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Current distribution cAlculations Antenna design and simulations Current distributions on metallic plates Inverse scattering simulations Experimental inverse scattering
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Ultra-Wideband Microwave Imaging Radar System
This system has been developed for non-destructive evaluation
(NDE) of metallic or dielectric objects and shows a super-resolution
capacity.
Super-resolution refers to the resolution which is better than the
Rayleigh Criterion.
Tomographic techniques can provide super-resolution from a full viewing angles of target
data collection. However, resolution tends to degrade to the Rayleigh resolution with
limited viewing angles data collection.
Spectral estimation is another method by which super-resolution can be achieved. The
spectral estimation and tomographic techniques produce super-resolution based on the
spatial-frequency bandwidth. However, they do not take multiple scattering effects into
account.
Introduction In the beginning of the 1990s, a nonlinear inverse scattering imaging algorithm, namely the distorted Born iterative method (DBIM), which accounts for both diffraction and multiple scattering effects was developed and implemented for both CW and transient excitations. For the transient case, a finite-difference time-domain (FDTD) algorithm is used as the forward solver. In the DBIM, the background medium is not constrained to be homogeneous and is updated at each iteration.
The super-resolution phenomenon in nonlinear inverse scattering has been reported
previously using numerically simulated data. What was shown was the ability of a nonlinear
inverse scattering method to resolve features that are much less than half a wavelength,
the criterion dictated by the Rayleigh criterion. The phenomenon was attributed to the
multiple scattering effect within an inhomogeneous body. The high spatial frequency (high
resolution) information of the object is usually contained in the evanescent waves when
only single scattering physics is considered. Multiple scattering converts evanescent
waves into propagating ones and vice versa. Hence, in an inverse scattering experiment,
even though an object is interrogated with a propagating wave, and that only scattered
waves corresponding to propagating waves can be measured, the scattered waves contain high
resolution information about the scatterer because of the evanescent=propagating waves
conversion in a multiple scattered field. therefore, an inverse scattering method that
unravels multiple scattering effects can extract the high resolution information on a
scatterer.
Experimental Setup
The inverse scattering experimental setup is based on a time-domain ultra-wideband radar
imaging system recently developed at the CCEM. The system consist of a Hewlett-Packard
(HP) 54120B digitizing oscilloscope mainframe, an HP 54121A 20GHz four-channel test set, a
Picosecond Pulse Lab (PSPL) 4050B step generator, a PSPL 4050RPH remote pulse head, two
PSPL 5210 impulse forming networks, a switched Vivaldi antenna array, two ultra-wideband
amplifiers and two microwave switches. The Vivaldi antenna array consists of 5
transmitting antennas and 6 receiving antennas
The system is automated and controlled by a computer via the IEEE-488 bus.
By moving your mouse here and you will get a slide presentation of the system and the inverse scattering algorithm used for the reconstructions. The above work is a collaboration between Dr. FuChiarng Chen and Prof. Weng Cho Chew. Please send suggestions, comments, and inquiries to: fchen@sunchew.ece.uiuc.edu.
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