Stealth Aircraft Research Articles

High temperature flexible 2D metasurface based on optimal design for thermal insulation and electromagnetic wave absorption skin

The development of radar stealth skin with long term stable service and flexible deformability is the premise and foundation of improving the battlefield survivability of deformable aircraft. Aiming at the bottleneck problem of mismatch between the flexible configuration and the electromagnetic configuration of the existing stealth composite materials, a new type of SiO2 fiber paper (SFP) with flame retardant, thermal insulation, low dielectric constant and super-hydrophobic was prepared by combining the papermaking process with surface modification. The effects of solid content and high temperature environment on the mechanical properties, thermal insulation properties, dielectric properties and hydrophobic properties of SFP materials were studied in detail. Based on this, the optimal design and construction method of radar stealth metasurface suitable for flexible deformation are proposed, and the high temperature resistant flexible stealth skin metasurface is obtained. The metasurface has been demonstrated to achieve an effective wave absorption of −8 dB in the 10.9–16.4 GHz range at 400 μm thickness, making it an ideal candidate for flame retardant, flexible, thermal insulation and radar stealth skin under extreme conditions. It provides theoretical basis and technical support for the innovative development of high-speed deformable stealth aircraft.

Structural‐Functional‐Integrated Ultra‐Wideband Microwave‐Absorbing Composites Based on In Situ‐Grown Graphene Meta‐nanointerface

AbstractUltra‐wideband microwave absorbing (MA) materials covering the low‐frequency range (2–6 GHz) are highly desirable in civil and military fields. These materials can be fabricated based on the design of electromagnetic meta‐structure. Herein, a structural‐functional‐integrated ultra‐wideband SiO2 fiber reinforced cyanate ester (CE) MA composite based on an in situ‐grown graphene meta‐nanointerface layer (GrMI) (SiO2f/GrMI/CE) is reported. The relationship between the periodic structure of the graphene nano‐interface layer and the MA performance is discussed through experiments and simulations. The results show that SiO2f/GrMI/CE with a thickness of 8.78 mm exhibits an effective absorption bandwidth of 15.46 GHz (2.54–18 GHz). Remarkably, the reflection loss remains basically unchanged upon increasing the incident angle from 5° to 50°. Additionally, GrMI is an effective load‐bearing constituent, which increases the interfacial shear stress between SiO2f and the CE by ≈210% and contributes to achieving composites with an ultra‐high flexural strength (552.7 MPa). The excellent structural‐functional‐integrated performances ensure that the SiO2f/GrMI/CE composites are suitable for use as the skin materials of microwave stealth aircraft and other civil facilities. The work provides a novel pathway for the design of thinner, wider, lighter, and stronger MA components.

Stealth Aircraft Penetration Trajectory Planning in 3D Complex Dynamic Based on Radar Valley Radius and Turning Maneuver

Based on the quasi-six-degree-of-freedom flight dynamic equations, considering the changes in the elevation angle caused by an increase in the rolling angle during maneuvering turns, which leads to a rise in the radar cross-section. A computational model for the radar detection probability of aircraft in complex environments was constructed. By comprehensively considering flight parameters such as turning angle, rolling angle, Mach number, and radar power factor, this study quantitatively analyzed the influence of these factors on the radar detection probability. It revealed the variation patterns of radar detection probability under different flight conditions. The results provide theoretical support for the Radar Valley Radius and Turning Maneuver Method (RVR-TM) based on decision trees, and lay the foundation for the development of subsequent intelligent decision-making models. To further optimize the trajectory selection of aircraft in complex environments, this study combines theoretical analysis with reinforcement learning algorithms to establish an intelligent decision-making model. This model is trained using the Proximal Policy Optimization (PPO) algorithm, and through precisely defining the state space and reward functions, it accomplishes intelligent trajectory planning for stealth aircraft under radar threat scenarios.

Frequency-Selective Radar-Absorbing Composites Using Hybrid Core-Shell Spheres.

