Abstract

Time-reversal invariance, a fundamental symmetry that holds nearly everywhere in microscopic physics, can be exploited in a unique way in Acoustics, to create a variety of useful instruments. In the past years, taking advantage of the reversibility of the acoustic propagation that holds in many situations (to the extent that everything is adiabatic) time reversal mirrors (TRMs) have been developed that create time reversed waves. Acoustic reversibility means that, for every burst of sound diverging from a source- and possibly reflected, refracted or scattered by any complex media- there exists in theory a set of waves (the time-reversed waves) that precisely retraces all of these complex paths and converges in synchrony, at the original source, as if time were going backwards. Therefore, an acoustic TRM refocuses an incident acoustic field to the position of the original source regardless of the complexity of the medium between the TRM and the "probe" source.

© 2005 Optical Society of America