Detection of an object in a reverberant environment using direct and differential time reversal

In this paper we investigate by numerical simulation
the effect that various size metal objects placed within a
reverberant environment have on spatial and temporal focussing
when differential and non-differential time reversal is applied. A
direct then a differential time reversal method at 2.4 GHz under
RF pulse excitation is discussed. The results show spatial
compression is achieved to within a radius of λ/2 distance around
the source position and width of the compressed pulse remains
constant regardless of the time reversal method and size and
position of the cluttering elements. The use of the differential time
domain method is preferential when small objects are detected as
they occur away from direct line of sight between the transmitter
and time reversal mirror. Such objects induce higher magnitude
changes then when the direct time reversal method is used. It is
also shown that the presence of such inclusions cannot be easily
identified through calculation of the RMS delay spread of the
object loaded cavity. This implies that the differential time
domain method would be useful for non-invasive identification of
dynamically evolving changes within a reverberant environment,
e.g. for crack detection in pipes.