Broadband Microwave Absorption Research Articles

Flexible SiO2/rGO aerogel for wide-angle broadband microwave absorption

Graphene aerogel has been a promising microwave absorber due to ultralow density and strong dielectric loss ability. However, its intrinsic brittleness, and poor absorbing properties because of impedance mismatch severely hinders practical engineering applications. Herein, flexible silica fibers with excellent impedance matching properties were introduced into graphene honeycomb structures to co-construct a dual-structure aerogel (GS) by eco-friendly and low-cost technology. The unique dual-structure significantly enhances its resilience, enabling it to rebound after 1000 cycles of 75% compression. In addition, it can withstand 450 times of 180° folding and 360° rotation without damage, featuring remarkable flexibility and reliability. Furthermore, the simulation and experimental results indicate that GS has excellent wave absorbing performance. When the thickness is 6 mm, the effective absorption bandwidth is 32.55 GHz; when the thickness increases to 10 mm, the reflection loss is less than −8 dB in the range of 2.79–40 GHz. Moreover, the reflection loss remains almost constant when the oblique incidence angle ranges from 5° to 45°, which further demonstrates the critical role of impedance matching in enhancing the microwave absorption performance. These superior characteristics make GS an ideal candidate for many microwave absorption applications such as flexible electronics and aerospace.

Hierarchical carbon nanotubes-modified heterogeneous composites derived from melamine-mixed ZIF-67/MXene for broadband microwave absorption

In this paper, carbon nanotubes (CNTs) modified TiO2/C/Co@C composites (TiO2/C/Co@C(CNTs)) with good electromagnetic (EM) wave properties were synthesized originated from ZIF-67/MXene composites supplemented with external carbon source melamine by in situ synthesis and high temperature pyrolysis. The effect of the melamine content on the microstructure, EM parameters, and the microwave absorption (MWA) properties of the TiO2/C/Co@C(CNTs) composites was investigated. The results showed that the in-situ grown CNTs were organically connected to the pyrolyzed ZIF-67/MXene derivatives to form a hybrid network structure. The composites achieve the minimum reflection loss (RLmin) value of −47.52 dB at a thickness of 1.5 mm, the effective absorption bandwidth (EAB) of 5.06 GHz at 1.8 mm with the RLmin value of −41.35 dB, and the RLmin value of −52.43 dB at 6.18 GHz. The excellent EM wave attenuation ability of the TiO2/C/Co@C(CNTs) composites covers nearly the entire frequency band of 2–18 GHz with the RLmin value almost less than −30 dB in the thickness of 1.5–5.0 mm. The unique microstructure, dielectric-magnetic synergistic effect, and multiple interfacial polarization optimize the impedance matching. This word proposes a promising new strategy for constructing highly efficient MOF-derived and MXene-based microwave absorbers.

MOF derived NiFe@C composites with controllable multi-dimensional microstructures for broadband microwave absorption

Metal-organic framework (MOF) derivatives exhibit great potential as microwave absorbing materials (MAMs) owing to their high porosity, abundant surface sites and tunable constituents. Herein, this paper proposed an efficient microstructure controllable strategy for synthesizing thin-thickness broadband MAMs named NiFe@C by regulating its material microstructure. NiFe-MOF-74 precursors were firstly prepared through solvothermal method. By controlling the supersaturation of precursors, three kinds of microstructures were obtained: 3-dimensional lotus-like nanorods self-assembled structure, 1-dimensional nanospheres/nanorods hybrid structure, and 0-dimensional nanospheres structure. Subsequently, NiFe@C derivatives were obtained by pyrolysis, inheriting the microstructures of NiFe-MOF-74. The lotus-like structure of NiFe@C achieves an effective absorption bandwidth (reflection loss < -10 dB) of 5.09 GHz (12.91–18.00 GHz) with thickness of only 1.6 mm, while the nanospheres structure of NiFe@C exhibits the maximum absorptance of 99.96% at 17.12 GHz with thickness of 2.3 mm. This work provides a facile direction for designing thin thickness MAMs with broadband microwave absorption capability.

