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Artykuły w czasopismach na temat "Radar absorbing structures"

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Chambers, B. "Symmetrical radar absorbing structures". Electronics Letters 31, nr 5 (2.03.1995): 404–5. http://dx.doi.org/10.1049/el:19950280.

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Aytaç, Ayhan, Hüseyin İpek, Kadir Aztekin i Burak Çanakçı. "A review of the radar absorber material and structures". Scientific Journal of the Military University of Land Forces 198, nr 4 (15.12.2020): 931–46. http://dx.doi.org/10.5604/01.3001.0014.6064.

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The development of technologies that can rival the devices used by other countries in the defense industry, and more importantly, can disable their devices is becoming more critical. Radar absorber materials (RAM) make the detection of the material on the radar difficult because of absorbing a part of the electromagnetic wave sent by the radar. Considering that radar is one of the most important technologies used in the defense industry, the production of non-radar materials is vital for all countries in the world. Covering a gun platform with radar absorber material reduces the radar-cross-sectional area (RCA) value representing the visibility of that platform on the radar. This review aims to present the electromagnetic principles and developed Radar Absorbent Materials (RAM) during decades from the 1960s. The frequency range 8-12 GHz in the electromagnetic spectrum is named the microwave region and used in airport radar applications. Revised basis of electromagnetic theory and defined by a variety of absorbent materials and some design classification types and techniques are described in this article.
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Kim, Jin-Bong. "Broadband radar absorbing structures of carbon nanocomposites". Advanced Composite Materials 21, nr 4 (sierpień 2012): 333–44. http://dx.doi.org/10.1080/09243046.2012.736350.

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Zhang, Zheng Quan, Li Ge Wang i En Ze Wang. "Microwave Absorbing Properties of Radar Absorbing Structure Composites Filling with Carbon Nanotubes". Advanced Materials Research 328-330 (wrzesień 2011): 1109–12. http://dx.doi.org/10.4028/www.scientific.net/amr.328-330.1109.

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Radar absorbing structures (RAS) can’t only load bearing but also absorb electromagnetic wave energy by inducing dielectric loss and minimizing reflected electromagnetic waves. Therefore, the development of the RAS haves become important to reduce RCS of the object. These composites possess excellent specific stiffness and strength. The electromagnetic wave properties of RAS can be effectively tailored by controlling the content of the lossy materials. Radar absorbing structures composed of glass fibers, carbon fibers and epoxy resin filling with carbon nanotubes (CNTs), was designed and prepared. Permittivity of the composite was measured by using a network analyzer, HP8510B. The contents of composites were observed to be different from each composite. Reflection of electromagnetic waves energy of RAS was calculated by using the genetic algorithm, it was discovered that the composites can be applied to design an optional RAS composites filling with CNTs.
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Eun, Se-Won, Won-Ho Choi, Hong-Kyu Jang, Jae-Hwan Shin, Jin-Bong Kim i Chun-Gon Kim. "Effect of delamination on the electromagnetic wave absorbing performance of radar absorbing structures". Composites Science and Technology 116 (wrzesień 2015): 18–25. http://dx.doi.org/10.1016/j.compscitech.2015.04.001.

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Rahmanzadeh, Mahdi, Hamid Rajabalipanah i Ali Abdolali. "Analytical Investigation of Ultrabroadband Plasma–Graphene Radar Absorbing Structures". IEEE Transactions on Plasma Science 45, nr 6 (czerwiec 2017): 945–54. http://dx.doi.org/10.1109/tps.2017.2700724.

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Wang, F. W., S. X. Gong, S. Zhang, X. Mu i T. Hong. "RCS Reduction of Array Antennas with Radar Absorbing Structures". Journal of Electromagnetic Waves and Applications 25, nr 17-18 (styczeń 2011): 2487–96. http://dx.doi.org/10.1163/156939311798806239.

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Shen, Lihao, Yongqiang Pang, Leilei Yan, Yang Shen, Zhuo Xu i Shaobo Qu. "Broadband radar absorbing sandwich structures with enhanced mechanical properties". Results in Physics 11 (grudzień 2018): 253–58. http://dx.doi.org/10.1016/j.rinp.2018.09.012.

