Radar Absorbing Research Articles

Design and study of electromagnetic wave absorbing structure of multilayer GN/GF/EP composites

With the improvement of radar absorption performance requirements, the research of absorbing materials is an important research direction. In this paper, a graphene/glass fiber/epoxy (GN/GF/EP) structure design scheme is proposed. By measuring the electromagnetic parameters, the influence of different GN content on the absorber performance is analyzed, and the bilayer absorber material combination with the best absorber performance is determined. The double layer absorbing material was made of GN/GF/EP-1.0% (thickness 0.4 mm) and GN/GF/EP-2.5% (thickness 1.7 mm). The peak reflection loss of the double layer absorbing material is −41.55 dB, the center frequency is 10.93 GHz, and the effective absorption bandwidth is 2.86 GHz (9.34∼11.20 GHz).

Multispectral compatible anti-reconnaissance strategy: Implementing a modulation system integrating visible light-hyperspectral-radar wave

To tackle the challenges of multi-spectral reconnaissance technology, a pioneering anti-reconnaissance device that integrates visible-light, hyperspectral, and microwave radar functionalities has been developed for the first time. By oxidative polymerization method to create a core–shell Fe3O4@polyaniline composite material for the counter electrode. This design optimized impedance matching, achieving wideband radar wave absorption up to 10.5 GHz (reflection loss < -10 dB). The core–shell structure enhanced specific surface area, improving charge exchange and electrochemical performance to meet stringent counter electrode requirements. And, constructed a frequency-selective metal electrode based on metamaterial principles, complementing the radar wave absorption capabilities of the counter electrode material. Additionally, synthesized an asymmetric viologen molecule as the working electrode, mimicking vegetation color transitions from green to yellow while preserving hyperspectral characteristics and radar wave absorption properties. To enhance hyperspectral compatibility without compromising radar wave absorption or color dynamics, we developed a cross-linked polyvinyl alcohol/hydroxyethyl cellulose film based on biomimetic principles. The device can switch between yellow and green under voltages of 0 or −1.2 V, with both states exhibiting a spectral similarity to foliage exceeding 0.95 and an effective bandwidth reaching 13.44 GHz. The integration of these three functionalities allows the device to operate independently without interference.

The improvement of radar absorption performance in MnxFe3–xO4/PANI/AC nanocomposites by manipulating the composition of 3d transition metal elements

The improvement of radar absorption performance in MnxFe3–xO4/PANI/AC nanocomposites by manipulating the composition of 3d transition metal elements

Three-Dimensionally Printed K-Band Radar Stealth Lightweight Material with Lotus Leaf Structure.

K-band radar waves have high penetration and low attenuation coefficients. However, the wavelength of this radar wave is relatively short; thus, designing and preparing both broadband and wide-angle radar wave absorbers in this band presents considerable challenges. In this study, a resin-based K-band radar wave absorber with a biomimetic lotus leaf structure was designed and formed by UV curing. Here, microscale lotus leaf papillae and antireflection structures were prepared using a DLP 3D printer, and the contact angle between the material and water droplets was increased from 56° to 130°. In addition, the influence of the geometric parameters of the lotus leaf antireflection structure on the electromagnetic absorption performance and mechanical strength was investigated. After simulation optimization, the maximum electromagnetic loss of the lotus leaf structure 3D-printed sample was -32.3 dB, and the electromagnetic loss was below -10 dB in the 20.8-26.5 GHz frequency range. When the radar incidence angle was 60°, the maximum electromagnetic loss was still less than -10 dB. The designed lotus leaf structure has a higher mechanical energy absorption per unit volume (337.22 KJ/m3) and per unit mass (0.55 KJ/Kg) than commonly used honeycomb lightweight structures during the elastic deformation stage, and we expect that the designed structure can be used as an effective lightweight material for K-band radar stealth.

