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.