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Choi, Ilbeom, Dongyoung Lee i Dai Gil Lee. "Radar absorbing composite structures dispersed with nano-conductive particles". Composite Structures 122 (kwiecień 2015): 23–30. http://dx.doi.org/10.1016/j.compstruct.2014.11.040.

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Nam, Young-Woo, Jae-Hwan Shin, Jae-Hun Choi, Hyun-Seok Kwon, Jae-Sung Shin, Won-Jun Lee i Chun-Gon Kim. "Micro-mechanical failure prediction of radar-absorbing structure dispersed with multi-walled carbon nanotubes considering multi-scale modeling". Journal of Composite Materials 52, nr 12 (11.09.2017): 1649–60. http://dx.doi.org/10.1177/0021998317729003.

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Conventional radar-absorbing structure is typically manufactured with high weight percentage (wt.%) of carbonaceous nano-conductive particles in the polymer matrix to tailor its microwave absorbing performance. However, these manufacturing methods have some physical limitations with regard to fabrication, due to the high viscosity in the polymer matrix and, inhomogeneous in mechanical and electrical properties. No study has been conducted with micro-mechanical failure prediction of radar-absorbing structure dispersed with multi-walled carbon nanotubes. In order to address these limitations, radar-absorbing structures dispersed with multi-walled carbon nanotubes were designed in the Ku-band (12.4–18 GHz). Additionally, to establish and verify the micro-mechanical failure analysis based on multiscale modeling, finite element analysis was carried out using the Mori–Tanaks mean-field homogenization model within the representative volume element model in the microstructure. In order to verify the Hashin criteria of radar-absorbing structure dispersed with multi-walled carbon nanotube (0.5 wt.%, 1.0 wt.% and 1.5 wt.%), mechanical tests (tensile, compressive and shear test) were conducted according to ASTM standards. In this paper, radar-absorbing structure with irregularly arranged filler and matrix with representative volume element was modeled from the micro-mechanical point of view and the results from Hashin failure criterion were verified both by simulations and experimental results of prediction strengths within the expected error range (lower than 6%). The reliability of application in micro-mechanical prediction of radar-absorbing structure was confirmed considering the multi-scale modeling.
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Rozprawy doktorskie na temat "Radar absorbing structures"

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Yildirim, Egemen. "Development Of Multi-layered Circuit Analog Radar Absorbing Structures". Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614314/index.pdf.

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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.
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Wu, Ti, i 吳迪. "Absorpbility of radar absorbing composites and circuit analog structures". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/55985458548607349925.

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碩士
逢甲大學
機械工程學所
91
The radar absorbing material (RAM) is an important military stealth material. The microwave absorptivity of RAM can be determined by the imaginary part of the complex permittivity. Particulate composites that have lossy carbon black spheres randomly imbedded in a dielectric epoxy matrix are studied as to their suitability for RAM. Wave propagations in an inhomogeneous medium undergo multiple scattering which results in a frequency dependent velocity and attenuation of coherent waves. To calculate the effective wavenumbers of electromagnetic waves propagating in particulate composites and composites with a interface, a generalized self-consistent multiple scattering model is used in this study. Numerical results for the effective phase velocity and attenuation of electromagnetic waves are calculated for a wide range of frequencies and concentrations. The proposed dynamic generalized self-consistent model for composites recovers the well-known Maxwell-Garnett’s effective dielectric constants (Maxwell-Garnett) in the static limit and the results at higher frequencies and concentrations agree well with published experimental data (Kuga et al. 1996). A Salisbury screen which consists of a thin sheet of lossy material placed over /4 air spacer is a narrow-band absorber. Replacing the thin sheet with a frequency selective surface (FSS) is called circuit analog RAM. The absorpbility of two FSS sheets with square loops and Jerusalem crosses is evaluated and compared with experiments.
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Lee, Shang-Yu, i 李尚諭. "Design, Analysis and Manufacture of Circuit Analog Radar Absorbing Structures". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/51836441448604351052.

