Radar Cross Section Research Articles

Biomass-derived carbon heterostructure composites modified with magnetic iron oxide for excellent EMW-absorbing materials

With the gradual spread of satellite navigation, broadcasting, and communication technologies, the problem of electromagnetic pollution in C- and Ku-band has increased. Electromagnetic wave (EMW) absorbing materials can effectively mitigate this problem. Here, we report the design of a biomass carbon heterostructure for the absorption of EMWs. This design takes advantage of the natural fiber mesh structure of the loofah and the voids, veins, and basal tissues surrounding the fibers. The material is then carbonized to create a radar antenna-like structure of fibers and nanosheets. This improves the material's conductive loss. In addition, modification with magnetic iron oxide in loofah sponges improves the impedance matching of the materials, enhances the magnetic loss, and increases the heterogeneous interface. We found that the maximum effective absorption frequency range of the prepared EMW-absorbing materials is 3.80 GHz, which is mainly concentrated in the C-band and Ku-band, and its maximum RLminvalue is −59.20 dB. The material's ability to absorb EMWs was also verified by simulating the radar cross section (RCS). In conclusion, this work develops a green and efficient composite material for absorbing EMWs and provides new design ideas for the development of EMW-absorbing materials.

Multi-heterointerface integration in nitrogen-doped Ti3C2Tx@Fe3O4 nanocomposites for superior microwave absorption

Engineering a lightweight and thin microwave absorber through the design of multiple heterogeneous interfaces represents a significant challenge. Here, we synthesized a nitrogen (N)-doped Ti3C2Tx@Fe3O4 (N–Ti3C2Tx@Fe3O4) nanocomposite with a sandwich-like structure through a solvothermal approach using hydrazine hydrate as the N donor. The numerous Ti3C2Tx electron transfer pathways of Ti3C2Tx enable the realization of a hierarchical conduction network within N–Ti3C2Tx@Fe3O4. The introduction of defects through N doping and the integration of Fe3O4 with Ti3C2Tx are pivotal for enhancing the dipole polarization. The heterogeneous interfaces in N–Ti3C2Tx@Fe3O4, coupled with Fe3O4 components, substantially boost the electromagnetic wave (EMW) absorption performance of the composite. An optimal N integration and the loading of Fe3O4 in Ti3C2Tx result in an improved impedance matching of N–Ti3C2Tx@Fe3O4. The synergistic effect of the improved impedance matching and the strong EMW attenuation capability endow N–Ti3C2Tx@Fe3O4 with enhanced microwave absorption (MA) properties. Specifically, at a thickness of 1.04 mm, the composite exhibits the effective absorption bandwidth (3.92 GHz; 14.08–18.00 GHz), surpassing that of Ti3C2Tx. At a thickness of 0.98 mm, it exhibits a maximum reflection loss of −40.28 dB at 17.25 GHz, which substantially exceeds that of Ti3C2Tx. Furthermore, it shows a maximum Radar Cross Section reduction of 21.32 dB cm2. A cotton fabric was coated with N–Ti3C2Tx@Fe3O4, and it was found to exhibit enhanced heat conduction and dissipation, at rates 3.83 and 4.64 times greater than those of uncoated cotton, respectively. These results highlight the considerable potential of N–Ti3C2Tx@Fe3O4 nanocomposites for use in far-field applications. It is envisaged that the exceptional MA and thermal management properties of N–Ti3C2Tx@Fe3O4 nanocomposites will provide a novel avenue for crafting lightweight and thin EMW absorbing materials.

Frequency selective rasorber based on cross bend resonators for wideband transmission and absorption

The wideband absorption and transmission of frequency-selective rasorber (FSR) remain a persistent challenge in the application of radar devices. In this article, a novel high performance wideband FSR design based on cross bend resonators was proposed. The FSR consists of an upper absorption lossy layer, which offers broad absorption and transmission bands, and a lower bandpass frequency-selective surface that enables a highly selective transmission of incident electromagnetic wave. Full wave simulation results showed that this novel design achieves an absorption bandwidth of 83.7% with more than 90% absorptivity in the frequency range of 5.2–12.7 GHz. Furthermore, the passband’s fractional bandwidth for the insertion loss (IL) less than −3 dB is 33.9%, ranging from 14.9 to 21 GHz, with the minimum IL recorded at 0.69 dB at 17.7 GHz. To further verify the proposed method, a prototype FSR with 10 × 10 units of 120 mm × 120 mm was fabricated and the performance of the FSR was tested. The experiment results were in good agreement with the simulated results, and it showed a significant monostatic radar cross-section reduction in the frequency range of 5.3 GHz to 18.3 GHz compared with a metallic plane of the same size.

