Dissertations / Theses on the topic 'Radar Absorbing Materials (RAM)'

Spacecloth design and development is vital and crucial in Radar Absorbing Materials (RAM) for achieving Low Observability in an Aircraft or an Unmanned Air Vehicle(UAV). The RAM design translates into the spacecloth design. The spacecloths form the constituent layers in a broadband Jaumann absorber in which case they have to be designed for various values of surface resistivity. The design specifications of spacecloth(s) in RAMS is well understood and documented in literature. But the design of spacecloth hitherto, has been the domain of materials' scientists wherein the specified properties of the spacecloth are achieved by an iterative, trial and error process, by mixing various constituents in different proportions to get the design specified surface resistivity in the final end-product. In an effort to bridge this gap, a novel spacecloth for RAM applications is proposed in the thesis. It is proposed that a repetitive geometrical grid network of chip resistors simulates spacecloth. The sheet resistivity of the spacecloth is derived by analyzing various geometries like square, rectangle, triangle and hexagonal grids. The transmission and reflection loss for the chip resistor spacecloth is derived. The design of chip resistor spacecloths for operation at S and C bands is given followed by experimental verification using waveguide simulator experiments. Numerical study of multilayer RAM has been carried out with exponential taper variation of surface resistivities for constituent spacecloth layers and design curves are given for multilayer RAM both for normal and oblique incidence for TE and TM polarizations.

Spacecloth design and development is vital and crucial in Radar Absorbing Materials (RAM) for achieving Low Observability in an Aircraft or an Unmanned Air Vehicle(UAV). The RAM design translates into the spacecloth design. The spacecloths form the constituent layers in a broadband Jaumann absorber in which case they have to be designed for various values of surface resistivity. The design specifications of spacecloth(s) in RAMS is well understood and documented in literature. But the design of spacecloth hitherto, has been the domain of materials' scientists wherein the specified properties of the spacecloth are achieved by an iterative, trial and error process, by mixing various constituents in different proportions to get the design specified surface resistivity in the final end-product. In an effort to bridge this gap, a novel spacecloth for RAM applications is proposed in the thesis. It is proposed that a repetitive geometrical grid network of chip resistors simulates spacecloth. The sheet resistivity of the spacecloth is derived by analyzing various geometries like square, rectangle, triangle and hexagonal grids. The transmission and reflection loss for the chip resistor spacecloth is derived. The design of chip resistor spacecloths for operation at S and C bands is given followed by experimental verification using waveguide simulator experiments. Numerical study of multilayer RAM has been carried out with exponential taper variation of surface resistivities for constituent spacecloth layers and design curves are given for multilayer RAM both for normal and oblique incidence for TE and TM polarizations.

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Universidade Estadual de Roraima
Were synthesized systems Ni0,5Zn0,5Fe2O4, i0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 and Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, the precursors citrate method. The decomposition of the precursors was studied by thermogravimetric analysis and spectroscopy in the infrared region, the temperature of 350?C/3h. The evolution of the phases formed after calcinations at 350, 500, 900 and 1100?C/3h was accompanied by X-ray diffraction using the Rietveld refinement to better identify the structures formed. The materials were also analyzed by scanning electron microscopy, magnetic measurements and analysis of the reflectivity of the material. The samples calcined at different temperatures showed an increase of crystallinity with increasing calcination temperature, verifying that for some compositions at temperatures above 500?C precipitates of second phase such as hematite and CuO. The compositions of manganese present in the structure diffusion processes slower due to the ionic radius of manganese is greater than for other ions substitutes, a fact that delays the stabilization of spinel structure and promotes the precipitation of second phase. The compositions presented with copper precipitation CuO phase at a temperature of 900 and 1100?C/3h This occurs according to the literature because the concentration of copper in the structure is greater than 0.25 mol%. The magnetic measurements revealed features of a soft ferrimagnetic material, resulting in better magnetic properties for the NiZn ferrite and NiCuZnMg at high temperatures. The reflectivity measurements showed greater absorption of electromagnetic radiation in the microwave band for the samples calcined at 1100?C/3h, which has higher crystallite size and consequently the formation of multi-domain, increasing the magnetization of the material. The results of absorption agreed with the magnetic measurements, indicating among the ferrites studied, those of NiZn and NiCuZnMg as better absorbing the incident radiation.
