Time-reversed acoustics

Abstract

The objective of this paper is to show that time reversal invariance can be exploited in acoustics to create a variety of useful instruments as well as elegant experiments in pure physics.Section 1 is devoted to the description of time reversal cavities and mirrors together with a comparison between time reversal and phase conjugation. To illustrate these concepts, several experiments conducted in multiply scattering media, waveguides and chaotic cavities are presented in section 2. Applications of time reversal mirrors (TRMs) in hydrodynamics are then presented in section 3. Section 4 is devoted to the application of TRMs in pulse echo detection. A complete theory of the iterative time reversal mode is presented. It will be explained how this technique allows for focusing on different targets in a multi-target medium. Another application of pulse echo TRMs is presented in this section: how to achieve resonance in an elastic target? Section 5 explores the medical applications of TRMs in ultrasonic imaging, lithotripsy and hyperthermia and section 6 shows the promising applications of TRMs in nondestructive testing of solid samples.

Self-Averaging Scaling Limits for Random Parabolic Waves

“…The conditions of smoothness and having a compact support are unnecessary; they are assumed here in order to make simple the key estimate (Proposition 5,6,7,8).…”

Chaotic Time-Reversed Acoustics: Sensitivity οf the Loschmidt Echo to Perturbations

“…Considerable progress to measure the LE with classical waves has been made by the development of "time--reversal mirrors" for classical waves in acoustics [12,13] and electromagnetics [14][15][16]. Such mirrors collect and record a propagating wave as a function of time, and at some later time propagate it in the opposite direction in a time-reversed fashion.…”

New Results in Chaotic Time-Reversed Electromagnetics: High Frequency One-Recording-Channel Time-Reversal Mirror

“…One of these phenomena is the time-reversal mirror (TRM). If all of the wave excitations in a system can be captured on a closed surface, and if they can be time-reversed and re-injected into (569) the system, then the wave excitations will undo any phase changes and distortions that they suffered in time-forward propagation [1]. The TRM can be used to focus waves back to their point of origin, or to create excitations that converge on scattering centers located in an inhomogeneous medium [2].…”