Exact ABC's have the advantage of giving accurate results, but since they are non-local, they are computationally expensive. Such approaches have been investigated by Ziolkowski et al. [29], Olivier [30], De Moerloose and De Zutter [31], and Tromp and Olivier [32]. In 1992 Mei and Fang [33] proposed a technique, superabsorption, which can be applied to many absorbing boundary conditions to improve their performance. In certain applications, such as the termination of a waveguide or a microstrip, dispersive boundary conditions have been used [34,35,36,37,38,39]. Lastly, many researchers, including Fang [10], Blaschak and Kriegsman [40], Moore et al. [41], Railton and Daniel [42], and most recently Andrew et al. [43], have compared the accuracy of various ABC's. Comparative studies of the accuracy of ABC's have also been performed for dispersive media [44,45].