Foram sintetizados os sistemas Ni0,5Zn0,5Fe2O4, Ni0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 e Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, pelo m?todo dos citratos precursores. A decomposi??o dos precursores foi estudada por an?lise termogravim?trica e espectroscopia na regi?o do infravermelho, na temperatura de 350?C/3h. A evolu??o das fases formadas ap?s as calcina??es a 350, 500, 900 e 1100?C/3h foi acompanhada por difra??o de raios X utilizando o refinamento de Rietveld, para melhor identifica??o das estruturas formadas. Os materiais foram tamb?m analisados por microscopia eletr?nica de varredura, medidas magn?ticas e an?lise da refletividade do material. As amostras calcinadas em diferentes temperaturas indicaram um aumento da cristalinidade com o aumento da temperatura de calcina??o, verificando-se que, para algumas composi??es, em temperaturas acima de 500?C ocorre a precipita??o de segunda fase, como hematita e CuO. As composi??es com mangan?s na estrutura apresentaram processos de difus?o mais lentos devido ao raio i?nico do mangan?s ser maior em rela??o aos outros ?ons substituintes, fato que retarda a estabiliza??o da estrutura espin?lio e favorece a precipita??o de segunda fase. As composi??es com cobre apresentaram precipita??o da fase CuO na temperatura de 900 e 1100?C/3h, fato que ocorre segundo a literatura porque a concentra??o de cobre na estrutura ? maior que 0,25 mol%. As medidas magn?ticas revelaram racter?sticas de um material ferrimagn?tico macio, obtendo-se melhores ar?metros magn?ticos para as ferritas de NiZn e NiCuZnMg em altas temperaturas. As medidas de refletividade mostraram maior absor??o da radia??o eletromagn?tica na faixa de microondas para as amostras calcinadas a 1100?C/3h, que tem maior tamanho do cristalito e em conseq??ncia forma??o de multidom?nios, aumentando a magnetiza??o do material. Os resultados de absor??o concordaram com as medidas magn?ticas, indicando dentre as ferritas estudadas, as de NiZn e NiCuZnMg como melhores absorvedoras da radia??o incidente.

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
Were synthesized ferrites of NiZn on systems Ni0,5Zn0,5Fe2O4, the precursors citrate method. The decomposition of the precursors was studied by thermogravimetric analysis and spectroscopy in the infrared region, the temperature of 350?C/3h. The evolution of the phases formed after calcinations at 350?C/3h, 600, 1000 and 1100?C/2h was accompanied by X-ray diffraction using the Rietveld refinement method for better identification os structures formed. Was observed for samples calcined at different temperatures increased crystallinity with increasing calcination temperature, being observed for the samples calcined at 900 and 1100 ? C/2h was the precipitation of a secondary phase, the phase hematite. The ferrocarbonila of industrial origin was analyzed by X-ray diffraction and Rietveld for the identification of its structure. The carbonyl iron was added NiZn ferrite calcined at 350?C/3h, 600, 900, 1000 and 1100?C/2h to the formation of hybrid mixtures. They were then analyzed by Xray diffraction and Rietveld. The NiZn ferrite and ferrocarbonila as well as the hybrid mixtures were subjected to analysis of scanning electron microscopy, magnetic measurements and reflectivity. The magnetic measurements indicated that the ferrite, the ferrocarbonila, as well as hybrid mixtures showed characteristics of soft magnetic material. The addition of ferrocarbonila in all compositions showed an increase in the results of magnetic measurements and reflectivity. Best result was observed in the increase of the magnetization for the hybrid mixture of Ferrocarbonila / ferrite of NiZn calcined at 600?C/2h. The mixture Ferrocarbonila / ferrite calcined 1000?C/2h presented better absorption of electromagnetic radiation in the microwave
