Radar Stealth Research Articles

Facile fabrication of biomass chitosan-derived magnetic carbon aerogels as multifunctional and high-efficiency electromagnetic wave absorption materials

Biomass chitosan-derived porous carbon-based materials take the advantage of light weight, adjustable intrinsic conductivity, and environmental friendliness, attracting more attention in the field of electromagnetic compatibility. However, exploring a facile fabrication method to achieve rational structure design and electrical-magnetic coupling for electromagnetic absorption performance enhancement still remains challenging. Here, a unique honeycomb-like porous cobalt/carbon aerogel is fabricated through the directional freezing-drying and carbonization process, and abundant and even-distributed cobalt particles in-situ grow on the carbon skeletons. The aerogel exhibits an impressive electromagnetic wave absorption performance of a −75.8-dB absorption intensity and a −256.9-dB mm−1 specific reflection loss at a low filling content (10%), as well as an 8.53-GHz effective absorption bandwidth. Besides, the aerogel also demonstrates classy radar stealth and thermal insulation performance. The eco-friendly, easily fabricated, and high-performance cobalt/carbon aerogel suggests broad application prospects for electromagnetic compatibility and protection, thermal management, and multifarious electron devices.

Nano-assembled modified graphene composites based on rapid microwave fabrication for thermal management

Carbon materials are commonly considered as the main wave-absorbing material for radar stealth in conventional stealth materials. In fact, nanoscale modulation can adequately exploit their superior properties to develop their potential as infrared stealth. In this paper, an ingenious strategy is proposed for rapidly preparing carbon-based materials through simple microwave radiation. Graphene oxide is modified by a “defect/ion matching” mechanism to accomplish the structural construction of the carbon chessboard/silver chess pieces (CCB-SCP). Additionally, inexpensive chitosan has been introduced via topological bonding without using binders. Due to the delicate structural design, CCB-SCP/Chitosan has low density (0.064 g cm−3), ultra-low thermal conductivity (0.018 W m−1 K−1), and significant thermal shielding temperature difference (ΔT ∼ 50℃). The cost-effective composite material can be applied to thermal management in medium–high temperature sections (∼200℃). At a heating platform of 190 °C, CCB-SCP/Chitosan can provide a temperature drop of up to 46℃. In addition, CCB-SCP/Chitosan exhibits good electrical conductivity, thermal insulation stability, and relatively low infrared emissivity. An innovative approach to the delicate design of carbon-based materials utilizing microwaves, including carbon layers encapsulation, three-dimensional structures, and five-fold twinned particles, is proposed, which opens a new avenue for nanostructure-based thermal camouflage applications in the medium to high temperature region.

In-situ synthesis of multi-principal-element (Mo0.25Cr0.25Ti0.25V0.25)3C2Tx MXene-based composites with enhanced electromagnetic wave absorption

Nowadays, the increasingly severe electromagnetic (EM) wave pollution requires high-performance EM wave absorbing materials. Multi-principal-element materials are acknowledged as promising for broadening the applications owing to their tunable chemistries and structures in many fields, including as EM wave absorbers. Herein, we prepared a high-entropy MXene, (Mo0.25Cr0.25Ti0.25V0.25)3C2Tx. Furthermore, multi-principal-element (Mo0.25Cr0.25Ti0.25V0.25)3C2Tx/FeCoNi and (Mo0.25Cr0.25Ti0.25V0.25)3C2Tx/FeCoNiCu composites were synthesized via an in-situ hydrothermal process by combining high-entropy MXene with medium-entropy magnetic alloys. In contrast with the relatively narrow effective absorption bandwidth (EAB) of (Mo0.25Cr0.25Ti0.25V0.25)3C2Tx MXene (2.56 GHz), (Mo0.25Cr0.25Ti0.25V0.25)3C2Tx/FeCoNi composite with 50 wt% MXene can attain an optimum EAB of 4.88 GHz with the matching thickness of only 1.73 mm. As for (Mo0.25Cr0.25Ti0.25V0.25)3C2Tx/FeCoNiCu composites, both the absorption efficiency and absorption bandwidth are significantly enhanced. The combination of multi-principal-component strategy and composite construction endows the composites with synergistic dielectric and magnetic losses, optimized impedance matching as well as enhanced attenuation ability, thus improving EM wave absorption performances. In addition, radar cross section (RCS) simulation confirms that the prepared composites have broad application prospects as radar stealth materials.

