Alessio Tamburrano

Single-Conductor Transmission-Line Model of Multiwall Carbon Nanotubes

The equivalent single-conductor model of a multiwall carbon nanotube (MWCNT) interconnect is derived analytically from the rigorous formulation of the complex multiconductor transmission-line propagation equations. The expressions of the per-unit-length (p.u.l.) equivalent quantum capacitance and kinetic inductance are obtained in closed form. A new accurate approximated expression of the equivalent p.u.l. quantum capacitance is proposed. It is demonstrated, through analytical derivations and numerical calculations, that the new expression is valid for the most of MWCNT interconnect configurations, whereas a more simplified formula, obtained on the basis of qualitative considerations, produces high approximation errors. The proposed model is solved in both the frequency and time domains. Transient analyses are performed in order to predict the attenuation and time delay of a pulse signal transmitted along an MWCNT as a function of the tube length and number of shells. Simulation results are also compared with measured data available in literature.

EMC Impact of Advanced Carbon Fiber/Carbon Nanotube Reinforced Composites for Next-Generation Aerospace Applications

This paper presents a comparative analysis of the electromagnetic properties of new composite materials that are of interest to future aircraft/aerospace structures. The fabrication process of single-phase and new multiphase micro/nanocomposites is described. Carbon black, carbon fibers, and multiwall carbon nanotubes are randomly mixed into an epoxy resin matrix at various weight fractions and compositions. The experimental characterization in the frequency range 8-18 GHz shows that the dispersion characteristics of short-carbon-fiber-reinforced composites can be properly controlled by the addition of nanopowders and nanotubes into the mixture. Numerical simulations demonstrate the feasibility of the fabricated materials for the design of new electromagnetic micro/nanostructured shields and radar-absorbing laminates. Thin dielectric Salisbury screens are especially designed to exhibit minimum reflection coefficient at 15 GHz. It shows that the total thickness of the screen can be reduced below 2 mm by using a lossy sheet made of three-phase composites.

Fast Transient Analysis of Next-Generation Interconnects Based on Carbon Nanotubes

The scaling of copper wires and the increase in signal switching speed produce transient crosstalk coupling between interconnect lines, which causes overshoots and additional time delay. The time-domain analysis of CMOS gates driving next-generation interconnects consisting of single wall carbon nanotube (SWCNT) bundles or multiwall carbon nanotubes (MWCNTs) is carried out. Accurate simulation models of SWCNT bundles and MWCNTs are proposed in the frequency domain by using both the multiconductor transmission line (MTL) formulation and the multiequivalent single conductor (MESC) approach. The fast transient voltage responses of two coupled nanointerconnects of 14 and 22 nm technologies to a pulsed input are computed by means of both the MTL and the MESC models. The obtained results are in good agreement. The same agreement is achieved by computing the 50% time delay of the output voltages.

Synthesis, Modeling, and Experimental Characterization of Graphite Nanoplatelet-Based Composites for EMC Applications

Graphite nanoplatelets (GNPs) are bidimensional carbon nanostructures consisting of stacks of graphene sheets, having thickness in the range from one up to a few tens of nanometers, and lateral linear dimension in the micrometer range. These nanostructures represent a good candidate to replace carbon nanotubes in composites for electromagnetic applications. This paper proposes a new model based on the Maxwell-Garnett approach to compute the effective complex permittivity of GNP-filled nanocomposites. The effect of the dimensional probabilistic distribution of the nanofiller is investigated. To this purpose, an extensive experimental characterization of the morphological and physical properties of the GNPs after synthesis is performed. The proposed model is validated by comparison with the measured effective permittivity of GNP-composites with different concentrations, and it is used for the design of radar-absorbing materials in the frequency range 1-18 GHz.

Innovative test method for the shielding effectiveness measurement of conductive thin films in a wide frequency range

This paper presents an innovative test procedure for the prediction of the shielding effectiveness of small sample materials, consisting of a dielectric substrate coated with thin conducting film, in a wide frequency range up to 8 GHz. The proposed technique overcomes the limitations of the ASTM D4935 test method concerning the upper operating frequency and the required minimum specimen dimensions. A new high-order equivalent circuit model of the test fixture is developed. A correction factor is applied to the measured insertion loss to eliminate both the resonance peak below cutoff appearing in the high-frequency range and the low-frequency errors due to the weak capacitive coupling between the flanges of the coaxial cell. The accurate prediction of the shielding effectiveness of the test material against a plane wave is then derived from the insertion loss measurements.

