1869 research outputs found
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Multi-resolution retrieval of non-measurable equivalent currents in microwave imaging problems – Experimental assessment
No full textIn this paper, an approach based on a multi-scaling strategy for the reconstruction of the non-measurable components of equivalent current distributions is tested against experimental data. An extensive set of simulations is carried out considering single and multiple scatterers with homogeneous as well as inhomogeneous properties. Selected results are reported and discussed to show potentialities and limitations of the method. (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=0907200
Analytic Techniques for the Design of Non-Regular Arrays
No full textThe cost, weight, power consumption, mutual coupling effects, HW and SW complexity of large arrays can be greatly reduced by suitable non-regular array design techniques, that is by considering array designs with a low number of elements with respect to that of a half‐wavelength equispaced array . Non‐regular arrays, however, are known to exhibit higher peak sidelobe levels (PSL) if not suitably designed. As a consequence, design techniques able to control and reduce the PSL of non‐regular arrays have been subject of research since their introduction
Time-Domain Inversion with the IMSA-FBTS Approach
No full textIn this paper, the problem of localization, shaping, and reconstructing the dielectric permittivity of a dielectric target is addressed. The inversion technique processes the time‐domain scattered field data to reconstruct with an increasing degree of accuracy the unknown scatterer by exploiting an iterative multiscaling procedure. Preliminary numerical results are presented to validate the time‐domain multi‐resolution multi‐step approach
ADS-Based Hybrid Methods for Array Thinning
No full textThis paper presents different Almost Difference Set (ADS)‐based hybrid methodologies to design linear thinned arrays. The proposed methods, which are based on genetic algorithms, allow one to overcome the limitations of ADS‐based thinned arrays in terms of design flexibility and/or performances. The numerical validation points out the efficiency of the proposed methodologies with respect to standard ADS designs as ll as standard stochastic techniques
Evolutionary-based Optimization Techniques for Inverse Scattering: A Review
No full textThe use of stochastic global optimizers has had a non‐negligible impact on several areas of research and industry and they have been effectively applied to several problems in engineering and sciences [1]. Thanks to the availability and growing of computational resources with the large diffusion of modern computers, optimization techniques based on Evolutionary Algorithms (EAs) have received a wide attention because of their attractive features. As a matter of fact, EAs are hill‐climbing algorithms and do not require the differentiation of the cost function, which is a "must" for gradientbased methods. They are based on stochastic iterative procedures where a pool of trial solutions is used to sample the solution space at each iteration thus improving the search capability as compared to single‐agent techniques (e.g., Simulated Annealing). A‐priori information can also be easily introduced in terms of additional constraints on the actual solution or the boundaries of the solution space. Moreover, they can directly deal with real values as well as with coded representations of the unknowns (e.g., binary coding). Their main drawback (i.e., the convergence rate) has been also further contrasted by exploiting their implicit and explicit parallelism thanks to modern computer clusters [2]
Real-Time Indoor Localization and Tracking of Passive Targets by Means of Wireless Sensor Networks
No full textRecently, the growing need of monitoring private or public areas for security purposes in civilian and military applications is driving the research community to design non‐invasive systems based on tiny sensing devices [1]. The tracking of a vehicle in a restricted area, the detection of animals in a dynamic environment, or the analysis of people behavior from movements are few examples of applications where the employment of systems for the localization and tracking of targets is mandatory. In the framework of wireless communications and technologies, the development of low‐power and low‐cost devices, such as Wireless Sensor Networks (WSN) [2], integrating on‐board processing and radio interface has favored the development of efficient cooperative signal processing algorithm for tracking purposes. Most of these systems are based on the processing of data acquired by dedicated sensor, or they assume to localize an active target, namely provided with some transmitting devices [3]. Unfortunately, in many applications the targets can not be equipped with wireless modules and the use of a complex system based on specific sensors is often not affordable. In this work, the localization problem is addressed by considering only the information provided by the quality indexes of the wireless links between the nodes of the WSN as in [4]. Consequently, unlike state‐of‐the‐art approaches, the infrastructure needed by the tracking procedure is limited to the nodes of the WSN, without the need of additional sensors. As a matter of fact, the target moving inside the scenario under test interacts with the electromagnetic signals transmitted by the wireless devices, thus modifying the values of the quality indexes measured at each node of the network. By reformulating such a problem in terms of a simplified electromagnetic inverse scattering problem, the localization and tracking of a passive target is carried out by means of a learning‐by‐example (LBE) strategy [5]. With respect to [4], the novelty of this paper lies in the application of the proposed approach to realistic indoor scenarios and in the use of differential measurements in order to remove the background contribution
PSO-Based Time-Domain Antenna Synthesis for Enhanced UWB Communication Systems
No full textIn Ultra‐Wideband (UWB) communication systems, the design and the analysis of the radiating element is a very demanding task, since also the quality of the transmitted and received signals must be taken into account [1]. In general, the characterization of the antennas is carried out in the frequency domain, by analyzing some parameters such as gain, input impedance, efficiency or radiation patterns. However, these terms are functions of frequency, and their analysis results to be computationally inefficient dealing with signals characterized by very large bandwidths. Therefore, the analysis of UWB systems seems to be more natural in the time domain, where all the frequencies are treated together [2]
Experimental Validation of Smart Antenna System Model
No full textIn the last decade, the need of effective mobile communication devices has favored the development of wireless technologies. Nowadays, the demand of dealing with complex communication scenarios characterized by multiple users and standards fosters the study of systems able to provide a suitable quality of service (QoS) and an enhanced security [1]. In such a framework, smart antennas have been recognized as promising tools for an efficient management of the physical layer. As a matter of fact, these systems are aimed at maximizing the signal‐to‐interference‐plus‐noise ratio (SINR) at the receiver by steering the main lobe of the beam pattern to track the desired signals and placing attenuations to cancel the interferences. With respect to standard solutions, smart antennas allow to increase the channel capacity and the service coverage [2]
Detection, Location and Reconstruction of Multicracks by Means of a GA-Based Electromagnetic Technique
No full textIn this work, an approach for the reconstruction of both geometrical and dielectric properties of multiple defects inside a known host medium is analyzed. In particular, the GA-based integrated strategy is applied starting from the knowledge of the scattered field in an external measurement domain in order to determine positions, sizes and dielectric permittivities of the defects, as well as the related field distribution. In order to evaluate the effectiveness in both locating the defects and reconstructing the corresponding permittivity profiles, a selected set of numerical results is presented
A Reconstruction Strategy Based on the Dort Method for Imaging Finite Dimension Scatterers
No full textThis paper presents a two stage strategy for the electromagnetic imaging of unknown lossless profiles. The first step is aimed at providing the localizations and an estimate of the number of the regions�]of�]interest (RoIs) where the scatterers are supposed to be located through the application of the DORT method enhanced with a suitable processing of the information associated with the eigenvalues of the time reversal operator. Towards this aim, a suitable procedure is developed and applied in an extended and unsupervised fashion for localizing the finite�]dimension scatterers under test. Successively, the second stage is devoted to reconstruct the unknown scatterer distributions by means of an iterative multi�]resolution non�]linear inversion performed only in the RoIs determined during the previous step