Design of a wideband and tunable radar absorber

To effectively address the challenges posed by intricate and dynamic electromagnetic environments, we propose a wideband and tunable radar absorber in this paper. The proposed absorber, composed of graphene capacitor, plasma enclosed within a sealed glass cavity, radar absorbing material (RAM), FR-4 and copper plate, allows for tunable radar absorbing performance through the manipulation of the electromagnetic properties of the graphene capacitor and plasma. Based on the equivalent circuit model, the reflectivity of the radar absorber is analyzed using transmission line theory (TLT). Good agreement is observed between the full-wave simulations and the TLT. The study thoroughly investigates the influence of graphene, plasma, and RAM components, as well as their sequential arrangement within the radar absorber, on its reflectivity, expounding the fundamental mechanism of these materials’ synergistic integration. Additionally, the effects of key factors, including the surface resistance R g of graphene, plasma frequency collision frequency and plasma thickness on the radar absorbing performance are examined. Our findings reveal that adjusting surface resistance R g controls the absorbing amplitude, and manipulation of the plasma frequency and collision frequency tunes the absorbing frequency and effective absorbing band. By appropriately adjusting the surface resistance R g of graphene, plasma frequency and collision frequency the proposed radar absorber exhibits superior performance in the frequency range of 1 GHz to 10 GHz. The radar absorber we propose serves as a significant reference for the application of tunable radar absorbers and adaptive radar stealth techniques.

Scattering characteristics of a perfect electromagnetic conducting cylindrical object covered with a general Bi-isotropic layer

Abstract An analytic theory has been developed for the scattering of electromagnetic plane wave from a perfect electromagnetic conducting (PEMC) cylindrical object coated with a general bi-isotropic (BI) material. The proposed problem has been solved using cylindrical vector wave function expansion approach along with the application of tangential boundary conditions. Analytic expressions of the scattering coefficients have been derived in their simplest forms. It is seen that by proper selection of admittance of PEMC core, electromagnetic parameters of BI coating, and coating thickness, one can optimize the scattering characteristics for specific applications. It is shown that the specific types of BI and strong chiral-coated PEMC cylinders having certain coating thicknesses can be used to significantly enhance the co-polarized forward scattering while keeping the cross-polarized forward scattering very small. Such types of enhanced co-polarized forward scattering are preferred in point-to-point communication. Some interesting features have been discussed where co-polarized and cross-polarized backscattering may be suppressed, which find applications in radar engineering problems and stealth technology.

Cut-wire metasurface embedded in magnetic mediums for ultra-wideband polarization-insensitive absorber with environmental adaptability

Metamaterials with artificial designability and perfect absorption provide a novel design method for the manipulation and attenuation of microwaves. However, owing to the limitations of meta-atomic resonance effect and the lossless medium, it is difficult to achieve effective microwave absorption in a broadband frequency range. Hence, an ultra-wideband metamaterial absorber (UWMA) composed of two magnetic media and a metasurface was designed, and the absorption bandwidth of 2.9 to 18 GHz for 90% absorptivity under normal incidence was achieved, covering almost the entire S, C, X, and Ku bands. Through detailed investigation of equivalent circuit, equivalent medium theory, electromagnetic field distribution and front-back interface interference, the internal physical working mechanism was clarified essentially. In addition, the multi-environment adaptabilities of the proposed absorber, including polarization sensitivity, large angle incidence, dual-station radar stealth, bearing capacity and corrosion resistance, were analyzed. The proposed metamaterial absorber presents an effective way to achieve ultra-wideband absorption and compatibility with environmental adaptability, and provides a new way of thinking for intelligent full-band stealth technology.

