Radar Absorbing Materials (RAM) for Aircraft

Aircraft design with reduced radar visibility and improved aerodynamics. The aircraft has an air intake, duct, and engine with a curved shape that allows pressure changes as air flows. Radar absorbing panels are inside the duct. The panels have regions with pressure decreasing, then increasing, as air flows. The curved duct shape and pressure variations optimize aerodynamics. The panels absorb radar waves inside the duct.

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RCS reduction has become prominent in the field of stealth technology. The primary design criterion for aircraft design is to increase survivability by decreasing detectability. The radar cross section (RCS) of a target is the equivalent area seen by radar. The RCS value indicates how easily an object will be detected by the radar. RCS has been reduced using approaches such as shaping, radar absorbent material (RAM), passive cancellation, and active cancellation. Because of the low RCS, the sidelobe level rises due to radiation from higher-order harmonics. This study describes an overview of current passive RCSR techniques for a variety of applications including frequency selective surface (FSS), electronic bandgap materials (EBG), split ring resonator (SRR), and complementary split ring resonator (CSRR). An extensive comparison chart is obtained based on antenna size, RCSR, gain, and the operating band for different types of techniques. Challenges and the scope of future research are also proposed in this review.

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Radar Absorbing Structures (RAS) are widely used in defense applications in order to reduce the electromagnetic reflections from predominant hotspots. With majority of military radars operating in X-band, thin frequency selective absorbers catering to this frequency range are the need of the hour especially for airborne platforms. In this regard, a novel ultra-thin Frequency Selective Surface (FSS) based RAS with superior absorption performance in the frequency range of 8GHz to 12GHz is presented. The absorption characteristics and radar cross-section (RCS) of the RAS has been analysed using commercially available EM simulation software. Further, the ultra-thin RAS, with a thickness of 0.053l at the centre frequency, has been fabricated and the performance parameters have been measured. The measurement results show that the percentage of power absorbed by the proposed RAS is greater than 90% over majority of X-band. In addition, it provides atleast 8dB RCS reduction (RCSR) in monostatic as well as bistatic modes of operation in comparison with its metallic counterpart of identical di... Read More

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A radar-absorbing structure for reducing radar cross-section in aircraft, comprising a composite material layer with anisotropic electrical conductivity, comprising carbon fiber reinforced fibers and a binding agent, and a barrier coating with rods disposed at predetermined angles to redirect incident radio waves. The structure's conductivity is adjusted by varying the density and length of the rods, with higher density and length near the aircraft's interior. The structure also incorporates transition metal particles for enhanced adhesion and iron-based nanoparticles for improved absorption.

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Electromagnetic wave absorbing foam-based sandwich composite for aircraft with a lightning protection metal layer that maintains load bearing and electromagnetic wave absorption performance even after being struck by lightning. The composite comprises a dielectric fiber, plated dielectric fiber, foam core, and metal layer with a periodic circular pattern applied to reduce radar cross-section and protect against lightning strikes. The metal layer is designed to exhibit high electrical conductivity and electromagnetic wave absorption performance, while the foam core provides structural integrity and electromagnetic wave absorption.

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Stealth or lower visibility is an inevitable feature of future-generation aircraft. A stealth aircraft is coated with a special type of material called radar absorbing material (RAM), which makes the aircraft invisible to radar. Stealth technology is a great threat to the Radar surveillance system. Anti-stealth radar can be built using low-frequency signals that are efficient in detecting stealth aircraft. The variation of radar cross section (RCS) under low frequency radar system is studied here also designed an antenna for low frequency radar.

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A radar-absorbing material with a honeycomb sandwich structure for stealth applications, comprising a core layer of hexagonal units formed from metal-coated dielectric fibers and skin layers on top and bottom surfaces. The material achieves broadband electromagnetic wave absorption through the electromagnetic properties of the metal-coated fibers, and can be used in aircraft structures to reduce radar cross-section.

