Finite-Difference Time-Domain (FDTD) Method
The FDTD method was first introduced by Yee in his 1966 seminal paper. The method was later refined by Taflove and is now one of the most widely used numerical techniques for solving EM problems. There are several advantages of this method over frequency domain techniques such as the finite element method (FEM) and boundary integral methods.

First, the method is a direct solution of Maxwell's time-domain equations. Consequently, it is a complete full-wave solution that contains no approximations that would prevent a correct solution from being reached. FEM and integral methods can be plagued by spurious non-physical solutions.

Second, the method is extremely general in the materials and geometries that it can analyze. Structures that contain inhomogenous, lossy ,or even anisotropic material properties can be handled easily.

Lastly, and most importantly, the memory requirements of FDTD are significantly less than other methods, which permits the efficient analysis of electrically large scatterers. This is of particular importance for the analysis of many practical SWDOEs, since their size may extend over hundreds of wavelengths.

The principal disadvantage of the classical implementation of FDTD is that all structures must conform to a Cartesian grid; consequently, all curved surfaces must be modeled by a "stairstep" approximation, which can introduce errors in the results.