Accurate and Stable Matrix-Free Time-Domain Method in 3-D Unstructured Meshes for General Electromagnetic Analysis

We develop a new time-domain method that is naturally matrix free, i.e., requiring no matrix solution, regardless of whether the discretization is a structured grid or an unstructured mesh. Its matrix-free property, manifested by a naturally diagonal mass matrix, is independent of the element shape used for discretization and its implementation is straightforward. No dual mesh, interpolation, projection, and mass lumping are required. Furthermore, we show that such a capability can be achieved with conventional vector basis functions without any need for modifying them. Moreover, a time-marching scheme is developed to ensure the stability for simulating an unsymmetrical numerical system whose eigenvalues can be complex-valued and even negative, while preserving the matrix-free merit of the proposed method. Extensive numerical experiments have been carried out on a variety of unstructured triangular, tetrahedral, triangular prism element, and mixed-element meshes. Correlations with analytical solutions and the results obtained from the time-domain finite-element method, at all points in the computational domain and across all time instants, have validated the accuracy, matrix-free property, stability, and generality of the proposed method.