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Streszczenie:
碩士
逢甲大學
航空工程所
92
Structural radar absorbing materials (RAM) are multifunctional composites with dual functions of high performance and reducing radar cross section (RCS). This dissertation is aimed to the design, analysis and manufacturing of circuit analog (CA) absorbers with broadband, light-weighted and excellent strength properties. CA RAMs are fabricated by replacing the resistive sheet of a Salisbury screen by a frequency selective surface (FSS). The FSS can be represented by its effective resistance (R), inductance (L) and capacitance (C) that are related to the thickness of the deposit and the geometric patterns of the lossy materials. Using an equivalent circuit method and transmission line theory the power of EM waves reflected and transmitted from the FSS is solved and obtained. The reflection of normally incident or oblique incident plane waves from CA structures using either square loop or Jerusalem cross patterns is analyzed using equivalent circuit techniques and Ansoft Designer electromagnetic analysis software. The bandwidth of the absorber is increased for employing CA sheets rather than simple resistive sheets through increased control of the impedance properties of the lossy material.
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Teng, Chun-chung, i 鄧淳中. "The Study and Application of Nanocarbon Materials in Radar Absorbing Structures". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/59896274283653125270.

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Streszczenie:
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.
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Liou, Jian-De, i 劉健德. "Microwave Characteristics of CarbonNanocapsules and their Application to Radar Absorbing Structures". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/36458836223840653063.

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碩士
逢甲大學
航太與系統工程所
99
Onion-like carbon nanocapsules with polyhedral carbon clusters are composed of multiple graphite layers. Carbon nanocapsules as well as C60 and carbon nanotubes are fullerene structures. The particle size of carbon nanocapsules is about 1~100 nm. Hollow carbon nanocapsules and metal-filled nanocapsules possess specific optical, electrical and magnetic properties which make carbon nanocapsules an important cluster material for wide application. In this study, hollow carbon nanocapsules and iron-filled nanocapsules are added into epoxy to fabricate composite absorbers in different weight ratios. The complex permittivity and permeability and absorbing properties of the test samples are compared with carbon black and carbon nanotube absorbers in 2–18 GHz. The maximum absorption is –19.52 dB at 6.96 GHz for hollow carbon nanocapsule/epoxy absorber and –21.82 dB at 7.12 GHz for iron-filled nanocapsule/epoxy absorber with 3 mm thickness. This study also uses carbon nanocapsules in the design of radar absorbing structures (RAS). With two frequency selective surfaces and two honeycomb layers in the RAS in which the lower honeycomb is coated with 15 wt% carbon nanocapsule/epoxy in 0.5 mm thickness, we can obtain wideband absorptivity greater than 10 dB in the frequency range of 3.7-18 GHz.
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Du, Pei-Lin, i 杜佩麟. "The Analysis of Frequency Selective Surfaces and Their Application to Radar Absorbing Structures". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/89445119201210117357.

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碩士
逢甲大學
航空工程所
92
Radar-absorbing materials (RAM) play a key role in the stealth technology and their use is a major factor in radar-cross-section reduction. RAM can be characterized into interference-type and absorptive-type according to their loss mechanisms. The simplest resonant absorber is the Salisbury screen absorber which works in a narrow frequency bandwidth. The resistive sheet of Salisbury screen can be replaced by an array of two-dimensional patterns (e.g., dipoles, crosses, triangles) of finite conductivity. The class of such absorber is known as circuit analog (CA) absorber. The reason for employing circuit analog sheets rather than simple resistive sheets in an absorber lay-up is to provide increased bandwidth through increased control of the impedance properties of the loss material. The form of these patterns is similar to that of the frequency selective surfaces (FSS). The FSS are periodic structures which performs a filter operation. This dissertation modifies Chen’s and Reed’s model methods to analyze a thin, planar, resistive FSS with rectangular patches. In this method Floquet modes are matched with the current modes to form an integral equation which is solved by method of moment technique. This method is further extended to analyze the CA absorbing structures. Theoretical analysis shows that the bandwidth of the reflected power is improved significantly. A genetic algorithm (GA) has been used to optimize the dipole FSS array geometry for special frequency response and a broadband CA absorber. The GA optimizes the FSS cell design, its x- and y-periodicities, and the impedance of the patches. All numerical results calculated by the present theory are consistent with those obtained by Ansoft Designer electromagnetic analysis software.
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Yeh, Han-po, i 葉翰柏. "Optimal Design of Frequency Selective Surfaces and Radar Absorbing Structures Using Micro-Genetic Algorithm". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/47478302596185290126.