Foram sintetizadas ferritas de NiZn no sistema Ni0,5Zn0,5Fe2O4, pelo m?todo dos citratos precursores. A decomposi??o dos precursores foi estudada por an?lise termogravim?trica e espectroscopia na regi?o do infravermelho na temperatura de 350?C/3h. A evolu??o das fases formadas ap?s calcina??es a 350?C/3h, 600, 1000 e 1100?C/2h foi acompanhada por difra??o de raios X utilizando o refinamento de Rietveld para melhor identifica??o das estruturas formadas. Foi observado para as amostras calcinadas em diferentes temperaturas o aumento da cristalinidade com o aumento da temperatura de calcina??o, sendo verificado que para as amostras calcinadas a 900 e 1100?C/2h ocorreu a precipita??o de uma fase secund?ria, a fase hematita. A ferrocarbonila de proced?ncia industrial foi analisada por Difra??o de raios X e por Rietveld para a identifica??o de sua estrutura. A ferrocarbonila foi adicionada ? ferrita de NiZn calcinada a 350?C/3h, 600, 1000 e 1100?C/2h para a forma??o das misturas h?bridas. Em seguida foram analisadas por difra??o de raios X e por Rietveld. A ferrita de NiZn, a ferrocarbonila, assim como as misturas h?bridas foram submetidas ? an?lises de Microscopia Eletr?nica de Varredura, medidas magn?ticas e refletividade. As medidas magn?ticas indicaram que a ferrita, a ferrocarbonila, como tamb?m as misturas h?bridas apresentaram caracter?sticas de material magn?tico macios. A adi??o de ferrocarbonila em todas as composi??es indicou um aumento nos resultados de medidas magn?ticas e de refletividade. Foi verificado melhor resultado no aumento da magnetiza??o para a mistura h?brida de Ferrocarbonila/ferrita de NiZn calcinada 600?C/2h. A mistura Ferrocarbonila/ferrita calcinada 1000?C/2h apresentou melhor resultado absor??o da radia??o eletromagn?tica na faixa de microondas em rela??o ?s outras misturas

A fast and efficient method for the design of multi-layered circuit analog absorbing structures is developed. The method is based on optimization of specular reflection coefficient of a multi-layered absorbing structure comprising of lossy FSS layers by using Genetic Algorithm and circuit equivalent models of FSS layers. With the introduced method, two illustrative absorbing structures are designed with -15 dB reflectivity for normal incidence case in the frequency bands of 10-31 GHz and 5-46 GHz, respectively. To the author&rsquo
s knowledge, designed absorbers are superior in terms of frequency bandwidth to similar studies conducted so far in the literature. For broadband scattering characterization of periodic structures, numerical codes are developed. The introduced method is improved with the employment of developed FDTD codes to the proposed method. By taking the limitations regarding production facilities into consideration, a five-layered circuit analog absorber is designed and manufactured. It is shown that the manufactured structure is capable of 15 dB reflectivity minimization in a frequency band of 3.2-12 GHz for normal incidence case with an overall thickness of 14.2 mm.

碩士
國防大學中正理工學院
兵器系統工程研究所
94
In this study, the electromagnetic wave absorbing (EMA) properties of graphite/epoxy sheets were investigated. The hybrid graphite/epoxy sheets were fabricated with the addition of graphite into epoxy resin. The graphite size, thickness of sheets, and weight amount varied for optimizing absorbing sheets. The corresponding EMAs of graphite sheets were measured by a free space vector network analyzer in the frequency range of 3~18 GHz. The experimental results have demonstrated that the graphite/epoxy sheets effectively absorb the electromagnetic wave, especially for the frequency of X-band range. The demand of light for EMA is therefore reached for further applications. The dispersion of graphites in the epoxy resin affects the microwave absorbing characteristics. The value of F*D decreases with the addition of ED211 up to 10 wt%. Nevertheless, the value increases when the weight amount higher than 10 wt%. With increasing the graphite particle size, the dielectric constant of the hybrid sheets increases and causes the microwave absorbing frequency shifts to lower frequency. As a usual, the value of F*D keeps the same for materials. In this case, the absorbing frequency also decreases with increasing the thickness. The dielectric constant increases with increasing the weight percentage of graphite, and, as a result, the absorbing frequency shifts to low frequency. The hybrid sheets mixed with G30 graphite powder absorb the loss more than 20 dB at a thickness of less than 1.0 mm with a density of 1.3kg/m2. The EMA of G30 sheets slightly modulates with the additions of carbonyl-iron, NG300, and G01 particles. The addition of ferrite could extend the 3 % lossy at the refection loss of 10 dB.

