Coaxial cables are used to connect several types of electrical components. A coaxial cable consists of two thin concentric cylindrical conducting shells, here with radii and and length . The conducting shells carry equal currents in opposite directions. There is a magnetic field in the volume between the shells that is always perpendicular to the area of the rectangle, shown in cyan (see it by rotating using the control for the angle ). The magnetic flux, self-inductance , and total stored energy can be calculated by integrating each differential strip along the radius .
The self inductance is and the total stored energy is , where is the permeability of free space.