 Time reversal acoustics

Time reversal acoustics uses recorded sound to send a field back toward the region that originally emitted it. An array of acoustic transducers records a pulse at multiple positions, reverses each recording in time, and emits the reversed signals from the corresponding positions. In a stationary reciprocal medium, the different paths can then contribute coherently near the original source.

A laboratory demonstration places a short-pulse source in a tank, records it at an array, removes or silences that source, and re-emits the reversed records. Mapping the returning pressure pulse tests the refocusing directly. Multiple propagation paths need not prevent focusing if they remain stable and are recorded; they can supply additional path diversity. Finite recording duration, limited bandwidth, incomplete spatial coverage and acoustic attenuation limit the reconstruction. Reversing recordings therefore implements a particular wave-control experiment, rather than undoing every dissipative process in the medium.