arXiv subjects

Alessandro Toscano

Publications and source records attributed to Alessandro Toscano.

At least 19 recordsLinked to original sources

arXiv2025

Tunable Transmissive Metagratings Using Single Layer Cylindrical Plasma Discharges

In this paper, we propose a novel single-layer reconfigurable transmissive metagrating based on plasma discharges. Each unit-cell consists of two side-by-side core-shell cylinders, with a tunable plasma core and a high-index dielectric shell. The structure is modeled using a free-electron plasma permittivity with adjustable plasma frequency. Analytical and numerical results show that the main transmission lobe can be switched between -41{\deg}, 0{\deg} and 41{\deg} by tuning the plasma frequencies. Transmission efficiency remains above 80% at broadside and 90% in the steered direction. This tunability enables effective directional control with low reflection and high overall power efficiency.

physics.app-ph↗

arXiv2025

Temporal multilayer structures for designing higher-order transfer functions using time-varying metamaterials

Temporal metamaterials are artificial materials whose electromagnetic properties change over time. In analogy with spatial media and metamaterials, where their properties change smoothly or abruptly over space, temporal metamaterials can exhibit a smooth variation over time, realizing a temporal non-homogeneous medium, or a stepwise transition, realizing the temporal version of dielectric slabs or multilayer structures. In this Letter, we focus our attention on temporal multilayer structures, and we propose the synthesis of higher-order transfer functions by modeling the wave propagation through a generalized temporal multilayer structure, consisting of a cascade over time of different media. The tailoring of the scattering response of temporal structure as a function of frequency is presented, deriving the corresponding scattering coefficients for a properly designed set of medium properties, i.e., permittivity and permeability, and application time, in analogy with what is typically done in optical and electromagnetic spatial multilayered structures. This allows us to design novel electromagnetic and optical devices with higher-order transfer functions by exploiting the temporal dimension instead of the spatial one.

physics.optics↗

arXiv2025

Metasurface Dome for Above-the-Horizon Grating Lobes Reduction in 5G-NR Systems

The use of 5G New Radio (NR) spectrum around 26 GHz is currently raising the quest on its compatibility with the well-established Earth Exploration-Satellite Service (EESS), which may be blinded by the spurious radiation emitted Above-the-Horizon (AtH) by Base Station (BS) antennas. Indeed, AtH grating lobes are often present during cell scanning due to the large inter-element spacing in BS array antennas for achieving higher gains with a reduced number of RF chains. In this letter, we propose an approach based on an electrically thin metasurface-based dome for the reduction of AtH grating lobes in 5G-NR BS antennas. The proposed scanning range shifting approach exploits the natural lower amplitude of the grating lobes when the antenna array scans in an angular region closer to the broadside direction. The grating lobe reduction is here demonstrated considering a 1x4 phased linear antenna array operating under dual-liner 45deg-slant polarization. A simple design procedure for designing the metasurface dome is reported, together with the antenna performances, evaluated through a proper set of numerical experiments. It is shown that the grating lobe radiation towards the satellite region is significantly reduced, whereas the overall insertion loss is moderate.

physics.optics↗

arXiv2025

Perfect matching of reactive loads through complex frequencies: from circuital analysis to experiments

The experimental evidence of purely reactive loads impedance matching is here provided by exploiting the special scattering response under complex excitations. The study starts with a theoretical analysis of the reflection properties of an arbitrary reactive load and identifies the proper excitation able to transform the purely reactive load into a virtual resistive load during the time the signal is applied. To minimize reflections between the load and the transmission line, the excitation must have a complex frequency, leading to a propagating signal with a tailored temporal envelope. The aim of this work is to design and, for the first time,experimentally demonstrate this anomalous scattering behavior in microwave circuits, showing that the time-modulated signals can be exploited as a new degree of freedom for achieving impedance matching without introducing neither a matching network nor resistive elements, that are typically used for ensuring power dissipation and, thus, zero reflection. The proposed matching strategy does not alter the reactive load that is still lossless, enabling an anomalous termination condition where the energy is not dissipated nor reflected, but indefinitely accumulated in the reactive load. The stored energy leaks out the load as soon as the applied signal changes or stops.

eess.SP↗

arXiv2024

Passive Time-Varying Waveform-Selective Metasurfaces for Attainment of Magnetic Property Control

We present circuit-loaded metasurfaces that behave differently in a passive manner even at the same frequency in accordance with the incoming waveform, specifically, its pulse width. Importantly, the time-varying waveform-selective metasurfaces reported thus far were mostly able to change their electric properties but not their magnetic properties; this severely limited the design range of their corresponding wave impedances and refractive indices and thus hindered the development of potential applications in antennas, sensors, imagers, signal processing, and wireless communications. In this study, passive time-varying waveform-selective metasurfaces were found to attain magnetic property control by introducing an additional circuit-loaded layer that generated an artificial magnetic dipole moment; this magnetic moment only occurred during the designed pulse duration in the time domain. Our proposed concept and structures were validated numerically and experimentally; thus, our results could be used to address electromagnetic and related issues sharing the same frequency component via the variation of the pulse width as an additional degree of freedom.

