Filiberto Bilotti

Università Degli Studi Roma Tre, Roma, Latium, Italy

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Publications (208)213.65 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Using two suitably tailored concentric cloaking metasurfaces, we demonstrate several interesting features of these covers, including significant broadband and/or dual-band scattering reduction. We also show that nearly perfect cloaking for moderately sized targets is enabled by complementary bilayer pairings. We apply these concepts to realistic bilayer cloaks covering a finite-length conductive rod for multiband and wideband operation, offering a $>5-text{dB}$ (70%) scattering suppression over bandwidths that exceed any passive mantle cloak demonstrated so far by over nine times. Finally, we apply the same covers to more complex geometries, showing that moderate scattering suppression is maintained, despite the change in geometry and increased size.
    IEEE Transactions on Antennas and Propagation 07/2015; 63(7):1-1. DOI:10.1109/TAP.2015.2421951 · 2.46 Impact Factor
  • Alessio Monti · Andrea Alù · Alessandro Toscano · Filiberto Bilotti
    Photonics 06/2015; 2(2):540-552. DOI:10.3390/photonics2020540
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    ABSTRACT: We present the design and realization of anisotropic mantle cloaks operating, at the same frequency, for both TM and TE incident polarizations. Starting from the analytical model of metasurfaces available in the literature, we first explore the potentials and limitations of the most common metasurface geometries for their application as mantle cloaks. Then, we introduce new types of patterned surfaces aimed at improving their polarization response. We demonstrate that, only by using four metasurface topologies, it is possible to obtain all required combinations of positive and negative reactance values in order to design effective mantle cloaks for planar, cylindrical, and three-dimensional (3-D) objects. We also show that the accuracy of the analytical formulas commonly used to design such metasurfaces is not necessarily sufficient for cloaking purposes. Therefore, we introduce and validate a numerical procedure to refine the analytical design and optimize the cloak performance. The effectiveness of the designed covers is checked with full-wave simulations. Finally, some antenna applications of dual-polarized mantle cloaks are proposed and several experimental measurements conducted on fabricated prototypes are also provided.
    IEEE Transactions on Antennas and Propagation 04/2015; 63(4):1775-1788. DOI:10.1109/TAP.2015.2396532 · 2.46 Impact Factor
  • A. Monti · A. Alù · A. Toscano · F. Bilotti
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    ABSTRACT: In this paper, we investigate the application of the mantle cloaking technique to near-infrared and visible frequencies, analyzing and designing thin covers consisting of 2D arrays of plasmonic nanoparticles. First, we validate and generalize an analytical model recently appeared in the literature to describe a 2D array of plasmonic nanoparticles as a metasurface characterized by its homogenized surface reactance. We prove that the proposed model allows to efficiently design 2D mantle cloaks with an assigned surface reactance, enabling, thus, the extension of the mantle cloaking technique to optical frequencies. Then, we design realistic optical mantle cloaks made of 2D arrays of spheroidal plasmonic nanoparticles with a high eccentricity. We show that the proposed cloaks allow significant, moderately broadband cloaking effects at visible frequencies. In our designs, we consider realistic losses and non-critical nanoparticle dimensions to envision a practical realization of the proposed cloaks.
    Journal of Applied Physics 03/2015; 117(12):123103. DOI:10.1063/1.4916257 · 2.19 Impact Factor
  • Mirko Barbuto · Fabrizio Trotta · Filiberto Bilotti · Alessandro Toscano
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    ABSTRACT: In this communication, we present the design of filtering horn antennas with band-stop characteristics obtained through the use of electrically small magnetic resonators. In particular, a split-ring resonator (SRR) etched on a Rogers Duroid RT5870 dielectric substrate is inserted within the metallic flare of the horn at a proper distance from the throat. At around the resonant frequency of the SRR transmission is highly reduced and a single notched-band is obtained. In order to extend the result to dual-band operation, we also present the design of the filtering module made by two SRRs with different dimensions. The validity of the proposed approach is verified through proper sets of full-wave simulations and experiments on fabricated prototypes. The proposed solution is economical, light, electrically small, easily implementable on already existing radiators, and can find application in wideband communication systems affected by narrowband interfering signals.