A flexible metamaterial absorber with temperature-insensitive design at microwave frequencies

Developing a metamaterial absorber (MA) with both flexibility and temperature insensitivity continues to be a challenge in the field of radar stealth. In this paper, we propose a compensation method for designing flexible and temperature-insensitive MA. This method is revealed through the relationship between the square resistance of the resistive film, the permittivity of the substrate, and the temperature. Importantly, the compensation method is applicable to both the MA in the plane state and the bending state. By utilizing the benefits of the compensation mechanism and the flexible designability of the bilayer cross-shaped structure, the flexible MA proposed in this paper can achieve temperature-insensitive absorption across a broad frequency range. Experimental results indicate that the absorption peaks achieve an absorptivity greater than 90% within the frequency of 7.2–9.4 GHz, exhibiting excellent temperature stability from 25 °C to 300 °C. In comparison to previous studies on flexible MAs, this design offers a distinct advantage in high-temperature environments and provides valuable guidelines for the design of integrated multi-functional absorbers in practical applications.

Reconfigurable integrated structures with functions of Fabry–Perot antenna and wideband liquid absorber for radar system stealth

This paper proposes a functionally reconfigurable integrated structure of a Fabry–Perot (FP) antenna and wideband liquid absorber. First, a two-layer partial reflecting surface (PRS) has been designed. Then, a patch antenna is used to act as the source antenna. By combining the source antenna with the PRS, an FP antenna has been designed. What’s more, taking full advantage of the reflective properties of PRS, a liquid broadband absorber is then designed. Last, the integrated structure with two functions has been realized. It can be used as the FP antenna or the liquid absorber through the extraction and injection of ethanol. In this way, it is effective to switch between stealth and detection states which can be used in different electromagnetic environments. The PRS is elaborately tailored to serve as both a component of the FP antenna and the metal ground of the broadband liquid absorber. Then the integrated structure is realized by combining the FP antenna with the liquid absorber. The PRS is composed of patches on the top layer of the substrate and the square loop on the bottom. The liquid absorber is composed of a 3-D printed container, 45% ethanol layer and the PRS is used to serve as the metal ground. The formula of Mie resonance theory has been extended and used to design the liquid absorber. The gain of the antenna is 19.7 dBi when the ethanol is extracted. When the ethanol is injected, a wideband liquid absorber is achieved. The absorption band (S11 < − 10 dB) ranges from 4 to 18 GHz. The absorption bandwidth is over 133%. The monostatic RCS reduction bands of the structure with ethanol range from 4 to 18 GHz and the average RCS reduction is 28.4 dBsm. The measured and simulated results are in good agreement.

Research on electromagnetic scattering characteristics of flexible stealth material based on its 3D model

With the widespread adoption of flexible stealth materials (FSMs) in radar stealth application, understanding their electromagnetic scattering information has become increasingly crucial. However, acquiring the electromagnetic scattering properties of FSMs solely through measurement can be challenging. Hence, this study proposes an electromagnetic scattering model for FSMs based on random undulating units formed by sweeping two parabola functions. Specifically, the multi-layer fast multipole method (MLFMM) is applied to calculate the model’s monostatic RCS within 8–12 GHz, enabling a comprehensive analysis of FSM’s electromagnetic scattering characteristics (ESCs). We fabricate an FSM sample for experimental validation and conduct meticulous measurements alongside theoretical calculations. Impressively, the calculated results exhibit relatively good agreement with the measured data, signifying our model’s reliability. Furthermore, by leveraging the proposed model and the MLFMM, we delve into the influence of various electromagnetic parameters, the undulating angle, and the size of undulation units on the ESCs of FSM. Our numerical results demonstrate that the ESCs of FSM exhibit regular variations in response to the changes in these parameters. In addition, we meticulously examine the interaction between electromagnetic waves and the material, further enriching our understanding of the observed results. This research provides valuable references for ESC investigation of flexible stealth material and radar stealth experimental design.

Design of an Ultra-Wideband Transparent Wave Absorber.

