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

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.