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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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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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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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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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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A dynamic camouflage system for aircraft and spacecraft that rapidly adapts its appearance through controlled manipulation of microscopic structure. The system employs an active coating with integrated, wavelength-dependent microscopic structures that can be precisely arranged to produce selective diffraction patterns. By varying the structure's arrangement, the system can dynamically change its appearance to evade detection, particularly in the infrared range. The system's control mechanism can be programmed to achieve specific camouflage patterns through electrical signals, enabling rapid adaptation to changing environmental conditions.

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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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A shielding device for protecting an optical imaging system from electromagnetic interference (EMI) emitted by a radar system within a common housing. The device captures and dissipates EMI signals reflected from a radome, while maintaining optimal radar performance. The shielding device is attached to the radar antenna assembly and features angular surfaces to reflect EMI signals away from the radar, and a capture surface to absorb signals directed towards the optical system.

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A method for manufacturing radar-absorbing composite materials with improved mechanical properties, comprising a three-block laminate structure. The second and third blocks form the active electromagnetic component, with the second block manufactured by superimposing layers of dry fiber sprayed with graphene nanoplatelets, interspersed with untreated dry fiber fabrics. The number of untreated fabrics is inversely proportional to the central frequency of the absorption band. The blocks are solidified through resin infusion and curing, enabling broadband radar absorption while maintaining mechanical properties comparable to the first block.

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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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A multi-layered resonant structure for absorbing electromagnetic radar energy on optically transparent surfaces, comprising thin conductive films sandwiched between quarter-wavelength thick lossy material layers. The conductive films have progressively increasing sheet resistances as they approach the base material, dissipating energy while the lossy layers cause destructive interference of the electromagnetic energy. The structure provides over 15 dB of energy absorption over a wide frequency range, enabling stealth applications on transparent surfaces such as windshields, canopies, and optical sensors.

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A heat dissipation system for supersonic aircraft that utilizes a novel coating to redirect thermal radiation from the engine to frequencies above the plasma frequency of surrounding medium, effectively preventing plasma formation and heat buildup. The coating selectively absorbs lower frequency radiation while selectively absorbing higher frequency radiation, creating a temperature gradient that enables efficient heat dissipation through the surrounding medium. The coating's variable emissivity profile adapts to changing operating conditions, ensuring optimal radiation management across the entire thermal spectrum.

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Mechanically durable radar-absorbing structure for aircraft and space vehicles that combines enhanced durability with improved radar absorption characteristics. The structure comprises a composite of glass and carbon fibers with strategically positioned rods that form an electrical network. The rods are arranged in a specific density gradient pattern across the surface, with denser rods near the aircraft surface and gradually increasing length towards the interior. This gradient enables controlled impedance matching between the radar-absorbing material and the aircraft surface, while the rods' electrical conductivity adjusts to optimize absorption. The structure's angularly positioned rods direct incident waves towards the absorbing material, ensuring efficient absorption while minimizing reflections.

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A radio wave absorber sheet for millimeter wave frequencies, comprising a radio wave reflection layer, a radio wave absorption layer, and a protective layer, wherein the radio wave absorption layer has a relative permittivity of 14.5-6i at 79 GHz, and the protective layer has a film thickness of 80-80 μm and an optical reflectance of 60-80°. The sheet exhibits high absorption performance in the 76-81 GHz frequency range, with an absorption peak of -42 dB at 79 GHz.

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A millimeter wave absorber structure comprising a metal member and a coating film formed on the metal member's surface, where the coating film contains carbon powder particles with a specific surface area of 30 m2/g or more, a binder, and a carbon powder particle content of 1-100 parts by mass per 100 parts by mass of binder. The coating film has a thickness of 100-400 μm and a specific gravity of 1.1-2.5 g/cm3. The structure exhibits millimeter wave absorption and can be manufactured by directly coating the metal member with a liquid paint.

