[show abstract][hide abstract] 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
[show abstract][hide abstract] 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
[show abstract][hide abstract] 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
[show abstract][hide abstract] 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
[show abstract][hide abstract] 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.
[show abstract][hide abstract] ABSTRACT: In this paper, the design of a metamaterial-based sensor, operating in
the mid-infrared frequency range, is proposed. The sensor consists of a
planar array of complementary circular inclusions. The resonant
frequencies of the sensor are designed to coincide with the proteins and
lipids spectral characteristics, in order to detect the presence of
cancer tissues, by absorption measurements. This sensor can be also used
for the recognition of different benign tumours in a highly accurate and
sensitive way. A new analytical circuit model has been developed, useful
to describe its resonant behavior. The sensing device is, then,
optimized to obtain high selectivity performances and has been tested
through proper full-wave simulations. The structure can be used as a
biological sensor with possible applications in medical diagnostics.
[show abstract][hide abstract] ABSTRACT: In this letter, we investigate the possibility of using the mantle cloaking approach to reduce mutual blockage effects between two electrically close antennas. In particular, we consider the case of two dipoles resonating at different, close frequencies and separated by an electrically short distance ( λ0 /10 at 3 GHz). We show that by covering the two antennas with properly patterned metasurfaces printed on realistic substrates, it is possible to make each antenna invisible to the other and preserve their individual operation as if they were isolated. This new cloaking application is confirmed by realistic full-wave numerical simulations.
[show abstract][hide abstract] ABSTRACT: In this contribution, we theoretically and numerically show that the operation bandwidth of an electrically small SRR loaded monopole antenna can be improved by using non-Foster active elements connected to the external gap of the SRR. The circuit implementation of the required non-Foster load in the VHF frequency band, as well as the stability analysis of the whole active component are also presented and discussed.
[show abstract][hide abstract] ABSTRACT: In this letter, we present the design and the experimental realization of an innovative self-filtering low-noise horn antenna. The proposed radiator consists of the following: a regular WR-62 waveguide connected to a horn antenna, a metallic screen with a vertical slit placed at the section connecting the waveguide and the horn, and a dielectric slab, with metallic omega shapes printed on both faces, placed across the slit. The goal of this design is to reduce the bandwidth of operation of the regular WR-62 horn in order to self-filter the noise captured within the antenna operation band. In the receiving mode, the metallic omega shapes placed across the slit allow transmission only in a narrow frequency band centered around the resonant frequency of the omegas. In such a frequency band, the radiating performances of the proposed antenna are comparable to the ones of a regular WR-62 horn radiator. A proper set of numerical simulations and measurements confirm the effectiveness of the proposed design, which can be successfully used in receiving satellite communication systems.
[show abstract][hide abstract] ABSTRACT: In this letter, we propose a new waveguide diplexer based on the employment of connected bi-omega particles. The component consists in a junction between three waveguides with the same cross-section. At either of the junction sections between the feeding waveguide and the two output ones, we place a set of connected bi-omega particles. The two sets of particles have different dimensions, in order to resonate at two different frequencies, enabling, thus, the frequency selective transmission required for the diplexer operation. The design is supported by proper full-wave numerical simulations and measurements.
[show abstract][hide abstract] ABSTRACT: In this Letter, we propose an engineered design of optical cloaks based on the scattering cancellation technique and intended to reduce the observability of cylindrical objects. The cover, consisting of a periodic arrangement of core-shell nanospheres, is designed in such a way to exhibit near-zero values of the real part of the homogenized effective permittivity at optical frequencies. Full-wave numerical simulations, considering the measured data of the dielectric function of the plasmonic material composing the shell, show that the cloak is able to reduce by about 6 dB the scattering cross section of a finite-length cylinder at around 740 THz with a -3 dB fractional bandwidth of about 7%. We show also that this result is not significantly affected by the perturbation of the periodic alignment of the core-shell nanospheres, due to possible fabrication issues or to an amorphous arrangement.
[show abstract][hide abstract] ABSTRACT: In this paper, an electromagnetic metamaterial resonator operating in
the terahertz frequency range is presented. By arranging the resonator
in a planar array, it is possible to use the structure as a sensing
device for organic and inorganic compounds. The sensor is designed to
detect the presence of a biological compound by permittivity or
absorption measurements. The presence of the biological matter modifies
the effective permittivity and, thus, the resonant frequency
significantly varies. In addition, biological compounds typically
exhibit absorption characteristics that depend on the corresponding
molecular structure. Therefore, it is necessary to illuminate the
material selectively. We show that by employing the "selective"
properties of the metamaterial resonator proposed, it is possible to
enhance the sensing performances. The proposed design is suitable to
sense the presence of healthy and malignant tissues, with possible
applications in food and medical diagnostics. The operation of the
sensing device has been demonstrated through proper full-wave
[show abstract][hide abstract] ABSTRACT: In this Letter, we present the design of a horn nanoantenna working at near-IR frequencies. The proposed layout consists of an Ag-air-Ag nanotransmission line terminated in a tapered horn. The antenna design is validated through proper full-wave numerical simulations, taking into account actual dispersion and losses of the involved materials. The numerical results show that the designed nanohorn is matched over a broad range of frequencies (more than 50% of fractional bandwidth) and radiates efficiently in the same frequency band (the realized gain is greater than 10 dBi). Such promising results may find application in different technical and scientific fields, ranging from smart lighting to optical wireless communications.