Novel graphene-based nanocomposites, consisting of a polymeric-based system filled with graphene nanoplatelets (GNP) are developed for application as low-cost lightweight electromagnetic shielding materials. A significant challenge in radar absorbing materials (RAM) technology is the development of lightweight absorbing materials with frequency selective properties for EM shielding and EM decoupling among radiating systems and antenna arrays. In fact, frequency selective radar-absorbing materials (FS-RAM) would allow the selective EM shielding of a specific frequency simultaneously providing low-reflectivity, which is a key-requirement in the case of multiple systems installed in closed bays, in order to avoid hot spots, as well as the case of open-sites, in order to avoid coupling between radiating antennas and EM shielding configurations. This work presents a series of strategies to obtain graphene-based nanocomposites with improved electromagnetic, electrical and mechanical properties. The main scope of this study is the scale-up of the fabrication processes, towards large-scale aeronautical distribution. To this purpose the use of commercially available GNP-powders are investigated, and incorporated into different thermosetting and thermoplastic resin systems. The complex dielectric permittivity of the resulting composites is studied in the frequency range between 8-12 GHz, and fitted through a novel multiscale Maxwell Garnett-based model that can estimate the agglomeration state of the nanofiller. The results show that the different electromagnetic and mechanical behaviors of the final composites, are conditioned by the interaction between the GNP in the different resins systems, and the filler concentration, as illustrated by scanning electron microscopy (SEM), and Raman spectroscopy.

碩士
國防大學理工學院
化學工程碩士班
105
Eelectromagnetic (EM) wave absorbing materials have been widely used in the commercial and military applications for years. More recently, considerable efforts have been made toward the development of the hybrid composition and structure microwave absorbers to meet the requirements such as strong absorption characteristics and wide absorption frequency, lightweight and anti-oxidation. A flexible composite consisting of up to 50 wt% β-phase silicon carbide powder and silicon resin, added with a little extra amount of multi-walled carbon nanotube (~1 wt%), was prepared via spray coating technique to manufacture the high temperature microwave absorber. The as-prepared composite was characterized by Thermal gravimetric analysis (TGA), X-ray Diffraction(XRD) and scanning electron microscope (SEM). The microwave absorbing performance was evaluated within the range of 8.2-12.4 GHz (X band) at elevated temperatures up to 450 ℃. Judging form TG analysis, the composite revealed a good thermal stability due to a slight weight loss of ＜5% as the temperature at 480 ℃. After heating, the composite still remained its appearance and microstructure. The optimal results at roomtemperature showed that the 1.6 mm-thick composite contained 50 wt% SiC and 0.2 wt% CNT possessed a maximum reflection loss of -58.9dB; in addition, the absorption bandwidth less than -10 dB was around 2 GHz. At the high temperature of 450 ℃, the absorption peak located at 10.30 GHz with a reflection loss of -11.3 dB; moreover, the absorption bandwidth with a reflection loss less than -10 dB was 2 GHz.

碩士
逢甲大學
航太與系統工程所
98
The radar absorbing structures (RAS) are multifunctional composites with dual functions of high strength performance and radar cross section (RCS) reduction. To improve the bandwidth of RCS, a circuit analog RAS is fabricated by replacing the resistive sheet of a Salisbury screen by a frequency selective surface (FSS). This dissertation is aimed to the design, analysis and manufacturing of circuit analog absorbers with broadband, light-weighted and excellent strength properties. Conductive nano-fillers such as carbon black and multi-walled carbon nanotube (MWNT) mixed with epoxy resin are added to honeycombs in an attempt to efficiently increase the absorbing capacity of RAS. The microwave absorbing composites samples are fabricated by mixing with epoxy resin and absorbent fillers in different weight ratios. The complex permittivity and permeability of composites are measured and the maximum absorption is -25.97 dB (at 9.76 GHz) for carbon black absorbers and -36.46 dB (at 8.24 GHz) for MWNT absorbers with 3 mm thickness. The FSSs are fabricated by a screen printing method with the conductive carbon ink instead of the costly sputtering method. The RAS with two FSSs are specially designed with 5 wt% carbon black or 10 wt % carbon nanotube embedded in the honeycombs so as to exhibit the 10 dB absorptivity in the frequency range of for 4-18 GHz.