Coconut shell waste-based ZnFe2O4/PANI/rGO nanohybrid composites as excellent radar-absorbing material

In this work, we developed ZnFe2O4/PANI/rGO nanocomposites based on coconut shell waste through in situ polymerization as excellent radar-absorbing material (RAM). This research mainly focused on adjusting the ZnFe2O4 content to obtain optimal absorption of radar waves, especially in the X-band. The results showed that the diffraction pattern of the ZnFe2O4/PANI/rGO nanocomposites showed multiple phases (crystalline and amorphous), which increased the ZnFe2O4 content and affected the increasing diffraction intensity. The functional group of the ZnFe2O4/PANI/rGO nanocomposites was identified with the presence of the M–O group originating from ZnFe2O4 at wavenumbers 517 and 419 cm−1 of Zn–O and Fe–O groups, respectively. Meanwhile, quinoid and benzenoid rings from PANI and CO from rGO were identified at wavenumbers 1580, 1504, and 1710 cm−1, respectively. The morphology of the ZnFe2O4/PANI/rGO nanocomposites showed PANI was distributed on the ZnFe2O4 nanoparticles, which were subsequently deposited on the rGO. The ZnFe2O4/PANI/rGO nanocomposites exhibited superparamagnetic properties, as confirmed by their coercivity values ranging from 9.2 to 124.4 Oe. Interestingly, the ZnFe2O4/PANI/rGO nanocomposites with the P3 sample showed optimal RAM performance with a minimum reflection loss value of −39.8 dB at 7.6-GHz frequency with an effective absorption bandwidth of 1.1 GHz.

Multispectral Hierarchical Metamaterials with Broadband Microwave Absorption, Gradient Infrared Emissivity, and High Visible Transparency

AbstractThe rapid progression of multispectral detectors poses a serious threat to weapon systems and personnel. The efficiency of stealth camouflage materials, however, has strong wavelength dependence, which limits their functionality to a specific spectral range. Here, a multispectral hierarchical metamaterial (MHM) with broadband microwave absorption, gradient infrared (IR) emissivity, and high visible transparency is proposed. The MHM design entails the integration of two distinct functional layers: the infrared camouflage layer (IRCL) and the radar absorbing layer (RAL). Specifically, leveraging the low‐pass and high‐impedance properties of capacitive frequency selective surfaces and adjustable filling ratio of low IR radiation materials, the IRCL achieves simultaneous high microwave transmission and gradient IR emissivity designs (emissivity gradients &gt; 0.15 at 3–5 and 8–14 µm). The RAL achieves broadband microwave absorption across radar C, X, Ku, and Ka bands through a circuit‐analog absorber designed with lossy materials. Furthermore, prioritizing materials with high transparency enhances the average optical transmittance (&gt;61.8%) of MHM in 380–760 nm. These distinctive features underscore the potential of the proposed MHM for advanced applications in camouflage and stealth technologies.

Fabrication of Al/Ni core–shell pigments via galvanic displacement and their application in radar-infrared compatible stealth coatings

The Al/Ni magnetic core–shell pigments were successfully synthesized in this study using the galvanic displacement method. A dense nickel shell was formed on the surface of a flake Al pigment (Al:Ni2+ = 1:0.5), resulting in a decrease in its lightness by 9 units while only slightly increasing the average infrared emissivity by 0.1 compared with the uncoated flake Al pigments. And it also exhibited soft magnetic characteristics, with a saturated magnetization value of 4.5 emu/g. Moreover, the impact of Al/Ni core-shell pigments on the infrared-radar stealth performance of the target was investigated based on the structure of “low-emissivity coating (LEC) + radar absorbing coating (RAC)”. The results showed that the emissivity of Al/Ni composite coatings maintained a low infrared emissivity (ε ≤ 0.23). The introduction of Ni shell improved the impedance matching between the Al/Ni coating and free space, allowing greater penetration of microwaves into the LEC and improving radar stealth performance of materials. The Al/Ni composite coatings (Al:Ni2+ = 1:0.5, the thickness of RAC:1.2 mm, and LEC: 60 μm) exhibited an extended effective absorption bandwidth (Reflection loss (RL) ≤ −10 dB) from 2.6 to 4.25 GHz and an enhancement of the average RL from −6.43 to −7.1 dB in the range of 2–18 GHz compared to the RAC. Consequently, the Al/Ni magnetic core–shell pigments can be used as novel low-emissivity pigments for infrared-radar compatible stealth research.