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 while the scattered waves are efficiently attenuated by graphene networks in the composites. On a metal substrate, a 2 mm-thick composite with an optimized structural composition and ratio of the two types of spheres exhibits a maximum absorption efficiency of 99.3%, effectively trapping and extinguishing incident waves. Combined with the structural tunability and frequency-selective properties of spherical fillers, our approach provides a scalable and effective method for creating functional isotropic coverings on various metallic surfaces.

Optically Transparent Dual-Band Metamaterial Absorber Using Ag Nanowire Screen-Printed Second-Order Cross-Fractal Structures

In this paper, we propose an optically transparent dual-band metamaterial absorber (MMA) that uses Ag nanowire screen-printed fractal structures. The proposed MMA exhibits near-perfect absorption in the C- and K-bands. This dual-band absorption property is achieved through two inductive–capacitive (L-C) resonances located at 6.45 and 21.14 GHz, which are generated by the second-order fractal structures. We analyzed the microwave absorbing mechanisms through the distributions of the surface current and electromagnetic field on the top and bottom layers. The MMA demonstrates an optical transmittance of 63.1% at a wavelength of 550 nm. This high optical transmittance is attained by screen printing transparent Ag nanowire ink onto a transparent PET substrate. Since screen printing is a simple and low-cost fabrication method, the proposed MMA offers the advantages of being low cost while having the properties of optical transparency and effective dual-band absorption. Consequently, it holds great potential for the radar stealth application of C- and K-bands in that it can be attached to the windows of stealth aircraft due to its optical transparency and dual-band near-perfect absorption property.

Lightweight zirconium modified carbon–carbon composites with excellent microwave absorption and mechanical properties

With the rapid development of space technology, multi-functional materials with advantages such as heat insulation, lightweight, and electromagnetic (EM) wave absorption have gained broad application prospects. Since porous carbon fiber reinforced carbon (C/C) composites often have lightweight and high heat insulation properties, improving their mechanical and electromagnetic wave absorbing properties will significantly expand their application. In this study, a new kind of zirconium-modified C/C (Zr-C/C) composites prepared by polymer infiltration and pyrolysis using zirconium-modified phenolic resin is presented. By adjusting the content of Zr, the compressive strengths of the composites are increased up to 48% compared with the composites without Zr, while the thermal insulation properties are little changed. The incorporation of zirconium can make the composites exhibit better microwave absorption performance to some extent, and Zr-C/C composites with 10% zirconium have the best microwave absorption performance among all the samples. The excellent electromagnetic wave absorption performance of Zr-C/C composites is attributed to the enhanced interfacial polarization effect and the improved electrical conductivities of the material due to its internal carbon microsphere structure. Multi-functional Zr-C/C composites that combine lightweight, high thermal insulation, high compressive strength, and high electromagnetic wave absorption have obvious applications in fields such as stealth aircraft. Therefore, this work provides a new way to prepare multi-functional materials.

Design, Analysis and making of RC Controlled Stealth Aircraft Working Model

Design, Analysis and making of RC Controlled Stealth Aircraft Working Model

Stealth Aircraft Penetration Trajectory Planning in 3D Complex Dynamic Environment Based on Sparse A* Algorithm

To find a trajectory with low radar detection probability for stealth aircraft under the assumption of 2D space, performing a rapid turning maneuver is a useful way to reduce the radar detection probability of an aircraft by changing the azimuth angle rapidly to reduce the time of high radar cross-section (RCS) exposure to radar. However, in real flight, not only does the azimuth angle to the radar change rapidly but the elevation angle also changes rapidly, and the change in the radar cross-section is also significant in this process. Based on this premise, this paper established a trajectory planning method based on the sparse A* algorithm in a 3D complex, dynamic environment, called the 3D sparse A* method, based on a log-normal radar model (the 3D-SASLRM method), which considers the RCS statistical uncertainty and the statistical characteristics of the radar signals. Simulations were performed in both simple and complex scenarios. It was concluded that the established 3D-SASLRM method can significantly reduce the radar detection probability. And the essence of reducing under the assumption of 3D space is also to reduce the time of high radar cross-section exposure to radar.

