On the Nature of Retarded Potentials and Radiation Mechanism in Electromagnetics - Physical and Philosophical Aspects

Dragan Poljak, Ph.D. Professor
Faculty of Electric Engineering, Mechanical Engineering and Naval Architecture, University of Split, Croatia

Mirko Jakić, Ph.D. Professor
Faculty of Humanities and Social Sciences, University of Split, Croatia

From a microscopic viewpoint of classical electromagnetism a radiation phenomenon occurs due to electric and magnetic field in the far zone generated by a a point charge moving with nonrelativistic velocity and related acceleration. The power radiated by the particle depends on the acceleration squared, so the higher the acceleration the higher is the amount of radiated power. However, the accelerated ellectrons resist and radiate energy away in the form of electromagnetic waves, but do not radiate as much energy as it is needed to push them into the conductor. This form of resistance is referred to as radiation resistance and it is related to the acceleration causing radiation. Therefore, the radiation resistance exists due to interaction of the electron with something. Possible approach to solve this problem is based on introducing an additional force - the retardation force, an inertial force being proportional to charge acceleration. The macroscopic viewpoint deals with retarded potentials over current densities, rather than with charged particles, thus resulting in the integral equations for the unknown current distribution flowing along thin wire structures. In antenna theory and engineering practise, instead of moving charges one rather considers the currents flowing along the antennas thus generating radiated power. Also, one rather deals with the concept of radiation resistance defined via the time–average radiated power and the squared current at antenna input terminals, instead of radiation reaction force. Some illustrative computational examples are given in this work.