Spatial focusing of a one-channel time-reversal acoustic mirror in an underground water storage tank at audible frequencies

We performed a one-channel time-reversal acoustic mirror for a wide-band (30 Hz to 20 kHz) impulse in a 30 × 5 meters (diameter X height) empty cylindrical tank made of concrete, with columns and beams. The time-reversed pulse (or equivalently, the autocorrelation of the impulse response) peaks 30 dB above the temporal sidelobes. We measured the two-dimensional spatio-temporal focusing pattern of the time-reversal process with a 7.5 cm grid resolution and observed a circular converging/diverging wave. The wide-band time-reversed pulse peak decays at the level of the sidelobes around 70 cm away from the focusing point. We also analyzed this focal spot width as a function of frequency and compared the results with a numerical simulation of the cavity using a finite element method.