In this paper, a multilayer ultra-wideband transparent metamaterial wave absorber is proposed, which has the characteristics of ultra-wideband wave absorption, light transmission and flexible bending; in addition, due to the complete symmetry of the structure, the absorber has polarization insensitivity to incident electromagnetic waves. Both simulation and experimental results show that the frequency range of the microwave absorption rate is higher than 90% between 8.7 GHz and 38.9 GHz (between which most of the absorption rate can reach more than 95%), the total bandwidth is 30.2 GHz, and the relative bandwidth is 126.9%, realizing microwave broadband absorption and covering commonly used communication frequency bands such as X-band, Ku-band, and K-band. A sample was processed and tested. The test results are in good agreement with the results of the theoretical analysis, which proves the correctness of the theoretical analysis. In addition, through the selection and oxidation of indium tin (ITO) materials, the metamaterial also has the characteristics of optical transparency and flexibility, so it has potential application value in the window radar stealth and conformal radar stealth of weapons and equipment.

An anisotropic broadband coding metasurface based on ultralight graphene‐assembled film

AbstractAs theoretical research further develops, coding metasurfaces have been widely studied and applied due to their uniqueness in digital characterization and sequence arrangement. In this work, based on highly conductive graphene‐assembled film (GAF), an ultralight anisotropic broadband coding metasurface (ABCM) is proposed. The GAF ABCM consists of 16 units with specific phase responses and enables complete metal substitution. By arranging the unit cells in a specific order, the GAF ABCM realizes the functions of anomalous reflection, polarization conversion, and radar cross‐section (RCS) reduction. Results validate that the GAF ABCM has a measured 10 dB normal incidence backward RCS reduction within the working frequency band of 7–18 GHz, which fully covers the X‐band and Ku‐band for radar application. Furthermore, due to the lightweight property of GAF, the density of the GAF ABCM is only 0.06 g/cm3 (surface mass density of 0.038 g/cm2). All results indicate that the lightweight GAF metasurface is promising in radar stealth and communication fields.

The microwave absorption properties variation with temperature of RF/SiO2 and improved microwave absorption by periodic structure

With the widespread application of radar detection systems in the military field, the development of radar stealth technology can effectively reduce the characteristic signals of targets, which was of great significance for the protection of important military targets. In this paper, the resorcinol/formaldehyde (RF) reinforced silica aerogel (RF/SiO2) was synthesized successfully. The RF was introduced into the sol/gel technology to build a porous skeleton, and the SiO2 aerogel was prepared by atmospheric pressure drying. The RF/SiO2 aerogel was then heat treated, and the microstructure and physical properties of the RF/SiO2 aerogel before and after heat treatment were characterized to study the influence of the heat treatment temperatures on the RF/SiO2 aerogel. With the increase of the heat treatment temperature, its electromagnetic wave absorption performance had been significantly improved. When the heat treatment temperature reached 1500 ℃, the RF/SiO2 aerogel possessed a minimum reflection loss of − 36.42 dB at 1.95 mm and an effective bandwidth of 2.94 GHz at 2.00 mm within the radar band of 8.00–12.00 GHz. In addition, this paper used CST software to optimize and design the periodic structure of metamaterial based on the RF/SiO2 aerogel. The optimization design of the patch size and substrate thickness on the substrate surface provided a reference for the future application of this material in specific radar stealth fields.

A Tunable Frequency Selective Rasorber with Broad Passband and Low Transmission Loss at X-Band.

In this paper, we propose a dual-mode frequency selective rasorber (FSR) with tunable transmission and absorption windows at the X-band, which shows a broad passband in each transmission window. The proposed tunable FSR consists of a lossy absorption layer, a lossless transmission layer, and an air gap between them. The top frequency selective surface (FSS) layer is a cross-shaped meandering line with resistors and varactors for tunable absorption, and the bottom layer is a cross-shaped gap with varactors to achieve tunable bandpass. The equivalent circuit model (ECM) is investigated, and the 3D full wave simulation is performed. The results are based on simulations, and the simulation results show that the passband can be tuned from 12 to 8 GHz with an insertion loss between 0.5 and 1.4 dB by sweeping the capacitance of the varactors. The proposed design decreases the chances of detection by adversary devices and assures spectrum-safe communication, thereby creating new avenues for radar stealth and target concealment.

