Entire X-band Research Articles

High-performance honeycomb porous microwave absorbers: Gelatin-based carbon nanotube/nickel nanowire aerogels

Biomass-derived carbon absorbent materials have received significant attention due to their renewability, diverse sources, and ease of preparation. In this work, a honeycomb porous electromagnetic wave absorber with excellent performance was successfully prepared by blending gelatin and multi-walled carbon nanotubes (MWCNTs), followed by freeze-drying. Metallic nickel nanowires (NiNWs) were then introduced as a second phase using an in-situ growth method. The minimum reflection loss (RL) of the aerogel containing 8.06 wt% MWCNTs and 3.36 wt% NiNWs was −36.1 dB at a thickness of 3.1 mm, with the effective absorption bandwidth (EAB) covering the entire X-band. Additionally, the aerogel exhibited a very low density (36 mg/cm3) and remarkable strength, capable of supporting over 1658 times its weight for more than 24 h without deformation. These properties make it highly valuable for commercial use and provide new inspiration for the future development of biomass carbon-based electromagnetic absorbing materials.

Construction of a 3D spider web structure with spherical Ho2O3 wrapped by carbon nanofibers for high-efficiency microwave absorption and corrosion protection

Reasonable composition control and microstructure design are the effective ways to realize multi-functional high-performance absorbing materials. In this work, a three-dimensional (3D) spider web structure was designed by the electrospinning and high temperature carbonization technology, where Ho2O3 spheres were wrapped by carbon nanofibers. Herein, the spherical Ho2O3 were surrounded by layers of carbon nanofibers (spider silk), which were like the preys inside the spider's web. This unique bionic structure working in conjunction with the tuned components enables the as-prepared composites with improved impedance matching and enhanced loss capacity. The superior electromagnetic wave absorption performance was obtained as the minimum reflection loss of −61.37 dB at 2.90 mm and the maximum effective absorption bandwidth of 6.88 GHz (11.12–18 GHz) at 2.64 mm. At a thickness of 3.44 mm, the effective absorption bandwidth is 4.80 GHz (8–12.80 GHz), covering the entire X-band. At the same time, the composite soaked in the corrosive medium for 7 days owns a low corrosion current density (10−4 ∼10−6 A cm−2) and a high polarization resistance (105∼107 Ω), which exhibits the obvious anticorrosion ability. This work designs a specific spider web structure with high-performance microwave absorption and corrosion protection.

Engineering of N doped carbon@FeCo alloy hollow spheres: Remarkable mid-frequency electromagnetic wave absorption performance exhibited by unique porous and wrinkled surface structure

The modulation of the shape and design of microstructures plays a crucial role in enhancing the efficient absorption of electromagnetic waves in absorbers. The electromagnetic parameters and scattering effects of these materials are directly influenced by their morphological characteristics. In this study, polystyrene microspheres were used as templates for a two-step in-situ growth process: Initially, Fe₃O₄ was coated onto the surfaces of these microspheres, followed by the in-situ growth of Fe-Co Prussian blue analogs. The rational design of electrical parameters during the conversion process was calculated and analyzed using Density Functional Theory. The precursor was calcined at various temperatures to generate a unique porous wrinkled surface hollow nanostructure. This nanostructure not only facilitates multiple reflections and scattering of incident electromagnetic waves but also promotes the occurrence of multiple interface polarizations. Doping with nitrogen and oxygen elements introduced abundant dipole polarization, thereby enhancing the electromagnetic wave attenuation capability of the composite material. The Fe3O4@PBA composite material synthesized at 600°C achieved a minimum reflection loss of −57.01 dB and a maximum effective absorption bandwidth of 4.58 GHz (7.52–12.1 GHz) at a thickness of 4 mm, covering nearly the entire X-band. This method provides a means to enhance magnetic loss by temperature adjustment to control the magnetic components in composite materials, providing a systematic approach to designing the microstructure of materials used for absorbing electromagnetic waves.

