Radar Absorbing Research Articles

Synergistic enhancement of radar wave absorption in SiC/Al2O3 composites via structural tuning, composition optimization, and unit design

Synergistic enhancement of radar wave absorption in SiC/Al2O3 composites via structural tuning, composition optimization, and unit design

Fast Simulation of Electromagnetic Scattering for Radar-Absorbing Material-Coated 3D Electrically Large Targets

In this paper, a modified Shooting and Bouncing Ray (SBR) method based on high-order impedance boundary conditions (HOIBCs) is proposed to analyze the electromagnetic (EM) scattering from electrically large three-dimensional (3D) conducting targets coated with radar-absorbing material (RAM). In addition, the edge diffraction field of coated targets is included in the calculation to improve the accuracy of the calculation. Firstly, the SBR method based on the bidirectional tracing technique is presented. It is concluded that the calculation of the scattered field of the coated targets requires the determination of the reflection coefficients on the coated surface. The reflection coefficients of the coated targets are then derived using HOIBC theory. Finally, the equivalent edge current (EEC) of the impedance wedge is derived by integrating the UTD solutions for the impedance wedge diffraction with the impedance boundary conditions. The simulation results show that the proposed method improves computational efficiency compared to MLFMA while maintaining accuracy. Furthermore, the RCS characteristics of targets coated with different RAMs, different coating thicknesses and with different angles of incidence were compared, as well as the RCS results of coated targets with those of conventional perfect electrical conductor (PEC) targets.

Microwave thermal imaging system for debonding detection of radar absorbing materials.

In this paper, a microwave thermal imaging system (MTIS) has been presented for debonding detection of radar absorbing materials (RAMs). First, an overview of the mechanism underlying microwave heating and the fundamental principle of defect detection within RAMs is presented. Then, a multifunctional MTIS capable of performing both microwave lock-in thermography (MLIT) and long-pulse microwave thermography (LPMT) has been introduced, specifically tailored for the in situ inspection of RAMs. In addition, in this system, the detection area for a single scan is 90 * 90mm2, with the emission source operating at a frequency of 5.8GHz and boasting a maximum output power of 20W. Next, based on MTIS, the above-mentioned two thermography techniques are applied to detect defects in RAMs. In addition, thermal contrast (Tc) and signal-to-noise ratio are introduced for the analysis of imaging results. Finally, the results show that LPMT can be used for preliminary detection of debonding defects in RAMs, while MLIT can be further used for detailed detection of debonding defects in RAMs. In addition, the minimum detection time of this MTIS is 45s, and the minimum detectable defect aperture is 3mm.

Barium strontium titanate and exfoliated graphite nanocomposite integrated with frequency selective surface for enhanced radar absorption

Barium strontium titanate and exfoliated graphite nanocomposite integrated with frequency selective surface for enhanced radar absorption

Fluid-Actuated Nano-Micro-Macro Structure Morphing Enables Smart Multispectrum Compatible Stealth.

Modern detection technology has driven camouflage technology toward multispectral compatibility and dynamic regulation. However, developing such stealth technologies is challenging due to different frequency-band principles. Here, this work proposes a design concept for a fluid-actuated multispectral compatible smart stealth device that employs a deformable mechanochromic layer/elastomer with a channeled dielectric layer. After fluid actuation, the deformable elastomer layer transmits mechanical strain to the mechanochromic layer, thereby altering the visible reflectance wavelengths in [568, 699] nm. Concurrently, the pumped-in liquid reconfigures the spatial structure parameter to alter microwave resonance and diffraction for dynamic radar absorption, enabling dynamic radar absorption with significant broadband absorption at [8.16, 18.0] GHz. Using the heat-absorption property also achieves dynamic infrared stealth, shown by a ΔT ≈ 16.5 °C temperature difference. Additionally, the device exhibits a rapid response time (∼1 s), excellent cycling performance (100 cycles), and programmability (10 codes), offering a new stealth strategy.