碩士
國防大學理工學院
化學工程碩士班
105
In this study, the high temperature was used to provide enough energy for fabricating the M-type microwave-absorbing materials Ba1-xLaxFe12O19-0.5x with the solid state reaction method. XRD patterns revel that the M-type Hexagonal crystal occurs along with α-Fe2O3 phases at 900℃ with 4 hours of a heating condition. When the temperature increased to 1300℃ in 4 hours, the alpha-Fe2O3 phases disappeared. It is also observed that the M-type Hexagonal crystal particle size increases with increasing temperature by using FE-SEM. The particle sized reaches up to 25um~50um at 1300℃in 4 hours. The magnetic hysteresis loop results indicated that the Ms, Mr, and Hc values of the M-type Hexagonal ferrite crystals are dependent on the calcing temperature and the chemical composition of materials. In which Ms and Mr decrease with increasing x value, while the Hc increases with increasing x value. The value of saturated magnetization (Ms) increases with increasing temperature and the value of Hc decreases with increasing temperature. The composite microwave-absorbing materials made by mixing the thermoset rubber (RTV-165) with hexagonal ferrites (7:3 by weight) were found having an obvious microwave-absorbing effect. A 1mm-thick of the composite material (Ba0.6La0.4Fe12O19.2/RTV-615) has about -4dB and -9dB of deflection loss at 9~11GHz and 16~18 GHz of electromagnetic radiation, respectively. The composite material of Ba0.6La0.4Fe12O19.2/ SiC /RTV-615 has the reflection lose -12dB at 17~18GHz.

Modern day stealth aircraft uses microwave absorbers for absorption of incident Radar signals transmitted by rival aircraft. Recently, several attempts were made to fabricate radar absorbing structures (RAS) of various configurations and embedding frequency selective surfaces (FSS), in the form of periodic 2-D patterns, is one of the approaches. The FSS is fabricated from resistive thin films which are usually coated on a dielectric substate. The use of thin films with optimum properties is essential for achieving broadband microwave absorption. For stealth aircraft structures, there exists a need to synthesize and investigate resistive thin films having properties ranging from good optical transparency, electrical conductivity coupled with good mechanical properties and structural integrity. In this work, sputter coating of thin films of Gold, Indium Tin Oxide (ITO), Silver Nanowire were attempted on Polymethyl Methacrylate (PMMA), a difficult substrate (PMMA) to process in vacuum, and characterized for their optical & electrical properties and environmental stability. Thin film of ITO emerged as the suitable candidate and the film properties were further tailored such that it can be employed as top FSS layer and backplane of the optically transparent RAS. The RAS was designed using CST microwave studio by employing Jerusalem Cross as FSS element. The absorber configuration was optimized for wide bandwidth performance, good angular stability and polarization insensitiveness. Similarly, Nickel thin films were deposited on E-Glass fabric and electromagnetic and mechanical properties were characterized to examine their suitability for load bearing structural members. Integral RAS for both optically transparent and structural applications were fabricated for the optimized configurations. The optically transparent microwave absorber was shown to exhibit polarization independent absorptivity with a bandwidth of 8.5 GHz and good angular stability up to 45o. The absorber for structural applications was shown to possess good absorptivity with a bandwidth of 6.5 GHz in comparison to the bandwidth of 4.5 GHz exhibited by a conventional particle loaded absorber which was also fabricated in this work

Questa tesi raccoglie il lavoro di tre anni di ricerche e studi nel settore dei nanomateriali, nanostrutture ed in generale dei compositi avanzati effettuati presso la Scuola di Ingegneria Aerospaziale della “Sapienza” Università di Roma. In particolare lo scopo è stato quello di approfondire l’interazione tra campi elettromagnetici ed alcune tipologie di compositi avanzati basati essenzialmente su strutture in carbonio e nanomateriali. Questo tentativo ha richiesto un approccio multidisciplinare tra diversi settori scientifici che comprendono quello dei materiali, delle strutture, dei processi di fabbricazione, delle nanotecnologie e dell’elettromagnetismo, i cui concetti di base sono, in questo contesto, dati per acquisiti e per il cui approfondimento si rimanda a testi specifici. L’obiettivo principale è stato quello di utilizzare queste conoscenze trasversali per progettare e costruire nuovi materiali/strutture in grado di assorbire efficacemente i campi elettromagnetici in un ampio intervallo di frequenze ed angoli d’incidenza con molteplici applicazioni anche se l’ambito su cui si è lavorato è quello aerospaziale. Per ottimizzare questi materiali/strutture si è fatto ricorso all’utilizzazione di algoritmi evoluzionistici che sono entrati a pieno titolo nello studio multidisciplinare con uno stretto collegamento tra la teoria sviluppata e le prove di laboratorio atte a validare sperimentalmente i modelli matematici proposti.
