Time reversal techniques obtain increased resolution by exploiting scattering and multipath in propagation through inhomogeneous channels. Time reversal has been used by Fink and collaborators to achieve super-resolution focusing in acoustics, [Fink, Prada, Wu, Cassereau, 1989,Fink, 1997] as demonstrated by their work with controlled ultrasonic experiments in water tanks. More recently large-scale acoustics experiments in the ocean have confirmed the resolution ability of time reversal, [Kuperman, Hodgkiss, and Song, 1998,Song, Kuperman, Hodgkiss, Akal, and Ferla, 1999]. In our work, we study matched field detection with time reversal in the electromagentic (EM) domain. In classical matched field processing (MFP), in the acoustical domain, e.g., [Baggeroer, Kuperman, Mikhalevsky, 1983], detailed modeling of the channel is used to predict the field as received by an array of sensors, after the wavefield propagates through an inhomogenous channel. MFP, in simple terms, solves an inverse problem (source detection or location) by steping through a sequence of forward problems, where in each forward problem the unknown location of the source is postulated at each one of potential positions. Practical implementation of MFP implies the solution of the wave equation for each forward problem assuming a given channel velocity propagation profile and given boundary conditions. This is computationaly demanding and requires good knowledge of the environmental conditions, both of which make MFP an expensive, sensitive solution for many practical problems. Time reversal provides a very good alternative to MFP, since it avoids the detailed modeling of the channel, while still providing the potential gain from matching to the propagated field, rather than matching to the original transmitted wavefield. In a sense, time reversal provides the actual channel Greens’ function, in contrast with MFP where the channel Greens’ function is computed from the model.

Work sponsored by DARPA DSO Advanced Mathematics Computational Program Initiative on Time Reversal Imaging through Army Research Office grant ARO W911NF-04-1-0031.

Collaborators

Faculty collaborations in this project:

• Dan Stancil, stancil@ece.cmu.edu
• Jian-Gang (Jimmy) Zhu, jzhu@ece.cmu.edu

Staff researcher affiliated with this project:

• Yuanwei Jin, (post-doc, then research engineer, in Time Reversal, 2004-2008, now Assistant Professor at University of Maryland Eastern Shore) [web]

Students collaborating in this project:

• Ahmet Gurkan Cepni (graduated, 2006, Dan Stancil)
• Yi Jiang, yij@andrew.cmu.edu (graduated February 2008, Jimmy Zhu, now at Apple)
• Ben Henty (graduated, 2006, Dan Stancil)
• Nicholas O’Donoughue (José M. F. Moura)