Broadband and High-Temperature-Resistant Microwave Absorber Using Additively Manufactured Ceramic Substrate

This paper presents an approach to achieve broadband absorption and temperature resistance using ceramic substrates. A specially formulated slurry suitable for additive manufacturing technology was developed to fabricate ceramic substrates with lattice structures. The lattice structure not only reduces the weight of the absorber but also facilitates the broadening of the absorption bandwidth. The experimental results demonstrate that the proposed structure exhibits absorption rates exceeding 88% within the frequency range of 19.9–30.41 GHz, with a relative absorption bandwidth of 41.8% under normal incidence. Furthermore, the absorber's performance was assessed under high temperatures of up to 200 ℃, revealing absorption spectra that closely match the initially measured spectrum. Additive-manufactured ceramic lattice structures present a promising avenue for designing multifunctional broadband microwave absorbers capable of withstanding elevated temperatures.

Magneto-Orientated Graphite Double-Layer Homo-Structure with Broadband Microwave Absorption

We utilized magnetic fields as an efficient tool to manipulate the orientation and electromagnetic properties of graphite micro-flakes (GMFs). As a result, we successfully developed a GMF double-layer homo-structure, which shows excellent electromagnetic absorption properties. By tuning the direction of a small magnetic field (850 G), vertical and horizontal aligned GMFs are produced. Their electromagnetic parameters are effectively tailored by this magneto-orientation effect, and the vertical and horizontal aligned GMFs achieve good results in terms of impedance matching and microwave absorption. With the combination of these two magneto-orientated layers, vertically oriented as the surficial impedance matching layer and horizontally oriented as the inner loss layer, we design a GMF-based double-layer homo-structure. After thickness optimization, −38.2 dB minimum reflection loss and 6.4 GHz (11.6–18.0 GHz) absorption bandwidth are achieved. Our findings further emphasize the importance of material orientation freedom and provide a magneto-strategy to design multiple-layer structures and to produce high-performance microwave devices.

Facile preparation of CoFe alloy/carbonized bamboo fibers for broadband microwave absorption

Multi-component design and microstructural regulation are commonly used strategies by researchers to improve the microwave absorption performance of materials, and it is essential to simultaneously explore sustainable and economical raw materials as well as simple preparation methods. In this study, the economical and sustainable bamboo fibers were used as a carbon source and template, and the CoFe alloy/carbonized bamboo fibers with different content were successfully prepared by the impregnation method and calcination method by controlling the nitrate concentration and calcination temperature. The analysis results display that the appropriate CoFe alloy content on carbonized bamboo fibers with nanopores can effectively improve the electromagnetic impedance matching and electromagnetic loss, resulting in excellent microwave absorption performance. The effective bandwidth almost simultaneously covers the X-band and Ku-band. This study not only facilitates the resource utilization of plant fibers, but also provides a new idea for the research of inexpensive, lightweight, and broadband microwave-absorbing materials.

Electromagnetic functionalization of mechanical lattice to metastructure with oblique incident broadband microwave absorption

Electromagnetic functionalization of mechanical lattice is an important method to integrate mechanical and electromagnetic properties into one structure with effective load bearing and broadband microwave absorption. Herein, the gradient lattice metastructure (GLM) is fabricated by dielectric-magnetic lossy nano composite strengthened by carbon fiber and glass fiber reinforced polymer. A large mutation genetic algorithm is developed to optimize the GLM with fine convergence property. Several large mutation modules are incorporated into the program to speed up the optimization process and improve global convergence. The measured −10 dB absorption bandwidth covers 2–5 GHz and 6.5–17.3 GHz while −9.5 dB absorption bandwidth covers 2–17.3 GHz. The oblique incident broadband absorption is achieved from normal incidence to the grazing incidence of 85° in traverse electrical (TE) and traverse magnetic (TM) polarization. Gradient lattice design is effective to overcome systemic oblique incident absorption deterioration originating from enhanced tangential electric field intensity in large incident angles. The nominal tensile strength of GLM reaches 108.4 MPa with maximum flexural load of 1.83 kN. The high electromagnetic and mechanical properties are achieved simultaneously by electromagnetic functionalization of mechanical lattice.

