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This paper proposes a new approach for the optimal design of microwave absorbing composites backed by a PEC layer and characterized by frequency dependent permeability and permittivity. The reflection coefficient is expressed as a function of the difference between the absorber hyperbolic input impedance and the free space wave impedance, considering an impinging plane wave with either normal or oblique incidence angle. The impedance matching condition for the selected frequency and incidence angle is solved in terms of literal expression of the optimal thickness, which is compared with the one quarter wavelength thickness given by a new accurate expression. The optimal thickness is used for the design of microwave absorbers made by dielectric-magnetic and dielectric composite materials. The frequency spectra of the absorber input impedances and reflection coefficients are computed in the frequency range from 2 GHz up to 18 GHz and for an incidence angle ranging between 0° and 30°. The obtained results prove the validity of the literal expression of the composite optimal thickness which explicitly shows the crucial parameters for the absorbing performances, obscured in common numerical procedures.

In this work, novel flexible metal-free polymeric cathode electrodes are developed through a cost-effective procedure for low energy generation applications. For this purpose, a nanocomposite film made of poly vinylidene fluoride (PVDF) filled with graphene nanoplatelets (GNPs) is produced through an easy process, without the use of any chemical or physical doping agent. The fabricated PVDF/GNP nanocomposite films are morphologically and chemically characterized and their applicability as polymeric electrodes is investigated through electrochemical tests.

A porous graphene based PVDF aerogel is produced through a cost-effective procedure, for possible application as sweat sensor. The aerogel samples were characterized in terms of porosity, density, morphological and electrical properties through high-resolution scanning electron microscopy (HR-SEM) and time-monitoring of the sample dc electrical resistance.

The electromagnetic field radiated by Cu-graphene interconnects is predicted in the frequency domain using the equivalent single conductor formulation, and it is compared with the field radiated by a single-wall carbon nanotube (SWCNT) bundle interconnect having the same cross section. The effect of the frequency, of the configuration, of the graphene, and SWCNT mean free paths is investigated. The scope is to predict the risk of electromagnetic interference against nearby components and devices, and to define the most critical conditions.

A new adaptive terahertz absorbing screen providing a reflection coefficient lower than −10 dB in the frequency range 0.6–2.2 THz and with total thickness around 70 μm is proposed. The designed Salisbury screen, backed by a perfect electric conducting plate, consists of a first graphene layer as lossy sheet and two spacers made of polyethylene terephthalate (PET), separated by a tunable graphene/SiO2 laminate (GL). An electrostatic field up to 0.06 V/nm is applied across the GL in order to tune the electrical conductivity of the graphene layers, with the aim of minimizing the screen total reflection coefficient. A design procedure based on the transmission line method is proposed and a parameter sensitivity analysis of the reflection coefficient is carried out. The influence of the carrier charge mobility and of the number of graphene sheets composing the GL is investigated, considering different values of the electrostatic field in the frequency range 0.1–5 THz.

Closed-form expressions describing the tensorial conductivity of an electrically or magnetically biased monolayer graphene are provided in order to highlight the low-gigahertz gyrotropic, shielding and sensing properties. The longitudinal and transverse (Hall) conductivities are given as explicit functions of the fundamental electromagnetic quantities, i.e. the magnetic and electric field bias, B 0 and E 0 , and the carrier charge mobility μ The developed simple expressions of the components of the electric field transmission coefficient are utilized to compute the polarization rotation angle θ and the shielding effectiveness (SE), in case of normally incident plane wave. The dependence of θ on B 0 is investigated, and the magnetic field value providing the maximum θ is found. The simulation model is applied to compute gyrotropic, SE and sensing performances of the biased graphene sheet at low-gigahertz regime. Moreover, exploiting the sensing properties of the biased graphene sheet, the measured value of θ is used to evaluate B 0 , E 0 and μ.

An innovative lightweight and flexible multilayered screen made by electrically doped graphene sheets laminated with thin films of polyethylene terephthalate (PET) is proposed. The shielding effectiveness (SE) of the screen is computed in the low GHz frequency range assuming that the graphene/PET multilayer is modelled as an equivalent single-layer shield having an effective conductivity. A rigorous simulation model is utilized to define the maximum frequency of applicability of the proposed approximate formulation of the SE. A SE of 40 dB is obtained in a wide frequency range, up to more than 200 GHz, with a screen consisting of 24 graphene layers electrically doped and having a total thickness of 0.69 µm.