Long wave infrared signature of swept back leading edges in aircraft frontal aspect

PurposeIn recent years, increased use of all-aspect infrared (IR)-guided missiles based on the long-wave infrared (LWIR; 8–12 µm) band has lowered the probability of aircraft survival in warfare. The lock-on of these highly sensitive missiles is difficult to break, especially from the front. Aerodynamically heated swept-back leading edges (SBLE), because of their high temperature and large area, serve as a prominent LWIR source for aircraft detection from the front. This study aims to report the influence of sweep-back angle (Λ, based on the Mach number [M∞]) on aerodynamic heating and the LWIR signature of SBLE.Design/methodology/approachThe temperature along SBLE is obtained numerically as radiation equilibrium temperature (Tw) by discretizing the SBLE length into “n” number of segments, and for each segment, emission based on Tw is evaluated. IR radiance due to reflected external sources (sky-shine and Earthshine) and radiance due to Tw are collectively used to determine the IR contrast between SBLE and its replaced background in the LWIR band (icont-SBLE,LWIR).FindingsThe results are obtained for low subsonic turboprop aircraft (Λ = 3°, M∞ = 0.44); high subsonic strategic bombers (Λ = 35°, M∞ = 0.8); fifth-generation stealth aircraft (Λ = 40°, M∞ = 1.6); and aircraft with supercruise/supersonic capability (Λ = 50°, M∞ = 2.5). The aircraft with supersonic capability (Λ = 50°, M∞ = 2.5) reports the maximum LWIR signatures and hence the highest visibility from the front. The results obtained are compared with values at Λ = 0° for all cases, which shows that increasing Λ significantly reduces aerodynamic heating and LWIR signatures.Originality/valueThe novelty of this study comes from its report on the influence of Λ on the LWIR signatures of aircraft SBLE in the frontal aspect for the first time.

Agresija NATO-a na SRJ 1999. godine - provera efikasnosti novih borbenih sredstava

Introduction/purpose: During the 1999 NATO attack on Yugoslavia, three new weapons were used and tested for the first time. The first is the strategically invisible B-2 bomber, the second is the new JDAM (Joint Direct Attack Ammunition) and the third is the "soft bomb", or the blackout bomb, made of thin electrically conductive fibers. The aim of the paper is to present the new combat devices used during the aggression on the FRY and to quantitatively detect the elements of electrically conductive fibers. The paper also presents the lawsuit of the Federative Republic of Yugoslavia (FRY) to the International Criminal Tribunal for the former Yugoslavia (ICTY) in The Hague. The lawsuit was rejected Methods: Physical and chemical analyzes of the fibers were performed. An electron microscope, SEM JSM Jeol 6610LV, was used to analyze the physicochemical characteristics of electrically conductive fibers. It provides the information on the morphology of the sample surface, resulting in a high-resolution image. The microscope is equipped with an X-ray detector (Oxford Instrumets X-Max 20 mm2) for EDS analysis (Energy Dispersive Spectroscopy). It enables the determination of the chemical composition of the material in the analyzed sample volume, based on the interaction between the directed electron beam and the sample atom. Results: The characteristics of the B-2 stealth aircraft used to bomb the FRY are shown. The JDAM bomb is an improved ordinary MK bomb with electronic devices added to guide the bomb via satellites. A semiquantitative analysis of the fibers was performed on the SEM, confirming that the metal layer of the fiber predominantly consists of aluminum, and the non-metallic layer has the highest proportion of silicon dioxide. The fiber is carcinogenic. Conclusion: In 1999, the territory of Yugoslavia was a testing ground for new combat weapons of NATO aviation - B-2 and JDAM guided bombs. Blackout bombs were dropped on the electrical power systems of Yugoslavia leaving the whole Serbia without electricity for hours. Not only was the bombing-caused environmental pollution radiological and chemical but it was also caused by glass-aluminum electrically conductive fibers as pollutants.

