Detection and Electromagnetic signature of hidden objects for transportation hubs and infrastructure security

The progresses in the area of Computational Electromagnetics, together with the cost reduction and continuous increase of the computational speed and power of modern computers, have contributed to the development and diffusion of numerical codes for the analysis and design of complex electromagnetic structures and systems. However, the way by which the available numerical techniques and codes deal with electromagnetic field singularities is completely unsatisfactory. Geometrical discontinuities of the physical structures, such as wedges and tips, as well as abrupt material discontinuities can heavily affect the electromagnetic fields, to the point to render the usual computational models inappropriate. In the neighborhood of sharp wedges and tips the electromagnetic fields could have singular (i.e., going to infinity) behavior and, for conducting structures, also the induced current and charge densities could be singular. The singular behavior depends on the geometrical and material parameters so that, in practice, one is faced with a wide variety of singular behaviors. For ultra-wideband (UWB) near-field imaging applications, it is of importance to numerically model this singular behavior in order to develop and validate the techniques used to track the diffracted field.
The UWB near-field imaging is expected to become an essential tool in providing airport security and other transportation system hubs security, via efficient screening of luggage and passengers. Numerically rigorous analysis of scattering is essential to the task of imaging in order to provide accurate data that allows testing and calibration of inherently approximate imaging algorithms. The imaging algorithms we intend to develop on a longer period of time necessarily require reliable and accurate forward solutions and back-propagation schemes.

Novel aspects of this project
The novel direct frequency and time domain (TD) solvers based on the Non-uniform Grid (NG) approach for analysis of scattering by arbitrary shaped objects embedded in complex environments will allows treatment of large problems of practical interest. In this method the computational savings are achieved since the fields are not computed directly like in the conventional techniques such as the method of moments. Rather the fields are computed first on NGs and subsequently interpolated at a much lower computational cost to the target points. The best efficacy will be achieved by performing the computations in a multilevel fashion using a hierarchy of NGs.

Research topics
The Politecnico di Torino project is subdivided into two Topics.

• TOPIC I - deals with the development of new numerical methods and one new fast-solver code to evaluate the electromagnetic field scattered by dangerous objects concealed in complex environments. The "objects" of interest could contain wire or wedge structures made of different electromagnetically impenetrable or penetrable media. The numerical method to be considered is the Method of Moments. We intend to develop a novel Non-uniform Grid (NG) approach to address analysis of scattering by electrically large structures. The techniques and the numerical codes will be assessed and validated by considering several reference problems, as well as the results obtained from measurements (the experimental activity will be carried out by the Italian National Research Council (CNR) research unit).
• TOPIC II - deals with asymptotic as well as new analytical and approximate-analytical methods to evaluate electromagnetic fields in regions of impenetrable or penetrable wedges immersed in arbitrary linear complex media. The results relative to the structures that define the canonical problems to be studied in Topic II will also be used to validate the numerical results obtained in Topic I.