Wideband radar cross-section reduction by a double-layer-plasma-based metasurface

Reduction of the radar cross-section (RCS) is the key to stealth technology. To improve the RCS reduction effect of the designed checkerboard metasurface and overcome the limitation of thin-layer plasma in RCS reduction technology, a double-layer-plasma-based metasurface—composed of a checkerboard metasurface, a double-layer plasma and an air gap between them—was investigated. Based on the principle of backscattering cancellation, we designed a checkerboard metasurface composed of different artificial magnetic conductor units; the checkerboard metasurface can reflect vertically incident electromagnetic (EM) waves in four different inclined directions to reduce the RCS. Full-wave simulations confirm that the double-layer-plasma-based metasurface can improve the RCS reduction effect of the metasurface and the plasma. This is because in a band lower than the working band of the metasurface, the RCS reduction effect is mainly improved by the plasma layer. In the working band of the metasurface, impedance mismatching between the air gap and first plasma layer and between first and second plasma layers cause the scattered waves to become more dispersed, so the propagation path of the EM waves in the plasma becomes longer, increasing the absorption of the EM waves by the plasma. Thus, the RCS reduction effect is enhanced. The double-layer-plasma-based metasurface can be insensitive to the polarization of the incoming EM waves, and can also maintain a satisfactory RCS reduction band when the incident waves are oblique.

An absorptive coding metasurface for ultra-wideband radar cross-section reduction

In this paper, an absorptive coding metasurface (ACM) is proposed for ultra-wideband radar cross section (RCS) reduction, the design process is presented in detail, in which a lossy polarization conversion metasurface (PCM) is proposed at first. The lossy PCM is an anisotropic resistive structure with both polarization conversion and absorption performances, so that its co-polarization reflection coefficients under u- and v-polarized incidences can be kept at less than − 10 dB in magnitude in the frequency range from 7.5 to 45.2 GHz. Though the magnitude of the cross-polarization reflection coefficient cannot be very small only due to the absorption, its phase will be changed by nearly 180° when the unit-cell structure of the lossy PCM is rotated by 90°. Thus, the lossy PCM can be used as one of the two types of lossy coding elements for an ACM when its unit-cell structure is rotated by 90° or not. Based on the lossy PCM, an ACM is proposed. The simulation and experimental results show that the ACM has an excellent RCS reduction performance under arbitrary polarized incidence, it can achieve effective RCS reduction under normal incidence in the ultra-wide frequency band from 7.4 to 45.5 GHz with a ratio bandwidth (fH/fL) of 6.15:1; moreover, an ultra-wideband RCS reduction can still be achieved when the incident angle is increased to 45°, which indicates that the ACM has good stealth performance under the detection of various radars working in X, Ku, K and Ka bands, it is very practical.

Analysis of multi-photon quantum radar cross section for targets in atmospheric medium

Analysis of multi-photon quantum radar cross section for targets in atmospheric medium

Terahertz VO2-Based Dynamic Coding Metasurface for Dual-Polarized, Dual-Band, and Wide-Angle RCS Reduction.

With the rapid development of terahertz radar technology, the electromagnetic device for terahertz radar cross-section (RCS) reduction is worth investigating. However, the existing research concentrates on the RCS reduction metasurface with fixed performance working in the microwave band. This paper proposes a terahertz dynamic coding metasurface integrated with vanadium dioxide (VO2) for dual-polarized, dual-band, and wide-angle RCS reduction. The simulation result indicates that by switching the state of the VO2 between insulator and metal, the metasurface can realize the effective RCS reduction at 0.18 THz to 0.24 THz and 0.21 THz to 0.39 THz under the left-handed and right-handed circularly polarized incident waves. When the polar and azimuth angles of the incident wave vary from 0° to 40° and 0° to 360° respectively, this metasurface can maintain a 10 dB RCS reduction. This work has potential value in the terahertz stealth field.

RCS-reduced patch antenna with wide frequency tuning range based on absorbing metasurface

A frequency-tunable patch antenna with reduced radar cross section (RCS) based on absorbing metamaterial is proposed. By controlling the external voltage of the varactor diodes, the working frequency of the patch can be adjusted. Through an investigation of the composite structure of the patch and absorbing metamaterial, RCS reduction is achieved over the entire wide tunable frequency range of the antenna. Measured results illustrate that the proposed patch antenna can dynamically operate in the range from 2.28 to 3.6 GHz with a gain variation of 7.1–8.7 dBi. Meanwhile, the RCS can be reduced by at least 7 dB and up to 20 dB in a fractional bandwidth of 44.9% of the antenna under a normal incidence. In comparison to conventional RCS-reduced antennas, the proposed one features a broader frequency tuning range and has potential value in wideband radar systems under complex electromagnetic interference environments.