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For at least four decades, scientists have been working on Radar Absorbing Materials (RAMs). The effectiveness of a system has been the primary criterion for evaluating military aircraft. The designer's objective is thus to optimise the efficiency of the system. Presented article describes a preliminary study of employing Radar Absorbing Shield (RAS) to reduce Radar Cross Section (RCS) on air channels. To begin, a three-dimensional model of a single and twin air channel has been generated through using the software "Computer Aided Three-Dimensional Interactive Application" (CATIA) for numerical computation. Following that, the possible applications of Radar absorbing shield (RAS) on the surface of the both air channel were assessed in order to lower their Radar Cross Section (RCS). The outcomes were then evaluated to see the feasibility of Radar absorbing shield (RAS).

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Radar absorbing structure for air and space vehicles that combines impedance matching and destructive interference to effectively dampen electromagnetic waves. The structure comprises an aerodynamic surface, a resistive layer, and multiple films with electroactive polymers and graphene, which are cured together to create a composite material. The films are arranged to provide both impedance matching and destructive interference, while also incorporating sensors and control units to enable active cancellation and spoofing capabilities.

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Abstract Multilayer radar absorbing materials with light weight, strong absorption, and wide absorption bandwidth are urgently demanded with the increase of electromagnetic pollution. However, the current design methods with only simulation operation or optimization strategy are not comprehensive. Here, a simulation-optimization approach including electromagnetic simulation and numerical calculation is proposed based on the interaction between different software, in which the homogeneous medium substitution method is presented to simplify the complicated structures. Besides, return loss and impedance matching of different layer structures are investigated. From the simulated results, it can be found that the structures with better impedance matching have superior absorbing performance. The optimal method shows the advantages of fast and efficient, which has tremendous potential for various applications, such as military stealth and electromagnetic wave elimination.

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A lot of airstrikes are being reported and other operations are done by the defense sector using modern aircraft that are not detected by radar in which this technology is named as stealth technology. Radar Absorbing Materials (RAM) is a type of stealth application process in aircraft that are composites that absorbs electromagnetic radiation from the source radar. In this work, the radar absorption material properties were analyzed by using High-Frequency Selective Surface (HFSS) software in ANSYS electronics desktop, and two different materials at different thickness 1 mm, 1.5 mm, 2mm, 2.5 mm&3mm are analyzed for the comparison of the input properties such as Permittivity, Permeability, Reflection loss, tan loss and bulk conductivity for impedance matching and reflection loss to analyze their absorbing properties. From which the efficient material is found out from the analysis for stealth application.

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Abstract There is some kind of materials widely used in microwave engineering that known as radar absorbers. Whether it is the aircraft coating, the anechoic chamber interior or waveguide feed load. Anechoic chamber absorbers are typically characterized by reflectivity at normal incidence of electromagnetic wave. The study of the angular dependence of reflectivity for several absorber samples and the appraising of the impact of their combination on the anechoic chamber performance are the main aims of present work. For this purpose the experimental studies were carried out in an antenna measuring and computing complex based on the anechoic chamber. Obtained results may be useful in the anechoic chamber design and construction stages as well as the modernization of existing ones. It can also be used for modelling of the internal electromagnetic field distribution of indoor field test ranges.

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Radar absorbers are one among the promising technologies toward radar cross section reduction at microwave frequencies. Hence, the key role of radar absorber is emerging in military aviation platform. Although the research on radar absorbers are continuing since decades using multilayer concept, viz., ferrite-based radar absorbers, they are narrow band in nature. Recently artificially engineered materials widely known as metamaterials are playing an important role toward performance enhancement of radar absorbers. This chapter provides a systematic review of the advances in metamaterial-based radar absorbers in conjunction with graphene and conducting polymer.

