A time-reversal mirror with variable range focusing

Recently a time-reversal mirror ~or phase-conjugate array! was demonstrated experimentally in the ocean that spatially and temporally refocused an incident acoustic field back to the original position of the probe source @Kuperman et al., J. Acoust. Soc. Am. 103, 25–40 ~1998!#. Here this waveguide time-reversal mirror technique is extended to refocus at ranges other than that of the probe source. This procedure is based on the acoustic-field invariant property in the coordinates of frequency and range in an oceanic waveguide @Brekhovskikh and Lysanov, Fundamentals of Ocean Acoustics, 2nd ed. ~Springer-Verlag, Berlin, 1991!, pp. 139–145#. Simulations are combined with experimental data to verify this technique. © 1998 Acoustical Society of America. @S0001-4966~98!03106-3#