We extend the volume conductor in the direction of the y-axis in both directions so that it forms a cylinder limited by two planes in the zx direction and having the cross section of the original volume conductor (Figure 11.27B).
Then we plate the end planes of the cylinder with a well-conducting material. If electrodes are connected to these plates and a reciprocal current is fed to them, an ideal lead field is created in the volume conductor (Figure 11.27B).