Manganese oxides/graphene aerogels as lightweight microwave absorbers for extreme environment application

The development of microwave absorbing materials (MAMs) with photothermal and electrothermal properties can satisfy special requirements for MAMs used in extreme environment. Herein, manganese oxide/graphene aerogel (MnOx/GA) composites were successfully fabricated by uniformly growing MnOx on GA through combining the hydrothermal and freeze-drying methods. The MnOx/GA composite exhibits a distinctive three-dimensional network structure with heterogeneous interfaces and lattice defects that can optimize the impedance matching and enhance the interfacial polarization, resulting in improved microwave absorption (MA) performance, including absorption intensity and bandwidth. The MnOx/GA sample prepared in this study exhibits an outstanding MA intensity of −54.70 dB at a frequency of 9.92 GHz, accompanied by an effective absorption bandwidth (EAB) of 5.60 GHz with a sample thickness of 2.60 mm and a filling content of 8.0 wt%. Meanwhile, the simulation of the radar cross section (RCS) further confirms the excellent MA performance and practical application potential of the MnOx/GA material. Additionally, MnOx/GA possesses outstanding electrothermal and photothermal properties, rendering it suitable for application in extreme environments. This work provides an economical, environmentally friendly, and efficient method for preparing lightweight and broadband multi-functional MAMs.

Ultra-wideband radar cross section reduction achieved by an absorptive coding metasurface

An absorptive coding metasurface (ACM) is proposed to achieve radar cross section (RCS) reduction in this paper. In the design progress of the ACM, two different lossy coding elements are proposed at first, which can both be regarded as a composite composed of a two-layer resistive frequency selective surface (RFSS) and a polarization conversion metasurface (PCM). The two-layer RFSS has a certain wave-absorbing property due to ohmic loss. In addition, the PCM can achieve ultra-wideband linear polarization conversion, and the polarization-converted reflected waves in the two coding elements under the same incidence will differ by nearly 180° in phase because the sub-unit-cell structures in them are perpendicular to each other. Thus, based on the two lossy coding elements, the ACM is proposed, which can achieve ultra-wideband RCS reduction due to absorption and phase cancelation. Numerical simulations demonstrate that the RCS of the ACM under normal incidence can be reduced more than 10 dB in the ultra-wide frequency band from 6.9 to 41.2 GHz with a relative bandwidth of 142.6%. Moreover, it has the advantages of polarization-insensitivity and wide incident angle. Finally, one effective experimental verification is carried out, and a reasonable agreement is observed between the simulation and experimental results.

Scattering properties of dual Bessel beams on chiral layered particle

The paper investigates the scattering analytical solution of arbitrary direction double zero-order Bessel beams (ZOBBs) incident on a non-uniform layered chiral sphere. Using the generalized Lorenz-Mie theory (GLMT), the electromagnetic field expansion expression of the double ZOBBs is obtained through the vector superposition of the spherical vector wave functions (SVWFs). Analytical solutions of the scattering on chiral layered particles by dual Bessel beams are derived based on the boundary condition. The iterative coefficient equations are constructed to obtain the expansion coefficients of the SVWFs in each region of the multi-layer chiral sphere. The variation of radar cross section (RCS) with angular distribution is numerically simulated, and the scattering results of layered chiral spheres degenerated into isotropic layered spheres are compared with the literature, which verifies the correctness of the theory and program. The effects of incident angle, polarization angle, cone angle and chiral parameters on the scattering characteristics of far region and internal field of the layered chiral particle are analyzed in detail. The theory and results can offer significant assistance in studying the optical properties of non-uniform chiral particles and complex biological cells irradiated by multiple beams and may also provide important practical value in the micromanipulation of multi-layered biological structures.

