Figure 1 : The principle of a dc concentrator.

From: Enhancement of Current Density by dc Electric Concentrator

Figure 1

(a) The current density vectors in the isotropic and homogeneous material illuminated by a planar source. (b) The current density vectors when a concentrator exists in the homogeneous background illuminated by the planar source, from which it is noticed that the currents are concentrated to the central region and enhanced. Here, the blue curves denote the current density vectors.