Flexible wideband microwave meta-absorber with designable digital infrared and visible camouflage

With the widespread use of multi-spectrum detection technology, the stealth of a single frequency band cannot meet the practical application requirements. Recently, the investigation of wearable and insulated multi-spectrum compatible stealth technology has become urgent. The flexible and thermally isolated wideband microwave meta-absorber with infrared and visible camouflage has been proposed, fabricated, and measured. An infrared shielding layer (IRSL) and a radar absorbing layer (RAL) are the two main components of the absorber. IRSL is realized by specifically arranging the pre-designed patch structure with three different filling ratios, which can confuse the detection of thermal infrared in 3–14 μm. RAL is achieved by etching the structure of the lossy material to form electrical loss in plane and magnetic loss between layers, so as to realize the broadband absorption of microwave higher than 90 % from 6.2-22.2 GHz. In addition, the absorber employs flexible and thermally isolated materials, providing excellent high-temperature stability normally at temperatures up to 130 °C. These unique properties confirm the feasibility of the proposed strategy. To effectively adapt to different thermal camouflage environments, it is essential to create IR digital camouflage patterns. Moreover, the additional flexibility and thermal insulation characteristics make it powerful in compatible camouflage-stealth facilities when used in complex environments and a wide range of high temperatures.

Topology optimization design of surface radar absorbing coatings

In this study, a topology optimization method is proposed to design the layout of the radar absorbing coatings (RACs) outside the surface. The radar cross section (RCS) of a structure with RACs is evaluated by the physical optics method. A material interpolation model oriented to the relative permittivity and relative permeability of RACs is established, while the sensitivity of the RCS with respect to the design variables is derived analytically. With the objective of minimizing the RCS at the specified incident angles and the constraint of the material usage, the strategy is implemented based on a gradient-based algorithm and the so-called three-field density method. Additionally, the phenomenon of the RCS increasing in certain regions when RACs are applied is explained in detail. Finally, the effectiveness of the proposed method is demonstrated by two numerical examples.

Multi-scale design of MWCNT/glass fiber/balsa wood composite multilayer stealth structure with wide broadband absorption and excellent mechanical properties

In unmanned aircraft applications, electromagnetic wave (EMW) absorbers suffer from defects in narrow absorption bands and poor mechanical properties. To solve the problems, a lightweight multilayer stealth structure with wide broadband absorption performance and excellent mechanical properties was designed and prepared by adjusting microscopically the number of multi-walled carbon nanotubes (MWCNT) and modulating macroscopically the thickness-matching relationship of the structure to promote the absorption of EMW synergistically. Under the MWCNT of 30 wt% and the depletion layer with the thickness of 0.2 mm, the effective absorption bandwidth (EAB) covers the entire Ku-band while maintaining a minimum reflection loss (RL) of −15 dB. Besides, the radar cross-sectional area attenuation is as high as 23.1 dBm2, as well as the mechanical properties of the radar absorbing structures (RAS) were improved significantly due to the reducing structural density from balsa wood and the enhancement effect of glass fiber mats (GFM). The study constructed balsa-based RAS with excellent EMW absorbing and mechanical properties from both micro-nano scale and macro-structure, providing a research route for designing high-performance and lightweight stealth structures.