An ultra-wideband reflective polarization conversion metasurface and its application in RCS reduction

ABSTRACT In this work, an ultra-wideband reflective polarization conversion metasurface (PCM) is proposed at first. Because the PCM is an anisotropic structure that is symmetric with respect to both x- and y-axes, and the reflection phase difference under x- and y-polarized incidences is close to 180° in an ultra-wide frequency range, the PCM can achieve both linear polarization conversion and circular-polarization (CP) maintaining reflection in the ultra-wide frequency band from 8.3 to 41.3 GHz except for near the frequency point of 38.8 GHz. Moreover, when its unit cell structure is rotated by 90°, its cross-polarized reflection coefficient under LP incidence, together with the co-polarized reflection coefficient under CP incidence, will be changed by almost 180° in phase. Thus, based on the PCM, an ultra-wideband coding diffusion metasurface (CDM) is further proposed for radar cross section (RCS) reduction. The simulation and experiment results indicate that the CDM can achieve effective RCS reduction in the ultra-wide frequency band of 8.2–41.7 GHz under normal incidence with arbitrary polarization; in addition, an ultra-wideband RCS reduction can still be realized under oblique incidence with an incident angle less than 45°, which shows that the CDM is of good application value in radar stealth technology.

Enhanced electromagnetic wave absorption in ultrathin cement-based composites with integrated multi-dimensional carbon materials

The challenges posed by electromagnetic waves (EMW) cause significant interference in electronic device operation, jeopardizing information security and disturbing normal biological functions, which necessitate attention. Multi-scale carbon/cement-based composites were developed for EMW absorption by integrating multi-dimensional carbon materials, including carbon nanotubes (1D), graphene (2D), and modified carbon microspheres (3D). These composites demonstrate exceptional EMW absorption capabilities, with a minimum reflection loss (RLmin) of −44.32 dB and an effective absorption bandwidth (EAB) of 3.644 GHz at X band, merely having a thickness of 1.90 mm. Furthermore, the superior EMW absorption properties of these composites are confirmed through radar cross-section (RCS) simulation and electric field distribution analysis. A small house is constructed of designed three-layer multi-scale carbon/cement-based composites in which the actual EMW reflection losses are less than –10 dB within the whole test frequency range, and these composites can effectively obstruct 5 G mobile phone signals. Therefore, multi-scale carbon/cement-based composites could be promising candidates for effectively solving the increasingly serious problem of electromagnetic radiation pollution.

Ultra-thin wideband frequency tunable metamaterial absorber and its application for antenna radar cross section reduction

A metamaterial absorber (MMA) with broadband and efficient absorption performance based on ultra-thin dielectric layer is proposed. In this unique configuration, the absorption frequency of the MMA can be continuously and dynamically tuned across a wide frequency range by manipulating the reverse voltage of the central varactor diode. From both the equivalent circuit and field distribution perspectives, we analyze the mechanisms behind broadband tuning and superior absorption. Simulation and experimental results demonstrate that the absorption peak of MMA can be continuously tuned over a range of 5.16–8.16 GHz, with the absorption rate consistently exceeding 90%, and the thickness is only 0.5 mm. Integrating MMA array with a microstrip patch antenna in a suitable manner can dynamically mitigates the radar cross section (RCS) within the associated frequency range, with virtually negligible impact on the antenna’s radiation performance.

Noninvasive inset-integrated meta-atom for achieving single-layer metasurface simultaneously with coded microwave reflectivity and digitalized infrared emissivity

Abstract With the rapid improvement of equipment integration technology, multi-spectrum detectors are integrated into compact volumes and widely used for object detection. Confront with this challenge, it is essential to propose a strategy to design a single-layer metasurface with multi-spectrum responses in microwave and infrared ranges. In this work, we proposed a method of designing meta-atoms, which is capable of achieving functional electromagnetic response at microwave and infrared individually. As a demonstration, a metasurface with four different occupation ratios and coding permutation features is designed, fabricated, and tested. In the microwave band, the pixel meta-atom is designed to realize highly efficient cross-polarization conversion between 5.0 and 10.0 GHz, which shows the metasurface can behave as ultra-low Radar Cross Section (RCS) reflectors in the working band; In the infrared band, different occupation ratio of meta-atoms are designed to realize the infrared emissivity from 0.60 to 0.80 in 3–14 μm, which can be used to exhibit digital infrared camouflage pattern. This work promotes the ability to use single-layer design to achieve digital infrared camouflage and microwave RCS reduction simultaneously. The one-layer design is simple in geometry, simplified in process, low cost in economy, and large scale in fabrication, which can promote practical use in compatible microwave stealth and infrared camouflage.

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.