Fabrication of MXene-encapsulated Co@C nanoparticles for efficient microwave absorption in the X-band

Two-dimensional MXene has structural advantages in electromagnetic wave scattering due to its layered structure, but MXene materials can lead to impedance mismatch problems due to their high dielectric constants, so it is still a challenge to design highly efficient wave-absorbing materials based on MXene with low reflection loss, thin thickness, and wide absorption frequency. In this study, composite wave-absorbing materials were fabricated from Co–Co PBA precursors and MXene using liquid nitrogen flash freezing and freeze-drying techniques. By treating MXene and the PBA precursor at a high temperature of 750 °C, a rich heterogeneous interface was formed between Co@C and MXene (CCM7), and the impedance matching was optimized to improve the reflection loss capability. The optimized sample has an effective absorption bandwidth of 4.1 GHz at 2.5 mm covering the entire X-band with a minimum reflection loss of −61.42 dB. It is also demonstrated that CCM7 is satisfactory for Radar Cross-Section of flat panels and unmanned aerial vehicles by CST calculations, and this work provides a fresh perspective on the use of effective MXene composites for microwave absorption.

Ultralight and rigid PBO nanofiber aerogel with superior electromagnetic wave absorption properties

Polymer-based aerogels are emerging as promising candidates for lightweight and high performance electromagnetic (EM) wave absorption materials. In this study, an ultralight and rigid poly(p-phenylene benzobisoxazole) nanofiber (PNF) based composite aerogel with excellent EM wave absorption performance was fabricated with cobalt-nickel alloy (CoNi) nanoparticles and carbon nanotubes (CNTs) as magnetic and conductive fillers, respectively. A CNT/PNF composite aerogel was first prepared through a sol-gel and freeze-drying method, and then CoNi nanoparticles were introduced therein through hydrothermal reaction and thermal annealing to obtain the CoNi/CNT/PNF aerogel. CNTs and PNFs were interwoven and constructed a three-dimensional conductive/magnetic cage-like skeleton structure decorating with magnetic CoNi nanoparticles. The cage-like skeleton structure allowed the dissipation of EM waves through multiple mechanisms encompassing conduction loss, magnetic loss, multiple reflection, scattering, and absorption. When its thickness was 4 mm, the CoNi/CNT/PNF aerogel showed a minimal reflection loss of −44.7 dB (at 6.88 GHz), and its broad effective absorption bandwidth covered the entire X-band and Ku-band and most of the C-band (12.32 GHz, from 5.68 GHz to 18 GHz). In addition, the rigid aerogel exhibited an ultralow density (0.107 g/cm3), excellent thermal insulation, and flame retardancy, demonstrating its potential application as a high-performance EM wave absorption material in the fields of aerospace and national defense.

Multiphase ceramic SiBCN-ZrO2/ZrC/ZrB2/SiC with ultra-wide bandwidth electromagnetic absorption

Broadband electromagnetic (EM) absorption is challenging for non-magnetic monolithic materials without any macro-structural design, primarily due to the impedance mismatch and insufficient EM dissipation. This study reports a multiphase ceramic made of SiBCN-ZrO2/ZrC/ZrB2/SiC, with an ultra-wide bandwidth EM absorption capability. The composites were prepared using a polymer-derived ceramic (PDC) method. The multiphase EM absorbers (ZrO2/ZrC/ZrB2/SiC) synergistically tune the dielectric properties and impedance matching of the composite ceramics, allowing the cross-band EM absorption at a low thickness. The SiBCN-ZrO2/ZrC/ZrB2/SiC composite ceramics pyrolyzed at 1400 °C for 2 h has an effective absorption bandwidth (EAB) of 11.06 GHz at a thickness of only 2.4 mm, covering parts of the C-band, the entire X-band and Ku-band (6.94–18.00 GHz). This research proposes a strategy for producing a monolithic composite ceramic with broadband EM absorption, which can also be used in high-temperature harsh environments.

Lightweight and thermally insulating ZnO/SiCnw aerogel: A promising high temperature electromagnetic wave absorbing material with oxidation resistance

Enhancing the microwave attenuation performance under high-temperature and oxidative conditions is a forefront issue for electromagnetic absorption materials. SiC nanowire material exhibits great potential due to its superior thermal stability and oxidation resistance. While, the relatively poor dielectric loss limits its further application as a high effective absorber. In this study, the strategy of laminated porous structure design, as well as the composition of ZnO nanocrystals were applied to promote the microwave attenuation capacity. A simple dual hydrolysis reaction method was employed to grow ZnO nanocrystals on SiC nanowires, followed by the preparation of a 3D layered structure of ZnO/SiCnw aerogel material using directional solidification processes. The ZnO/SiCnw aerogel demonstrated effective broadband attenuation (>90 %) across the entire X-band from room temperature to 873 K. Moreover, the material chemistry remained constant at temperatures as high as 1073 K in air. It exhibited ultralightweight properties and possessed a low thermal conductivity of approximately 0.056 W/m·K, with a density of 0.167 g/cm3. The combination of its lightweight, oxidation resistance, thermal insulation, and attractive X-band absorption efficiency positions ZnO/SiCnw aerogel as a promising EM absorption candidate at both room and high temperatures.

