We present the design of miniaturized resonant inclusions to be employed in the practical realization of metamaterial samples with anomalous values of the real part of the permeability. Such inclusions, in fact, can be employed in the design of both mu-negative (MNG) materials and artificial magnetodielectrics (with negative and high-positive values of the real part of the permeability, respectively). The inclusions here considered are the multiple split-ring resonators (MSRRs), that represent a straightforward extension of the commonly used split-ring resonators (SRRs), and the spiral resonators (SRs), that enable a greater miniaturization rate. Some physical insights on the resonance mechanism and on the inherent saturation of the resonant frequency when increasing the number of the rings of the MSRRs and the number of the turns of the SRs are given in the paper. New and accurate analytical design formulas, based on a quasi-static model, for both MSRRs and SRs are derived and tested through a proper comparison with the existing formulas and full-wave numerical results. Both MSRRs and SRs are shown to be useful to reduce the electrical dimensions of the resonant inclusions when synthesizing artificial metamaterials.

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.

In this paper, we derive quasi-static equivalent-circuit models for the analysis and design of different types of artificial magnetic resonators-i.e., the multiple split-ring resonator, spiral resonator, and labyrinth resonator-which represent popular inclusions to synthesize artificial materials and metamaterials with anomalous values of the permeability in the microwave and millimeter-wave frequency ranges. The proposed models, derived in terms of equivalent circuits, represent an extension of the models presented in a recent publication. In particular, the extended models take into account the presence of a dielectric substrate hosting the metallic inclusions and the losses due to the finite conductivity of the conductors and the finite resistivity of the dielectrics. Exploiting these circuit models, it is possible to accurately predict not only the resonant frequency of the individual inclusions, but also their quality factor and the relative permeability of metamaterial samples made by given arrangements of such inclusions. Finally, the three models have been tested against full-wave simulations and measurements, showing a good accuracy. This result opens the door to a quick and accurate design of the artificial magnetic inclusions to fabricate real-life metamaterial samples with anomalous values of the permeability.

We analyze the matching and radiation properties of subwavelength resonant patch antennas filled with double-negative, double-positive, and/or single-negative metamaterial blocks. Analyzing the theoretical limits inherently present when loading such common radiators with metamaterials, we show how these configurations may exhibit in principle an arbitrarily low resonant frequency for a fixed dimension, but they may not necessarily radiate efficiently when their size is electrically small. However, interesting possibilities are suggested to overcome these limitations by employing circular or more complex patch geometries in order to select specific modes that, when appropriate loading ratios between the filling materials are chosen, also ensure radiation performance comparable qualitatively with a regular patch radiator of standard dimensions. Realistic numerical simulations, considering material dispersion, losses and the presence of the antenna feed are presented, showing how a practical realization is foreseeable. This may open novel venues in the design of small-scaled radiators with enhanced performance, which is of interest for many applications

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 ( λ ₀ /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.

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.