Time-varying metamaterials and metasurfaces for antennas and propagation applications

In this contribution we present the most recent results from our group about the opportunities offered by time-varying metamaterials and metasurfaces for conceiving antenna systems and devices exhibiting artificial non-reciprocity, frequency conversion, energy accumulation and temporal electromagnetic scattering. Such artificial metastructures are characterized by constitutive parameters (permittivity, permeability and/or surface impedance) that are modulated in time through an external control or requires modulated excitation signal for enabling anomalous scattering behaviour. Here, we briefly describe the physical insights of the unusual interaction arising between the electromagnetic field and such metamaterials and metasurfaces, and then we present some antennas and propagation applications, showing the performances of non-reciprocal antenna systems, magnet-less isolators, Doppler cloaks, temporal devices and metasurface-based virtual absorbers.

EBG waveguides for contactless surface impedance measurements

A method for the estimation of sheet impedance of thin sample which does not require a direct contact with the sample under test is proposed. The surface impedance is calculated through an inversion procedure exploiting the scattering parameters obtained through a waveguide measurement setup. An inversion procedure based on the representation of the waveguide-air-waveguide section as a π junction is employed. In order to prevent the field leakage from the air gap created for hosting the thin sheet, an EBG surface is introduced on the flange of the waveguide. It is shown that the introduction of the EBG surface remarkably improves the estimation of the surface impedance of the thin sheet with respect to the case without EBG.

Artificial and natural electromagnetic structures with strongly inductive surface impedance

Artificial and natural electromagnetic structures with strongly inductive surface impedance are considered. The object of the research is layered structures of the “dielectric-conductor” type. The existence of impedance media with the maximum possible phase of a strongly inductive impedance in the range from a few hertz to tens of gigahertz has been established. The results of numerical modelling of the propagation of decimeter radio waves over a plane strongly inductive surface are presented, these numerical results are necessary for calculating the attenuation function W and the field level E of microwave electromagnetic waves.