Heaviside absorbing layer for a TLM mesh of symmetrical condensed node

Abstract

The transmission line matrix (TLM) method has been successfully applied to solve electromagnetic wave propagation, scattering and diffraction problems in the time domain. In order to truncate the computation region and avoid unwanted non-physical reflection, an absorbing boundary is needed. Several absorbing boundary conditions have been proposed. For the TLM mesh of symmetrical condensed nodes (SCN), the absorbing boundary is usually realized by terminating the link lines at the edge of the mesh in their own characteristic impedance so that the incident waves are absorbed completely. A so-called perfectly matched layer (PML) absorbing boundary condition was mentioned in Navarro et al. (see Elec. Lett., vol.30, p.1654-1656, 1994) for use with the FDTD method. One of the important characteristics of PML is that it possesses both electric loss and magnetic loss. Navarro et al. have shown that for a certain frequency range, the reflection coefficient of a PML of 20 cells thick can be as low as -60 dB. Arising from this absorbing boundary, a so-called Heaviside absorbing layer (HAL) is presented for use with the TLM method. It is shown that the HAL gives reduced wideband boundary reflection, as supported by dispersion analysis.