Hole inductance in braided cable shields

The shielding effectiveness of metal braids of cables is governed by the geometry and the materials of the braid. The shielding effectiveness can be characterised by the transfer impedance of the metal braid. Analytical models for the transfer impedance contain in general two components, one representing diffusion of electromagnetic energy through the metal braid, and a second part representing leakage of magnetic fields through the braid. The second part is a local phenomenon, which again has three parts: hole inductance, braid inductance and skin inductance. The hole inductance is governed by the penetration of magnetic fields through the apertures of the braid. Well-known analytical models overestimate the contribution of the hole inductance by a factor two. This can be easily corrected by multiplying the hole inductance terms by a factor (2/π)^3/2.