A novel three-layer woven fabric composite reinforced by (polyaniline + carbonyl iron) core-shell/carbonyl iron/polyaniline fillers for high-performance broadband radar absorbing structure

One of the most important applications of electromagnetic wave absorption is in stealth aircrafts and electromagnetic protection of avionic systems. The main limitations in the design of these structures are aerodynamics, thickness or weight, mechanical strength, manufacturing process, and reasonable cost. In this study, a novel three-layer woven fabric composite laminate (with a total thickness of about 3 mm) is proposed which each layer is reinforced by individual polyaniline, carbonyl iron, or (PANI + CI) core-shell fillers. The developed Non-dominated Sorting Genetic Algorithm II optimization algorithm suggests the stacking sequence of layers, the appropriate thickness of each layer, and the filler weight fraction in each layer to achieve a broadband absorption. Due to using both dielectric and magnetic absorbing fillers, this structure shows well-impedance matching and approximately absorbs 80% of the X-band (8-12 GHz) electromagnetic waves. The maximum reflection loss is about −14dB. Finally, the effect of the addition of absorbent particles on the mechanical properties has been investigated. Experimental results showed that the tensile modulus and strength decrease by about 21.5% and 20.6%, respectively, and the flexural modulus and strength reduce by 21.7% and 19.7%, respectively. However, the (PANI + CI) core-shell filler can be introduced as a high performance absorber filler because it suggests maximum reflection loss with low weight fraction compared to other fillers and consequently the minimum reduction in mechanical properties.

Achieving broadband electromagnetic absorption at a wide temperature range up to 1273 K by metamaterial design on polymer-derived SiC-BN@CNT ceramic composites

High-temperature broadband electromagnetic wave (EMW) absorption has emerged as a forefront challenge of EMW functional materials for harsh environment applications such as aerodynamically heated parts of stealth aircraft and aero engines. Herein, an innovative strategy for broadband absorption at high temperatures is proposed by combining the microstructural design of the EMW absorption phase in the polymer-derived SiC with a periodic structure design. The metamaterial was designed on SiC-BN@CNT ceramic composites with the shape of a frustum pyramid. The experimental results reveal that SiC-BN@CNT metamaterials exhibit excellent absorption performance even under a high-temperature environment of 1273 K, in which the effective absorption bandwidth (EAB) (below −10 dB) can achieve 15.52 GHz, almost covering the whole S, C, X, and Ku bands. Moreover, the CST simulation results show that the SiC-BN@CNT metamaterials have an impressive EAB of 34.62 GHz and the average absorption intensity is remarkably high with a value of 21.07 dB (<99 % absorption) in the frequency range of 2–40 GHz. The exciting EMW attenuation capability is ascribed to favorable impedance matching, enhanced conduction loss abilities, and multiple polarization loss at high temperatures. This work provides valuable insights for the development of broadband-absorbing material in high-temperature harsh environments.

RCS reduction of composite transparent flexible coding metasurface combined phase cancellation and absorption.

A wideband low-scattering metasurface with optical transparency and flexibility is proposed by using the combination of phase cancellation and absorption mechanisms. Electromagnetic (EM) diffusion is achieved through the random phase distribution design of the two coding elements. The enhanced energy absorption can be obtained in a wide spectrum by using indium tin oxide (ITO) with suitable sheet resistance in the supercells. The experimental results show that the radar cross section (RCS) reductions of less than -10 dB under the planar and conformal cases are in 6.65-19.40 GHz and 6.11-17.37 GHz, corresponding relative bandwidth are 97.89% and 95.91%, respectively. Both theoretical analysis and simulated results are good accordance with the experiment. Furthermore, the analyses of the surface current, EM field distribution and power loss density are given to explain the hybrid RCS reduction mechanism. The proposed composite transparent flexible coding metasurface (CTFCM) maintains good angular stability within 0°-60° oblique incidence and has polarization insensitivity. The CTFCM has excellent flexibility and high optical transparency, which provides a way to reduce RCS in a wider band and has important application potential for stealth aircraft cockpit and transparent radome.

