Time reversal in a waveguide: study of the temporal and spatial focusing

Temporal and spatial focusing properties of time-reversal mirrors (TRMs) are studied in a waveguide. The experiments are done using an ultrasonic TRM in an idealized waveguide. The width of the focal spot, and the spatial and temporal sidelobe levels are experimentally and numerically analyzed with respect to the characteristics of the waveguide-TRM system. An algorithm is developed to compute directly in the time domain the time-reversed field. This algorithm is based on the application of the mirror theorem to both the source and the TRM placed in the waveguide. Because time reversal is a stable and robust process, some of the ultrasonic results can be extended to ocean acoustics. Applications to underwater acoustic transmissions as well as ultrasonic medical imaging are discussed.