Enhancement of the microwave absorption performance of flaky FeSiCr powder through the compounding of cobalt ferrite

FeSiCr/CoFe2O4 composites were prepared by mechanical ball milling of cobalt ferrite prepared by hydrothermal method and flaky FeSiCr alloy powder. The phase and element of the composites was observed by XRD and XPS. The microstructure and surface elements of the composites were observed by SEM and EDS. The findings from the analyses confirmed the successful synthesis of the FeSiCr/CoFe2O4 composites. The results of EMP tests indicated that the electromagnetic parameters were balanced and the impedance matching was improved. When the mass percentage of cobalt ferrite was 20 %, the impedance matching was the best, and the RLmin reached −41.04 dB at 4.8 GHz. And the maximum EAB reached 5.4 GHz. By adjusting the thickness of the absorber, the EAB can be extended to 9.5 GHz (2.6–12.05 GHz), encompassing the entire C-band and X-band. The EMA performance of the composites has been greatly improved. FeSiCr/CoFe2O4 composites may serve as potential microwave absorbing materials in the future due to the wide range of economical raw materials, strong microwave absorption capacity and extensive absorption frequency range.

Enhanced multifunctionality in carbon fiber/carbon nanotube reinforced PEEK hybrid composites: Superior combination of mechanical properties, electrical conductivity, and EMI shielding

This study presents a novel approach to manufacturing carbon fiber and carbon nanotube-reinforced PEEK hybrid composites (CF/CNT/PEEK) using compression molding. The hybrid composite characteristics were compared with those of a control composite (CF/PEEK). Various tests were conducted on both composite types to investigate the impact of incorporating a carbon nanotube sock layer (an ultra-thin layer of a low-density CNT network), including three-point bend, electrical conductivity, and EMI shielding. The research also underscored the importance of EMI shielding simulation. An important aspect of the study involved performing multiscale simulations on control and hybrid composites, employing a digital twin methodology, and validating the results with experimental findings. For the hybrid composite, double multiscale simulations were performed by integrating two local-scale models, a CF/PEEK unit cell (micro-scale) and a CNT/PEEK representative volume element (RVE) (nano-scale), into a global-scale model. A detailed post-processing analysis of the simulation results was conducted to analyze stress distribution on local and global scale models. It was noted that there was an over 8 % increase in the flexural strength of the hybrid composite, along with a reduction of over 27 % in the standard deviation of the results. The introduction of CNTs enhanced the electrical conductivity by more than 36 %. It conferred remarkable EMI shielding effectiveness exceeding 50 dB across the entire X-band frequency range, attributed to enhanced reflection and absorption. EMI shielding simulations suggest that refining the manufacturing process of the hybrid composite could enhance its shielding properties. The developed multiscale simulation has been demonstrated as an efficient prediction tool, as the simulation outcomes closely align with experimental findings. The resultant hybrid composite is promising for potential multifunctional applications.

Enhancing X-band microwave absorption properties with nickel ferrite and carbon-based composites

The present study focuses on synthesizing a composite material comprising of nickel ferrite and carbon derived from cotton, to exhibit exceptional microwave absorption capabilities over a wide frequency range. By adopting a mechanical alloy method, the microwave-absorbing composite is developed. The microwave absorption characteristics of the developed composites are further unearthly in terms of their permittivity and permeability. Combining magnetic and dielectric phases produces better eddy current loss and polarization, which are primarily responsible for absorption characteristics. The developed composites are cast into rectangular pallets to evaluate microwave absorption characteristics and examined using a vector network analyzer within the 8.2–12.4 GHz frequency range. With a pallet thickness of 2.55 mm, the entire X-band frequency is effectively covered, yielding a remarkable minimum reflection loss of −20.46 dB at 10.01 GHz. The current work's findings, owing to the synergistic combination of nickel ferrite and carbonized carbon provide a practical approach for developing a hybrid material with remarkable electromagnetic performance.

