ABSTRACT
An essential point for elaborating a common approach to the inves-
tigation 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 beginning of non-stationary
behaviour. 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 the field of vision of 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, an
investigation of non-stationary electromagnetic phenomena should
be based on equations which 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.
