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Electromagnetic Inversion of Amplitude-Only Data Through a Two-Step Strategy
No full textIn the following contribution an innovative two step strategy for the inversion of amplitude-only data in microwave imaging applications is presented. At the first step an inverse source problem is solved for computing the incident field in the investigation domain. Then, in the successive step, an iterative multi-resolution method combined with an evolutionary optimiser is applied in order to extract the reduced amount of information of the problem at hand. Some numerical and experimental results show the effectiveness and the limit of this technique. This is the author's version of the final version available at IEEE
Enhancement of the Contrast Source Inversion Method Using Fuzzy Logic
No full textThe problem of determining the proprieties of an unknown object by means of electromagnetic waves probing the object is intrinsically instable with respect to the presence of noise and measurement errors on scattering data. In several practical condition in the framework of medical imaging, non-destructive testing, and sub-surface inspection, these errors are unavoidable and the ill-posedness of the system leads to inaccurate reconstructions of the scenario under test. In [1], an innovative fuzzy-logic-based strategy has been proposed for properly taking into account the presence of the noise and errors on the data. Such a system provides, in an unsupervised way, two series of coefficients that can be used as weighting parameters of the arising cost function to be minimized. In that paper, the mathematical formulation was presented considering the contrast and the fields equations. In this work, a further assessment of the proposed fuzzy-logic approach is carried out operating with data and state equations expressed in terms of the contrast and the contrast sources as suggested in [2]. Selected results from the numerical simulations are reported to assess the performances of the system with single and multi-frequency data with and without total-variation-based regularization. This is the author's version of the final version available at IEEE
Effective Exploitation of the Information Content of Noisy Data in Inverse Scattering Problems: a Fuzzy-Logic-Based Strategy
No full textOne of the main drawbacks when dealing with inverse scattering problems is their intrinsic ill-conditioned nature, emphasized by the presence of the noise in the measured data. The proposed fuzzy system allows to take into account the corrupted nature of the data in a simple and effective way. The effectiveness of the proposed inversion strate4gy is shown by comparing the achieved results with those obtained with state-of-the art inverse scattering techniques
Clues of Personal Events in Online Photo Sharing
No full textThere is currently a trend in media management and the semantic web to develop new media processing methods and knowledge representation techniques to organise and structure media around events. While this increased interest for events as the central aggregator when organising media is supported by strong research in the fields of knowledge representation and computer vision; it is not yet clear how the digital era users use events when sharing their personal media collection. In this paper, we explore how users share photos online and discuss the results of a preliminary automatic processing of the data collected. We show that while media sharing services do not support events as yet, users still share their media around personal events, either by providing explicit spatio-temporal metadata, or by using an event-centric vocabulary
Sidelobe Reduction through Element Phase Control in Uniform Sub-arrayed Array Antennas
No full textWhen dealing with the synthesis sub-arrayed array antennas, the phase control, necessary for beam steering purposes, can be also exploited to reduce the undesired secondary lobes caused by the periodic spatial distribution of the amplitude excitations on the aperture when contiguous and identical subarrays are used. In order to determine the phase values of the array elements for a fixed sub-array amplitude weighting, the iterative projection method is adopted. Some representative results are shown to assess the effectiveness of the method. (c) 2009 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works
Pattern synthesis in time-modulated linear arrays through pulse shifting
No full textIn this study, an innovative approach for the synthesis of time-modulated linear array (TMLA) antennas is presented. The switch-on instants of the time-modulated elements are taken into account as additional degrees of freedom to optimise the array pattern. Towards this end, a technique based on a particle swarm optimisation is proposed to fully exploit the dependence of the sideband radiations (SR) on the shift of the time pulses. A set of representative results are reported to assess the effectiveness of the proposed approach as well as its flexibility. "This paper is a postprint of a paper submitted to and accepted for publication in IET Microwaves, Antennas & Propagation and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital Library
Exploitation of TE-TM scattering data for microwave imaging through the multi-scaling reconstruction strategy
No full textIn this paper, the solution of two-dimensional inverse scattering problems is addressed by probing the unknown scenarios with TE and TM waves. To better exploit the information content of the scattered data the multi-zooming approach is used. The results of experiments with single as well as multiple scatterers are reported and discussed also in comparison with single-polarization inversions. "(c) The Electromagnetics Academy. The final version of this article is available at the url of the journal PIER (Progress In Electromagnetics Research) http://www.jpier.org/PIER/pier.php?paper=09101105"
ADS-Based guidelines for thinned planar arrays
No full textWe propose an analytical technique based on almost difference sets (ADSs) for thinning planar arrays with well controlled sidelobes. The method allows one to synthesize bidimensional arrangements with peak sidelobe levels (PSLs) predictable and deducible from the knowledge of the array aperture, the filling factor, and the autocorrelation function of the ADS at hand. The numerical validation, concerned with both small and very large apertures, points out that the expected PSL values are significantly below those of random arrays and comparable with those from different sets (DSs) although obtainable in a wider range of configurations. “(c) 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.
Subarrayed Time-Modulated Arrays with Minimum Power Losses
No full textIn recent years, several works have been devoted to show the potentialities of time‐modulated arrays (TMAs) [1][2]. It is now well‐established that TMAs synthesize low‐sidelobe average patterns by using a set of simple on‐off radio‐frequency (RF) switches that modulate the static excitation weights. Moreover, a fast and simple control of the radiation pattern is enabled by just modifying the pulse sequence of RF switches. By exploiting this latter property, it would be of great interest for practical array applications the possibility of reconfiguring the pattern just modifying a reduced number of control elements [3][4] in order to simplify the overall feeding network architecture