EM Waves in Coaxial Cable

Question

I've been educated that a coaxial cable has two conductors: inner or the central core and the outer conductor or the sheath. Both these carry currents but in opposite directions. The AC current produces Electromagnetic radiation that propagates in the form of a wave. The energy or the information(intelligence) is carried by the Electric and Magnetic fields. My query is that whether the EM waves propagate between the inner and the outer conductor or inside the inner copper (clad with steel) conductor? If so, does the EM wave travel along the dielectric insulation between the inner and outer conductor?

Ron Schmitt's "Electromagnetics Explained" tells that EM waves travel between the wires and not inside the wires. Does this also apply to a coax cable?

Answer 1

Yes, we normally assume electric field goes to zero inside a good conductor (otherwise very large currents would be produced). As Eugene says in comments, this provides a boundary condition when calculating the fields in the dielectric.

In a non-ideal conductor, the electric field does penetrate somewhat. The depth that it penetrates is called the skin depth, which depends on the signal frequency and the conductivity of the conductor. Calculating skin depth is important when determining the loss of the coaxial cable and how it varies with frequency.