Time-reversed acoustics in random media and in chaotic cavities (Q2782724)

The authors use the time-reversal invariance in acoustics to accurately control wave propagation through media with chaotic ray dynamics. It is well known that, for every burst of sound \(p(r,t)\) diverging from a source, there exists in theory a set of waves \(p(r,-t)\) that precisely retraces all of many complex paths and converges in synchrony, at the original source, as if time were going backwards. In any propagation experiment, the acoustic sources and the boundary conditions determine a unique solution \(f(r,t)\) in a fluid. The goal, in time-reversal experiments, is to modify the initial conditions in order to generate the dual solution \(f(r,T-t)\), where \(T\) is a delay due to causality requirements. In this paper, the authors conduct several experiments with `time-reversal mirrors'. It is show that chaotic dynamics reduces the number of reversible transducers needed to ensure an accurate time-reversal experiment. The experiments presented in the paper are mainly two-dimensional. However, the results can be extended to three-dimensional configurations and to electromagnetic propagation through random and chaotic media.