    IEEE Transactions on Antennas and Propagation 02/2015; 63(2):781-785. DOI:10.1109/TAP.2014.2378269 · 2.46 Impact Factor
  • Progress In Electromagnetics Research 01/2015; 151:65-72. DOI:10.2528/PIER15022002 · 5.30 Impact Factor
  • Giacomo Oliveri · Filiberto Bilotti · Alessandro Toscano · Andrea Massa
  • Mirko Barbuto · Filiberto Bilotti · Alessandro Toscano
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    ABSTRACT: In this paper, we present a new class of waveguide components based on the use of complementary electrically small resonators etched on metallic sheets. We first show a rectangular-to-circular waveguide transition that allows to effectively match waveguides with different cross-sections and to transform the linearly polarized TE10-mode of a rectangular waveguide into a circularly polarized TE11-mode of a circular waveguide. Then, using similar structures, we present the design and the numerical results of two power dividers and of an orthomode transducer. All these components, employing only thin metallic sheets with properly shaped slits, can be integrated in waveguide transmission systems without increasing their space occupancy. A proper set of full-wave numerical simulations proves the validity of the proposed approach
    Photonics and Nanostructures - Fundamentals and Applications 08/2014; 12(4). DOI:10.1016/j.photonics.2014.03.005 · 1.35 Impact Factor
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    ABSTRACT: We discuss the use of metasurfaces and plasmonic metamaterials to minimize the scattering from receiving antennas and sensors, with the goal of maximizing their absorption efficiency. We first analytically study and highlight the potential of these approaches to realize optimized sensors with the desired level of efficiency, being able to minimize the electrical presence of a receiving antenna for a chosen level of overall absorption. Realistic cloak designs, investigated using full-wave simulations, verify the behavior analytically predicted by Mie theory. These optimized cloaks offer a practical way to flexibly tailor the scattering of receiving antennas, with great benefits in the design and optimization of near-field sensors, remote communication systems, spoof targets and improved antenna blockage resiliency. Optimized covers may also provide other interesting features for the same receiving antenna by just tuning its resistive load, such as optimal wireless power harvesting or high-to-low tunable absorption efficiency.
    IEEE Transactions on Antennas and Propagation 08/2014; 62(8):4220-4229. DOI:10.1109/TAP.2014.2322891 · 2.46 Impact Factor
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    ABSTRACT: This contribution aims at investigating the possibility to cloak a spherical object from an acoustic wave by applying the scattering cancellation approach. In electromagnetism, the scattering problem is treated using the Mie expansion technique, through which the scattered field by a spherical object can be represented as a superposition of TE and TM spherical harmonics. It is possible to extend this concept to the acoustic field by defining an analogous approach; the pressure field, generated by an elastic wave impinging on a spherical object, can be expressed applying the Mie expansion technique, as well. In acoustics, to achieve scattering suppression at a given frequency, the constitutive parameters to control are density and compressibility. By varying these parameter values, it is possible to define an engineered material with anomalous properties, which cannot be found in nature, able to reduce the scattering cross-section (SCS) from a spherical object. We propose a study about the effectiveness of the SCS reduction from an elastic sphere coated with a properly-designed acoustic metamaterial. The sensitivity of the SCS to parameter variations is analyzed for different coating thicknesses and sphere dimensions. Our analysis is supported by both the analytical modelling of the structure and numerical simulations.
    Sustainability 07/2014; 6(7):4416-4425. DOI:10.3390/su6074416 · 1.08 Impact Factor
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    ABSTRACT: Purpose - A novel model of the upper arm under transcutaneous electrical stimulation with multi-pad electrodes is presented and experimentally validated. The model aims at simulating and analysing the effects of surface electrical stimulation on biceps brachii. The paper aims to discuss these issues. Design/methodology/approach - Both the passive properties of tissues surrounding nerve bundles and the active characteristics of the nervous system are included. The output of the proposed model is nerve recruitment and muscle contraction. Findings - Simulations and experimental tests on six healthy young adults have been conducted and results show that the proposed model gives information on electrically elicited muscle contraction in accordance with in-vivo tests and literature on motor unit recruitment order. Tests with different electrodes configurations show that the spatial distribution of active electrodes is a critical factor in electrically elicited muscle contractions, and that multi-pad electrodes can optimise the stimulation effectiveness and patient comfort with sequences of biphasic pulses of 350 mu s at 30 pulses/s and threshold values of 2 mA. Originality/value - Results encourage the use of the proposed model of the upper arm as a valid and viable solution for predicting the behaviour of the neuromuscular system when surface electrical stimulation is applied, thus optimising the design of neuroprosthetics.