Multi‐physical honeycomb metastructure fabricated by fused deposition modeling with broadband radar absorption and mechanical resistance for drones

AbstractComplex structural configuration design is necessary for dielectric‐magnetic lossy composites to achieved broadband microwave absorption in civil and defense applications. Based on the unique space filling characteristic of fractal structure, the honeycomb metastructure can possess microwave absorption and mechanical resistance. However, traditional molding technique was difficult to realize complex shape of metastructure. Herein, the dielectric‐magnetic filament with different concentration of carbonyl iron particles was fabricated by high‐temperature extrusion process. The multi‐physical honeycomb metastructure with gradient layers was printed by fused deposition modeling (FDM) in a large size. The printed dielectric‐magnetic samples exhibited strong dielectric‐magnetic loss with high printing quality. The honeycomb metastructure achieved broadband microwave absorption in the −10 dB bandwidth of 9.6–18 GHz with tensile strength of 31 MPa. The results indicate that FDM is useful to fabricate metastructure with complex shape for broadband microwave absorption. The dielectric‐magnetic properties of filament are magnified by metastructure design. The proposed design‐fabrication process is promising for functional structure realization with complex shape in the future.Highlights1. Magnetic filament was fabricated for functional 3D printing.2. Structural magnetic dissipation mechanism for microwave was presented.3. Magnetic metastructure was designed and printed for broadband absorption.4. Integrated design of mechanical and electromagnetic function was presented.5. Structural absorption effect of honeycomb metastructure was revealed.

Highly Visible–NIR Transparent Metamaterial‐Window for Broadband Microwave Absorption and Shielding

AbstractOptically transparent metamaterial absorbers have unexceptionally encountered a great challenge in further improving optical transparency ranging from visible (Vis) to near‐infrared (NIR) and environmental applicability, due to the limitations of constituent materials and multilayer structures. To overcome this limitation, a highly Vis‐NIR transparent metamaterial‐window with outstanding microwave broadband absorption and practical durability is proposed in this paper, which adopts a typical sandwich structure consisting of a cross‐ and cross‐ring‐shaped resonator and a reflective backplane, separated by a quartz glass. Experimental results indicate that the proposed metamaterial‐window achieves &gt;80% absorptivity, covering a wide frequency range of 6.6–13.8 GHz with a relative bandwidth of 70.59%, while the measured shielding effectiveness is &gt;16.94 dB, at 4.0–16.0 GHz. In addition, the corresponding physical mechanism is revealed by exploiting a classical multiple reflections interference model. More significantly, both the patterned resonator and backplane layers are formed by microscale gold meshes with high Vis‐NIR transmittance and environmental resistance, thereby enabling excellent salt spray corrosion resistance and high‐temperature stability, as well as an average optical transmittance of ≈87.35% at 400–1 800 nm. These advantages endow the design a promising candidate for addressing anti‐electromagnetic interference and electromagnetic shielding both in military and civilian.

A broadband low-profile microwave absorber based on ferromagnetic material doped hybrid stereo metamaterial

This study introduces a ferromagnetic material-doped hybrid stereo metamaterial absorber (HSMA) that has been developed to overcome the limitations in broadband absorption of electromagnetic wave. This metamaterial combines a ferromagnetic block with a blind via in the center and a standing resistive trapezoidal patch together in a stereo meta-atom to enable a continuous and broad absorption band for 90% absorptivity from 2.3 GHz to 40 GHz, with a thickness only as 0.079 times the maximum working wavelength. The hybrid absorber also exhibits angular stability under oblique incidence and polarization insensitivity. Furthermore, a sample of proposed HSMA was fabricated and measured. The broadband absorption properties of such hybrid stereo metamaterial were validated by both simulated and experimental results. Our study provides a promising implementation approach for broadband and low-profile microwave absorbers.

Dual Resonance Behavior and Enhanced Microwave Absorption Performance of Fe3O4@C@MoS2 Composites with Shape Magnetic Anisotropy.