Adjusting microwave sensing frequency through aspect ratio variation and bending repetitions in Permalloy ellipses

The Ferromagnetic Resonance (FMR) phenomenon, marked by the selective absorption of microwave radiation by magnetic materials in the presence of a magnetic field, plays a pivotal role in the development of radar absorbing materials, high speed magnetic storage, and magnetic sensors. This process is integral for technologies requiring precise control over microwave absorption frequencies. We explored how variations in resonance fields can be effectively modulated by adjusting both the shape and stress anisotropies of magnetic materials on a flexible substrate. Utilizing polyethylene-naphthalate (PEN) as the substrate and Permalloy (Ni79Fe21, noted for its positive magnetostriction coefficient) as the magnetic component, we demonstrated that modifications in the aspect ratio and bending repetitions can significantly alter the resonance field. The results, consistent with Kittel’s equation and the predictions of a uniaxial magnetic anisotropy model, underscore the potential for flexible substrates in enhancing the sensitivity and versatility of RF-based magnetic devices.

Porous-multilayered Ti3C2Tx MXene hybrid carbon foams for tunable and efficient electromagnetic wave absorption

The rapid development of modern wireless communication technology makes electromagnetic wave pollution increasingly serious, necessitating the development of high-performance electromagnetic wave-absorbing materials. This study introduces a Ti3C2Tx MXene hybrid carbon foam (HCF) that exhibits a tunable and efficient electromagnetic wave absorption performance. The HCF features a porous, multilayered structure, which enhances its multi-reflection properties, and a heterogeneous interface between the carbon foam and MXene boosting its dielectric loss. By regulating the content of MXene, the ratio of polarization loss to conduction loss can be regulated to achieve better impedance matching. As a result, the HCF demonstrated superb electromagnetic wave absorption performance with RLmin = −72.25 dB and EABmax = 6.55 GHz. Furthermore, the minimum absorption frequency domain could be tuned within 8–14 GHz by varying the MXene content. The performance in radar wave absorption and electromagnetic-thermal conversion (ramp rate 85.81 °C/s from RT to 200 °C) proves that HCF is an efficient and reliable electromagnetic wave absorber, suitable for radar technology, microwave heating, and communication systems applications.

Study on the relationship between reflectivity and thickness of radar-absorbing material

Study on the relationship between reflectivity and thickness of radar-absorbing material

Design of a Radar Signature Measurement Model of an Unmanned Aerial Vehicle with Low Radar Signature

Existing databases of RCS benchmarks lack a complex, low-observable target. This paper describes the design of such a complex and low-observable measurement model. Starting point of the design is the so-called Muldicon model, developed by the NATO/STO/AVT panel. Hot spots of the original model are identified and treated with radar-absorbing materials. Simulations on the treated model demonstrate that the model is indeed low observable. The effect of the manufacturing process of 3D-printing and separable parts is assessed experimentally on a cone-sphere; the effect is found to be negligible. These results give confidence that the model, when built, satisfies the requirements of being complex and low observable; and that artefacts of the manufacturing process will not impair its signature.

A dual-mode infrared thermal stealth structure compatible with radar bands

Currently, multi-spectral stealth technology has become crucial in countering advanced military and civilian detection methods. Metamaterials, known for their adaptable designs and superior wavefront manipulation capabilities, effectively meet the complex requirements of infrared and radar bands for material properties, thus being widely used in developing multi-band thermal stealth materials. In this study, we propose a tunable metamaterial structure based on phase-change material vanadium oxide. This structure operates in two modes facilitated by the temperature-induced phase transition of vanadium oxide, which modifies the effective cavity thickness and influences the infrared resonance of the coupled cavity-plasma system. This modulation enables tunable control of thermal radiation within the 3 μm–14 μm wavelength range, achieving effective infrared thermal camouflage across varying environmental backgrounds. Additionally, the structure achieves high radar absorption across the ultra-wideband radar frequencies of 3.65 GHz–18 GHz and 26.5 GHz–34 GHz, with average absorption of 0.89 and 0.85, respectively. Hence, the proposed metamaterial structure effectively provides infrared thermal stealth compatibility with radar bands in both low-temperature (270 K–310 K) and high-temperature (380 K–420 K) environments.

