Roberto Pastore

Broadband Electromagnetic Absorbers Using Carbon Nanostructure-Based Composites

In this paper, we present the design of nanostructured multilayer absorbers, carried out with the aid of a genetic algorithm (GA). Waveguide measurements are performed to recover the dielectric properties of micrographite single-walled carbon nanotube, micrographite walled carbon nanotube, carbon nanofiber, and fullerene-based composite materials. Conductive fillers are uniformly dispersed in an epoxy resin at different weight percentages (1, 3, 5 wt.%). The electromagnetic (EM) analysis is performed embedding the forward/backward propagation matrix formalism in an in-house GA, thus able to carry out optimization upon oblique incidence over a finite angular range. Developed code minimizes both the reflection and the transmission coefficients under the thickness minimization constraint. Comparison between micrographite and nanopowders absorbers is presented and discussed, when a broadband quasi-perfect absorber is achieved among the X-band combining the two filler families, i.e., exhibiting a loss factor greater than 90% in most of the band, for a thickness of about 1 cm. It is demonstrated that the nanofillers with higher aspect ratio mainly contribute to the EM absorption. Findings are of interest in both radar-absorbing material and shielding structures.

Optimization of Multilayer Shields Made of Composite Nanostructured Materials

In this paper, we propose a multilayer nanostructured composite for broadband shielding applications. Layers disposal, electrical parameters, and thicknesses are optimized through a winning particle optimization algorithm to achieve the minimization of the transmitted waves. The structures are simulated by including the forward/backward scattering matrix formalism in the optimization code. The adopted algorithm is the recently introduced winning particle optimization. Manufacturing of the composites is grounded on the optimization procedure. Thanks to the macroscopic absorption features of such nanostructured layers, very thin and lightweight composites can be produced. Several weight percentages of multiwall carbon nanotubes are considered in composite base material manufacturing, also including 6wt% and 15wt% in order to enhance the electromagnetic shielding performance. Prototypes are tested in the microwave region, showing the reliability of the optimization procedure.

Tunable nanostructured composite with built-in metallic wire-grid electrode

In this paper, the authors report an experimental demonstration of microwave reflection tuning in carbon nanostructure-based composites by means of an external voltage supplied to the material. DC bias voltages are imparted through a metal wire-grid. The magnitude of the reflection coefficient is measured upon oblique plane-wave incidence. Increasing the bias from 13 to 700 V results in a lowering of ∼20 dB, and a “blueshift” of ∼600 MHz of the material absorption resonance. Observed phenomena are ascribed to a change of the dielectric response of the carbon material. Inherently, the physical role of tunneling between nanofillers (carbon nanotubes) is discussed. Achievements aim at the realization of a tunable absorber. There are similar studies in literature that focus on tunable metamaterials operating at either optical or THz wavelengths.

Electromagnetic Characterization of Composite Materials and Microwave Absorbing Modeling

This book chapter is based on the experimental activities conducted mainly at Sapienza University of Rome: Astronautic, Electric and Energetic Engineering Department in collaboration with University of Maryland, Institute for Research in Electronics and Applied Physics (IREAP). A branch of scientific research about composite materials is focused on electromagnetic characterization and subsequent application of electric conductive polymers. The use of such structures is relevant in aerospace/aeronautics, for electromagnetic (EM) protection from natural phenomena (lightning), and intentional interference with radar absorbing materials (RAM), in nuclear physics for shields adopted in particle accelerators, and for nuclear EM pulses (NEMP) protection, in electromagnetic compatibility (EMC) for equipment-level shielding, high-intensity radiated fields (HIRF) protection, anechoic chambers (for the realizations of wedges and pyramidal arrays), and human exposure mitigation. In this chapter, composite reinforced by carbon nanostructured materials are considered, mainly because of their interesting electromagnetic characteristics, such as high electrical conductivity and excellent microwave absorption. Composite materials as well their absorption capability are analyzed and numerical design of wide frequency band microwave absorbing structures is presented and discussed in details. It is crucial to highlight the need of interdisciplinary research fields to go through nanomaterials: besides nanotechnology, also electromagnetic wave propagation theory, composite materials manufacturing techniques, evolutionary computation algorithms, and use those to design the “quasi perfect absorber” are strongly required. In particular, we propose an inhomogeneous multilayer absorber made of micrometric graphite (at different wt%), and nanometric carbon particles (SWCNTs, MWCNTs, CNFs, at different wt%). At the end, an improvement of the traditional absorbers has been achieved upon optimization through an in-house winning particle optimization (WPO) algorithm, this last appositely conceived for absorbers optimization. Main goal of the presented work is to optimize the absorbers

Matter’s Electromagnetic Signature Reproduction by Graded-Dielectric Multilayer Assembly

A lot of effort has been devoted in the last decades by technology research to realizing materials with a priori defined electromagnetic (EM) properties. One of the challenges at present is to configure the reflection coefficient (RC) of a structure so that any shape of a fixed microwave response is followed. A method for realizing microwave absorbers made by carbon nanocomposite layers assembly able to mimic a given reflection profile is described and experimentally validated. The multilayer design (layer sequence, material, and thickness) is pursued by means of a customized numerical optimization algorithm, which allows to get the required microwave behavior. The novelty of the research is the possibility of tuning the EM field propagation through the combination of different materials in a specific layered compound, in order to imitate the response of any “real” object (i.e., with known EM properties). For the experimental validation of the process, three multilayered structures were designed and manufactured, and their microwave RC was measured in the frequency range of 2–18 GHz. The comparison with the related targets (an ideal frequency selective pattern and the defined profiles of dry soil and salt water as retrieved from literature survey) highlights the effective simulating capability of the realized structures. The preliminary results suggest to exploit the graded-dielectric properties provided by carbon-based nanocomposites for EM mimicking purposes: this would be an ideal approach to tackle still unsolved issues in EM compatibility, remote sensing, communication, and safety fields, as well as for low-cost and time-saving metrology applications.

