Abstract (Invited)

 

A Comparison Between Time Reversal Mirrors and Phase Conjugated Mirrors

M.Fink (Laboratoire Ondes et Acoustique ESPCI, University Paris, Paris, France)

e-mail: mathias.fink@espci.fr

Time reversal symmetry holds for acoustic wave propagating in linear and non linear regime.  Based on this invariance, time reversal mirrors and phase conjugated mirrors have been built. In this lecture the fundamental differences between time reversal mirrors and phase conjugated mirrors will be emphasized.  To illustrate these concepts, several experiments conducted with time reversal mirrors and phase conjugated mirrors are presented.  They show that chaotic dynamics reduces the number of reversible transducers needed to insure an accurate time-reversal experiment.  Multiple scattering in random media and reverberation in chaotic cavities enhances resolution in time-reversal acoustics by making the effective size of time reversal mirrors much larger than its physical size.  Comparisons with phase conjugated experiments will show that this effect is typical of broadband time-reversed acoustics and is not observed in monochromatic phase conjugation.  Self averaging properties of time reversal experiments conducted in chaotic scattering environments will be emphasized.  Applications of this concept for telecommunications will be discussed.

 

Section : 10