Accurate Computation of Internal Impedance of Two-Layer Cylindrical Conductors for Arguments of Arbitrary Magnitude

Formula for per-unit-length internal impedance of two-layer cylindrical conductors is derived and then upgraded from the standpoint of numerical stability and performance. The proposed formula consists of combinations of modified Bessel functions of the first and second kind, which are better suited for dealing with larger function parameters. Modification of the derived internal impedance formula and a different approach in solving modified Bessel functions produce an algorithm that is numerically stable and highly accurate for arguments of arbitrary magnitude.