Ternary hierarchical Fe3O4@C@MoS2 composites and binary hierarchical Fe3O4@C composites were successfully fabricated by a modified mixed solvothermal method, a self-oxidation polymerization method, and a hydrothermal process. Their magnetic properties and microwave absorption performance were investigated. Dual resonance behavior was observed in the Fe3O4@C@MoS2 composites. One of the resonances was attributed to natural resonance with a resonance frequency of 2.58 GHz, which was much higher than that for Fe3O4 bulk (1.5 GHz). The other originated from the superparamagnetic/ferromagnetic relaxation with a resonance frequency of 12.45 GHz. The minimum reflection loss (RLmin) reached -64.30 dB with a matched thickness of 2.24 mm at 11.64 GHz, and the maximum effective absorption bandwidth (EABmax) covered 6.39 GHz with a matched thickness of 1.89 mm. In addition, the maximum Radar cross section (RCS) reduction value reached 31.90 dB m2 at a scattering angle of 0°. Electron holography analysis confirmed a dense magnetic absorption network in the Fe3O4@C@MoS2 composites. The boost in microwave absorption performance was caused by the synergistic effects of magnetic and dielectric properties owing to the ternary hierarchical structure, shape magnetic anisotropy, and incorporation of 1T/2H MoS2. Besides, the binary hierarchical Fe3O4@C composites also exhibited good absorbing performance caused by natural resonance, with an RLmin of -52.90 dB at 5.80 mm, an EABmax of 5.98 GHz at 3.38 mm, and a relatively high RCS reduction value of 13.04 dB m2 at θ = 20°. This work paves the way for designing multicomponent hierarchical absorbers with broadband and intensive microwave absorption.

Functional additive manufacturing of large-size metastructure with efficient electromagnetic absorption and mechanical adaptation

Broadband microwave absorption as a hot research topic plays important roles on electromagnetic compatibility, electromagnetic radiation protection and radar detection disguise. However, traditional molding method is difficult to fabricate large-size curving structures for broadband microwave absorption. Herein, the material extrusion with high-speed printing process was effective to manufacture large-size metastructures for broadband microwave absorption. The polylactic acid was mixed and extruded with nano pyrolytic carbon in high temperature to manufacture functional filaments with high dielectric loss. The printed metastructure integrated with 0.5 mm quartz fiber reinforced composite (QFRC) achieved -10 dB broadband microwave absorption in 3.03-18 GHz and effective load bearing performance in tensile and flexural tests. Severe impedance mismatch brought by QFRC was overcome by appropriate structure design and high-speed printing technique. The proposed design-manufacturing closed loop is a promising approach to fabricate aircraft skin with broadband microwave absorption performance and suitable aerodynamic properties for heavy unmanned aerial drones.

A broadband microwave absorber with properties optimized by an all-dielectric structure

Impedance matching is the premise of obtaining a perfect absorbing effect. Through improving the impedance matching condition of the grid-structured absorber by covering a layer of 0.5 mm thick 3D printed disk structure. The bandwidth of the new structure with the reflection loss less than −10 dB is optimized from 5.3–10.2 GHz and 14.8–18 GHz to 5.3–18 GHz. And the total thickness is 3.5 mm. The experimental results further validated the simulation results. The broadband absorption attributes to the synergistic effect of the dielectric loss and magnetic loss. Additionally, the optimized impedance matching is the critical precondition. Due to the 3D printing technology, the printing layer all-dielectric structure can be flexibly fabricated. The tailored strategy of optimizing the impedance matching by the 3D printed all-dielectric plays a guiding role in the realization of broadband absorption.

