Radar Absorbing Materials (RAM) for Aircraft

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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A 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 provide both impedance matching and destructive interference properties. The structure can also incorporate sensors and a control unit to detect changes in the electroactive polymer films and transmit spoofing signals to the radar source.

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An air vehicle with a structure for absorbing electromagnetic waves, comprising a cylindrical air duct with panels positioned to absorb electromagnetic waves while maintaining aerodynamic performance. The panels are arranged in an "S" shape with varying distances between them, creating a flat surface against low-frequency electromagnetic waves. The structure provides both low radar frequency (RF) visibility and passive flow control by developing minimum drag resistance against the flow.

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Radar-absorbing materials (RAMs) covering the exterior surfaces of installed parts and assembled devices are crucial in absorbing most incident electromagnetic (EM) waves. This absorption minimizes reflected energy, thereby enhancing pilot safety and the stability of operating electronic devices without interference. Particularly, active stealth aircraft require effective protection from near- and far-field EM radiation across a wide spectrum of frequencies from both highly integrated electronic components and advanced enemy radars. Studies of RAMs often prioritize absorption over crucial tunability in frequency selectivity, revealing a research gap. In this study, we propose smart RAMs with frequency-selective absorption capabilities. Our approach involves incorporating two types of core-shell spheres in a polymer matrix, which feature shells of either wave-diffuse reflecting metal or wave-absorbing graphene. The key innovation lies in the ability to tailor absorption frequencies in the X-band range (8.2-12.4 GHz) by adjusting the interstitial spaces between the metallic spheres whi... Read More

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Abstract The iterative upgrading of the means of warfare has promoted the development of detection technology, and military activities are increasingly demanding target stealth. In this paper, a multifunctional metamaterial absorber is recommended, which simultaneously realizes the integrated stealth functions of ultra-wideband radar wave absorption, low infrared emission, and optically transparent. The structure is composed of an infrared shield, a radar-absorbing layer, and a reflective layer. Simulation results indicate that the absorption bandwidth in the radar band (1.8120.4 GHz) is more than 90%, and the infrared emissivity is as low as 0.271 in the IR band (314 m). Moreover, it has the features of flexibility, angle stability (045), polarization insensitivity (090), and so on. Furthermore, the electric field current distribution and equivalent circuit model of the structure are analyzed, and a 180 mm*180 mm sample is built and tested; the results show that the simulated and actual measurements are in agreement, and it is expected that such absorbers will be used in are... Read More

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A modular lightning protection system for composite aircraft structures, comprising a barrier coating made of MXene-based transition metal alloy layers with controlled nitrogen and carbon atom density. The coating is applied in multiple layers, with nitrogen atom density decreasing and carbon atom density increasing from the outermost layer to the innermost layer, providing impedance matching and electromagnetic wave absorption. The MXene-based coating is compatible with composite materials, corrosion-resistant, and can be applied using spray coating or other methods.

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This chapter discusses the importance of functional paints and coatings. The types of materials used, their processing, and different methods of testing of the final products are discussed. The range of applications is immense and especially important for strategic applications in defence and aerospace systems and platforms. Some specific functional applications include camouflage and stealth coatings; thermal imaging coatings; anti-static coatings; thermal insulating paints; high performance anti-corrosion coatings; anti-skid coatings; antifouling coatings; self-healing and self-cleaning coatings. Over the years DMSRDE, Kanpur, has made considerable efforts to develop specialized paints and coatings. In this chapter particular attention is paid to DMSRDE-developed camouflage and stealth coatings.

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Electromagnetic wave absorbing material (EWAM) plays an essential role in manufacturing stealth aircraft, which can achieve the electromagnetic stealth (ES) by reducing the strength of the signal reflected back to the radar system. However, the stealth performance is limited by the coating thickness, incident wave angles, and working frequencies. To tackle these limitations, we propose a new intelligent reflecting surface (IRS)-aided ES system where an IRS is deployed at the target to synergize with EWAM for effectively mitigating the echo signal and thus reducing the radar detection probability. Considering the monotonic relationship between the detection probability and the received signal-to-noise-ratio (SNR) at the radar, we formulate an optimization problem that minimizes the SNR under the reflection constraint of each IRS element, and a semi-closed-form solution is derived by using Karush-Kuhn-Tucker (KKT) conditions. Simulation results validate the superiority of the proposed IRS-aided ES system compared to various benchmarks.

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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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A radar-compatible coating for vehicle parts that achieves a silver-metallic appearance without using metal pigments. The coating consists of two layers: a base layer containing absorbent pigments and a top layer containing flake-form effect pigments with absorbent properties. The base layer is designed to have minimal color difference between coated black and white backgrounds, while the top layer provides the desired metallic appearance. The coating is free from metal pigments and achieves radar transparency while maintaining high hiding power and lightness flop.

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Abstract. The article presents the characteristics of modern reconnaissance systems in the radar range and camouflage methods for this range. Two absorbers of electromagnetic radiation in the 4-18 GHz range were tested, measuring their attenuation properties. Carbonyl iron and thin-walled hollow microspheres based on soda-lime-borosilicate glass were tested, on the basis of which paint coatings with different shares of absorbers and different coating thicknesses were produced. The attenuation properties of both absorbers were determined and attention was paid to the maximum values and frequencies for which they occur. Further directions of research were also proposed in order to obtain varnish coatings that are an effective camouflage agent in radiolocation.

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The paper proposes a theoretical and numerical study of the quality criteria of radar absorbing layer. Simple analytical expressions for the minimum of the reflection coefficient of a homogeneous absorbing layer are obtained. It is shown that this quantity is not a correct characteristic of absorption. To describe the quality of an absorber, other quality criteria are needed, such as relative bandwidth of operating waveband or the ratio of the operating waveband to the layer thickness. The first of these values may be useful in obtaining a broadband absorber, and the second, in obtaining a small thickness of an absorber.

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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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The so-called aircraft stealth refers to coating or pasting absorbing materials on the relevant parts of the aircraft, reasonably designing the aircraft shape and layout, so that the enemy detection system (such as radio radar, infrared radar, lidar, etc.) can only receive the greatly weakened aircraft reflection signal. In this way, the possibility of aircraft being found or tracked is reduced. The basic research of stealth technology includes designing the absorbing material into a reasonable shape to maximize its efficiency. Its achievements can be applied not only to military equipment such as aircraft, ships and tanks, but also to other scientific and technological fields. Although the mathematical and physical problems composed of Maxwell equations and corresponding boundary conditions can be analyzed and calculated strictly in theory, the model is complex and the calculation is complicated. Focusing on the problem of radiation absorption, the microwave absorption performance of wedge shaped absorber is studied in this paper. Simulation results show the effectiveness of the res... Read More

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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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