CONSTRUCTION OF THE ABSORBING BOUNDARY-CONDITIONS FOR THE FDTD METHODWITH TRANSFER-FUNCTIONS

The absorbing boundary conditions (ABC's) are essential to terminate t he computational space when the finite-difference time-domain (FDTD) m ethod is applied to analyze electromagnetic (EM) problems. With the AB C's, the fields on the truncated boundaries are evaluated by the inter ior fields. In this paper, the relationship between the fields on the terminated boundaries and the interior fields is expressed as the tran sfer functions in the Z-domain. The proper transfer functions are dete rmined from the radiation condition or the transmission condition. Sim plifying these transfer functions into rational functions, we obtain d ifferent schemes of the ABC's. In this paper, both the transfer functi ons and coefficients of the final ABC's are derived and expressed as r ecurrence formulas for the convenience of programming. This method has the property of simplicity and flexibility. The ABC's obtained by thi s method show good absorbing performance and numerical stability in th e practical applications.