A. Vricella

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.

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.

Electromagnetic Characterization of Materials by Vector Network Analyzer Experimental Setup

Abstract This chapter deals with the vector network analyzer systems used for the study of the electromagnetic properties of materials. The focus of the chapter is not the device itself, about which plenty of literature is available, but its application in materials characterization at the microwave and millimeter wave levels. Some interesting measurement techniques are presented and discussed in detail with the help of numerous experimental results. Moreover, the measurement criteria are commented on as a function of the materials under test. The waveguide, coaxial air line, Naval Research Laboratory Arch bistatic system, free-space, and reverberation chamber methods are presented and analyzed. Examples of measurements of conventional materials used in architectural building up to advanced foam and nanocomposite materials considered in defense and aerospace applications are presented. The authors have tried to transfer their wide laboratory expertise in this chapter, with the aim to be useful to other researchers in the field of electromagnetic characterization of materials.

Shell absorbing nanostructure for low radar observable missile

This research is focused on simulation, manufacturing and measuring of shell radar absorbing structure of missiles. The novelty of the work is the study of a curved radar absorbing structure. The enhancement of electromagnetic wave absorption is obtained by using carbon nanotube filler in different weight ratio with respect to the epoxy-resin adopted in shell manufacturing. The structural resistance is granted by the use of conventional fiberglass. A radar absorbing prototype of an half shell, having the section of 15 cm radius has been built and characterized. The thickness of the shell is around 6.5 mm and is made of two different loaded layers. The measurements of electromagnetic reflection coefficient has been performed for two different incidence angles of 0° and 45°. The reflection coefficient show values down to -18 dB around 3 GHz and -10 dB around 11 GHz for 0° incidence angle, and -6 dB around 3 GHz and -10 dB around 12 GHz for 45° incidence angle. An electromagnetic simulation of a flat structure having the same layering configuration of the shell shows values of reflection coefficient very similar to the measured one for 0° incidence angle.

Advanced Radar Absorbing Ceramic-Based Materials for Multifunctional Applications in Space Environment

In this review, some results of the experimental activity carried out by the authors on advanced composite materials for space applications are reported. Composites are widely employed in the aerospace industry thanks to their lightweight and advanced thermo-mechanical and electrical properties. A critical issue to tackle using engineered materials for space activities is providing two or more specific functionalities by means of single items/components. In this scenario, carbon-based composites are believed to be ideal candidates for the forthcoming development of aerospace research and space missions, since a widespread variety of multi-functional structures are allowed by employing these materials. The research results described here suggest that hybrid ceramic/polymeric structures could be employed as spacecraft-specific subsystems in order to ensure extreme temperature withstanding and electromagnetic shielding behavior simultaneously. The morphological and thermo-mechanical analysis of carbon/carbon (C/C) three-dimensional (3D) shell prototypes is reported; then, the microwave characterization of multilayered carbon-filled micro-/nano-composite panels is described. Finally, the possibility of combining the C/C bulk with a carbon-reinforced skin in a synergic arrangement is discussed, with the aid of numerical and experimental analyses.

Fully Configurable Electromagnetic Wave Absorbers by Using Carbon Nanostructures

The configurable electromagnetic wave absorber (CEMA) defines a new method for the full design of layered carbon-based nanocomposites able to quasi-perfectly reproduce any kind of EM reflection coefficient (RC) profile. The method involves three main factors: (a) nanofillers-like carbon nanotube (CNT), carbon nanofiber (CNF), graphene nanoplatelet (GNP), and polyaniline (PANI) in different concentration versus the matrix; (b) the dielectric parameters of the nanoreinforced materials in the microwave range 2–18 GHz; (c) a numerical technique based on particle swarm optimization (PSO) algorithm within the MATLAB code of the EM propagation engine. Output is the layering of the wave absorber, that is, number of layers and material/thickness of each layer and the reflection/transmission simulated profiles. The frequency selective behavior is due to the multilayered composition, thanks to the direct/reflected wave combination tuning at interfaces. The dielectric characterization of the employed nanocomposites is presented in details: these materials constitute the database for the optimization code running toward the multilayer optimal solution. A FEM analysis is further proposed to highlight the EM propagation within the material’s bulk at different frequencies. The mathematical model of layered materials, the PSO objective function used for RC target fitting, and some results are reported in the text.

Microwave behavior of nanostructured composite for low observable nanosatellites

Microwave absorbing and shielding material tiles are proposed for improving the stealthness capability of nanosatellites, by using composite materials consisting in polymeric matrix filled by carbon nanotubes. The electric permittivity of the composite nanostructured materials is measured and discussed, and the data allow the modeling algorithm to design the microwave absorbing and shielding faces of the cube satellite. The electromagnetic modeling takes into account for several incidence angles (0-80°), extended frequency band (2-18 GHz), and minimization of the electromagnetic reflection coefficient. The proposed structure is experimentally validated by comparing the electromagnetic simulation to the measurement of the manufactured radar absorber tile. Finally, a finite element method analysis of the electromagnetic scattering by cube stealth satellite is performed.