A Novel Low-Density-Biomass-Carbon Composite Coated with Carpet-like and Dandelion-Shaped Rare-Earth-Doped Cobalt Ferrite for Enhanced Microwave Absorption.

A novel low-density composite for the absorption of microwaves was prepared by loading La-doped spinel cobalt ferrite (La-CFO) onto biomass carbon (BC) derived from corn stalks using a hydrothermal method. This composite (La-CFO@BC) not only maintained the advantageous properties of low density and abundant porosity, but also exhibited a unique morphology, with La-CFO displaying a carpet-like structure interspersed with dandelion-shaped particles. The incorporation of La-CFO effectively tuned the electromagnetic parameters of the composite, thereby improving its impedance-matching attributes and its ability to absorb microwave radiation. At a frequency of 12.8 GHz for electromagnetic waves and with a thickness of 2.5 mm, La-CFO@BC demonstrated remarkable performance in microwave absorption, attaining a noteworthy minimum reflection (RLmin) of -53.2 dB and an effective absorption bandwidth (EAB) of 6.4 GHz. Furthermore, by varying the thickness of the La-CFO@BC within the range of 1.0 to 5.5 mm, the EAB could be broadened to 13.8 GHz, covering the entire X-band, the entire Ku-band, and a substantial portion of the C-band. This study demonstrated that La-CFO@BC was a promising alternative for electromagnetic wave attenuation, which offered superior performance in microwave absorption.

Excellent microwave absorption property of 3D printed SiCN matrix metamaterial

The combination of 3D printing, polymer derived ceramics, and electromagnetic wave (EMW) absorption metamaterials is particularly useful for spacecraft stealth in extreme environments and is gradually gaining significant interest. While the 3D printing of SiOC has been extensively researched, the high temperature stability and mechanical performance of SiOC are not as favorable as SiCN. However, it remains challenging to prepare SiCN metamaterials with both high mechanical and microwave absorption properties by 3D printing. Herein, we demonstrate a SiCN EMW absorption metamaterial with high mechanical properties using digital light processing 3D printing, which achieves a minimum reflection loss of −31.01 dB (99.9 % absorption), and the widest effective absorption bandwidth covers the entire X-band from 8.2 to 12.4 GHz. And the EMW absorption performance can be adjusted based on the size of the unit structure.

Fusedly Deposited Frequency-Selective Composites Fabricated by a Dual-Nozzle 3D Printing as Microwave Filter.

We report a fusedly deposited frequency-selective composite (FD-FSCs), fabricated with a dual-nozzle 3D printer using a conductive carbon black (CB) polylactic acid (PLA) composite filament and a pure PLA polymer filament. The square frequency-selective pattern was constructed by the conductive CB/PLA nanocomposite, and the apertures of the pattern were filled with the pure dielectric PLA material, which allows the FD-FSC to maintain one single plane, even under bending, and also affects the resonating frequency due to the characteristic impedance of PLA (εr' ≈ 2.0). The number of the deposition layer and the printing direction were observed to affect electrical conductivity, complex permittivity, and the frequency selectivity of the FD-FSCs. In addition, the FD-FSCs designed for an X-band showed partial transmission around the resonant frequency and was observed to, quite uniformly, transmit microwaves in the decibel level of -2.17~-2.83 dB in the whole X-band, unlike a metallic frequency selective surface with full transmission at the resonance frequency. FD-FSCs embedded radar absorbing structure (RAS) demonstrates an excellent microwave absorption and a wide effective bandwidth. At a thickness of 4.3 mm, the 10 dB bandwidth covered the entire X-band (8.2~12.4 GHz) range of 4.2 GHz. Therefore, the proposed FD-FSCs fabricated by dual-nozzle 3D printing can be an impedance modifier to expand the design space and the application of radar absorbing materials and structures.

MOF Derivatives with Gradient Structure Anchored on Carbon Foam for High-Performance Electromagnetic Wave Absorption.

