Wiring Up Displacement Currents

Realizing that conduction currents couldn’t sufficiently explain the behavior of capacitors, Maxwell postulated the existence of displacement currents and changed the face of electromagnetics forever. Conduction currents (Jf ) involve the transport of “free” electrical charges, and in Ampere’s law (∇×H = Jf ) they are the sole source of curled magnetic fields. Maxwell realized that time-varying displacement fields (D = εE) are also a form of current (JD = ∂D/∂t). His correction to Ampere’s law underpins the electromagnetic wave phenomena central to photonics and befuddles physicists who work in high-speed electronics. As microchip engineers try to cram greater numbers of faster wires into smaller volumes, for instance, inevitable and undesired displacement currents leech power, generate cross talk, and distort the delicate timings within circuits [1]. Can displacement currents be corralled with the level of ease associated with conventional low-frequency wiring? In a paper in Physical Review Letters, Brian Edwards and Nader Engheta from the University of Pennsylvania, Philadelphia, take a serious step in this direction with an experimental demonstration of displacement current wiring [2] (see also the authors’ video abstract).