Highly resolved detection and selective focusing in a waveguide using the DORT method

The D.O.R.T. method (French acronym for Decomposition of the Time Reversal Operator) is a scattering analysis technique using an array of transducers. The method is effective to achieve detection and selective focusing on poi ntlike scatterers through inhomogeneous media [J. Acoust. Sec. Am. 99, 2067 -2076 (1996)]. Laboratory measurements in a water waveguide are presented. Taking advantage of the multiple reflections at the interfaces of the guide , high resolution is achieved with the D.O.R.T. method. The separation of t wo scatterers and the selective focusing are obtained with a transverse res olution at least nine times better than the free-space limit prediction. Th e detection of a scatterer from the water/air interface of the guide is als o achieved with high resolution (1/20 of the free space diffraction spot). The effect on the D.O.R.T, method of surface waves produced at one interfac e of the guide is measured. Finally, the impulse response function of each scatterer to the array is computed as a combination of the eigenvectors of the time-reversal operator obtained at each frequency. Using these impulse Green's functions, selective focusing with high temporal and spatial compre ssion is performed. (C) 1999 Acoustical Society of America. [S0001-4966(99) 00505-6].