The impedance matching and high loss capabilities of composites with homogeneous distribution are limited owing to high addition and lack of structural design. Developing composites with heterogeneous distribution can achieve strong and wide electromagnetic (EM) wave absorption. However, challenges such as complex design and unclear absorption mechanisms still exist. Herein, a novel composite with a heterogeneous distribution gradient is successfully constructed via MOF derivatives Co@ nitrogen-doped carbon (Co@NC) anchored on carbon foam (CF) matrix (MDCF). Notably, the concentration of MOF can easily control the gradient structure. In particular, the morphologies of MOF derivatives on the surface of CF undergo a transition from the collapse of the inner layer to the integrity of the outer layer, accompanied by a continuous reduction in the size of Co nanoparticles. Correspondingly, enhanced interface polarization from the core-shell of Co@NC and good impedance matching of MDCF can be obtained. The optimized MDCF exhibits the minimum reflection loss of -68.18dB at 2.01mm and effective absorption bandwidth covering the entire X-band. Moreover, MDCF exhibits lightweight characteristics, excellent compressive strength, and low radar cross-section reduction. This work highlights the immense potential of composites with heterogeneous distribution for achieving high-performance EM wave absorption.

Scalable fabrication of lightweight carbon nanotube aerogel composites for full X-band electromagnetic wave absorption

Electromagnetic waves (EMWs) from advanced electronic devices can hinder normal operation of other electronic equipment, negatively affecting their performance and cause harmful impacts on human health by breaking down DNA strands and causing cancer. In this study, we thrivingly prepared new lightweight EMW absorbing aerogel composites by first blending polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), carbon nanotube (CNT), reduced graphene oxide (rGO), and carbonyl iron (CI), followed by freeze-drying. The materials are promising for up-scale production with the current pilot-scale samples sizing 35 cm × 35 cm. The effects of CNT types, CNT, rGO, CI, and crosslinker contents on EMW absorption ability are comprehensively investigated. The obtained aerogel composites exhibit a 3D porous structure with low densities (0.088–0.210 g/cm3), high thermal stability (227 °C), and high Young's modulus (670.9 kPa) compared to past aerogels. Notably, the materials with 3.0–3.5 mm in thickness achieve the minimum reflection loss (RLmin) of up to −42 dB (99.99 % EMW energy lost) and provide coverage across the entire X-band (8.2–12.4 GHz) with RL < −10 dB, indicating a 90 % attenuation of EMW energy. Compared to commercial Ni/CNT and other existing composites, our materials boast a broader effective bandwidth of 1.2–2.2 GHz. These properties make our aerogel composites highly promising for valuable commercial use, offering lightweight, durable, and efficient EMW absorption capabilities.

A new hybrid metamaterial absorber composed of ceramic resonators stacked on thin conductive rubber layer

In this letter, a hybrid metamaterial absorber made of ceramic resonators stacked on the traditional thin conductive rubber layer (RAT) has been developed. While RAT has been proven to be an effective absorber with good absorption around 10.5 GHz, its ability to absorb electromagnetic (EM) waves is inconsistent due to its flexible characteristic. Meanwhile, the absorption bandwidth above 90 % for RAT is constrained by its dispersion, limiting the coverage across the entire X-band (8–12 GHz). To address these limitations, we have incorporated the ceramic artificial nanostructure to enhance absorption intensity and broaden the absorption bandwidth by leveraging the strong magnetic Mie resonance of the ceramic resonator. Simultaneously, the number of absorption peaks and the bandwidth of each absorption peak can be controlled by adjusting the offset distance of the ceramic resonators and by varying the sintering temperature of the ceramics. Through the integration of metamaterial design and ceramic materials optimization, we have experimentally demonstrated the feasibility of multi-band, high-absorption devices by utilizing the hybrid structure of ceramic resonators and RAT, which opens up new possibilities for the further development of absorber devices.