In recent years, several studies have demonstrated the strong cytotoxicity toward bacteria of graphene-based materials, suggesting their use as antimicrobial agents. The objective of this study was to evaluate the antibacterial activity against Streptococcus mutans, the principal microbiological agent in the etiology of dental caries, of two types of graphene nanoplatelets (GNPs), characterized by different thickness and lateral dimensions of the flakes. The antimicrobial properties of GNPs were valued on some plaque and saliva samples extracted from children with dental caries. Our results show that the killing effect of GNPs on S. mutans cells is both lateral size and thickness dependent. In fact, lower thickness and smaller size GNPs exhibit stronger antibacterial activity than larger and thicker ones. Scanning electron microscopy analysis revealed that GNPs interact strongly with cells. This study suggests that GNPs may be highly effective against S. mutans and therefore caries.

Innovative multilayered screens made of laminated graphene sheets, with SiO $_{2}$ as interlayer, over a glass substrate are proposed as electrically-tunable electromagnetic shields at terahertz. The shielding effectiveness (SE) modeling is developed applying the transmission line method in a reverberating environment (i.e., with the screen surface illuminated by an infinite set of plane waves impinging with all possible propagation directions), which is of particular relevance in electromagnetic compatibility (EMC) studies. A new equivalent single layer (ESL) model of the graphene/SiO $_{2}$ laminate (GL) is also proposed in order to provide a simple computationally-efficient method for the EMC design of GL shielding configuration via numerical EM tools. The approximate model is validated by comparison with the results obtained applying the exact one. The sensitivity analysis of the SE in reverberating environment is performed in the frequency range up to several tens of terahertz with respect to: the electric field bias of the graphene sheets, affecting their chemical potential level through an electrostatic carrier doping; the relaxation time characterizing the electron transport in graphene; the thickness of the SiO $_{2}$ interlayers. Finally, the SE computed for different shielding configurations against a plane wave with normal or oblique incidence is compared with the one obtained in a reverberating environment in order to highlight the most significant differences at terahertz frequencies.

In this work we investigate the shielding properties of graphene-based films, produced by spray casting deposition, which is a cost-effective technique that can be directly scaled to industrial applications. The deposition process is optimized in order to produce uniform films made of well dispersed graphene nanoplatelets (GNP), having thicknesses in the range 3–8 microns. The sheet resistance and the shielding effectiveness up to 18 GHz of films produced using GNP-suspensions at different concentrations are measured and compared with the ones of carbon nanotube (CNT)-based films, produced in the same conditions. The obtained results demonstrate the superior shielding properties of graphene-based films with respect to CNT-ones, mainly due to the bi-dimensional shape of GNPs, which contributes to minimizing the contact resistances among adjacent nanostructures. It is also demonstrated that after a thermal annealing at 250°C, the final measured shielding effectiveness of the produced GNP-film triplicates in linear scale, reaching the value of 30.6 dB.

Terahertz communication technologies are based on the use of a frequency range from 300 GHz up to 3 THz, according to standardization and regulation activities of the IEEE 802.15 IG THz. Graphene, which is characterized by excellent electrical, thermal and mechanical properties, is an attractive choice for EMI shielding applications. New models are proposed for the analysis of the shielding effectiveness of graphene multilayer thin films in the lower THz range taking into account the frequency dependence of the electrical conductivity. Already known models are applied to estimate the optical transmittance. Moreover, transparent substrates coated by graphene multilayer sheets are simulated. The proposed modeling approach is applied to the performance analysis of graphene multilayer thin sheets in the frequency range up to 1 THz.

Graphene films are grown by chemical vapour deposition on copper layer and then transferred onto a silicon substrate, coated with silicon dioxide. The topological characterization of the produced film is performed by atomic force microscopy, and the sheet resistance is measured by applying the four-probe test method. The equivalent single conductor model is then used in order to analyze the signal propagation along a nanointerconnect made with multilayer graphene over silicon dioxide, in a wide frequency range, up to 100 GHz. The comparison of the radio-frequency performances of the nanointerconnect, modeled by using either the measured value of effective resistivity or a theoretical estimation of the p.u.l. resistance, suggests that graphene films grown by chemical vapor deposition are more suitable for application as low frequency electrical interconnections in flexible electronics, than in high-speed integrated circuits.