A Minkowski-like fractal composite metamaterial for S-C band radar and infrared compatible stealth

Due to the opposite stealth mechanisms of radar and infrared waves, and the lack of narrow-band absorption at a single frequency point in metamaterials, it is difficult for low-frequency broadband radar and infrared waves to be compatibly stealthy at thin thickness. In order to solve the problem, Minkowski-like fractal metamaterial with frequency-selective surface of ''passing-low-frequency and blocking-high-frequency'' property is designed. The multiscale property of Minkowski-like fractal constructs multiple absorption frequency points and its suitable iteration factor achieves broadband reconfiguration of the absorption frequency points, which enables broadband absorption in S and C bands. Besides, the magneto-electric dual loss mechanism brought by the fractal and the intrinsic loss of the medium are the most fundamental reasons for the stealth being caused. In addition, the selection of iterative cell with infrared emissivity below 0.3 and the self-similarity property of Minkowski-like fractal make the metamaterial embody excellent infrared stealth performance. Ultimately, the 2.24 mm thick fractal metamaterial achieves cross-band radar wave absorption in the range of 3.41–5.82 GHz while being compatible with infrared wave stealth. The layered fractal model provides a new design idea for broadband stealth under multi-band compatible stealth.

Barium-doped Mg-Zn ferrites: synthesis, characterization, and microwave absorption properties for radar absorption applications

Barium-doped Mg-Zn ferrites: synthesis, characterization, and microwave absorption properties for radar absorption applications

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.

Mechanical and radar absorption properties of sheep wool/epoxy composites

PurposeThe aim of this study is to determine the fracture behavior of wool felt and fabric based epoxy composites and their responses to electromagnetic waves.Design/methodology/approachNotched and unnotched tensile tests of composites made of wool only and hybridized with a glass fiber layer were carried out, and fracture behavior and toughness at macro scale were determined. They were exposed to electromagnetic waves between 8 and 18 GHz frequencies using two horn antennas.FindingsThe keratin and lignin layer on the surface of the wool felt caused lower values to be obtained compared to the mechanical values given by pure epoxy. However, the use of wool felt in the symmetry layer of the laminated composite material provided higher mechanical values than the composite with glass fiber in the symmetry layer due to the mechanical interlocking it created. The use of wool in fabric form resulted in an increase in the modulus of elasticity, but no change in fracture toughness was observed. As a result of the electromagnetic analysis, it was also seen in the electromagnetic analysis that the transmittance of the materials was high, and the reflectance was low throughout the applied frequency range. Hence, it was concluded that all of the manufactured materials could be used as radome material over a wide band.Practical implicationsSheep wool is an easy-to-supply and low-cost material. In this paper, it is presented that sheep wool can be evaluated as a biocomposite material and used for radome applications.Originality/valueThe combined evaluation of felt and fabric forms of a natural and inexpensive reinforcing element such as sheep wool and the combined evaluation of fracture mechanics and electromagnetic absorption properties will contribute to the evaluation of biocomposites in aviation.

Radio-Absorbing Magnetic Polymer Composites Based on Spinel Ferrites: A Review.

Ferrite-containing polymer composites are of great interest for the development of radar-absorbing and -shielding materials (RAMs and RSMs). The main objective of RAM and RSM development is to achieve a combination of efficient electromagnetic wave (EMW) absorption methods with advantageous technological and mechanical properties as well as acceptable weight and dimensions in the final product. This work deals with composite RAMs and RSMs containing spinel-structured ferrites. These materials are chosen since they can act as efficient RAMs in the form of ceramic plates and as fillers for radar-absorbing polymer composites (RAC) for electromagnetic radiation (EMR). Combining ferrites with conducting fillers can broaden the working frequency range of composite RAMs due to the activation of various absorption mechanisms. Ferrite-containing composites are the most efficient materials that can be used as the working media of RAMs and RSMs due to a combination of excellent dielectric and magnetic properties of ferrites. This work contains a brief review of the main theoretical standpoints on EMR interaction with materials, a comparison between the radar absorption properties of ferrites and ferrite-polymer composites and analysis of some phenomenological aspects of the radar absorption mechanisms in those composites.