Table of Contents
International Journal of Microwave Science and Technology
Volume 2011, Article ID 425710, 14 pages
Research Article

Time Reversal in Subwavelength-Scaled Resonant Media: Beating the Diffraction Limit

Institut Langevin, Ecole Supérieure de Physique et de Chimie Industrielle de la Ville de Paris, UMR CNRS 7587, 10 Rue Vauquelin, 75005 Paris, France

Received 14 December 2010; Revised 5 April 2011; Accepted 15 June 2011

Academic Editor: M. C. E. Yagoub

Copyright © 2011 Fabrice Lemoult et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Time reversal is a physical concept that can focus waves both spatially and temporally regardless of the complexity of the propagation medium. Time reversal mirrors have been demonstrated first in acoustics, then with electromagnetic waves, and are being intensively studied in many fields ranging from underwater communications to sensing. In this paper, we will review the principles of time reversal and in particular its ability to focus waves in complex media. We will show that this focusing effect depends on the complexity of the propagation medium rather than on the time reversal mirror itself. A modal approach will be utilized to explain the physical mechanism underlying the concept. A particular focus will be given on the possibility to break the diffraction barrier from the far field using time reversal. We will show that finite size media made out of coupled subwavelength resonators support modes which can radiate efficiently in the far field spatial information of the near field of a source. We will show through various examples that such a process, due to reversibility, permits to beat the diffraction limit using far field time reversal, and especially that this result occurs owing to the broadband inherent nature of time reversal.