This Thesis is focused on scientific research on composite materials electromagnetic characterization and electric conductive polymers applications. Mainly two different composite materials types are taken into account, those based on epoxy-resin and those achieved through pyrolisis of a phenolic-resin more often known as Carbon-Carbon. 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 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 order to modulate the electromagnetic characteristics, like electrical conductivity and microwave absorbing capability, the epoxy-resin composite materials taken into account, are reinforced using carbon nanomaterials in different weight percentage. The microwave absorbing capability of these fancy materials is analyzed, and numerical design of wide frequency band microwave absorbing structures and microwave shielding structures are presented and discussed in details in terms of both microwave reflection loss and transmission attenuation i.e., shielding effectiveness. In this Thesis, different branches of research field are applied: nanotechnology, electromagnetic wave propagation theory, composite materials manufacturing, evolutionary computation, and all of them are used to design the “quasi perfect absorber” from electromagnetic point of view. Traditional composites are loaded by graphene/graphite micrometric mixtures. In this work, we propose an inhomogeneous multilayer absorber made of micrometric graphite (at different wt%), and nanometric carbon particles (SWCNTs, MWCNTs, CNFs, at different wt%). Thus, an improvement of the traditional absorbers has been achieved upon optimization through an in-house genetic algorithm (GA), Particle swarm Optimization (PSO), and winning particle optimization (WPO), this last appositely developed. Main goal of the work is to achieve lower values (< -10 dB) of both reflection and transmission coefficients for angular apertures within 40°. The evolutionary computation codes are flexible in the selection of the algorithm parameters such as frequency band, incidence angular range, overall maximum multilayer thickness, possibility to decide if the design optimization procedure must privilege thickness minimization and/or losses maximization. With respect to the present literature, the developed method considers the absorbing capability taking into account both the reflection and the transmission properties of the entire multilayer structure. Moreover, the absorbing properties of the multilayer structures have been analyzed considering oblique incidence at fixed angles within a finite range. This work is organized into six main chapters. Chapter 1 describes electromagnetic theory of plane multilayer structures made of lossy materials. Electromagnetic theory about propagation in no-lossy and lossy materials is also discussed using examples to clarify concepts. Reflection and Transmission Coefficients are discussed, oblique incidence and Snell’s law, Transverse Impedance, Brewster angle and Critical Angle, Complex Waves, Zenneck Waves, are introduced. At the end, Surface Plasmons are analyzed and simulated using genetic algorithm. Chapter 2 describes composite materials manufacturing, chemical/physical analysis, and problems in manufacturing large tiles of composite materials. Composite materials considered here are based on epoxy matrix reinforced with several species of filler in particular carbon nanomaterials are considered. These latter have been chosen taking into account the lowest market prices: the economic aspects, normally neglected in small laboratory applications, are on the contrary important in real applications where the amount of carbon nanopowders could be relatively high. In such scenario a good compromise in terms of cost/performances has been obtained using industrial grade multiwall carbon nanotubes (MWCNTs, about 300 $/kg), graphite micropowder (about 40 $/kg), and carbon nanofibers (CNFs, about 30 $/g). As far as composite materials manufacturing is concerned, the main problem discussed is nanopowders dispersion in relatively high weight percentages within the epoxy-matrix. In fact, microwave absorption properties of the composites are definitively compromised if dispersion is not good