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Radar absorbing structures with multiple resistive frequency selective surfaces (FSSs) are of great potential in the aerospace and marine fields. However, reliable theoretical prediction models of multilayer circuit-analog (CA) absorbers together with proper optimizing programs have not yet well been established despite the large number of reported investigations. Herein, a precise and comprehensive optimization method was proposed for the design of lightweight and broadband absorbing structures based on improved genetic algorithm. To this end, the spatial scale effect of the entire structures and interlayer interference effects between FSS films were firstly considered. Several absorbing sandwich structures composed of fiber-reinforced epoxy facesheets, polyvinyl chloride (PVC) foam and FSS films with square patterns of various periods were then fabricated. The environmental adaptabilities of the as-obtained absorbing structures were assessed through electromagnetic and load-bearing experimental tests under different ambient temperatures and marine corrosion durations. The optimized... Read More

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A multi-functional heating sandwich composite for large wing structures, comprising a face skin and a honeycomb core. The face skin absorbs electromagnetic waves, while the honeycomb core, made of metal electroless plated dielectric fibers, converts electromagnetic wave power loss into thermal energy. The composite enables selective heating and high-speed temperature control through electromagnetic wave absorption technology.

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A radar absorber comprising a water-filled cavity between two dielectric layers, where the cavity dimensions are optimized to absorb a wide range of radar frequencies. The absorber can be manufactured by assembling the dielectric layers and frame, injecting water into the cavity, and applying a waterproof coating. The design enables efficient absorption of radar waves across multiple frequency bands without the need for expensive or specialized materials.

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The growing demand for stealth technology in military and aerospace applications has driven the development of advanced radar-absorbing structures. In particular, honeycomb absorbing structures (HASs) have shown promise due to their unique properties. In order to enhance the absorption characteristics of HASs and evaluate its application effect on aircraft, firstly, the mechanism of enhancing the electromagnetic (EM) absorption capacity of honeycomb structures by using a gradient design for the impregnation material is studied. Secondly, a multi-layer gradient honeycomb absorbing structure (MGHAS) with top skin and intermediate bonding layers is proposed. The influence of the type and arrangement of impregnation materials on reflectivity is analyzed to obtain design strategies that can enhance the absorption performance of the MGHAS. An improved particle swarm optimization (PSO) algorithm is proposed to optimize the EM absorption performance of the MGHAS. The optimized MGHAS achieves broadband absorption below 10 dB in a 2-18 GHz range, and the reflectivity even reaches 30 dB near ... Read More

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A stealth structure that selectively controls infrared emissivity to emit infrared radiation through atmospheric absorption windows while absorbing microwave radiation. The structure comprises a radar absorption unit, a low-frequency transmission filter unit, and an infrared radiation unit. The radar absorption unit absorbs broadband microwaves, while the low-frequency transmission filter unit absorbs microwaves in the 2-4 GHz range. An infrared radiation unit emits infrared radiation through atmospheric absorption windows. This configuration enables the structure to selectively emit infrared radiation while absorbing microwave radiation, providing effective infrared stealth through both radar and infrared detection windows.

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Due to the large size of grounded aircraft and the difficulty in using shielding cloth to completely cover the aircraft, it is necessary to study efficient RCS shielding schemes for grounded aircraft to ensure that they can quickly hide on the spot. By covering key parts, the RCS of the aircraft can be reduced, the probability of being detected by radar can be reduced, and the survival rate of the aircraft can be improved. The geometric model of the aircraft is established using SolidWorks, and the RCS distribution of the electromagnetic model is determined by FEKO simulation calculation. Suitable shielding materials are selected to design the shielding scheme, and the radar characteristics of the shielding model are simulated and calculated. The effectiveness of the shielding scheme is evaluated by comparing the RCS distribution with the numerical change results. The study found that using magnetic absorbers combined with high-toughness epoxy resin materials reduced the average RCS by 10.757 dBm² at a frequency of 9.14 GHz after coating the aircraft model, providing a the... Read More

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A radio-wave anti-reflection sheet for reducing radar wave reflections from multilayer substrates, particularly in automotive applications. The sheet features a lower-density foam layer facing the substrate and a higher-density foam layer facing away from the substrate, which together create destructive interference patterns to suppress reflections. The sheet is particularly effective in reducing reflections from multilayer substrates used in vehicle body components, enabling improved radar detection of pedestrians and small vehicles.

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