Shielding effectiveness of carbon nanotube reinforced concrete composites by reverberation chamber measurements

The shielding effectiveness of carbon nanotube reinforced concrete composite is analyzed by using a reverberation chamber. The frequency band is 0.8-8 GHz and the weight percentages of carbon nanotube are 0, 1, 3 wt%. Results highlight that about 30 mm thick of 3 wt% reinforced concrete composite is able to perform a shielding effectiveness greater than 15 dB around 2 GHz and up to 30 dB at 8 GHz. The here reported results suggest the employment of carbon nano-powder reinforced concrete in building structures, having issues related to the electromagnetic interference mitigation, such as the influence on the medical devices working in hospital environments as well as the increasing of protection against electromagnetic attacks to strategic targets and sensible places.

Modeling of microwave absorbing structure using winning particle optimization applied on electrically conductive nanostructured composite material

This work presents the design and optimization of a Radar Absorbing Material system in the X-band frequency using evolutionary algorithm. Winning Particle Optimization is a new evolutionary algorithm. Due to its elementary evolving mechanism, it recall in mind primordial life form in trying to search the best place to proliferate. It is shown that such method, is quite simple but at the same time very effective in finding an optimal solution in Radar Absorbing Material design and optimization problems. Radar Absorbing Material optimized is mainly a multilayer structure based on carbon nanomaterials like Carbon-Nanotube, Fullerene, Micrographite, Carbon-Nanofiber. The design and optimization process consists in find the best multilayer structure in terms of lowest thickness and simultaneously lowest electromagnetic reflection coefficient within all the frequency range and for several incidence angles. In order to validate the design procedure a simple multilayer structure has been built and tested using NRL arch method, the close behavior between simulated and measured RAM confirmed the validity of design procedure.

Impact Response of Nanofluid-Reinforced Antiballistic Kevlar Fabrics

In the last decades the research on composite materials have been acquiring importance due to the possibility of increasing the material mechanical performances while contemporary decreasing both mass and volume of the structures. Mass lowering is a “must” especially in military and space applications, since aircraft aerodynamic profile needs to be optimized and because of the high costs of launch and launcher and payload mass constraints [1]. The need to face up to the well know problem of the so called “space debris” has led many aero‐ space researchers to look for advanced lightweight materials for ballistic applications. Among all innovative materials, a promising branch of such research focuses on the poly‐ meric composite materials with inclusions of nanostructures [2]. The present work fits in a more general research project, the aim of which is to realize, study and characterize nano‐ composite materials. These latter are currently manufactured in the SASLab of Astronautic Engineering Department of University of Rome “Sapienza” (www.saslab.eu) by mixing the nanoparticles within polymeric matrixes in such a way to obtain a material as homogeneous as possible, in order to have a final composite with improved physical characteristic [3]. The goal of the present study is to perform a ballistic characterization of the nanocomposites by means of an in-house built electromagnetic accelerator. The realization of such experimental apparatus, and mostly the optimization with a view to space debris testing planes, is quite complex since the fundamental machine parameters have high non-linearity theoretical be‐ havior [4]. Hereafter experimental preliminary results of a prototypal device are presented and discussed. An intriguing issue of nanoscience research for aerospace applications is to produce a new thin, flexible, lightweight and inexpensive material that have an equivalent

Ballistic characterization of nanocomposite materials by means of “Coil Gun” electromagnetic accelerator

In this paper the authors present their activity in the field of electromagnetic machine applications for aerospace solutions. A three stage electromagnetic accelerator is under construction to perform ballistic characterization of carbon-based nanocomposite materials for anti-debris application. Preliminary experiments as well as numerical simulation have been performed with promising results in terms of bullets energy. Further implementation are needed in order to come closer the velocity of typical space debris (8km/s).

Advanced concrete materials for EMI reduction in protected environment and IEMI threats suppression

The enhancement of microwave shielding effectiveness of commercial concrete by the inclusion of carbon nanotubes powder is addressed and experimental testified. A microwave characterization is performed by direct measurements of materials dielectric parameters in the frequency range 1.7-2.6 GHz. A significant lowering of the microwave transmission magnitude is founded for the nanoreinforced material respect to the naked concrete. The results allow to evaluate the microwave shielding capability of wallshaped concrete structures: a shielding effectiveness grater than 50 dB is achieved for a 30 cm thick wall with carbon nanotube filling percentage of 3wt%. The route of nanoparticles filling within the composite mixture is straightforwardly included in the concrete typical on-site manufacturing procedures, thus planning out a time/cost saving procedure with the final aim to promote such typology of materials for commercial purpose in the next future. The here reported preliminary findings pave the way for the employment of carbon nano-powder reinforced concrete in building walls, in order to deal with issues related to the electromagnetic interference mitigation, such as the influence on the medical devices working in hospital environments as well as the increasing of protection against electromagnetic attacks to strategic targets and sensible places.