  It is demonstrated in this paper that the propagation of the electric wave
field in a heterogeneous medium in 3D can sometimes be governed well by a
single PDE, which is derived from the Maxwell's equations. The corresponding
component of the electric field dominates two other components. This justifies
some past results of the second author with coauthors about numerical solutions
of coefficient inverse problems with experimental electromagnetic data. In
addition, since it is simpler to work in applications with a single PDE rather
than with the complete Maxwell's system, then the result of this paper might be
useful to researchers working on applied issues of the propagation of
electromagnetic waves in inhomogeneous media.