Highly stretchable radar absorber based on kirigami metastructures with tunable electromagnetic properties

Highly stretchable radar absorber based on kirigami metastructures with tunable electromagnetic properties

Study on Novel Radar Absorbing Grilles of Aircraft Engine Inlet Based on Metasurface Design Theory

In modern warfare, the advancement of low detectable technology has made the reduction of an aircraft radar cross section (RCS) crucial for survivability, while engine inlets significantly impact the overall detectability index as major forward scattering sources. Inspired by radar absorbing structures (RASs) based on metasurface theory, as well as the spoof surface plasmon polariton (SSPP) theory, this paper proposes a comprehensive design of radar absorbing grilles (RAGs) which are installed at the inlet aperture of the aircraft intake, where RAGs allow airflow to cross through and absorb the detecting radar wave. To enhance the ability of electromagnetic wave attenuation, an indium tin oxide (ITO) film is added in the middle of the RAGs to change the impedance characteristics. This study clarifies the mechanism influencing radar wave absorption characteristics through design parameters (unit length and sheet resistance) and radar characteristic parameters (frequency, incident angle, and polarization mode). The absorption peak gradually shifts towards lower frequencies with the increase in unit length from 8 to 16 mm of the grille. The integrated average absorption first increases and then decreases with the increase in sheet resistance from 100 to 800 Ω/□ applied as ITO film in the middle of the grille. When the unit length of RAG is 12 mm and 400 Ω/□, the sheet resistance is applied, and a 90% absorption bandwidth is achieved to 100% within the 8–18 GHz band. The 90% absorption bandwidth reaches 72.3% in the 2–18 GHz band while maintaining absorption above 40% in the 2–8 GHz band. The integrated average absorption reaches 0.887, and the 90% absorption bandwidth increases to 255.6% of the original model’s bandwidth. The results indicate that the proposed RAGs based on metasurface exhibit broadband absorption performance and high angular stability, providing technical support for further application of these grilles in aircraft engine inlets.

Immobilization of Cerium(IV) Oxide onto Reduced Graphene Oxide in Epoxy Resin Matrix as Radar Absorbing Composite for X-band Region

The rGO/CeO2/epoxy composite has been successfully prepared as radar absorbing material (RAM) for the X-band (8–12 GHz) region. The reduced graphene oxide (rGO) originated from pencil graphite oxide (GiO) was synthesized through the modified Hummer method. The synthesis of rGO/CeO2/epoxy was conducted by immobilization of cerium(IV) oxide into rGO (rGO/CeO2) via hydrothermal method and followed by composited the rGO/CeO2 with epoxy resin matrix. Morphological analysis by SEM-EDX indicates that the rGO/CeO2 structure appears to be a tangled layer of edges randomly aggregated, and CeO2 is uniformly anchored on the rGO surface. From the diffractogram result of the XRD instrument, rGO exhibits changes in crystallinity, indicating a transformation of the interlayer structure from multilayer GiO to a single layer of rGO. The presence of Ce–O was indicated at wavenumber 553 cm−1 of rGO/CeO2 by FTIR. The microwave absorbing performance of rGO/CeO2/epoxy conducted by vector network analyzer (VNA) showed that the RL value of the composite was −3.22 dB (47% of electromagnetic wave absorption) at a frequency of 9.25 GHz at the thickness of 1 mm composite. The composite has the promising prospect of being developed as a captivating candidate for the new type of microwave absorptive materials.

Experimental radar absorption in high-filling factor magnetic composites

Experimental radar absorption in high-filling factor magnetic composites

A Novel Frequency-Selective Surface-Enhanced Composite Honeycomb Absorber with Excellent Microwave Absorption.

Multifunctional structures with excellent wave-absorbing and load-bearing properties have attracted much attention in recent years. Unlike other wave-absorbing materials, honeycomb wave-absorbing materials have appealing radar absorption and mechanical properties. However, the existing honeycomb wave-absorbing materials have problems such as narrow absorption band and poor compression resistance. In this study, a novel frequency selective surface-enhanced composite honeycomb absorbers (FSS-CHAs) are fabricated by combining a honeycomb structure with wonderful load-bearing capacity and FSS through screen-printing and inlay-locking techniques. After reflectivity measurements, the effective absorption band (RL < -10 dB) of CHA is 6.25-17.47 GHz and a bandwidth of 11.22 GHz, the effective absorption band of the FSS-CHA is 3.96-18 GHz and a bandwidth of 14.04 GHz, 25.13% improvement compared to the CHA, the mechanism of wave absorption is explained using transmission line theory. The simulation results show that the wide bandwidth is due to the different absorption mechanisms of FSS-CHA at low and high frequencies. The compression test shows that the compression strength of FSS-CHA is 17.10 MPa. In addition, FSS-CHA has a low cost of only USD 270.7/m2. This study confirms the possibility of combining FSS with radar-absorbing honeycombs, which provides a reference for the design of future broadband wave-absorbing structures, offers a novel approach to integrating FSS with CHA, and aims to optimize their efficacy and utility in stealth technology.

A Review of Polyurethane Foams for Multi-Functional and High-Performance Applications.

