Consider an infinitely long, straight coaxial cable consistingof a homogeneous cylindrical center conductor with radius a and asurrounding conductive tube (shield) with inner radius b.
The space between the center conductor and the screen is filledwith a dielectric with er (epsilon r) = 1. In the innerconductor, a direct current I is distributed evenly over the crosssection. In the outer conductor there is a corresponding returncurrent. On the surface of the inner conductor there is a constantsurface charge density Ρs,1 which determines how thepower is transported in the cable.
(On the inside of the screen there is a corresponding constantsurface charge density Ρs,2= -a / b * Ps,1)
Determine the Poynting vector S =E x H for the cable.
Neglect the center conductor and the screen resistivities.
Tip: Calculate S and H in '' Normal '' way.
