F. Bilotti

Università Degli Studi Roma Tre, Roma, Latium, Italy

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Publications (191)169.71 Total impact

  • 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; · 1.79 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; 6:4416-4425. · 1.08 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). · 2.33 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 01/2014; 62(8):4220-4229. · 2.33 Impact Factor
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    ABSTRACT: A new application of a metamaterial-inspired inclusion, i.e. the Split-Ring Resonator (SRR), combined with a commercial Ground Penetrating Radar (GPR) is presented. An SRR is embedded within a soil sample and excited by the GPR antenna. Exploiting the resonant properties of the inclusion, the dielectric permittivity of a typical soil is estimated by observing the GPR data. The proposed method turns out to be very quick and the results are in agreement with many findings in the open technical literature. The point of strength of this approach is the combination of GPR technology and metamaterial concepts that leads to a quick and accurate in-situ estimation, i.e. not-destructive, of the dielectric properties of the underground.
    2013 7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS 2013); 09/2013
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    M. Manzini, A. Alu, F. Bilotti, L. Vegni
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    ABSTRACT: We present the design of a flat lens, made by a conventional material and an epsilon near-zero metamaterial, to plug up the aperture of a short horn antenna, in order to achieve radiation performances similar to the ones of the corresponding optimum horn over a broad frequency range. Lens operation is based on the phase-compensation concept: phase-fronts of the field propagating along the short flare of the horn propagate with different phase velocities in the two lens materials, resulting in an uniform phase distribution on the aperture. Starting from the theoretical study of the transmission properties of a bulk epsilon near-zero slab, we derive the analytical formulas for the design of the flat lens and validate them through full-wave numerical simulations. Then, a realistic version of the lens, realized with a wire-medium and exhibiting a near-zero real part of the effective permittivity in the frequency range of interest, is presented. Considering two examples working in the C-band, we show that the lens can be designed for both conical and pyramidal horn antennas. In both cases, the length of the horns is half the one of the corresponding optimum versions, while the obtained radiation performances are similar to those of the optimum horns over a broad frequency band. This result may open the door to several interesting applications in satellite and radar systems.
    IEEE Transactions on Antennas and Propagation 06/2013; 61(6):2929-2937. · 2.33 Impact Factor
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    ABSTRACT: In this paper, we investigate on the use of non-Foster active elements to increase the operation bandwidth of a split-ring resonator (SRR) for possible application in metamaterial-inspired components. First, we design the circuit topology of the active load required to compensate the intrinsic reactance of the SRR and get a broadband response. Then, we show that the same procedure can be successfully applied to the case of a SRR-based monopole antenna and, in principle, to any metamaterial-inspired device employing SRRs. Finally, integrating an electromagnetic and a circuit simulator, we propose a possible realistic implementation of the active load, based on the employment of commercially available circuit elements. The obtained results (seven times improvement of the impedance bandwidth of the SRR-based monopole antenna) prove that non-Foster active loads can be successfully used to overcome the inherent narrow-band operation of SRR-based passive metamaterials and metamaterial-inspired components. The implementation issues related to circuit element dispersion, parasitic effects, and stability of the active circuit are fully considered in the proposed design.
    IEEE Transactions on Antennas and Propagation 03/2013; 61(3):1219-1227. · 2.33 Impact Factor
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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 01/2013; 32(6). · 0.28 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 01/2013; 32(6). · 0.28 Impact Factor
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    ABSTRACT: Recently, our group has proposed a self-filtering linearly polarized horn antenna that can be used to reduce the noise captured by regular horn feeds. However, the approach used in that design is inherently limited to linear polarization, while possible interesting applications are likely in satellite receiving systems, which are typically based on circularly polarized signals. In this letter, we propose a new approach to obtain a filtering horn antenna working in circular polarization. The proposed solution is based on the design of a linear-to-circular polarization transformer that consists of a complementary electrically small resonator etched on a metallic screen. We first show that this component is able to transform the linear polarization of a regular rectangular waveguide working on the fundamental mode into a circular one. Then, integrating this polarization transformer in a conical horn, we show how it is possible to obtain a circularly polarized filtering horn antenna. The numerical simulations and the measurements performed on a prototype prove that the proposed structure can be effectively used to design a bandpass filtering horn antenna for circularly polarized signals.
    IEEE Antennas and Wireless Propagation Letters 01/2013; 12:1065-1068. · 1.67 Impact Factor
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    ABSTRACT: In this contribution, we present the design of efficient electrically small apertures loaded with metamaterial-inspired sub-wavelength resonators. The employment of omega and modified protractor resonators enables efficient radiation and automatic impedance matching, without increasing the physical dimensions of the aperture. This phenomenon is applied to the design of several microwave components, some of which are presented in the paper: a. linearly-polarized open-ended waveguides and horn antennas and b. linear-to-circular polarization transformers. The results are supported by proper numerical simulations and measurements.
