Appendix

Figure A1 shows mutual Z_G(ω) calculated with Pollaczek algorithm (Uribe et al., 2004), Gauss/Lobatto quadrature routine (Gander and Gautschi, 2000), Ametani method (Dommel, 1986) and complex depth formula (Saad, Gaba and Giroux, 1996) for the buried cable system shown in Figure 1, with x = 30 m and σ = 1 S/m.

It can be noticed from this figure that closed-form approximations behaves well at certain ranges, while the same situation occurs with direct numerical integration which oscillates at certain h, r, x, σ and ω values. Thus, a general assessment of approximate methods ofZ_G(ω) is still missing.