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A wave-absorbing metamaterial structure for aircraft radar cross-section reduction, comprising a stacked arrangement of microstructure arrays with alternating absorbing and transmitting elements. The absorbing elements, comprising ring-shaped conductive structures with resistors, absorb electromagnetic waves in a specific frequency band, while the transmitting elements, comprising polygonal conductive structures, reflect and transmit waves in adjacent frequency bands. The structure achieves wideband angular absorption and transmission while minimizing grating lobes.

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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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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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Radar is a sensitive detection tool that uses electromagnetic radio waves to determine the position and motion of objects. Since its development, the methods for reducing radar wave reflections have been explored to improve stealth technology. One of the methods for reducing radar reflection is coating the aircraft using radar absorbing metamaterial. This research studies the radar absorption properties of a metamaterial honeycomb structureHoneycomb structure which has gradient protruded inner walls that are made of a radar absorbing material fabricated of Carbon Nanotube (CNT) Iron Oxide composite. The CNT Iron Oxide material was first prepared, then EMI measurement was conducted to obtain the permeability and permittivity values of the material. Then, the effect of changing the geometrical parameters of the honeycomb structureHoneycomb structure (size, height, thickness, and tilted angle) on the radar absorption properties has been simulated using Multi-Physics COMSOL. Simulation results showed that the optimum structure can absorb more than 90% of the radar incident waves in X-ban... Read More

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Microwave absorbent materials (MAMs) are significant in a extensive range of civil and military applications, including national defense security, healthcare, electronic reliability, and anti-radar detection of war fighters, as information technology advances quickly, and recent years have seen an explosion in the investigation of nanomaterials for use in microwave absorption applications. Therefore, the creation of high-performance MAMs with thin thickness, low density, wide bandwidth, and robust absorption has attracted a lot of attention. MAMs nanocomposites are also used to make radar-absorbing materials (RAMs) for stealth aircraft. By combining RAMs with geometry, stealth technology (ST) reduces the reflection of electromagnetic waves back to a radar system. In this article, we discuss the fundamental theory, components, and mechanism of electromagnetic microwave absorption. It will be detailed how to improve the microwave absorbent materials' (MAMs') absorption characteristics. Metal-based composites often show significant efficacy in achieving desired magnetic and dielectric p... Read More

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In this paper, we will present recent work at QUB in the area of ink-jet printed absorbers with applications in electromagnetic compatibility and spectral response control. A radio frequency (RF) enhanced spacecraft multi-layer insulator (MLI) was engineered by patterning its outermost layer using a resistively loaded hexagonal patch FSS. The structure ranges in thickness between /213 /25 and absorbs unwanted reflections to decouple onboard antennas from the spacecraft's structure. In addition, we also show the design of an antenna superstrate absorber designed for radar cross-section (RCS) reduction. The new antenna arrangement is capable of beam steering, preserving its beam shape when compared to the reference antenna, whilst reducing the RCS by 10 dB over a wide frequency range.

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Electromagnetic wave absorbing member for radar devices using millimeter waves, comprising a multi-layer structure with a metal mesh pattern, resin layer, and metal layer, where the mesh pattern occupancy rate varies between two distinct regions, and the metal mesh pattern in one region has a plating layer and uneven surface features. The member is designed for placement around radar devices or their communication units to mitigate electromagnetic interference.

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Abstract In order to reduce the radar cross section (RCS) of the unmanned aircraft while suppressing its infrared signature, a comprehensive design method (CDM) based on sorting factor Pareto solution is presented. The physical optics and physical diffraction theory are used to evaluate the electromagnetic scattering characteristics of the aircraft, and the Monte Carlo and ray tracing method are used to evaluate the infrared radiation intensity of the exhaust system. CDM is used to evaluate and screen each individual in each offspring, and the design parameters and sub-models of the aircraft exhaust system are continuously improved. The results show that the exhaust port model, lower baffle and nozzle height are the main factors affecting the RCS indicators, nozzle stages, exhaust port model, lower baffle and outer width make the main contribution to infrared radiation suppression. The presented CDM is efficient and effective in enhancing the radar/infrared integrated stealth performance of the aircraft.

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