A review: Advancement in metamaterial based RF and microwave absorbers

Microwave absorbers (MAs) are specially designed structures which dissipate an incident electromagnetic (EM) wave by converting it into thermal energy and thereby prevents reflection and/ or transmission. The MAs are extensively in demand due to their property to reduce the electromagnetic wave interference (EMI) and to enhance electromagnetic shielding (EMS). MAs are also used in potential military applications as a stealth technology to design stealth aircrafts, warships and army clothing etc. due to the reduction of radar cross section (RCS) of the defense equipment by the absorber coating. In this review work, study of metamaterial-based MAs, their characteristics viz. left-handed material property, permittivity and permeability have been discussed in detail. Metamaterials (MMs) or artificial materials that play a significant role in reducing the size and thickness of MAs depending upon the frequency of operation. In this work, theoretical background of MM-based absorbers detailing the effect of permittivity and permeability on absorber performance has also been discussed. Different applications of absorbers are elaborately covered in this paper. Furthermore, frequency selective surface (FSS) which is a two-dimensional array has the capability to reflect or transmit EM wave completely or partially depending upon the nature of FSS. Therefore, distinct categories of FSS-based absorbers are discussed according to the frequency of operation, bandwidth and material specification where the effect of different design parameters is also critically analyzed. The objective of this review paper is to provide an exhaustive study of the unique attributes of MAs having a diverse range of applications for frequencies ranging from microwave, terahertz upto optical frequency domain. This review paper is certainly a vital tool for researchers to accurately understand, explore and work on MA design and selection as per user defined specific frequency and applications.

Novel radar absorbing material using resistive frequency selective surface based polymer composites for enhanced broadband microwave absorption

In this paper, a novel approach using glass fibre laminate composite (GFLC) with nanoparticle embedded nanofibres and frequency selective surfaces (FSS) for improved electromagnetic (EM) wave absorption has been proposed. For enhanced absorption, the FSS was coated with polyvinylidene fluoride (PVDF) mixed with multi-walled carbon nanotubes (MWCNTs). The coatings were prepared through electrospinning technique. The composite prepared from FSS, PVDF-MWCNT layers and GFLC showed enhanced absorption properties. It was demonstrated that the fabricated composites reduced reflection of electromagnetic waves by the material when compared to metals. An 80% increase in EM absorption (with respect to metal) was observed over a wide frequency range with the novel composite at an overall thickness of only 3 mm. X-ray diffraction (XRD) spectra showed an improvement in the electroactive β-phases in the electrospun PVDF/MWCNTs compared to Plain PVDF. Scanning electron microscopy analysis on various weight percentages of PVDF/MWCNTs revealed the formation of nano fibres with an average diameter of 75–160 nm. In addition, the proposed novel EM wave absorbing composites were of simple configuration and the mechanical properties of the fabricated composites were comparable to that of GFLC. Experimental results indicated that RAS with 0.25 wt % MWCNT/PVDF had 87.5% bandwidth for over 90% absorption from 8.5 to 12 GHz compared to all other configurations. The tailored composite material could be used as excellent radar absorber structures (RAS) and can find tremendous application in the manufacture of stealth aircrafts.

Conversion and Active Control between Electromagnetic Induced Transparency and Absorber in Terahertz Metasurface

In this study, we use a phase-changing material vanadium dioxide (VO2) to design a multilayer metasurface structure to achieve the transition from an electromagnetically induced transparency(EIT) device to an absorber. The structure consists of a gold layer, a polyimide spacer layer, a VO2 layer, and a sapphire substrate. The top layer consists of one cut wire and two split-ring resonators with the same parameters. When the VO2 layer is in its insulating phase at room temperature, the peak of the EIT device will appear near 1.138 THz. When the VO2 layer is in the metallic state, two absorption peaks above 99.5% appear separately at 1.19 and 1.378 THz, respectively. To the best of our knowledge, this is the first time that a coupled mode equation is used to perform theoretical calculations for EIT devices and perfect absorbers simultaneously, and this is also the first time that coupled mode equations are used for the theoretical calculations of two absorption peaks in an absorber. The proposed metasurface combines the advantages of terahertz absorption, EIT and active device control, which will provide more ideas for the design of future terahertz devices and is also significant for the design and development of radomes for future stealth aircraft.