[show abstract][hide abstract] ABSTRACT: In this paper, we present the design of miniaturized narrowband-microwave absorbers based on different kinds of magnetic inclusions. The operation of the proposed components originates from the resonance of a planar array of inclusions excited by an incoming wave with a given polarization. As in common absorber layouts, a 377 Ω resistive sheet is also used to absorb the electromagnetic energy of the impinging field. Since the planar array of magnetic inclusions behaves at its resonance as a perfect magnetic conductor, the resistive sheet is placed in close proximity of the resonating inclusions, without perturbing their resonance condition. In contrast to other typical absorber configurations presented in the literature, the absorber proposed in this paper is not backed by a metallic plate. This feature may be useful for stealth applications, as discussed thoroughly in the paper. The other interesting characteristic of the proposed absorbers is the subwavelength thickness, which has shown to depend only on the geometry of the basic resonant inclusions employed. At first, regular split-ring resonators (SSRs) disposed in an array configuration are considered and some application examples are presented. Absorbers based on SRRs are shown to reach thickness of the order of λ<sub>0</sub>/20. In order to further squeeze the electrical thickness of the absorbers, multiple SRRs and spiral resonators are also used. The employment of such inclusions leads to the design of extremely thin microwave absorbers, whose thickness may even be close to λ<sub>0</sub>/100. Finally, some examples of miniaturized absorbers suitable for a practical realization are proposed.
IEEE Transactions on Electromagnetic Compatibility 03/2011; · 1.33 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this contribution, we investigate the tunneling and radiating phenomena associated to coupled bi- omega particles placed across a sub-wavelength aperture. We show that, when properly excited, the strong resonances arising in this inclusion may lead to dramatically enhanced transmission through the sub-wavelength aperture. The description of the physical phenomena behind the operation of the proposed setup and the discussion on its possible applications in a new family of radiating components will be the subject of the present paper. The results of this investigation are supported by a newly proposed analytical representation of the bi-omega inclusion, whose results are in good agreement with full-wave numerical simulations.
[show abstract][hide abstract] ABSTRACT: In this contribution, we present the electrical and radiation properties of a horn nano-antenna working at near infrared frequencies. The proposed nano-antenna consists of an Ag-SiO2-Ag nano-transmission line terminated in a tapered horn. We numerically demonstrate that such a nano-antenna is able to efficiently capture/radiate light at the frequencies of interest. The obtained impedance bandwidth and simulated gain make the proposed nano-antenna a promising solution for telecommunication and energy harvesting applications.
[show abstract][hide abstract] ABSTRACT: In this paper, we numerically demonstrate that plasmonic covers designed through the scattering cancellation approach can be successfully used to enhance the performance of near-field scanning optical microscopy (NSOM) systems based on the employment of aperture tip probes. The material used to partially cover the tip exhibits a near-zero value of the real part of the permittivity function at the working frequency and is designed in such a way to dramatically reduce the undesired electromagnetic coupling between the sample to be imaged and the metallic coating of the aperture tip. We show that minimizing such an unwanted interaction may lead to enhance the maximum achievable resolution of the NSOM system. The approach proposed is numerically tested at optical frequencies through a proper set of full-wave simulations, taking into account material losses and frequency dispersion. The proposed results represent a proof-of-concept and can be scaled at lower frequencies (infra-red and THz), where fabrication issues are more relaxed and possible implementation can be made practical using alternating plasmonic/non-plasmonic multi-layers or even some natural materials.
[show abstract][hide abstract] ABSTRACT: In this work, a metasurface consisting of an array of circular holes in a metal conducting sheet with a sub-wavelength periodicity is considered. The surface partially reflects the incident field according to the shape and geometrical dimensions of the inclusions and, due to this property, is widely employed in antenna systems to improve the radiation pattern of regular radiators. Since the reflection properties of the metasurface are determined by the current density distribution on the metal, we inspect this distribution and coherently develop a new, easy, and accurate analytical model to describe the grid impedance of the metasurface. In order to validate the model, we compare the reflection coefficient of the array obtained through our approach to the one resulting from full-wave numerical simulations and to other accurate analytical methods available in the open technical literature.
Progress In Electromagnetics Research M. 01/2011; 18:209-219.