Bimetallic nanocubes embedded in biomass-derived porous carbon to construct magnetic/carbon dual-mechanism layered structures for efficient microwave absorption

Biomass-derived porous carbon materials have great potential for the development of lightweight and efficient broadband microwave absorbers. In this study, we reported the successful immobilization of Co3O4/CoFe2O4 nanocubes on porous carbon derived from ginkgo biloba shells by activated carbonization and electrostatic self-assembly processes. The optimal reflection loss value of the prepared BPC@Co3O4/CoFe2O4 reaches −68.5 dB when the filling load is 10 wt%, and the effective absorption bandwidth is 6.2 GHz with a matching thickness of 2 mm. The excellent microwave absorption (MA) performance is attributed to the rational three-dimensional structural design, the modulation of magnetic/carbon components, the optimized impedance matching, and the coordinated action of multiple mechanisms. It was further demonstrated by high-frequency structural simulation that the composite can effectively dissipate microwave energy in practical applications. Therefore, the results indicate a favorable potential of the synthesis and application of semiconductor/magnetic component/biomass-derived carbon microwave absorbing materials.

Multi-morphology composite: Particle & petal-shaped ZnFe2O4/flower-shaped ZnO@Porous biomass carbon with excellent broadband microwave absorption performance

Utilizing carbon and magnetic components to construct microwave-absorbing composites with broadband and strong absorption has become a research focus. Improving the structural coupling of these materials to enhance impedance matching and dielectric performance remains a significant obstacle. Particle and petal-shaped ZnFe2O4/flower-shaped ZnO@chestnut shell biomass-carbon composites (ZnFe2O4/ZnO@CBC) were synthesized via a one-step sintering method. The biomass carbon-based material presents a three-dimensional framework structure, while the particle and petal-shaped ZnFe2O4 and flower-shaped ZnO are uniformly distributed on its surface. This distribution significantly improves the dielectric polarization performance and magnetic loss of the material, ultimately leading to good microwave attenuation ability through impedance matching. Taking the addition of 1 g of biomass as an example, the minimum reflection loss (RLmin) of the composite material is −50.43 dB, and the widest effective absorption bandwidth (EAB) reaches 7.13 GHz (10.87–18 GHz). Notably, the EAB of the different composite materials all remains above 6.4 GHz when the biomass addition is adjusted within the range of 1–2.5 g, indicating that they are not sensitive to the amount of biomass used and have good stability in microwave absorption performance. Moreover, the results of the simulation and modeling analyses of the radar cross section (RCS) further validate the efficacy of composite materials in attenuating microwaves. These results offer valuable insights into the stability of bandwidth in materials and the potential application of biomass in wave-absorbing materials. It also shows that the composites are highly promising and reliable candidates for microwave absorption applications due to their high-performance, wide-band, and thin-absorption properties.

Low-cost and broadband microwave absorption materials derived from carbonized papers

Low-cost microwave absorption materials with broad bandwidth are highly attractive in practical applications. Herein, three kinds of low-cost biomass papers, that are printer paper, toilet paper and newspaper, have been utilized to fabricate microwave absorbers by a facile one-step carbonization method. These three kinds of carbonized papers show potentials in microwave absorption, where the carbonized toilet paper (CTP) exhibits the best performance. It is found that the fibers in CTP exhibits a helix-like morphology with loose and porous state, which would be beneficial to induce the unique cross-polarization loss for the chiral materials and multiple scatting of microwave. Besides, a hybrid structure of polycrystalline-amorphous carbon is formed in the fibers by controlling the carbonization temperature, which would increase the interfacial polarization and tune the conductivity that leads to a good impedance matching. Consequently, the minimum reflection loss of CTP reaches −47 dB at 18.0 GHz with a thickness of only 2.0 mm. Meanwhile, CTP also exhibits as wide as 7.2 GHz effective absorption bandwidth at a thickness of 2.5 mm. This study provides a useful guidance for recycling the biomass materials to design and prepare low-cost and broadband microwave absorbers.

Synthesis of nitrogen-doped reduced graphene oxide/magnesium ferrite/polyaniline composite aerogel as a lightweight, broadband and efficient microwave absorber