Design exploration and optimization of aerodynamics and radar cross section for a fighter aircraft

The design for the conflicting requirements of low drag and low Radar Cross Section (RCS) causes difficulty in achieving an aerodynamically superior stealth aircraft. To cater the issue, a multidisciplinary design exploration and optimization framework is proposed. A shared parameterized aircraft geometry is used for high fidelity aero-stealth analysis using Computational Fluid Dynamics (CFD) and Shooting and Bouncing Rays (SBR) techniques. A surrogate model using a machine learning approach involving Gaussian Process (GP) modelling is generated for efficient and rapid design space exploration. A gradient-free metaheuristic optimization scheme using multi-objective Genetic Algorithm (GA) is employed to minimize drag and RCS. The results show that the proposed framework provides a reliable environment for the multidisciplinary design exploration of an aerial vehicle.

Research on the Influence of Model Surface Conductivity on RCS Test Accuracy

The accuracy of the RCS (Radar Cross Section) test is closely related to the conductivity of the model surface. The Chinese military standard has stringent surface resistance criteria for models. If the resistance criteria are appropriately relaxed, model processing can be more effective and expenses can be reduced. However, there are few quantitative evaluations of the relationship between surface resistance and RCS test error, making it impossible to design the model surface resistance in accordance with RCS test accuracy requirements. In this paper, firstly, the influence of model surface resistance on RCS is clarified through theoretical, simulation, and experimental research. The RCS analysis approach of the finite conductivity model is established. Subsequently, taking various typical shapes as research objects, such as the sphere, cube, flying wing aircraft, wing-body combination, and stealth aircraft, the simulation analysis of radar scattering characteristics is carried out under varied sheet resistances and multiple frequencies. A more attainable surface conductivity control standard for the RCS test model has been formulated, which is relaxed by 93% and 727% for models with average RCS of less than and higher than −30dBsm compared with the indicator in the Chinese military standard.

In Situ Construction of TiC-Ti3SiC2 Gradient Hybrid Interphase Coated SiC Fibers for Suppression of Specular Reflection and Non-Specular Scattering

TiC-Ti3SiC2 gradient hybrid interphase on the surface of SiC fibers was successfully obtained through the molten salt method. The electromagnetic parameters of the prepared samples can be accurately controlled by adjusting the reaction temperature. A significant bimodal effect is observed in electromagnetic parameters patterns, corresponding to the double interface layer. TiC-Ti3SiC2 gradient hybrid interphase plays a dominant role in impedance matching, as well as in the attenuation layer through multi-interfacial polarization and conduction loss. Through the co-evaluation of the suppression of specular reflection and non-specular scattering properties of the samples, the SiC fiber with the TiC-Ti3SiC2 gradient hybrid interphase is expected to be a high temperature resistant radar absorbing material for future stealth aircraft.

Multifunctional Coding-Feeding Metasurface Based on Phase Manipulation.

Multiple functionalities on a shared aperture are crucial for metasurfaces (MSs) in many applications. In this paper, we propose a coding-feeding metasurface (CFMS) with the multiple functions of high-gain radiation, orbital angular momentum (OAM) generation, and radar cross-section (RCS) reduction based on phase manipulation. The unit cell of the CFMS is composed of a rectangular emission patch and two quasi-Minkowski patches for reflective phase manipulation, which are on a shared aperture. The high-gain radiation and multiple modes of ±1, ±2, and ±3 OAM generation were realized by rationally setting the elements and the phase of their excitation. The CFMS presents a broadband RCS reduction of 8 dB from 3.18 GHz to 7.56 GHz for y-polarization and dual-band RCS reduction for x-polarization based on phase interference. To validate the concept of the CFMS, a prototype was fabricated and measured. The results of the measurement agree well with the simulation. A CFMS with the advantages of light weight and low profile has potential application in detection and wireless communication systems for stealth aircraft.