilevel fast multipole algorithm (MLFMA), which involves distributing the global linear system into two algorithmic subsystems and trimming the octree structure. The PO subsystem generates most of the contribution to the global system, resulting in a smaller but not negligible contribution from the MLFMA subsystem. The octree structure in the MLFMA subsystem is trimmed by evaluating the contribution of the PO subsystem to the global system, which can reduce the matrix–vector product computation and improve the convergence of the MLFMA subsystem. The results show a significant acceleration effect for large-scale electromagnetic scattering simulations, and the proposed method achieves higher accuracy than the high-frequency asymptotic method.