Enlarged cell technique in FDTD method at the dielectric curved surface

The standard FDTD method is second-order accuracy for the numerical simulation of electromagnetic problems in homogeneous media. However, its accuracy descends if the problems include dielectric material interfaces, in this case properly constructed averages of the media permittivities have been proposed, although those efforts increase the FDTD accuracy at the interfaces, the second-order accuracy is not really achieved because the uniform lattice is still employed in those efforts. The second-order accurate FDTD equations with nonuniform grids at dielectric interface have been presented in the work of Chu et al. (2002), and a good result was obtained at the magnetic material interface. The improved subgridding method has been proposed based on the traditional subgridding method by the introduction of the nonuniform grids and the application of the auxiliary magnetic fields to obtain the second order accuracy of the electric fields at the interface. But these methods can work only in the condition of planar interface, the case of dielectric surface still need to investigate. Q.H.Liu presented the ECT (enlarged cell technique) to solve the problem of the time reduction in the distortion grids in the conformal FDTD method. In this paper ECT is applied into the dielectric surface to improve the accuracy of the traditional staircase method. In the proposed method, the uniform grids are enlarged with some distance, and the enlarged distance is calculated by the Maxwell´s equation and Taylor´s series. The tangential electric fields at the interface can be obtained the second order accuracy. The numerical experiments are carried out to verify the better accuracy.