Ch. Pichot

Microwave Diffraction Tomography for Biomedical Applications

This short paper points out the realizability of a method suitable for quasi real-time coherent microwave tomography for biomedical applications.

A new regularization scheme for inverse scattering

The reconstruction of the complex permittivity profile of inhomogeneous objects from measured scattered field data is a strongly nonlinear and ill-posed problem. Generally, the quality of the reconstruction from noisy data is enhanced by the introduction of a regularization scheme. Starting from an iterative algorithm based on a conjugate gradient method and applied to the nonlinear problem, this paper deals with a new regularization scheme, using edge-preserving (EP) potential functions. With this a priori information, the object to reconstruct is modelled with homogeneous areas separated by borderlike discontinuities. The enhancement is illustrated throughout some examples with noisy synthetic data.

Conjugate-Gradient Method for Soliving Inverse Scattering with Experimental Data

The reconstruct of the complex permittivity profile of lossy dielectric objects from measured far-lied data is considered, with application to perfectly conducting (PEC) objects. From an integral representation of the electric field (EFIE), and applying a moment-method solution, an iterative-reconstruction algorithm based on a conjugate-gradient method, is derived. In order to start the iterative procedure with an initial guess, a back-propagation scheme is used. For testing the algorithm on real, measured data, the reconstruction of two PEC (cylinder and strip) objects is presented.

Planar microwave imaging camera for biomedical applications: Critical and prospective analysis of reconstruction algorithms

This paper is dealing with the biomedical applications of active microwave imaging. As a result of extensive preliminary evaluations conducted by means of a 2.45-GHz planar camera, it has been proven that active microwave imaging is able to provide a very sensitive means of investigation in such applications. While technological problems have been conveniently solved, the main problem still remains to determine the most efficient way to process the measured data in order to get the best quality of the reconstructed images. Until now, diffraction tomography algorithms based on a spectral approach have been used. The main limitations of this approach and some attempts to reduce them are analyzed. A more prospective discussion allows to identify the most promising reconstruction techniques. Among them, iterative space-domain formulations appear to provide a suitable base for achieving quantitative imaging thanks to a convenient use of the available a priori information.

Inversion algorithm and measurement system for microwave tomography of buried object

The detection and identification of buried inhomogeneities using electromagnetic waves are of crucial importance for many applications. The paper deals with reconstructed images from measurements using an inversion qualitative algorithm for microwave tomography. The algorithm is based on diffraction tomography for detecting and locating buried objects. The backscattered field is measured at different frequencies over a probing line above or in contact with the soil at different receiver locations and for different positions of a transmitting antenna (multistatic configuration). The reconstruction algorithm processes the backscattered field generated by the buried inhomogeneities and incorporates the incident near-field distribution transmitted in the soil by the broadband antenna. Tomographie reconstructions of buried objects are presented for a situation of practical interest using bow tie antennas in the frequency band [0.3–1.3] GHz.

Foreign Objects Debris Detection (FOD) on Airport Runways Using a Broadband 78 GHz Sensor

This paper describes a compact broadband (73-80 GHz) mm-Wave front-end used for FOD detection application. The design philosophy of our system is to have several low-profile, low-cost mm-Wave sensors placed along the runway. Tests were conducted on the small airport of Aix Les Milles (south of France). High sensitivity and simultaneous objects detection capabilities were shown. Even very small objects like nuts were seen. The extension of the actual detection range is needed in order to go from 110 m (in the most favourable case) to 500 m.

A Microwave Diffraction Tomography System for Biomedical Applications

This paper describes a 3 GHz experimental set-up for quasi real time tomography of biological media. Experiments on animal organs illustrate the main features of this imaging process.

Microwave Tomography System for Reinforced Concrete Structures

This paper is devoted to a new imaging technique for the Non-Destructive Testing (NDT) of civil engineering structures such as bridges. This technique uses microwave radiation to interrogate the concrete medium in a reflection mode configuration. The backscattered electromagnetic field, generated by the presence of the rebars, is measured with a linear sensor probe array and processed numerically in order to provide tomographic images of the volume under investigation. A compact prototype of a so-called Microwave Camera operating in the microwave X-band region between 7-13 GHz with frequency diversity is presented. Computer simulations for theoretical performance limit study as well as experimental performance, evaluation of the prototype have been conducted on reinforced concrete slabs with practical configurations and on a bridge beam. The performance has been compared with that of magnetic metal detectors which are available on the market.

Radiofrequency conical emission from femtosecond filaments in air

We show that the broadband conical emission associated with filaments in air extends down to the radiofrequency region. This rf emission which originates from the longitudinal oscillation of charged ions formed during filamentation is strongly enhanced by the presence of a longitudinal static electric field.

Conjugate-gradient algorithm with edge-preserving regularization for image reconstruction from Ipswich data for mystery objects

This paper presents some evidence of the effectiveness of adding edge preserving (EP) regularization to the conjugate radient (CG) method, in reconstructing the shape and permittivity profile of dielectric objects. Without any a priori information, our CG algorithm is also still efficient, and succeeded in reconstructing two mystery targets. As the two targets are now known, we hope we can greatly enhance the reconstruction quality by choosing better values for the calibration factors, and by applying our EP regularization to these data.