Well-Dispersed CoNiO2 Nanosheet/CoNi Nanocrystal Arrays Anchored onto Monolayer MXene for Superior Electromagnetic Absorption at Low Frequencies

Developing microwave absorbers with superior low-frequency electromagnetic wave absorption properties is one of the foremost important factors driving the boom in 5G technology development. In this study, via a simple hydrothermal and pyrolysis strategy, randomly interleaved CoNiO2 nanosheets and uniformly ultrafine CoNi nanocrystals are anchored onto both sides of a single-layered MXene. The absorption mechanism demonstrated that the hierarchical heterostructure prevents the aggregation of MXene nanoflakes and magnetic crystallites. In addition, the introduction of the double-magnetic phase of CoNiO2/CoNi arrays can not only enhance the magnetic loss capacity but also generate larger void spaces and abundant heterogeneous interfaces, collectively promoting impedance-matching and furthering microwave attenuation capabilities at a low frequency. Hence, the reflection loss of the optimal absorber (M–MCNO) is −45.33 dB at 3.24 GHz, which corresponds to a matching thickness of 5.0 mm. Moreover, its EAB can entirely cover the S-band and C-band by tailoring the matching thickness from 2 to 7 mm. Satellite radar cross-section (RCS) simulations demonstrated that the M–MCNO can reduce the RCS value to below −10 dB m2 over a multi-angle range. Thus, the proposed hybrid absorber is of great significance for the development of magnetized MXene composites with superior low-frequency microwave absorption properties.

Reconfigurable water-based metamaterial with hybrid mechanism for backward-scattering reduction

A hybrid mechanism water-based metamaterial (HMWM) with polarization conversion, absorption and phase cancellation mechanisms is proposed in this paper. The absorption and polarization conversion mechanisms are integrated by combining the water layer with polarization conversion structure, and the absorption conversion rate reaches more than 90% in the dual band (4.0–4.7 GHz and 8.2–15.7 GHz). Based on the above mechanism, the phase cancellation mechanism makes use of the opposite phase between HMWM and its mirror structure for checkerboard configuration to reduce the wideband radar cross section (RCS) by 3–18 GHz, achieving wide-angle RCS reduction and polarization insensitivity. In addition, the model realizes stealth control by adjusting RCS reduction capability under different water layer conditions. The results of simulation and experiment agree well, which fully demonstrates that the HMWM has scattering suppression capability and has potential application in multifunctional metamaterial.

Magnetic media synergistic carbon fiber@Ni/NiO composites for high-efficiency electromagnetic wave absorption

Electromagnetic wave (EMW) absorbing materials have garnered significant attention for their potential applications in information security and military stealth fields. However, the development of highly efficient EMW absorbing materials possessing characteristics such as being “thin, lightweight, broadband and strong” remains a considerable challenge. Addressing this challenge involves the construction of low-dimensional composite material systems, which proves to be an effective approach. In this study, we developed a simple and innovative sol–gel strategy to fabricate carbon fiber (CF)@Ni/NiO composites. The results demonstrate that the incorporation of Ni/NiO particles into CF materials substantially enhances the ferromagnetic properties of CF@Ni/NiO composites. An optimum reflection loss (RL) of CF@Ni/NiO-3 is −55.58 dB at 15.4 GHz with a corresponding thickness of merely 1.7 mm. An effective absorption bandwidth (EAB) reaches a maximum of 6.0 GHz at a thickness of 1.8 mm. Meanwhile, the radar cross section (RCS) reduction value at 6 GHz reaches 29.92 dB m2. The uniform distribution of Ni/NiO nanoparticles not only establishes a magnetic coupling network but also creates abundant heterogeneous interfaces with CF, thereby enhancing interfacial polarization. The successful fabrication of CF@Ni/NiO composites will facilitate the development and broad application of advanced EMW absorption materials in the aviation and aerospace sectors.

Enhancing microwave absorption via ion exchange-regulated metal elemental-alloy transition behavior

Metal-organic frameworks (MOFs) are considered as suitable candidates for excellent microwave absorption (MA) materials. However, the influence of the transition behavior from metal to alloy dominated by the metal ion ratio and the accompanying multi-phase coexistence model on the MA mechanism is unclear. This study successfully prepared a series of porous electromagnetic composite materials through ion-exchange in-situ pyrolysis synergistic strategy. The results indicate that the modulation of the Fe/Co ion ratio can easily manipulate the phase transition from Co metal to FeCo alloy-cobalt ferrite and the crystal defects within. The state of metal/alloy coexistence obtained at a low ion exchange degree has the highest concentration of vacancies, which is conducive to wideband absorption (6.03 GHz) and efficient loss (−67.44 dB) of MA performance. In contrast, the MA performance of samples at medium/high ion exchange degrees is not ideal. In addition, the application prospects of this material were demonstrated by simulating the actual absorption situation using radar cross-section. In summary, this work reveals the intrinsic relationship between the phase evolution behavior determined by the ion exchange degree in MOF derivatives and the electromagnetic performance, as well as the MA mechanism, providing a new reference for the preparation and design of outstanding MA materials.