ABSTRACT
An essential point for elaborating a common approach to the investigation of transient electromagnetic phenomena is the evolutionary character of such phenomena, and an initial moment, when the non-stationary condition starts, takes an important meaning. The introduction of the non-stationary initial moment is dictated in many cases by a necessity to separate the moment of “switching on” the field and the moment of the non-stationary behavior beginning. The non-stationary state, which starts at some definite moment of time, is accompanied by the appearance of a transient (non-harmonic) field. These so-called “transients” can exist for a long time, being a significant part of the total field. However, they fall out of view in a stationary approach when all periodic processes are assumed to start at the infinite past. It should be noted that the commonly used approximation of an adiabatic “switching on” of a process at the infinite past can easily lead to indefiniteness in the problem formulation because of the irreversibility of the non-stationary phenomenon. Therefore, 10an investigation of non-stationary electromagnetic phenomena should be based on equations that include a general representation of the medium parameters, where an inhomogeneity has a time-dependent shape and time-dependent medium properties inside it. A mathematical approach to the theory of transient electromagnetic phenomena should contain a description of both continuous and abrupt changes of both the field functions and the medium parameters. This technique also has to take into account the correlation between spatial and temporal changes in the media. Such a correlation occurs, for example, when a medium boundary moves in space. In this case, a sharp time-jump of the medium parameters occurs at every fixed point passed by the medium boundary.
