Speaker:
Fernando L. Teixeira
Associate Professor 
Ohio State University 
Columbus, OH, USA
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http://www.ece.osu.edu/~teixeira

Date: Monday December 22, 2008 
Time: 1:00 – 3:00 pm 
Location: Main NU Building (B2) – Auditorium. 

Abstract

The invariance of the wave equation under time-reversal (TR) enables optimal refocusing of time-reversed signals. This can be achieved using a TR antenna array (a special kind of MIMO radar), where received signals due to a (possibly unknown) scatterer(s)/source(s) are retransmitted back to the original media in a time-reversed fashion. As the time-reversed signals backpropagate in the medium, they interfere constructively (due to phase conjugation) at the original source position(s). Under certain conditions, the focusing resolution obtained by TR techniques can outperform the classical diffraction limit, characterizing super-resolution.  A further advantage of TR techniques is that they are statistical stable under ultrawideband (UWB) operation.

We discuss and illustrate TR techniques for the remote sensing of subsurface objects. We consider the decomposition of the time-reversal operator to provide selective focusing in scenarios where the background (e.g., soil) media is modeled by continuous random medium models with prescribed first and second order statistics, and possibly including frequency dispersive effects. Since frequency-dispersion breaks the TR invariance, several compensation methods for dispersive effects are compared. Noise sensitivity and spatial spectra of the eigenvalues (and corresponding excitation eigenvectors) are used as a criterion to distinguish (distributed) background clutter eigenvalues from those of discrete scatterers. The advantages of polarimetric operation are also considered.  

Biography 

Fernando L. Teixeira is an Associate Professor with the Department of Electrical and Computer Engineering at The Ohio State University. He received the Ph.D. degree in electrical engineering from the University of Illinois at Urbana-Champaign and did post-doctoral work at Massachusetts Institute of Technology. His research interests include computational electromagnetics/optics, inverse scattering, and study of wave and transport phenomena for remote sensing applications. Dr. Teixeira has authored over 90 journal articles in those areas and currently serves as Associate Editor for the IEEE Antennas and Wireless Propagation Letters. He has received a number of  prizes for his research, including the CAREER Award from the National Science Foundation in 2004 and the triennial Booker Fellowship from the International Union of Radio Science in 2005.