Layered metamaterials with Sierpinski triangular fractal metasurface: Compatible stealth for S-band radar and infrared

Due to the completely opposite stealth mechanisms of radar and infrared waves, and the limitation of the Planck–Rozanov limit, compatible stealth of S-band radar and infrared is extremely difficult to realize at thin thicknesses. In order to solve the problem, a layered metamaterial consisting of infrared stealth layer (IRSL) with aluminum foil and radar stealth layer (RASL) with carbonyl iron powder is designed. The excellent infrared stealth performance (infrared emissivity < 0.3) is achieved because of the low infrared emissivity aluminum foil and reasonable area design. Meanwhile, the Sierpinski triangular fractal structure of IRSL not only serves to reduce the reflection of radar waves, but also introduces the electromagnetic double resonance mechanism of one-dimensional electric resonance and two-dimensional magnetic resonance to lose waves. Therefore, the effective absorption (RL < −10 dB) of 2.12–3.5 GHz in S-band is achieved with a thickness of only 2.24 mm. The double-layer model with fractal structure in this work realizes the perfect compatible stealth for S-band radar and infrared at extremely thin thickness, which provides a new design idea for the development of multi-band compatible stealth.

Structural design of a coding absorber filled with graphene/carbonyl iron powder composite microspheres

Electromagnetic stealth technology played a crucial role in national defense. Encoded metasurfaces and metamaterials had been widely applied in the fields of radar and electromagnetic stealth. In this study, a filled absorber based on scattering enhancement was investigated. Graphene/iron carbonyl composite microspheres were filled into a 3D-printed shell as the absorbing material. The scattering characteristics were controlled by adjusting the absorption gradient, reflection amplitude, and reflection phase of each basic unit. The filled absorber allowed for control of the reflection amplitude through phase modulation, achieving a combined effect of electromagnetic loss and scattering characteristics, resulting in the reduction of radar cross-section. The study also examined the effect of the area fraction of the two cells on the performance of the reduced RCS. The best performance is achieved when the area fraction of cell 0 is 0.5. Simulation results show that the filled absorber effectively reduces the radar cross section in the frequency range of 9.92 GHz to 18 GHz with a minimum value of −34.58 dB. Compared with the simulation results, the measured data show that it effectively reduces the radar cross section in the frequency range of 8.32 GHz to 16.03 GHz with a minimum value of −25.08 dB. This study provided a novel approach for designing high-performance absorbers based on scattering enhancement, which held significant potential in the fields of electromagnetic wave absorption and stealth technology.

Terahertz broadband near-perfect absorber with a single-layer coating on doped semiconductor

We demonstrate that a single-layer coating on a doped GaAs or Si substrate enables broadband antireflection and, hence, broadband perfect absorption in the terahertz frequency range. This broadband behavior can be generally expected when the substrate material has a Drude-type dispersion. Our mathematical analyses show that the reflection from Drude-type material may have an anomalously dispersive phase shift. The anomalous dispersion of the reflection phase is used to compensate for the normal dispersion of the accumulation phase in the single-layer coating film. Consequently, the antireflection conditions are satisfied in a wide frequency range, and broadband antireflection is achieved. Thus, broadband perfect absorption is realized with only a single-layer coating film on the substrate. Our method provides a simple and efficient approach to achieving broadband perfect absorption, which is critical in many applications such as radar stealth techniques and solar cells.