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碩士
逢甲大學
航太與系統工程所
94
Frequency selective surfaces (FSSs) are two-dimensional periodic structures with the filtering characteristics of total reflection or transmission in the neighborhood of the element resonant frequency. In the microwave region, the FSS are used to design band-pass radomes and the frequency reflector antenna systems. In the far-infrared and submillimeter wave region, the FSS are used as polarizers and beam splitters. In the near-infrared spectrum, they are used as solar selective surfaces, etc. In the thesis, we employ the spectral Galerkin method to analyze the scattering phenomena of the FSS. In the spectral domain, Floquet’s theorem allows the induced surface currents to be expressed in terms of a Fourier series and reduces the computation domain from an infinite array into a single cell. In order to calculate the incident wave of each layer, we employ the vector potential to decouple TE (transverse-electric) and TM (transverse-magnetic) waves. For the FSS with multilayered structures, we also employ the spectral immitance approach to derive the spectral dyadic Green’s functions which relate the induced surface currents to the scattered field. In order to analyze any shape of FSS structures, the subdomain basis functions are adopted to expand the induced currents. In the case of large unknowns, the computation speed can be improved by using a fast Fourier transform based iterative approach (conjugate gradient method, FFTCG). For electromagnetic bandgap absorbing structures, its must be added a conducting ground plate on the bottom of the whole structure and the FSS must be with finite conductivity. Finally, we employ the micro-genetic algorithm to optimize the electromagnetic bandgap structures (EBG) for different purposes, such as FSS structures, wideband electromagnetic bandgap absorbers, artificial magnetic conductor (AMC), ultra-thin electromagnetic bandgap absorbing structures and micron-scale planar infrared metallodielectric photonic crystals. In this thesis, the numerical results show perfectly matches with the results of the experimental works and the results from electromagnetic software Ansoft Designer.
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HO, LING-CHANG, i 何玲璋. "Development of Stealth Technology for Unmanned Aerial Vehicles Using Circuit-analog Radar Absorbing Structures". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/17799518951465877765.

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碩士
逢甲大學
航太與系統工程學系
105
In this study, the radar cross section (RCS) of the entire unmanned aerial vehicle (UAV) at 10 GHz is calculated by the physical optics (PO) method and the method of moment (MoM) by using the high frequency electromagnetic simulation software ANSYS HFSS. This study uses MoM and the domain decomposition method to overcome the high frequency calculation problem. PO is also used to obtain the electric current distribution over the UAV and locate the bright returns of RCS. The radar absorbing structure (RAS) with dual functions of high-strength performance and broadband microwave absorption is designed with the incorporation of a frequency selective surface (FSS) with two-dimensional arrays and finite surface resistance. In this study, FSS is fabricated by a low-cost screen-printing technique with conductive carbon ink instead of the high-cost sputtering deposition method. The bright high scattering area is then further covered with a layer of RAS to reduce the RCS of the UAV. The results show that the UAV covered with 3-mm-thick RAS can maximally reduce the RCS from 11.71 dBsm to -6.33 dBsm at 10 GHz, i.e., from 14.82 m^2 to 0.232 m^2 which significantly improves the stealth capability of the UAV.
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LIN, JHE-YI, i 林哲逸. "Development of Stealth Technology for Unmanned Aerial Vehicles Using Electro-Thermal Deicing Radar Absorbing Structures". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/y8wq2b.