enough. Chapter 3 is related to the electromagnetic characterization of composite materials used to build microwave absorbing and shielding structures. The electromagnetic characterization of composite materials consists in determining the dielectric properties like electrical permittivity, which in turns can be used in order to compute microwave electrical conductivity, skin depth penetration, etc. Several measuring methods are possible: wave guide, coaxial line, free space antennas, resonant cavities, and so on. In this work, the wave guide method has been adopted: the reason for such choice is due to the problems intrinsically existing with other methods where mechanical machining of composite materials is required, thus affecting the final dielectric permittivity values determination. Meanings of microwave scattering parameters, electrical conductivity, and permittivity are discussed. Main algorithms used to convert values of scattering parameters measured by Vector Network Analyzer into permittivity are shown. Chapter 4 deals with the algorithms adopted for the numerical design of microwave absorbing and shielding structures. In order to modeling absorbing structures where the microwave absorbing performances are the best obtainable in a wider frequency band and for all possible microwave incidence angles, transmissions line equations have been applied to multilayer structures. Here in particular each layer can assume the dielectric properties of one particular composite material in the data base composed by all composite materials electromagnetically characterized. In such model, the number and the thickness of each layer determine the entire multilayer structure electromagnetic wave absorbing properties. Frequency band considered is in the range 5-18 GHz. Two main design scenarios have been considered, the first classically called radar absorbing material (RAM) where the multilayer structure is supposed baked with a perfect electric conductor (PEC), the second baptized microwave shielding structure (MSS) where at the end of multilayer structure there are again free space conditions for microwave propagation. Such last scenario is useful in application where the composite material posses also mechanical structural properties and is used in place of metal structure (aircraft structure applications). Since the absorber’s overall thickness is sometimes an important constraint in the design process, then the design and optimization algorithms are capable to take into account simultaneously for both, i.e., electromagnetic performances and overall thickness of the multilayer structure. For such kind of problems, evolutionary computation represents a promising method, assuring at the same time good global performances and reasonable computation time. In this work, a new algorithm called winning particle optimization (WPO) is presented and applied. In order to check the soundness of WPO results, an in-house built genetic algorithm (GA) and Particle Swarm Optimization (PSO) are presented and applied too, and final results compared. Chapter 5 presents the experimental validation of the developed electromagnetic absorbing and shielding mathematical theoretical model. Validation is obtained comparing measurements and simulations of reflection loss (RL), and shielding effectiveness of some realized microwave absorbing and shielding structures based on carbon nanostructured composite materials. Measurements of (RL) in free space using NRL Arch technique are performed on large RAM multilayer structure tiles obtained by numerical design and optimization process. Measurements of shielding effectiveness in free space using directional shielding effectiveness measurement (DSEM), developed by us and Università Politecnica delle Marche (Dipartimento di Elettromagnetismo e Bioingegneria), are performed on materials and multilayer structures obtained by numerical design and optimization techniques presented. All the cited equipments i.e., NRL arch system, DSEM system, sample holders system, have been appositely in-house manufactured. Chapter 6, is focused on carbon-carbon (CC) composite materials. Electromagnetic characterization is shown and electrical conductivity, absorbing and shielding properties discussed. NRL arch and DSEM measurements are presented and analyzed. Due to high electrical conductivity of CC, measurements using wave-guide methods do not permit us to determine the absorption and electrical conductivity properties in a precise way. Then a microwave wave-guide has been built using CC, and the attenuation of microwave signal measured using vector network analyzer. Using the measured attenuation values, the electrical conductivity of CC has been computed.