Reducing radar cross section of flat metallic targets using checkerboard metasurface: Design, analysis, and realization

Aiming at the large-scale application of metasurface in the field of radar stealth, we present a hybrid resonance-based and dispersion substrate integrated checkerboard metasurface (CMS) for reducing the radar cross section (RCS) of flat metallic targets. Considering the frequency-dependent characteristics of such a dispersion material, a pair of single and dual resonant artificial magnetic conductor meta-atoms with the modified “crusades-like” cell topologies is employed to maximize the operating bandwidth; besides, a comprehensive and thorough investigation on the resonance mechanism is conducted in this paper to provide an intuitive physical insight of meta-atoms’ reflection responses. By comparing the predicted results with simulations, the quasi-periodic effect is introduced to explain the frequency shift of 10 dB RCS reduction bandwidth. In the implementation procedure, a prototype of the designed RCS reducer with a total dimension of 180 × 180 mm2 is fabricated and measured, the 10 dB RCS reduction bandwidth of theoretical simulation and experimental measurement are basically consistent, and the performance improvement of 8 dB RCS reduction in the experimental results can be attributed to the dispersion effects of the dielectric substrate. With a better figure of merit, our efforts may serve as a useful exemplar for the economical CMS architecture in radar evasive applications.

Integrated Electromagnetic Device with On‐Off Heterointerface for Intelligent Switching Between Wave‐Absorption and Wave‐Transmission

AbstractIntelligent electromagnetic wave absorbers (IEAs) are in high demand due to their dynamic electromagnetic parameters that can adapt to the complex and volatile application environments of the current 5G era. Despite of this, there is currently a lack of research on the convertible electromagnetic wave (EMW) absorption mode (switching between wave‐absorption and wave‐transmission) and their integrated design with external physical stimulations, so that the electromagnetic device will realize intelligent switching in any conditions. In this work, a V2C‐VO2(M) heterostructure that exhibits a reversible metal–insulator transition at the temperature of 62 °C is fabricated via oxidation of MXene. The heterostructures demonstrate near wave‐transmission characteristics at 25 °C while wave‐absorption behavior with wide effective absorption bandwidth (4.04 GHz) at 70 °C. VO2(M) exhibits stronger intrinsic conductivity after phase transition, and the “on‐off” heterostructure between V2C and VO2 lead to poor/strong local conductive network and interfacial polarization in 25/70 °C, thus creating “quantized” dielectric loss. Furthermore, a multilayered electromagnetic functional device is developed to facilitate the absorber's phase transition temperature at a voltage of 17.5 V. This work presents promising opportunities of the V2C‐VO2(M) heterostructure for various applications, including radar stealth, portable stealth suits, signal regulation, and deicing.

A direct laser-synthesized magnetic metamaterial for low-frequency wideband passive microwave absorption

Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions. Herein, we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies, which results in a wide bandwidth in the L- to S-band. Control of the electrical sheet resistance uniformity has been achieved with less than 5% deviation at 400 Ω sq−1 and 6% deviation at 120 Ω sq−1, resulting in a microwave absorption coefficient between 97.2% and 97.7% within a 1.56–18.3 GHz bandwidth for incident angles of 0°–40°, and there is no need for providing energy or an electrical power source during the operation. Porous N- and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing. The proposed low-frequency, wideband, wide-incident-angle, and high-electromagnetic-absorption microwave absorber can potentially be used in aviation, electromagnetic interference (EMI) suppression, and 5G applications.

Study on the Comprehensive Optimization of Quantum Radar Stealth Based on the Waverider Warhead

Quantum radar is a novel detection method that combines radar and quantum technologies. It exceeds the detection threshold and poses a threat to conventional stealth targets. This work aims to derive the expression of the quantum radar cross-section of a new complex target. The calculation formula of QRCS was derived after introducing the relative photon parameters and vector dot product. Subsequently, a comprehensive optimization model of quantum stealth and lift–drag ratio based on a genetic algorithm was proposed for the waverider warhead. During the optimization process, we proposed an optimization method with the objective function of the QRCS pioneering design value and achieved better outcomes than the optimization method using the average value in terms of QRCS performance and lift–drag ratio in the important azimuths of the waverider. By changing the design variables of the waverider warhead and using this new optimization method, the QRCS of the waverider in the forward and lateral angles were minimized, remarkably improving the aerodynamic performance of the waverider. Similarly, the optimization results show that the proposed design value optimization method is feasible.