The fabrication of graphene-based microwave absorbing materials with low density, small filling ratio, broad bandwidth and strong absorption remains a huge challenge. In this work, nitrogen-doped reduced graphene oxide/magnesium ferrite/polyaniline (NRGO/MgFe2O4/PANI) composite aerogel was synthesized by a three-step method of solvothermal reaction, in situ chemical oxidation polymerization and hydrothermal self-assembly. The results showed that the obtained aerogels had a unique three-dimensional (3D) porous network structure and low bulk density (11.1–13.0 mg cm−3). It was worth noting that in the NRGO/MgFe2O4/PANI ternary composite aerogel, MgFe2O4 coated with a thin PANI layer was anchored on the surface of NRGO sheets. Furthermore, the NRGO/MgFe2O4/PANI ternary composite aerogel showed much better microwave absorbing capacity compared with pure NRGO aerogel and NRGO/MgFe2O4 binary composite aerogel. When the filling ratio was as low as 11.5 wt.%, the obtained ternary composite aerogel exhibited the maximum effective absorption bandwidth of 7.0 GHz at a matching thickness of 2.1 mm, and the minimum reflection loss of -42.9 dB at a thickness of 3.57 mm. Additionally, the probable microwave dissipation mechanism was also elucidated. It was believed that this study would pave the way for the construction of 3D graphene-based composites as lightweight, broadband and efficient microwave absorbents.

3D printed labyrinth multiresonant composite metastructure for broadband and strong microwave absorption

3D printed labyrinth multiresonant composite metastructure for broadband and strong microwave absorption

Constructing honeycomb-like hierarchical foam via electromagnetic cooperation strategy for broadband microwave absorption

The application of wireless electronic devices inevitably leads to electromagnetic pollution. Three-dimensional porous foam structures have been shown to be an effective strategy to construct high-performance microwave absorbers. Herein, the honeycomb-like hierarchical foams were fabricated via melamine-formaldehyde (MF) foam as substrate coupled with flaky carbonyl iron (CI)-MXene lamellae. Inside the synthesized composite foam, flaky CI is interlaced into MXene nanosheets to form hierarchical structures, which effectively alleviates the originally self-stacking phenomenon and provides numerous heterogeneous interfaces, resulting in the optimization of impedance matching. In addition, owing to the construction of consecutive electromagnetic networks, the CI-MXene/MF foams exhibit significant dielectric loss and magnetic loss capability. Moreover, the honeycomb-like structure offers multiple reflections/scattering for electromagnetic waves, which effectively prolongs the transmission paths, further improving the microwave attenuation ability. Hence, the synthesized composite foam exhibits superior microwave absorption performance with a minimum refection loss of −61.4 dB and a maximum effective absorption band of 7.18 GHz. The construction of unique microstructure and regulation of electromagnetic components is demonstrated to be feasible strategies for the design of efficient microwave absorbers in future.

Thermal energy compensation strategy to achieve rambutan-like CoFe@C-CNTs composites with controllable cross-linked networks for broadband microwave absorption

Combining carbon nanotubes (CNTs) with dielectric/magnetic materials is an attractive strategy to obtain high-performance microwave absorbing materials. However, it remains great challenges to overcome the agglomeration of CNTs and balance magnetic components to achieve impedance matching and broadband absorption. Herein, a thermal energy compensation strategy is designed to construct rambutan-like CoFe@C-CNTs composites with excellent microwave absorption performances via a catalyst chemical vapor deposition method and the subsequent reduction process. This strategy fully utilizes the thermal energy released during the C2H2 carbonization process, allowing the cracking of C2H2 and the growth of CNTs to continue at a temperature of lower than 430 °C. By adjusting the C2H2 introduction time in the cooling process of preheated cobalt iron oxide (CoFeO) nanoparticles, the number and length of CNTs on the carbon shells covering the surface of CoFeO cores can be controlled without forming metal carbides. The abundant interfaces, defects and grain boundaries in CoFe@C-CNTs composites contribute to enhancing the polarization loss via various polarizations and relaxations. Meanwhile, the appropriate 3D conductive network constructed by properly controlled CNTs provides remarkable additional conductivity loss. Furthermore, the effective retention of magnetic components greatly improves the impedance matching of the composites and offers considerable magnetic loss. Therefore, the optimized CoFe@C-CNTs-3 composite shows an effective absorption bandwidth of 9.00 GHz with a thickness of 2.1 mm. The proposed thermal energy compensation strategy provides a novel insight into developing magnetic metal-CNTs composites with potential practical applications.