arXiv subjects

Enrica Martini

Publications and source records attributed to Enrica Martini.

6 recordsLinked to original sources

arXiv2024

Ultra-Long-Range Bessel Beams via Leaky Waves with Mitigated Open Stopband

Open stop-band (OSB) mitigation techniques are commonly used to improve the far-field radiating properties of leakywave antennas based on periodic structures. Recently, leaky waves have been proposed to focus energy in the near field through Bessel beams. However, the focusing character of Bessel beams is notably limited to a maximum distance known as the nondiffractive range. In this work, an OSB mitigation technique is originally exploited to significantly extend the nondiffractive range of a Bessel beam generated by a leaky-wave launcher in the microwave/millimeter-wave range. A comprehensive analysis of this device is presented, comparing the performance of the proposed launcher with the typical structure of a leaky-wave Bessel-beam launcher where the OSB is not suppressed. Theoretical results corroborated by full-wave simulations demonstrate that the proposed device, designed around 30 GHz, achieves an impressive nondiffractive range of approximately 25 m, which corresponds to 2500 vacuum wavelengths and to 50 times its aperture diameter of 50 cm. These results look particularly attractive for, e.g., near-field communications and wireless power transfer applications, where focusing energy in narrow spots and over large distances is a key factor.

physics.optics↗

arXiv2023

A New Strategy for Designing Dual-band Antennas Based on Double-layer Metasurfaces

We present a new strategy for the design of dual-band planar antennas based on metasurfaces (MTSs) in the microwave and millimeter-wave regimes. It is based on a double layer structure obtained by cascading two subwavelength patterned metallic claddings supported by a grounded dielectric slab. Each metallic layer is responsible for controlling radiation at one frequency, and it is engineered to be transparent at the other frequency. Hence, the two metallic layers can be designed independently using the well-established techniques for the design of single-layered MTS antennas. Layers decoupling is achieved by suitably exploiting Foster's reactance theorem, which regulates the frequency response of the impedance sheet modeling the metallic layer. By using the proposed strategy, a dual-band double-layered MTS antenna radiating a circularly polarized broadside beam in two popular frequency bands for climate science applications is designed and numerically verified.

physics.app-ph↗

arXiv2021

Smart Radio Environments

This Roadmap takes the reader on a journey through the research in electromagnetic wave propagation control via reconfigurable intelligent surfaces. Meta-surface modelling and design methods are reviewed along with physical realisation techniques. Several wireless applications are discussed, including beam-forming, focusing, imaging, localisation, and sensing, some rooted in novel architectures for future mobile communications networks towards 6G.

physics.class-ph↗

arXiv2020

Perfect conversion of a TM surface-wave into a TM leaky-wave by an isotropic periodic metasurface printed on a grounded dielectric slab

This paper presents an exact solution for a perfect conversion of a TM-polarized surface wave (SW) into a TM-polarized leaky-wave (LW) using a reciprocal and lossless penetrable metasurface (MTS) characterized by a scalar sheet impedance, located on a grounded slab. In contrast to known realizations of leaky-wave antennas, the optimal surface reactance modulation which is found here ensures the absence of evanescent higher-order modes of the field Floquet-wave expansion near the radiating surface. Thus, all the energy carried by the surface wave is used for launching the single inhomogeneous plane wave into space without accumulation of reactive energy in the higher-order modes. It is shown that the resulting penetrable MTS exhibits variation from an inductive to a capacitive reactance passing through a resonance. The present formulation complements a previous paper of the authors in which a perfect conversion from TM-polarized SW to TE-polarized LW was found for impenetrable boundary conditions. Here, the solution takes into account the grounded slab dispersion and it is convenient for practical implementation.

physics.class-ph↗

arXiv2020

Surface waves on self-complementary metasurfaces: intrinsic hyperbolicity, dual-directional canalization and TE-TM polarization degeneracy

Self-complementary metasurfaces have gained significant attention due to their unique frequency-independent transmission and reflection properties and the possibility of the polarization transformation of plane waves. In this paper, we focus on the near-field spectrum to investigate both theoretically and experimentally the properties of surface waves supported by anisotropic self-complementary metasurfaces. We show that as a consequence of the electromagnetic Babinet's duality, such structure is hyperbolic for any frequency. We reveal the polarization degree of freedom inherent to plane waves by demonstrating the broadband TE-TM polarization degeneracy of the surface waves along two principal directions. We demonstrate the possibility of switching the canalization direction of 90 degrees by a very small frequency shift paving a way to the extreme tunability and surface wave routing. The results obtained open a plethora of opportunities for practical applications, including flat polarization devices, optical data processing systems and antennas.

physics.app-ph↗

arXiv2018

Exact Solution for the Protected TEM edge mode in a PTD-Symmetric Parallel-Plate Waveguide

A Parity Time-reversal Dual (PTD) symmetric structure constituted by a Perfectly-Electric-Perfectly magnetic (PEC-PMC) parallel plate waveguide (PPW) is analyzed. This waveguide supports unimodal transverse electromagnetic (TEM) edge mode propagation protected against back-scattering from a certain class of deformations and defects. The TEM solution is found in analytical form by using three different methods, namely conformal mapping, mode-matching, and Fourier-transform methods. It is shown through numerical simulations that the mode propagation is robust with respect to deformations such as 90° bends and discontinuity such as transition to free-space. Implementation of the PMC boundary conditions via both a bed of nails and a mushroom structure is also successfully investigated.

physics.class-ph↗