Electromagnetic Design and Realization of Innovative Fiber-Reinforced Broad-Band Absorbing Screens

This paper presents the design and the realization process for radar absorbing panels made of composite materials. It is demonstrated that the proper selection of the carbon fiber length and volume fraction allows reducing sensibly the overall thickness of the screen compared to a standard absorber, and obtaining at the same time broad-band absorption response in the X- and Ku-bands. To this end, the carbon fiber composite material realizing the lossy sheet of the absorbing screen is designed by simulation in order to have tailored complex effective permittivity. Two prototypes of absorbing screens are realized and tested experimentally. The first one is a three-layer panel, characterized by reflection coefficient lower than -10 dB in the frequency range from 8 to 14 GHz, and total thickness of 4.5 mm. The second one is a five-layer panel with reflection coefficient less than -20 dB in the range 9-18 GHz, and total thickness of 5.5 mm.

Electromagnetic Analysis of Radio-Frequency Signal Propagation Along SWCN Bundles

The analysis of electromagnetic signal propagation at radio-frequency along single-walled carbon nanotube bundles is performed applying the multiconductor transmission line formalism. The approximated single-conductor transmission line model and the lumped-parameter equivalent circuit are derived to simplify the analysis when the bundle is supplied in the common mode configuration, like in the case of nano-interconnects. Numerical calculations are performed in order to assess the limits of validity of the proposed simulation approaches.

Electromagnetic absorbing nanocomposites including carbon fibers, nanotubes and graphene Nanoplatelets

Nanocomposites loaded with different types of micro/nanofillers are developed and characterized for use in electromagnetic radar absorbing materials with minimum thickness. It is demonstrated that the tailoring of the desired EM properties can be achieved by the proper choice and combination of both the filler and the matrix. In particular, graphene Nanoplatelets dispersed in a bisphenol-A based epoxy matrix feature a loss tangent lower than a few percent and tailored dielectric permittivity. The designed bilayer absorbers entirely made with nanocomposites have thicknesses of 2 mm and 1.5 mm for the X-band and Ku-band respectively.

A flexible and highly sensitive pressure sensor based on a PDMS foam coated with graphene nanoplatelets

The demand for high performance multifunctional wearable devices is more and more pushing towards the development of novel low-cost, soft and flexible sensors with high sensitivity. In the present work, we describe the fabrication process and the properties of new polydimethylsiloxane (PDMS) foams loaded with multilayer graphene nanoplatelets (MLGs) for application as high sensitive piezoresistive pressure sensors. The effective DC conductivity of the produced foams is measured as a function of MLG loading. The piezoresistive response of the MLG-PDMS foam-based sensor at different strain rates is assessed through quasi-static pressure tests. The results of the experimental investigations demonstrated that sensor loaded with 0.96 wt.% of MLGs is characterized by a highly repeatable pressure-dependent conductance after a few stabilization cycles and it is suitable for detecting compressive stresses as low as 10 kPa, with a sensitivity of 0.23 kPa−1, corresponding to an applied pressure of 70 kPa. Moreover, it is estimated that the sensor is able to detect pressure variations of ~1 Pa. Therefore, the new graphene-PDMS composite foam is a lightweight cost-effective material, suitable for sensing applications in the subtle or low and medium pressure ranges.

Comparative analysis of TL models for multilayer graphene nanoribbon and multiwall carbon nanotube interconnects

The multiconductor transmission line model of a multilayer graphene nanoribbon (MLGNR) interconnect is proposed for the analysis of current distribution and signal propagation at radio frequency (RF) up to 100 GHz. The equivalent single conductor model is also developed in order to analyse the common mode propagation. The comparison of the RF performances of a MLGNR interconnect and a multi-wall carbon nanotube (MWCNT) interconnect is also performed. The obtained results show that the MLGNR interconnect has a higher current carrying capability than an MWCNT nanoline having the same dimension and configuration above the ground.