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碩士
逢甲大學
航太與系統工程學系
107
In recent years, the design of unmanned aerial vehicles (UAV) has drawn much attention in the needs of High-Altitude Long Endurance (HALE). Airframe icing exists when the air contains droplets of supercooled liquid water at high altitudes. This study combines frequency selective surfaces (FSS) with chip resistors to develop a novel electro-thermal anti-icing radar absorbing structures for UAVs. SoildWorks is used to create a 3D model of the UAV and an ice accretion software is performed to predict the accretion and distribution of ice on the UAV. The effects of the accumulated rime ice and glaze ice on the aerodynamic performance of the NACA4412 airfoil are studied and discussed. In this study, ANSYS HFSS is used to optimally design the pattern of FSS with lumped resistors for the electro-thermal anti-icing radar absorbing structures aiming at X-band and Ku-band. The FSS is fabricated by wet etching method and the chip resistors are manually soldered to FSS. The as manufactured radar absorbing structure is tested in a microwave anechoic chamber to measure the reflection loss at oblique incidence and then compared with results of simulation. Finally, the DC power supply is applied from 0 to 24 volts to the electro-thermal anti-icing radar absorbing structures and the elevated temperature distribution of the structure is obtained by an infrared thermal imager to verify the feasibility of anti-icing.
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MICHELI, DAVIDE. "Design of Microwave Absorbing Structure and Microwave Shielding Structure by using Composite Materials, Nanomaterials and Evolutionary Computation". Doctoral thesis, 2011. http://hdl.handle.net/11573/495297.

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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.
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Książki na temat "Radar absorbing structures"

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Singh, Hema, Ebison Duraisingh Daniel J, Harish Singh Rawat i Reshma George. Fundamentals of EM Design of Radar Absorbing Structures (RAS). Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-10-5080-0.

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Singh, Hema, Harish Singh Rawat i Ebison Duraisingh Daniel J. Fundamentals of EM Design of Radar Absorbing Structures. Springer, 2017.

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Singh, Hema, Harish Singh Rawat, Ebison Duraisingh Daniel J i Reshma George. Fundamentals of EM Design of Radar Absorbing Structures. Springer, 2017.

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Nair, Raveendranath U., Hema Singh, Vineetha Joy i Vishal G. Padwal. Optimization of Multilayered Radar Absorbing Structures Using Nature Inspired Algorithm. Taylor & Francis Group, 2021.

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Nair, Raveendranath U., Hema Singh, Vineetha Joy i Vishal G. Padwal. Optimization of Multilayered Radar Absorbing Structures (RAS) Using Nature Inspired Algorithm. Taylor & Francis Group, 2021.

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Optimization of Multilayered Radar Absorbing Structures (RAS) Using Nature Inspired Algorithm. Taylor & Francis Group, 2021.

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Nair, Raveendranath U., Hema Singh, Vineetha Joy i Vishal G. Padwal. Optimization of Multilayered Radar Absorbing Structures (RAS) Using Nature Inspired Algorithm. Taylor & Francis Group, 2021.

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Micheli, Davide. Radar Absorbing Materials and Microwave Shielding Structures Design: By using Multilayer Composite Materials, Nanomaterials and Evolutionary Computation. LAP Lambert Academic Publishing, 2011.

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Części książek na temat "Radar absorbing structures"

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Singh, Hema, Ebison Duraisingh Daniel J, Harish Singh Rawat i Reshma George. "Design of Radar Absorbing Structure". W Fundamentals of EM Design of Radar Absorbing Structures (RAS), 3–17. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-5080-0_2.

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Eldo, Anusha, i Balamati Choudhury. "Design Optimization of Broadband Radar Absorbing Structures". W Metamaterial Inspired Electromagnetic Applications, 149–73. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-3836-5_6.

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Singh, Hema, Ebison Duraisingh Daniel J, Harish Singh Rawat i Reshma George. "Introduction". W Fundamentals of EM Design of Radar Absorbing Structures (RAS), 1–2. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-5080-0_1.

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Singh, Hema, Ebison Duraisingh Daniel J, Harish Singh Rawat i Reshma George. "Equivalent Circuit Model-Based RAS Design". W Fundamentals of EM Design of Radar Absorbing Structures (RAS), 19–25. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-5080-0_3.

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Singh, Hema, Ebison Duraisingh Daniel J, Harish Singh Rawat i Reshma George. "Smith Chart-Based RAS Design". W Fundamentals of EM Design of Radar Absorbing Structures (RAS), 27–35. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-5080-0_4.

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Singh, Hema, Ebison Duraisingh Daniel J, Harish Singh Rawat i Reshma George. "Conclusion". W Fundamentals of EM Design of Radar Absorbing Structures (RAS), 37. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-5080-0_5.

