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26 DESIGN007 MAGAZINE I FEBRUARY 2023 Light Maxwell described light as a propagating wave of electric and magnetic fields. More generally, he predicted the existence of elec- tromagnetic radiation—coupled electric and magnetic fields traveling as waves at the speed of light. Displacement current plays a vital role in the propagation of electromagnetic radiation, such as light and radio waves, through empty space. A traveling, varying magnetic field is associated with a periodically changing elec- tric field that may be conceived in terms of a displacement current. Maxwell's insight on displacement current, therefore, made it pos- sible to understand electromagnetic waves as being propagated through space completely detached from electric currents in conductors. e displacement current density term, appearing in Maxwell's equations, is the quan- tity ∂D/∂t that is defined in terms of the rate of change of D, the electric displacement field. Displacement current density has the same units as electric current density, and it is a source of the magnetic field just as the actual current is. However, it is not an electric current of moving charges, but rather a time-varying electric field. is implies that a changing elec- tric field creates a magnetic field, even with no charged particles in motion. In physical mate- rials (as opposed to vacuum), there is also a contribution from the slight motion of charges bound in atoms, called dielectric polarization. Displacement current explains how elec- tromagnetic energy propagates but is really just a fudge. Scientists have a creative way of accounting for what they do not compre- hend: ey add a constant. For instance, astro- physicists cannot explain why the universe is expanding when it logically should be con- tracting due to the attraction of gravity. ey then created "dark energy" to account for the force of expansion. Displacement current is just another "unexplained phenomenon" that accounts for current. Few theories in physics have caused as much confusion and misunder- standing as that of displacement current. ere are two types of current: 1. Conduction current is the net flow of charges at DC. is is what we tradition- ally think of as current flow. 2. Displacement current is the rate of change of the electric displacement field. It is not electron current flow but rather a time- varying electric field that creates a magnetic field along a transmission line mimicking current flow. Transmission Lines Dan Beeker stated that: "Field energy moving through a space is the current flow in a trans- mission line. e magic here is the displace- ment current flowing through the dielectric at the wave-front, along the transmission line. Fields do all the work. Current flow is a mea- sure of moving field energy through a space. Current flow occurs in the space between the conductors that bound the dielectric 2 ." Ralph Morrison summed it up beautifully: "Light energy can be directed by lenses; radar energy can be directed by waveguides and the energy at power frequencies can be directed by copper conductors. us, we direct energy flow at different frequencies by using differ- ent materials. We have learned how to control where we want the field energy to go. "e Laws of Physics apply to everything in the universe. If we accept the concept that Displacement current plays a vital role in the propagation of electro- magnetic radiation, such as light and radio waves, through empty space.