    COMPEL International Journal of Computations and Mathematics in Electrical 07/2014; 33(4). DOI:10.1108/COMPEL-04-2013-0118 · 0.44 Impact Factor
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    ABSTRACT: In this paper, we present a new analytical model of the connected bi-omega structure consisting of two bi-omega particles connected together through their arms. A single bi-omega particle consists of a pair of regular equal omegas with mirror symmetry. Assuming the individual bi-omega particle electrically small, the equivalent circuit is derived, in order to predict its resonant frequency. Then, two bi-omega particles are connected together, obtaining a symmetric structure that supports two fundamental modes, with even and odd symmetries, respectively. The proposed analytical model, then, is used to develop a procedure allowing the design of the particle for a desired resonant frequency. The effectiveness of the proposed analytical model and design guidelines is confirmed by proper comparisons to full-wave numerical and experimental results. We also demonstrate through a proper set of experiments that the resonant frequencies of the connected bi-omega particle depend only on the geometrical and electrical parameters of the omegas and are rather insensitive to the practical scenario where the particle itself is actually used, e.g. in free-space, rectangular waveguide or across an aperture in a metallic screen.
    IEEE Transactions on Antennas and Propagation 03/2014; 62(4). DOI:10.1109/TAP.2014.2301445 · 2.46 Impact Factor
  • Mirko Barbuto · Fabrizio Trotta · Filiberto Bilotti · Alessandro Toscano
    Progress In Electromagnetics Research 01/2014; 148:23-30. DOI:10.2528/PIER14050204 · 5.30 Impact Factor
  • 01/2014; 1:1. DOI:10.1051/epjam/2014002
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    ABSTRACT: The introduction of electromagnetic (EM) media with unique field manipulation properties, collectively labelled as metamaterials, has boosted the interest toward the design, the fabrication, and the testing of artificial materials whose features can be engineered according to the applicative requirements and user objectives. In this framework, the long-term promise of reconfigurable metamaterial theory (i.e., the possibility to change the EM response of a 2-D/3-D material arbitrarily and in real time) has given the designers an extremely wide number of new degrees of freedom for the synthesis of innovative adaptive systems. Moreover, successful experimental validations of reconfigurable metamaterials in the entire EM spectrum from microwaves to optical frequencies have further stimulated academic and industrial interests in developing devices with enhanced performances, efficiency, and robustness. Nevertheless, the exploitation of reconfigurable metamaterials in commercial devices is still an open problem with several challenges from both the theoretical and technological viewpoints. This paper is then aimed at reviewing the latest advances on reconfigurable metamaterial engineering from the methodological perspective also providing a comprehensive and balanced survey on latest concepts, current trends, and envisaged future developments on this active field of research.
    International Journal of Antennas and Propagation 01/2014; 2014(7):1-2. DOI:10.1155/2014/215394 · 0.83 Impact Factor
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    ABSTRACT: A new family of waveguide power splitters based on the use of connected bi-omega particles is presented. The new layout consists of a H-plane T-junction, whose ports are characterised by the same cross-section. The output ports are both closed with a metallic screen and energy is allowed to pass through by means of a vertical slit drilled into each metallic screen. To make the transmission efficient, two identical particles, printed on the two faces of a dielectric slab, are placed across the slits. Depending on the design, at the resonant frequencies of the two bi-omega particles, either balanced or unbalanced power splitting is obtained between the two output ports. A proper set of numerical simulations and measurements confirm the effectiveness of the proposed design, which can be successfully used for realising compact and highly selective waveguide power splitters.
    Electronics Letters 11/2013; 49(24):1504-1506. DOI:10.1049/el.2013.1565 · 1.07 Impact Factor
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    ABSTRACT: Purpose ‐ Metamaterial unit cells composed of deep subwavelength resonators brought up new aspects to the antenna miniaturization problem. The paper experimentally demonstrates a metamaterial-inspired miniaturization method for circular patch antennas. In the proposed layouts, the space between the patch and the ground plane is filled with a proper metamaterial composed of either multiple split-ring or spiral resonators (SRs). The authors have manufactured two different patch antennas, achieving an electrical size of ?/3.69 and ?/8.26, respectively. The paper aims to discuss these issues. Design/methodology/approach ‐ The operation of such a radiative component has been predicted by using a simple theoretical formulation based on the cavity model. The experimental characterization of the antenna has been performed by using a HP8510C vector network analyzer, standard horn antennas, automated rotary stages, coaxial cables with 50 O characteristic impedance and absorbers. Before the characterization measurements we performed a full two-port calibration. Findings ‐ Electrically small circular patch antennas loaded with single layer metamaterials experimentally demonstrated to acceptable figures of merit for applications. The proposed miniaturization technique is potentially promising for antenna applications and the results presented in the paper constitute a relevant proof for the usefulness of the metamaterial concepts in antenna miniaturization problems. Originality/value ‐ Rigorous experimental characterization of several meta material loaded antennas and proof of principle results were provided.