Polyurethane (PU) foams are cellular polymeric materials that have attracted much attention across various industries because of their versatile properties and potential for multifunctional applications. PU foams are involved in many innovations, especially in multi-functional and high-performance applications. Special attention is given to developing tailored PU foams for specific application needs. These foams have various applications including flame retardancy, sound absorption, radar absorption, EMI shielding, shape memory, and biomedical applications. The increasing demand for materials that can perform multiple functions while maintaining or enhancing their core properties has made PU foams a focal point of interest for engineers and researchers. This paper examines the challenges faced by the PU foam industry, particularly in developing multifunctional products, as well as the strategies for improving sustainability, such as producing PU foams from renewable resources and recycling existing materials.

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).

Mechanical and dielectric properties of SiCf/NBAS composites with dip-coated La2Ti2O7 interphase

To improve the properties of SiC fiber-reinforced ceramic-matrix composites for potential use as radar-absorbing materials, La2Ti2O7 interphase was dip-coated on the surface of the SiC fibers, and the SiCf/NBAS composites were then prepared. The pristine SiC fibers with relatively high electrical resistivity were mainly composed of amorphous SixCyO and a small amount of β-SiC and free carbon. A weak La2Ti2O7 interphase improved the flexural strength and toughness of the composites due to the fiber pull-out and crack deflection. The measured room-temperature complex permittivity of the composites increased, and the dielectric loss was greater than that of the pristine SiC fibers owing to the production of excess free carbon in the degradation of SiC fibers during the preparation of SiCf/NBAS composites. The excess free carbon with higher electrical conductivity was also believed to play a significant part in the increase of dielectric permittivity of the composites with the increasing heat-treatment temperatures even below 1000 °C. A dual-layer structure was designed to expand the bandwidth for microwave absorption.

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

Radar-absorbing materials (RAMs) have been extensively employed, particularly in national security stealth technologies. Even though various novel RAMs have been invented, iron oxides still attract tremendous attention due to their distinctive properties that are suitable for radar absorption applications. However, some development should still be carried out to improve the feasibility of iron oxides as RAMs. In this study, iron oxides-based RAMs were developed by manipulating the composition of 3d metal transition elements, Fe and Mn, which mainly influence the radar absorption performance. We also use a compositing strategy by combining this iron oxide with conductive and dielectric polymer materials to form MnxFe3–xO4/PANI (polyaniline)/AC (activated carbon) nanocomposites. The nanocomposites were synthesized using the coprecipitation method with x = 0–1.2 variation. The RAMs functioned in the X-band frequency range (approximately 7–13 GHz) with a thickness of 2 mm to 5 mm. The MnxFe3–xO4/PANI/AC nanocomposites were successfully fabricated by various examinations. The Mn2+ ion was incorporated into Fe3O4, while the nanocomposites exhibited sphere-like morphologies constructed from MnxFe3–xO4, AC, and PANI having aggregates, granules, and chains forms, respectively. Moreover, the nanocomposite sample exhibited superparamagnetic properties, with the saturation magnetization decreasing with the increase in the Mn2+. Interestingly, the MnxFe3–xO4/PANI/AC nanocomposites with x = 1.2 showed a high radar absorption performance with a reflection loss of –42 dB at 9.3 GHz, which mainly attributed to the magnetic loss mechanism and, thus, makes the obtained nanocomposite very potential for radar absorption applications. We believe our findings could pave the way for the realization of iron oxide-based RAMs for radar absorption applications.

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.

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.

Modification of Rice Husk-based Activated Charcoal as Microwave Absorbing Material

Stealth technology is one of the technologies being developed to eliminate RADAR traces from the enemy. The spectrum used in this technology is in the microwave range (8-12 GHz). RAM (Radar Absorbing Material) is one of the techniques that can be used in the design of stealth technology. One material that has the potential to be used as RAM is activated charcoal as a dielectric material. In the manufacture of activated charcoal, a chemical activation method is used with an activator in the form of 5 M HCl to obtain good porosity properties in charcoal. Modification of active charcoal was also carried out using mechanical milling method with time variations of 50, 100, 150, and 200 minutes which were then characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy - Energy Dispersive Spectroscopy (SEM-EDS), and Vector Network Analyzer (VNA). Mechanical milling is proven to be able to change the shape of the charcoal structure from amorphous to semicrystalline with the crystalline phase formed in the form of C60-fullerene. Activated charcoal samples with a time variation of 100 minutes have the best absorbing ability with absorption reaching 78.22% and a reflection loss value of -25.96 dB at a frequency of 9.69 GHz with a frequency bandwidth of 3.68 GHz.Keywords—stealth technology; rice husk activated charcoal; mechanical milling; microwave absorber.

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.