The crosstalk analysis among MWCNTs in a complex bundle is performed in the frequency domain in the range up to 100 GHz. Numerical simulations are performed by using both the multiconductor transmission line (MTL) method and reduced-order equivalent models based on the equivalent single conductor (ESC) approach in order to reduce the complexity of the system. Each MWCNT of the bundle is firstly modeled as an ESC; next, the parallel connected ESCs of the bundle are further represented by only one equivalent conductor. The accuracy of the proposed approximation is assessed and discussed.

The use of novel nanocomposites, consisting in polymeric-based system filled with graphite-nanoplatelets (GNP), is proposed to increase the shielding performance and to reduce the Q of small enclosures excited by impinging plane waves in the gigahertz frequency range. Structure and electrical characteristics of the realized GNP-based composites are described. Absorbing performances of a planar infinite screen made with two layers panel backed on a metallic surface, illuminated by a TM and a TE polarized plane waves, are computed in reverberating conditions. The same absorbing nanostructure is considered to realize the walls of a small-dimensions cubic box with a slot aperture. The full-wave numerical simulations demonstrate that the use of the new material produces resonance damping of microwave electric field and a factor 104 reduction of the Q of a full-metallic enclosure.

The transient shielding performances of small transparent cubic boxes illuminated by an impulsive plane wave, exciting the frequency range up to several gigahertz, are analyzed by applying an 3D full wave method. The box is made by transparent polycarbonate walls coated with a thin nanostructured transparent film, consisting of alternating thin layers of metal (Ag) and dielectric (TiO 2 ) materials, and contains a total of 68 nm of silver. A GNP-based nanocomposite absorber, custom designed and tuned on the first resonance frequency of the enclosure is used to panel the inside of the box in order to dump unwanted reflections.

This paper investigates the shielding effectiveness properties of different types of carbon fiber reinforced composites (CFRC), typically used aboard air-vehicles, in the frequency range from 100 kHz up to 18 GHz. Both single-layer and multilayer, unidirectional or woven, CFRCs are analyzed, and the critical issue concerning sample preparation is addressed. The study is aimed at defining an effective single layer model of the CFRC laminate, characterized by an effective frequency-dependent electrical conductivity, which is extracted from the measured shielding effectiveness.

Carbon nanostructures such as carbon nanotubes and graphite nanoplatelets can be included in very low weight percentages in a polymer matrix to create new lightweight nanocomposites with improved performances. The development of simulation models for the prediction of the effective complex permittivity of such composites is very important for design and performance optimization purposes. In this study we propose a multiscale expression of Maxwell Garnett formula, with the aim of modeling the effective permittivity of multifiller composites, including multiwall carbon nanotubes or graphite nanoplatelets at the nanoscale, and nickel-coated short carbon fibers at the micro/macro-scale. A statistical model is also implemented in order to account for variations of the filler geometrical properties, which cannot be fully controlled at the synthesis level, in particular at the nanoscale.

The electromagnetic field radiated by a multiwall carbon nanotube is predicted in the frequency domain using the equivalent single conductor (ESC) formulation, and it is compared with the field radiated by a single wall carbon nanotube bundle having circular cross section and the same external diameter. The effect of the frequency and of the configuration on the near field level is investigated, in order to predict the risk of electromagnetic interference against nearby components and devices, and to define the most critical conditions.

Graphite nanoplatelets (GNPs) can be included in very low weight percentages in a polymer matrix to create new lightweight nanocomposites with desired electromechanical properties, for application in strain sensors. The development of simulation models for the prediction of the electromechanical characteristics of such composites is very important for design and performance optimization purposes. In this study we propose an electromechanical model for the prediction of the response of a strain sensor made of GNP-filled composite. The developed simulation approach is based on the tunneling-percolation model of the electrical transport in the composite, and on the experimental characterization of the dc conductivity of GNPs and GNP-filled composites at different concentrations, produced in the CNIS Labs of Sapienza University.

A bundle of single wall carbon nanotubes (SWCNTs) with circular cross-section is treated as a homogeneous material with a.c. effective conductivity σ(ω), which is evaluated by using the Drude's complex expression. The effective d.c. conductivity of the homogeneous bundle is obtained from the total d.c. resistance. The frequency-domain distribution of current density along radial direction of the bundle is utilized to obtain the expressions of the skin depth and the effective impedance. Applications of the proposed formulation to SWCNT bundles of different configurations are carried out. The obtained results show the saturation behaviour of the effective resistance and inductance above a critical frequency, which depends on the momentum relaxation time of the CNTs.