    Antennas and Propagation (EuCAP), 2013 7th European Conference on; 01/2013
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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 01/2013; 32(6). · 0.28 Impact Factor
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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 01/2013; 32(6). · 0.28 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 01/2013; 32(6). · 0.28 Impact Factor
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    ABSTRACT: Enhanced transmission through circular and rectangular sub-wavelength apertures using omega-shaped split-ring resonator is numerically and experimentally demonstrated at microwave frequencies. We report a more than 150,000-fold enhancement through a deep sub-wavelength aperture drilled in a metallic screen. To the authors’ best knowledge, this is the highest experimentally obtained enhancement factor reported in the literature. In the paper, we address also the origins and the physical reasons behind the enhancement results. Moreover, we report on the differences occurring when using circular, rectangular apertures as well as double-sided and single-sided omega-like split ring resonator structures.
    Photonics and Nanostructures - Fundamentals and Applications 08/2012; · 1.79 Impact Factor
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    ABSTRACT: We present a novel switched beam antenna (SBA) consisting of four identical metamaterial-inspired electrically short printed monopoles, vertically placed at the corners of a grounded square board. The antenna is designed to operate in the frequency range 1600-2700 MHz, with global dimensions 120 mm × 120 mm × 30 mm. The SBA has been first numerically simulated and optimized and, then, fabricated and tested. Numerical and experimental results show a good agreement. The obtained switched beam capabilities, the achieved realized gain levels, and the synthesized radiation pattern shapes on the horizontal plane, make the proposed SBA a good candidate as a radiating element of a receiving module for wireless telecommunication systems (DCS, UMTS, Wi-Fi, LTE) in areas with reduced signal coverage and/or high interference levels.
    IEEE Transactions on Antennas and Propagation 08/2012; 60(8):3583-3593. · 2.33 Impact Factor
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    ABSTRACT: Metamaterials (MTMs) exhibiting a near-zero real part of the permittivity function in a given frequency range have been demonstrated to be useful in several application fields, including field localization and focusing. So far, however, the realistic implementations of such materials working at optical frequencies and exhibiting a reasonable level of losses are rare. In this work, we propose a possible implementation of optical epsilon-near-zero (ENZ) MTMs based on the employment of an array of core-shell nano-spheres embedded in a dielectric medium. The core of the nano-spheres and the host medium are both made of silica, while the shell is formed by a plasmonic material (i.e. silver). Using classical homogenization formulas, we show that it is possible to design the array in such a way to exhibit near-zero values of the effective real permittivity with relatively low losses at optical frequencies. These results are supported and confirmed by proper full-wave simulations and design examples.
    Optics Communications 07/2012; 285(16):3412–3418. · 1.44 Impact Factor
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    Filiberto Bilotti, Levent Sevgi
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    ABSTRACT: In this article, we review definition, origin, terminology, fundamental properties, design concepts and procedures, basic applications, modeling, and numerical simulation of metamaterials. It is shown that metamaterial origin can be easily understood by placing metamaterials in the more general context of artificial electromagnetic materials and of the efforts performed by the scientific community working in complex materials to mimic and overcome the properties of natural materials. The basic properties of some classes of metamaterials as well as the related limitations are reviewed and discussed. A new application-oriented definition of metamaterials is given in terms of a functionalizing layer placed in between the traditional concepts of materials and devices. Metamaterial applications and the design steps of metamaterial-based and metamaterial-inspired components are also discussed, with particular emphasis on the numerical simulation of ideal metamaterials through available solvers. In this frame, finite-difference time-domain (FDTD) modeling and simulation of the electromagnetic properties of metamaterials are deeply discussed. The recently introduced virtual MTM-FDTD tool is used to simulate the interaction between the electromagnetic field and metamaterials and show some metamaterial effects, such as beam focusing, existence of negative refractive angle, and so forth, through various examples in different scenarios. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22:422–438, 2012. © 2012 Wiley Periodicals, Inc.
    International Journal of RF and Microwave Computer-Aided Engineering 07/2012; 22(4):422-438. · 0.75 Impact Factor

Publication Stats

894 Citations
169.71 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
  • 2007–2010
    • Bilkent University
      • Department of Physics
      Ankara, Ankara, Turkey
  • 2009
    • University of Texas at Austin
      • Department of Electrical & Computer Engineering
      Austin, Texas, United States
  • 2005–2007
    • University of Pennsylvania
      • Department of Electrical and Systems Engineering
      Philadelphia, PA, United States
  • 2003–2005
    • University of Texas at Brownsville and Texas Southmost College
      Brownsville, Texas, United States
  • 2000–2005
    • The American University of Rome
      Roma, Latium, Italy