Equivalence and optimization of absorbing boundary conditions

Four types of absorbing boundary conditions (ABC) widely used in finite-difference time-domain (FDTD) simulations are discussed from the point of view of their equivalence. They include Mur´s (1981) ABC, dispersive ABC, Liao´s (1986) ABC and Higdon´s (1986) operator, and an analytical expression of Liao´s ABC is given. These ABCs are essentially equivalent and can be embodied by an analytical equation with variable factors. The absorbing performance of this equation is optimized through the appropriate choice of those factors