Demonstration of time reversal methods in a multi-path environment

Time reversal methods (TRM) offer a unique opportunity for solving the problem of electromagnetic (EM) wave propagation and focusing in a spatially varying (inhomogeneous) medium. While the concept of time reversal is new to the field of EM wave propagation, it has been applied in the area of acoustics and ultrasonics for several years (Fink, M. and Prada, C., Inverse Problems, vol.17, p.R1-38, 2001). In any finite size array that occupies a limited spatial area, the system is diffraction limited; however in acoustics, it has been shown that, in an inhomogeneous medium, a time reversal array is not always diffraction limited and can achieve super-resolution. Basically, scatterers near the transmitting array and/or focal point act as an extension of the array in the focusing process. The paper shows that the same phenomenon exists for EM waves. While the feasibility of applying TRM to EM problems has been demonstrated, many issues must be investigated and resolved before TRM can be implemented practically in a communications or radar imaging system.