physics.app-ph↗

arXiv2024

Design of reconfigurable Huygens metasurfaces based on Drude-like scatterers operating in the epsilon-negative regime

In this study, we investigate the feasibility of designing reconfigurable transmitting metasurfaces through the use of Drude-like scatterers with purely electric response. Theoretical and numerical analyses are provided to demonstrate that the response of spherical Drude-like scatterers can be tailored to achieve complete transmission, satisfying a generalized Kerker's condition at half of their plasma frequency. This phenomenon, which arises from the co-excitation of the electric dipole and the electric quadrupole within the scatterer, also exhibits moderate broadband performance. Subsequently, we present the application of these particles as meta-atoms in the design of reconfigurable multipolar Huygens metasurfaces, outlining the technical prerequisites for achieving effective beam-steering capabilities. Finally, we explore a plausible implementation of these low-loss Drude-like scatterers at microwave frequencies using plasma discharges. Our findings propose an alternative avenue for Huygens metasurface designs, distinct from established approaches relying on dipolar meta-atoms or on core-shell geometries. Unlike these conventional methods, our approach fosters seamless integration of reconfigurability strategies in beam-steering devices.

physics.app-ph↗

arXiv2023

Phase-Gradient Huygens Metasurface Coatings for Dynamic Beamforming in Linear Antennas

The beamforming capabilities of conformal cylindrical Huygens metasurface (HMS) coatings for linear antennas are assessed. It is shown that by engineering the phase-gradient profile of the HMS, the original omnidirectional radiation pattern of the linear antenna can be shaped to form multi- or single-beam configurations. A closed-form expression for the phase-insertion profile of the cylindrical coating required to achieve the desired radiation pattern profile is derived, and several full-wave numerical examples supporting our claims are reported. A configuration exploiting a realistic HMS layout is also discussed and it is shown that, by making the metasurface reconfigurable through the use of tunable lumped elements, the radiated beams can be dynamically steered in space. This new design methodology could find application in smart electromagnetic environment scenarios for dynamically rerouting the signal towards multiple users.

physics.app-ph↗

arXiv2022

Pulse-Driven Self-Reconfigurable Meta-Antennas

Wireless communications and sensing have notably advanced thanks to the recent developments in both software and hardware. Although various modulation schemes have been proposed to efficiently use the limited frequency resources by exploiting several degrees of freedom, antenna performance is essentially governed by frequency only. Here, we present a new antenna design concept based on metasurfaces to manipulate antenna performances in response to the time width of electromagnetic pulses. We numerically and experimentally show that by using a proper set of spatially arranged metasurfaces loaded with lumped circuits, ordinary omnidirectional antennas can be reconfigured by the incident pulse width to exhibit directional characteristics varying over hundreds of milliseconds or billions of cycles, far beyond conventional performance. We demonstrate that the proposed concept can be applied for sensing, selective reception under simultaneous incidence and mutual communications as the first step to expand existing frequency resources based on pulse width.

physics.app-ph↗

arXiv2022

Quadratic-Gradient Metasurface-Dome for Wide-Angle Beam Steering Phased Array with Reduced Gain-Loss at Broadside

The quest for increasing the scanning range of a phased array is a challenging task for antenna engineers, and its solution could lead to significant advances in different applicative scenarios, ranging from 5G and beyond 5G communications to radar and satellite systems. For this purpose, the use of a deflecting meta-dome is one of the most promising solutions recently proposed that, however, still presents some inherent limitations, such as the significant reduction of the broadside gain of the array, due to the diverging effect of the dome, as well as the complexity of the implementation due to the need of a continuous phase profile. In this framework, the paper aims at proposing some technical solutions for maximizing the meta-dome performance and relaxing the implementation complexity. In particular, by properly discretizing and engineering the phase profile along the dome and by taking into account the different angles of incidence onto the meta-cells, we show how it is possible designing realistic meta-domes with reduced insertion loss at broadside, improved steering capabilities, and a reduced profile. In addition, a complete design workflow for a realistic meta-dome based on cascaded metasurfaces is presented.

