Time reversal techniques for multitarget identification

Since the seminal paper by M. Fink et al., time reversal is a subject of very active research. The main idea is to take advantage of the reversibility of wave propagation phenomena such as it occurs in acoustics, elasticity or electromagnetism in a non dissipative unknown medium to back-propagate signals to the sources that emitted them. Number of industrial applications have already been developed: touchscreen, medical imaging, non destructive testing and underwater communications. However, the resolution of these applications is restricted by the diffraction limit. We have designed a method named TRAC (Time Reversed Absorbing Conditions) that enables to go far beyond the diffraction limit without knowing the physical properties of the targets. We present here two examples of applications for multitarget identification.