    COMPEL International Journal of Computations and Mathematics in Electrical 11/2013; 32(6). DOI:10.1108/COMPEL-10-2012-0276 · 0.44 Impact Factor
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    ABSTRACT: Purpose ‐ The purpose of this paper is to present an analytical expression for the characteristic impedance of a microstrip line in presence of a dielectric cover. Design/methodology/approach ‐ Assuming a quasi-TEM propagation mode, a rigorous conformal mapping based on the Schwarz-Christoffel transformation is employed to derive the equivalent capacitance model, which can then be applied to derive a closed analytical expression for the effective permittivity and the characteristic impedance of the line. Findings ‐ Such a formulation is not limited to the case of a single cover layer, but an arbitrary number of electric overlays can be considered as well. Comparisons with published numerical results and full-wave simulations in the case of a single cover layer have been also performed to test the validity of the proposed approach. Originality/value ‐ The new analytical formula for the characteristic impedance of a microstrip line with a single dielectric cover shows better performances compared to the one of closed formulas already presented in the literature.
    COMPEL International Journal of Computations and Mathematics in Electrical 11/2013; 32(6). DOI:10.1108/COMPEL-10-2012-0283 · 0.44 Impact Factor
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    ABSTRACT: Purpose ‐ The purpose of this paper is to show how metamaterials with extreme values of permittivity and permeability, may be effectively used to design artificial magnetic conductors (AMC) at a given frequency. In particular, this paper theoretically determines, for the different polarizations of the incidence field, the conditions under which metamaterials can behave as an AMC. Design/methodology/approach ‐ In order to find out the required values of the constitutive parameters, this paper has done a theoretical analysis based on the transmission-line theory. The obtained analytical reflection coefficient has been particularized for the different possible polarizations of the incidence field in order to find the constitutive parameters values that this paper needs for the AMC behavior. Findings ‐ Depending on the polarization of the field, it is shown that different values of the constitutive parameters are needed to get AMCs. In particular, it is shown that in the case of TEM and TE polarizations, a large value of the permeability is enough to obtain an AMC boundary condition. In the case of the TM polarization, instead, the AMC boundary condition is effectively achieved by using a material with vanishing permittivity. The role of the permittivity in the three polarizations is discussed. Finally, possible implementations and applications at microwave and optical frequencies are presented. Originality/value ‐ The idea of using miniaturized inclusions to obtain AMCs is not completely new. However, to the authors' best knowledge, a complete and rigorous theoretical analysis showing the capabilities and the limits of this approach has not yet been presented in the open technical literature.
    COMPEL International Journal of Computations and Mathematics in Electrical 11/2013; 32(6). DOI:10.1108/COMPEL-10-2012-0281 · 0.44 Impact Factor
  • Davide Ramaccia · Filiberto Bilotti · Alessandro Toscano · Lucio Vegni
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    ABSTRACT: Purpose ‐ The purpose of this paper is to design simple and high-performing screens capable to separate circularly polarized electromagnetic waves in Ku band from the ones in Ka band. Design/methodology/approach ‐ The proposed screen consists of an inductive double resonant element FSS, i.e. a regular array of circular holes in a metal thick plate, in order to grant the robustness to mechanical stress for antenna applications in extreme conditions. Findings ‐ The proposed design of a multi-band frequency selective surface (FSS) is able to separate circularly polarized electromagnetic waves in Ku band from the ones in Ka band. Originality/value ‐ The paper shows the capabilities of a novel FSS that combine the transmission properties of two simple FSSs which allows us to achieve an interesting behaviour in three typical bands of the satellite communications.
    COMPEL International Journal of Computations and Mathematics in Electrical 11/2013; 32(6). DOI:10.1108/COMPEL-10-2012-0278 · 0.44 Impact Factor

Publication Stats

2k Citations
213.65 Total Impact Points

Institutions

  • 1999–2014
    • Università Degli Studi Roma Tre
      • • Department of Applied Electronics
      • • Department of Electronic Engineering
      Roma, Latium, Italy
  • 2010
    • The University of Arizona
      Tucson, Arizona, United States
  • 2003–2005
    • University of Texas at Brownsville and Texas Southmost College
      Brownsville, Texas, United States
  • 2001–2002
    • The American University of Rome
      Roma, Latium, Italy