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Nilotpal, R. S., i Somak Bhattacharyya. "Metamaterial-based High-Performance Radar Absorbing Structure". W Metamaterials Science and Technology, 1–46. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-15-8597-5_2-1.

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Nilotpal, R. S., i Somak Bhattacharyya. "Metamaterial-based High-Performance Radar Absorbing Structure". W Metamaterials Science and Technology, 63–108. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-6441-0_2.

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Jiang, Shicai, Li Ying Xing i Bin Tai Li. "Study on a Novel Radar Absorbing Structure Composite". W Materials Science Forum, 1023–28. Stafa: Trans Tech Publications Ltd., 2005. http://dx.doi.org/10.4028/0-87849-960-1.1023.

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Jiang, Shicai, Li Ying Xing, Bin Tai Li i Xiang Bao Chen. "Optimization of Radar Absorbing Structure Using the Genetic Algorithm". W Materials Science Forum, 1603–8. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-432-4.1603.

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Streszczenia konferencji na temat "Radar absorbing structures"

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Tennant, Alan, i Barry Chambers. "Adaptive radar absorbing structures with active FSS". W SPIE's International Symposium on Smart Materials, Nano-, and Micro- Smart Systems, redaktor Alan R. Wilson. SPIE, 2002. http://dx.doi.org/10.1117/12.468647.

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Truong, Vo-Van, Ben D. Turner, Richard F. Muscat i M. S. Russo. "Conducting-polymer-based radar-absorbing materials". W Far East and Pacific Rim Symposium on Smart Materials, Structures, and MEMS, redaktorzy Alex Hariz, Vijay K. Varadan i Olaf Reinhold. SPIE, 1997. http://dx.doi.org/10.1117/12.293483.

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Es, J., A. Hulzinga, P. Tensen, H. Schippers, R. Heijmans i M. Journee. "Analysis of Radar Absorbing FSS on Foldcores and Honeycombs". W I European Conference On Multifunctional Structures. CIMNE, 2020. http://dx.doi.org/10.23967/emus.2019.009.

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Liubetski, N., H. Volunets, Y. Padrez i D. Bychanok. "Creation of Radar-Absorbing Structures Based on Carbon Films". W 2020 IEEE Ukrainian Microwave Week (UkrMW). IEEE, 2020. http://dx.doi.org/10.1109/ukrmw49653.2020.9252716.

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Rao, X. S., S. Matitsine i H. Lim. "Ultra-thin radar absorbing structures based on short strip pairs". W Proceedings of the International Conference on Materials for Advanced Technologies (Symposium P). WORLD SCIENTIFIC, 2007. http://dx.doi.org/10.1142/9789812709547_0036.

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Şentürk, Berkant, i Hüsnügül Yılmaz Atay. "Production of Radar Absorbing Composite Materials Using Carbon Nanotubes". W 6th International Students Science Congress. Izmir International Guest Student Association, 2022. http://dx.doi.org/10.52460/issc.2022.046.