physics.app-ph↗

arXiv2021

Metasurfaces 3.0: a New Paradigm for Enabling Smart Electromagnetic Environments

So far, the environment has been considered as a source of fading, clutter, blockage, etc., with detrimental consequences for the efficiency and robustness of communication systems. However, the intense research developed toward beyond-5G communications is leading to a paradigm change, in which the environment is exploited as a new degree of freedom and plays an active role in achieving unprecedented system performances. For implementing this challenging paradigm, it has been recently proposed the use of intelligent surfaces able to control almost at will the propagation of electromagnetic waves. In this framework, metasurfaces have emerged as a promising solution, thanks to their field manipulation capabilities achieved through low-cost, lightweight, and planar structures. The aim of this paper is to review some recent applications of metasurfaces and cast them in the scenario of next-generation wireless systems. In particular, we show their potentialities in overcoming some detrimental effects presented by the environment in wireless communications, and discuss their crucial role towards the practical implementation of a smart electromagnetic environment.

physics.app-ph↗

arXiv2021

Design of High-Q Passband Filters Implemented Through Multipolar All-Dielectric Metasurfaces

We propose a novel class of ultrathin high Q passband filters designed by properly combining different multipolar resonances sustained by an all dielectric metasurface. A rigorous analytical model, based on surface impedance homogenization and accounting for the effects of both dipolar and the quadrupolar contributions to the overall scattering response, is derived and verified through numerical simulations. Then, it is described how it is possible to engineer the interactions between dipoles and quadrupoles in a metasurface made by core shell spherical elements to design ultrathin and broadband dielectric mirrors with a narrow transmission band. The proposed filters exhibit high Q factor resonances and can be implemented using realistic materials at either microwave or optical frequencies. Finally, we discuss how the proposed dielectric filters can be used to design self filtering aperture antennas exhibiting higher out of band selectivity compared with those implemented through metallic resonators.

physics.app-ph↗

arXiv2021

On the Use of Nonlinear Metasurfaces for Circumventing Fundamental Limits of Mantle Cloaking for Antennas

The aim of this communication is to investigate and demonstrate the possibility to overcome the fundamental limitations of mantle cloaking for antennas by exploiting nonlinear metasurfaces. First, we recap and give additional physical insights about the fundamental bounds that apply to the electric properties of an antenna that is made invisible at its own resonance frequency. Then, an innovative strategy is proposed to circumvent these limits through the introduction of nonlinear elements that are able to dynamically transform the geometry of the cloaking metasurface depending on the power level of the impinging field. Different nonlinear designs are discussed, and their effectiveness is assessed through the relevant benchmark example of a half-wavelength dipole antenna able to efficiently transmit high-power signals while being invisible to low-power ones. In addition, the capability of such nonlinear mantle cloaks to enable the shaping of the radiation pattern of an antenna array depending on the power level of the received/transmitted signal is demonstrated. These innovative cloaking devices may find applications in different radiating systems enabling unprecedented functionalities.

physics.app-ph↗

arXiv2021

Temporal interfaces by instantaneously varying boundary conditions

Temporal metamaterials have been recently exploited as a novel platform for conceiving several electromagnetic and optical devices based on the anomalous scattering response arising at a single or multiple sudden changes of the material properties. However, they are difficult to implement in realistic scenarios by switching the permittivity of a material in time, and new strategies to achieve time interfaces in a feasible manner must be identified. In this paper, we investigate the possibility to realize a temporal metamaterial without acting on the material properties, but rather on the effective refractive index and wave impedance perceived by the wave during the propagation in an empty guiding structure by varying the boundaries in time. We demonstrate analytically and through numerical experiments that suddenly changing the physical distance between the metallic plates of a parallel-plate waveguide will induce an effective temporal interface. In addition to the standard backward and forward scattered fields at different frequencies due to the temporal interface, we also identify the presence of a static field necessary to satisfy the continuity of the electromagnetic field across the interface. The proposed concept can be extended to temporally controlled metasurfaces, opening an easier path to the design and realization of novel devices based on time-varying metamaterials at microwave and optical frequencies.

physics.optics↗

arXiv2021

Electromagnetic Isolation Induced by Time-Varying Metasurfaces: Non-Reciprocal Bragg Grating

In this letter, we propose a magnet-less non-reciprocal isolating system based on time-varying metasurfaces. Two parallel time-varying metasurfaces, one for frequency up-conversion and one for down-conversion by the same amount, are used for realizing a region of space where incident waves from opposite directions experience an opposite Doppler frequency shift. As a result, any device within this region becomes sensitive to the illumination direction, exhibiting a different scattering response from opposite directions and thus breaking reciprocity. Very importantly, thanks to the opposite frequency shift of the metasurfaces, the frequency of the transmitted electromagnetic field is the same as for the incident one. Here, we demonstrate this general approach by using a Bragg grating as the device between the time-varying metasurfaces. The combined structure of the metasurfaces and the grating exhibits different transmission and reflection properties for opposite illumination direction, thereby realizing an isolator. More broadly, this letter presents a strategy for converting any conventional electromagnetic device to a non-reciprocal one by placing it between two time-varying metasurfaces. This approach opens the door to several new non-reciprocal components based on thin and lightweight metasurfaces, which are simpler to realize compared to their volumetric counterparts.

