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Imaging objects present in a cluttered medium

The detection and the characterization of objects using electromagnetic waves as probing field is of great interest in many areas, such as non invasive testing, medical imaging or subsoil probing. In most applications, the imaging issue is made difficult by the inhomogeneities of the natural medium that blur the signature of the targets. Moreover, the emitting and receiving antennas are generally located only on one side of the investigation domain so that the information obtained from the response of the medium to the wave excitation is spatially limited. To solve this problem we couple a non-linear inversion method to an eigenvector analysis of the Time Reversal Operator (DORT technique) for imaging the targets.

In this web page we present a brief overview of our research in characterization of targets buried in a natural medium. For more details on each topic have a look at the references.

The pdf files of the references can be downloaded from my webpage.

Imaging of targets buried in a cluttered medium using an hybrid Inversion-DORT method
Three-dimensional imaging of targets buried in a cluttered semi-infinite medium

Imaging of targets buried in a cluttered medium using an hybrid Inversion-DORT method

We consider an infinite homogeneous lossless medium of permittivity. The targets under study are defined by their relative permittivity. They are surrounded by an inhomogeneous medium. A two-dimensional array of N crossed-dipole monochromatic antennas lying in a plane above the targets is used to illuminate and observe the scene. This configuration resembles that which is encountered in the detection of buried objects, see figure below on the left side. The middle figure shows the Iso-surface of the reconstructed permittivity profile using the Inversion-DORT procedure and left figure shows the Iso-surface of the reconstructed permittivity profile with classical inversion procedure. It is clear from the figures that the Inversion-DORT procedure permits to avoid the ghosts that are present around the targets in the classical reconstruction.


Reference :

  • T. Zhang, P. C. Chaumet, E. Mudry, K. Belkebir and A. Sentenac Electromagnetic wave imaging of targets buried in a cluttered medium using an hybrid Inversion-DORT method, Inverse problems 28, 125008 (2012). pdf

Three-dimensional imaging of targets buried in a cluttered semi-infinite medium

The poor impedance matching between the antennas and the host medium limits significantly the effective numerical aperture of the imaging system. To reconstruct the targets, we propose to combine the DORT method with an iterative inversion technique and a frequency hopping procedure. Numerical experiments show that this approach permits the reconstruction of the targets even when they are located in a highly cluttered medium.

Figure below shows the permittivity reconstruction obtained by the DORT Hybrid method when the targets are placed in a homogeneous semi-infinite medium. (a) and (c) only one frequency (λ) is used and (b) and (d) the frequency hopping procedure (with three frequencies : 3λ ; 1.5λ ; λ) has been applied.


Reference :

  • T. Zhang, P. C. Chaumet, A. Sentenac and K. Belkebir,
    Three-dimensional imaging of targets buried in a cluttered semi-infinite medium, J. Appl. Phys. 114, 143101 (2013). pdf