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

A new advanced railgun system for debris impact study

The growing quantity of debris in Earth orbit poses a danger to users of the orbital environment, such as spacecraft. It also increases the risk that humans or manmade structures could be impacted when objects reenter Earth's atmosphere. During the design of a spacecraft, a requirement may be specified for the surviv-ability of the spacecraft against Meteoroid / Orbital Debris (M/OD) impacts throughout the mission; further-more, the structure of a spacecraft is designed to insure its integrity during the launch and, if it is reusable, during descent, re-entry and landing. In addition, the structure has to provide required stiffness in order to allow for exact positioning of experiments and antennas, and it has to protect the payload against the space environment. In order to decrease the probability of spacecraft failure caused by M/OD, space maneuver is needed to avoid M/OD if the M/OD has dimensions larger than 10cm, but for M/OD with dimensions less than 1cm M/OD shields are needed for spacecrafts. It is therefore necessary to determine the impact-related failure mechanisms and associated ballistic limit equations (BLEs) for typical spacecraft components and subsys-tems. The methods that are used to obtain the ballistic limit equations are numerical simulations and la-borato-ry experiments. In order to perform an high energy ballistic characterization of layered structures, a new ad-vanced electromagnetic accelerator, called railgun, has been assembled and tuned. A railgun is an electrically powered electromagnetic projectile launcher. Such device is made up of a pair of parallel conducting rails, which a sliding metallic armature is accelerated along by the electromagnetic effect (Lorentz force) of a cur-rent that flows down one rail, into the armature and then back along the other rail, thanks to a high power pulse given by a bank of capacitors. A tunable power supplier is used to set the capacitors charging voltage at the desired level: in this way the Rail Gun energy can be tuned as a function of the desired bullet velocity. This facility is able to analyze both low and high velocity impacts. A numerical simulation is also performed by using the Ansys Autodyn code in order to analyze the damage. The experimental results and numerical simulations show that the railgun-device is a good candidate to perform impact testing of materials in the space debris energy range

CVD nano-coating of carbon composites for space materials atomic oxygen shielding

The present work analyzes the possibility to employ carbon nanostructures as a basic material to prevent the erosion effects of atomic oxygen suffered by the carbon fiber reinforced polymeric material used in low earth orbit space environment. The application of thin protecting coatings to base materials is a widely used method for preventing the atomic oxygen induced erosion, and thus degradation. The generic purpose is to integrate carbon nanostructures onto carbon composites surface in order to develop the basic substrate of advanced nanocomposite for atomic oxygen protection. The final goal is the characterization of carbon nanostructures-reinforced carbon composites by means of on-ground atomic oxygen simulation facility, with the future objective to assess and optimize the process of carbon-multiscale advanced composites production. With such an aim, a wide investigation on the methane chemical vapor deposition (CVD) over catalyzed carbon fiber-based substrates has been carried out. The as grown nanostructures have been analyzed in terms of morphology, as well as regarding the main features of the resulting growth (yield, purity, homogeneity, coating uniformity, etc.) and the influence of the deposition route operating parameters (catalyst typology, gas flowing rate, growth time/temperature, etc.). A high degree of reproducibility in terms of the relationship between the carbon deposit type/yield and the main process variables (catalyst and protocol) has been thus obtained. Finally, atomic oxygen ground tests have been conducted in order to evaluate the coating process effectiveness. The on-ground test in atomic oxygen environment, with respect to the performances of the reference carbon composites (in terms of total mass loss and atomic oxygen rate of erosion), showed a worsening for the disordered carbon deposit, while an intriguing improvement was achieved by the high-yield carbon nano-filaments deposition

Mimic materials electromagnetic reflection and transmission coefficient

The paper is focused on a design method to build layered materials able to mimic the reflection and transmission coefficient profile of really existing or even invented dielectric materials. The design method is based on particle swarm optimization algorithm and electromagnetic matrix formalism which allows the minimization of an objective function. Goal of the procedure is to obtain a layered materials mimicking the target reflection and transmission coefficient profile a priori established. The design algorithm is coded in Matlab and it selects the best material for each layer by accessing to a database of dielectrically characterized materials. Materials in the database are made using different species and amount of carbon nanomaterials dispersed epoxy matrix. Thickness and the number of layers of final layered structures are optimized by the iterative design procedure. In the paper some interesting example of mimic optimization are shown. The numerical finite element method analysis complete the electromagnetic discussion showing how each layer of the optimized layered structures takes part in the final goal of mimicking the target electromagnetic profile

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

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

RADAR ABSORBING MATERIALS FOR CUBE STEALTH SATELLITE

ABSTRACT Cube Stealth Satellite is proposed for potential applications in defense system. Particularly face of satellite exposed to the Earth are made of nanostructured materials able to absorb radar surveillance electromagnetic wave, conferring stealth capability to the cube satellite. Microwave absorbing and shielding materials tiles are proposed using composite materials consisting in epoxy-resin and carbon nanotubes filler. In the paper, electric permittivity, of composite nanostructured materials are shown. Such data are used by the modeling algorithm to design the microwave absorbing and shielding face of cube satellite. The electromagnetic modeling takes into account for several incidence angles (0-80°), extended frequency band (2-18 GHz), and for the minimization of electromagnetic reflection coefficient. The evolutionary algorithm used for microwave layered microwave absorber modeling is recent Winning Particle Optimization. Mathematical model of absorbing structure is finally experimentally validated by comparing electromagnetic simulation and measurement of the manufactured radar absorber tile. Nanostructured composite materials manufacturing process and electromagnetic reflection measurements methods are described. At the and the finite element method analysis of the electromagnetic scattering by cube stealth satellite is performed

Synthesis and electromagnetic characterization of frequency selective radar absorbing materials using carbon nanopowders

A new method for the synthesis of multilayered radar absorbing materials is analyzed by using carbon nanomaterials. With respect to the literature, a desired profile of reflection coefficient is a priori established as a function of the frequency. The goal of the synthesis is to follow this target profile by computing thickness and type of the material of each layer until the reflection coefficient of the electromagnetic-wave absorber best approximates the wanted reflection coefficient. The material available for each layer is epoxy-resin reinforced by different kind of carbon-based nano/micro powders: graphene nanoplatelets, carbon nanofibers, multi-walled carbon nanotubes and polyaniline. The dielectric characterization of the composite materials is performed in the frequency range 2÷18 GHz. The synthesis uses evolutionary computation by drawing on the electric permittivity of composite materials. Three square layered electromagnetic wave absorbers of 25 cm side are manufactured. The comparison between the target, the simulated and the measured reflection coefficients shows a good agreement thus confirming the scientific validity of the dielectric characterization and the proposed design method. Finally, a finite element analysis has been carried out to explain the mechanism of electromagnetic wave absorption by a multilayer and to simulate a low radar observable naval military gun

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