physics.app-ph↗

arXiv2021

Phase-Induced Frequency Conversion and Doppler Effect with Time-Modulated Metasurfaces

Metasurfaces consisting of electrically thin and densely packed planar arrays of subwavelength elements enable an unprecedented control of the impinging electromagnetic fields. Spatially modulated metasurfaces can efficiently tailor the spatial distribution of these fields with great flexibility. Similarly, time modulated metasurfaces can be successfully used to manipulate the frequency content and time variations of the impinging field. In this paper, we present time-modulated reflective metasurfaces that cause a frequency shift to the impinging radiation, thus realizing an artificial Doppler effect in a non-moving electrically thin structure. Starting from the theoretical analysis, we analytically derive the required time modulation of the surface admittance to achieve this effect, and present a realistic time-varying structure, based on a properly designed and dynamically tuned high-impedance surface. It is analytically and numerically demonstrated that the field emerging from the metasurface is up-,down-converted in frequency according to the modulation profile of the metasurface. The proposed metasurface concept, enabling a frequency modulation of the electromagnetic field on-the-fly, may find application in telecommunication, radar, and sensing scenarios.

physics.app-ph↗

arXiv2020

Waveform-Selective Mantle Cloaks for Intelligent Antennas

We present the design of an innovative wire antenna able to automatically hide or reveal its presence depending on the waveform of the received/transmitted signal. This unconventional behavior is achieved through the use of a novel waveform-selective cloaking metasurface exploiting a meander-like unit cell loaded with a lumped-element circuit capable to engineer the scattering of the antenna depending on the waveform of the impinging signal. Due to the time-domain response of the lumped-element circuit, the antenna is able switching its scattering behavior when interacts with either a pulsed wave (PW) or a continuous wave (CW) signal. The proposed configuration paves the way to a new generation of cloaking devices for intelligent antenna systems, extending the concept of antenna as a device capable to sense the external environment and change its electromagnetic behavior accordingly.

physics.class-ph↗

arXiv2020

A Topological Design Tool for the Synthesis of Antenna Radiation Patterns

Patch antennas are among the most popular radiating elements, yet their quasi-2-D structure reduces the degrees of freedom available to tailor their radiation pattern. To overcome this limitation, a possible solution consists in etching on a grounded substrate two concentric radiating elements and combining two modes (one for each element) with proper amplitude/phase relations. Although this technique leads, in principle, to an infinite number of possible configurations (i.e., each patch element can support an infinite number of modes), the theoretical and experimental verifications available in the literature are limited to the first two radiating modes (TM 11 and TM 21 ) of a circular patch antenna. Recently, we have shown that the design of this circular patch can be effectively performed by exploiting the topological properties of vortex fields and, in particular, by controlling the phase singularity exhibited by the higher order right-handed circularly polarized (RHCP) TM 21 mode of the circular patch. Since the number of RHCP higher order modes of a circular patch is infinite, we can in principle deal with an arbitrary number of phase singularity points, whose combined control leads to unprecedented possibilities to shape the radiation pattern of a circular patch. In this article, we present a complete design tool to determine the number and position of phase singularity points arising when combining the RHCP modes of a circular patch antenna and, eventually, manipulate them to synthesize the required radiation pattern. As a realistic application example, we show how the proposed tool can be used to effectively design a single antenna whose radiation pattern can be properly tailored to switch between two different states, i.e., a sector and a saddle shape, widely used in base stations for mobile and satellite communications, respectively.

physics.class-ph↗

arXiv2020

Waveguide Components and Aperture Antennas With Frequency- and Time-Domain Selectivity Properties

Filtering modules are essential devices of modern microwave systems given their capability to improve the signal-to-noise ratio of the received signal or to eliminate the unwanted interferences. For discriminating between different components, a filter exhibits a frequency-selective response that, however, is not able to distinguish between different signals whose spectrum falls within the passband of the filter itself. In this regard, some electromagnetic structures exhibiting, at the same frequency, different responses depending on the waveform of the incoming waves have been recently proposed. In this communication, we extend the aforementioned approach to the case of a standard waveguide filtering module. In particular, by loading a bandpass filtering iris with a proper lumped-element circuit, we design a waveguide component able to distinguish between different pulsed waves, even at the same frequency, depending on their pulsewidth. Moreover, by using this filter for capping an open-ended rectangular waveguide, a radiating element with both frequency- and time-domain selectivity properties is presented. The structures discussed in this communication may pave the way to a new class of microwave systems that, being both frequency selective and time selective, are less sensitive to noise and interferences.

physics.class-ph↗