WC-incorporated carbon hollow-hetero sphere derived from WO4-node hybrid crystalline framework for efficient electromagnetic wave absorption

Constructing hetero-interfaces in dielectric type electromagnetic wave absorbing materials (EWAMs) is of great significance, yet remains a formidable challenge. Herein, a WC-incorporated carbon hollow-hetero sphere was constructed from 3d/5d-bimetallic ZnW hybrid zeolitic imidazolate framework (ZnW-HZIF) through chemical etching and calcination. The RLmin reaches −63.72 dB at a thickness of 2.4 mm under a filler loading of 15 wt%, providing a wide effective absorption bandwidth of 10.4 GHz that covers the entire X-band at a thickness of 3.5 mm. The designed hollow structure and tunable WC/NC heterogeneous interfaces effectively enhance the dipolar/interfacial polarization while also facilitating the impedance matching. This research reveals a rational structural design strategy and practical technical methods for fabricating high-performance hollow and heterostructured non-magnetic carbon-based electromagnetic wave absorbing materials.

Electromagnetic and microwave absorption properties of flexible fabric coatings containing Ag decorated spherical graphene powders with FSS incorporation

Flexible textile microwave absorbing materials own the advantages of flexibility, foldability and cuttability, have become a research hotspot in electromagnetic stealth technology. In this study, a microwave absorbing coating was prepared on a fabric substrate using Ag decorated spherical graphene (SG) as the absorbent. XRD results demonstrated the metallic Ag ion was successfully reduced. TEM photographs showed the silver nanoparticles were stuck to the spherical graphene. The complex permittivity was enhanced after compositing with Ag particles. Along with the increase of silver content from 0 to 20 wt%, the complex permittivity rises from 3.29–0.42j to 6.93–2.22j owing to its higher electric conductivity and stronger relaxation effect. Meanwhile, the flexible coating containing Ag decorated spherical graphene (Ag@SG) also exhibited better microwave absorption performance. The minimum reflection loss (RLmin) for the coating with a thickness of 3.0 mm was −15 dB. And the effectively absorbing broadband (EAB) is located at 9.08–11.52 GHz. In addition, the microwave absorbing performance was greatly enhanced after being combined with periodic frequency selective surface (FSS). The EAB was obtained over the entire X-band frequency range, and the RLmin value achieved −41.72 dB at 10.25 GHz. What's more, the coating owned an EAB in a wide range incident angle of 60°–90°. This work was help to developing high performance flexible fabric coating containing Ag decorated spherical graphene with FSS incorporation.

Design and analysis of X-band metamaterial absorber

This study introduces a novel metamaterial absorber operating in X-band frequency range, characterized by two resonating peaks. The proposed structure consist of four circular sectors connected by two cross resonators enclosed by a circular strip with the dielectric between them. FR4 is used as a substrate backed by a copper ground plane. Simulation results reveal that the reflection co-efficient remains consistently below -10dB across the entire X-band, ensuring effective absorption of incident electromagnetic waves. Moreover, the absorber achieves 100% absorptivity with the gain of -25dB under normal incidence. The validity of absorber performance is confirmed through impedance plot and Voltage Stand Waving Ration (VSWR) analysis, verifying the accuracy of S11 parameter. Furthermore, the proposed structure has a compact size of 0.1666 λ. The absorber’s robust performance validated through numerical analysis, positions it as a compelling candidate for various X-band applications, including radar systems, communication devices, and stealth technology. This research establishes the proposed metamaterial absorber as a promising solution for X-band electromagnetic wave attenuation needs, offering both superior performance and compact design.

Photonic generation and transmission for an X-band dual-chirp waveform with frequency multiplication and power-fading compensation.

The generation of an X-band dual-chirp waveform, which is capable of pulse compression, plays an important role in radar, electric warfare, and satellite communication systems. With the development of applications such as multi-static radar, transmission over long distances has attracted considerable attention. In this paper, a photonic system for X-band dual-chirp waveform generation and transmission based on frequency multiplication and power-fading compensation is put forward and experimentally carried out. Based on a compact dual-parallel Mach-Zehnder modulator (DPMZM), the dual-chirp waveforms of 8.6-9.6GHz and 9.6-10.6GHz are generated by an RF carrier of 4.8GHz and transmitted through a 40km single-mode fiber (SMF) spool. The dispersion-induced power fading of the chirp waveform is compensated for by about 13dB. The full width at half maximum (FWHM) and the peak-to-sidelobe ratio (PSR) of the compressed pulses are 1ns and 11.5dB, respectively. Moreover, the compensation of power fading in the entire X-band is verified to demonstrate the applicability of our system. By flexibly adjusting the bias voltage of the built-in phase shifter, the system can be applied in more scenarios.