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Streszczenie:
In order to increase the combat effectiveness of any platform or long-range munition in use today, it is necessary to reduce its visibility to radar. In this sense, important development in radar systems started after World War II. The interaction between electromagnetic waves at radar frequencies and different materials was investigated, electromagnetic radiation absorption mechanism; it has been observed that the materials consist of electrical, magnetic and dielectric properties. In line with this information, radar absorbing material design studies gained momentum. A significant development in radar systems of stealth technology made radar absorbing materials RAMs gaining a long-standing interest as a possible way to disguise aircrafts and submarines from radar systems. Carbon nanotubes and magnetic materials such as Fe, Ni, and Co have attracted researchers' significant interest as radar absorbers. In recent years, numerous studies have been made using carbon nanotubes due to their unique properties. However, few studies have considered the influence of both particle size and weight fraction. This work aims to produce material with unique properties such as solid absorption, low weight/thickness, and cost-effective, minimizing the reflection of electromagnetic waves using a polymeric composite structure reinforced with carbon nanotubes. Carbon nanotubes with different particles sizes of 8 nm,18 nm, and 78 nm were mixed with polyester in different weight fractions of 1%, 2%, and 3%. Three different composites structures were prepared in single, double, and three layers. Composites were characterized using XRD, SEM, and network analyzer in the frequency range of 8 to12 GHz. According to the results, it was observed that radar absorption increased with the increase in grain size, but the number of layers had no linear effect on the results. Network analyzer results show that the minimum reflection loss value at 9.9 GHz with a thickness of 1.5 mm is −33.1 dB, and the effective bandwidth is 9.9 GHz. Multi-layer carbon nanotubes composites might be a potential radar absorber because of their flexibility to adjust their absorption band to fit different applications in different frequency bands by modifying their particle sizes and weight.
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Singh, Arunima, Ravi Panwar, Smitha Puthucheri, Dharmendra Singh i Vijaya Agarwala. "Parametric analysis of frequency selective surfaces over radar absorbing nanocrystalline structures". W 2015 National Conference on Recent Advances in Electronics & Computer Engineering (RAECE). IEEE, 2015. http://dx.doi.org/10.1109/raece.2015.7510229.

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Kantikar, Rohit, Vineetha Joy i Hema Singh. "Radar Cross Section Analysis of Multi-Layered Resistive Material based Planar/Conformal Radar Absorbing Structures". W 2021 IEEE International Conference on Electronics, Computing and Communication Technologies (CONECCT). IEEE, 2021. http://dx.doi.org/10.1109/conecct52877.2021.9622561.

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NIELSEN, DEVIN, JUHYEONG LEE i YOUNG-WOO NAM. "DESIGN OF COMPOSITE DOUBLE-SLAB RADAR ABSORBING STRUCTURES USING FORWARD, INVERSE, AND TANDEM NEURAL NETWORKS". W Proceedings for the American Society for Composites-Thirty Seventh Technical Conference. Destech Publications, Inc., 2022. http://dx.doi.org/10.12783/asc37/36409.

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The survivability and mission of a military aircraft is often designed with minimum radar cross section (RCS) to ensure its long-term operation and maintainability. To reduce aircraft’s RCS, a specially formulated Radar Absorbing Structures (RAS) is primarily applied to its external skins. A Ni-coated glass/epoxy composite is a recent RAS material system designed for decreasing the RCS for the X-band (8.2 – 12.4 GHz), while maintaining efficient and reliable structural performance to function as the skin of an aircraft. Experimentally measured and computationally predicted radar responses (i.e., return loss responses in specific frequency ranges) of multi-layered RASs are expensive and labor-intensive. Solving their inverse problems for optimal RAS design is also challenging due to their complex configuration and physical phenomena. An artificial neural network (ANN) is a machine learning method that uses existing data from experimental results and validated models (i.e., transfer learning) to predict complex behavior. Training an ANN can be computationally expensive; however, training is a one-time cost. In this work, three different Three ANN models are presented for designing dual slab Ni-coated glass/epoxy composite RASs: (1) the feedforward neural network (FNN) model, (2) the inverse neural network (INN) model – an inverse network, which maintains a parallel structure to the FNN model, and (3) the tandem neural network (TNN) model – an alternative to the INN model which uses a pre-trained FNN in the training process. The FNN model takes the thicknesses of dual slab RASs to predict their returns loss in the X-band range. The INN model solves the inverse problem for the FNN model. The TNN model is established with a pretrained FNN to train an INN that exactly reverses the operation done in the FNN rather than solving the inverse problem independently. These ANN models will assist in reducing the time and cost for designing dual slab (and further extension to multi-layered) RASs.
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Manmohan C.T., R. U. Nair i Hema Singh. "Radar absorbing structures using carbon nano-composites: EM design and performance analysis". W 2016 Asia-Pacific Microwave Conference (APMC). IEEE, 2016. http://dx.doi.org/10.1109/apmc.2016.7931404.

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Raporty organizacyjne na temat "Radar absorbing structures"

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Huling, J., i D. Phillips. Microcellular ceramic foams for radar absorbing structures. Office of Scientific and Technical Information (OSTI), wrzesień 1996. http://dx.doi.org/10.2172/369687.

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