Broadband Microwave Absorption Research Articles

Cross‐Scale Synergistic Manipulation of Dielectric Genes in Polymetallic Sulfides from Micropolarization to Macroconductance Toward Wide‐Band Microwave Absorption

AbstractRecently, the design and development of efficient microwave absorbents by facile engineering approaches have attracted much attention. Particularly, some unique structures caused by cross‐scale design are promising in enhancing the absorbing capability toward microwave irradiation. Herein, the cross‐scale design strategy is implemented to enhance the electromagnetic wave absorption performance of polymetallic sulfides (PMS). In PMS, the dipole polarization unit is optimized, and the distribution of electronic states is improved by doping Ti atoms; Meanwhile, the MS/M3S4 homogeneous hetero‐phases interfaces is constructed in PMS using a phase separation strategy; and the conductivity of PMS is modulated by the addition of acetylene black (ACET). The cross‐scale synergy of microwave absorption leads to a significant enhancement of the microwave absorption (MA) performance of PMS/ACET composites. The optimal reflection loss value of Ti‐LES with 10% ACET addition reaches −55.49 dB and the effective absorption bandwidth reaches 6.73 GHz. The 17.5% ACET‐conditioned Ti‐HES achieves a reflection loss of −37.2 dB at a low frequency of 4.8 GHz. This study not only provides a novel strategy for the development of new broadband MA materials but also validates a new idea for the multi‐scale synergistic optimization of MA materials.

Multifunctional integrated metamaterials for radar-infrared-visible compatible multispectral stealth

Metamaterials offer exciting opportunities for developing multispectral stealth due to their unique electromagnetic properties. However, currently transparent radar-infrared-visible compatible stealth metamaterials typically involve complex hierarchical designs, leading to thickness and transparency limitations. Here, we propose an integrated metamaterial for multispectral stealth with high transparency. Our design features an ITO/dielectric/ITO sandwich structure, with the upper-layer ITO acting as a resonator for broadband microwave absorption while maintaining a high filling ratio to suppress infrared (IR) radiation. Experimental results demonstrate excellent performance, with over 90% microwave absorption in 8–18 GHz, an IR emissivity of approximately 0.36 in 3–14 µm, an average optical transmittance of 74.1% in 380–800 nm, and a thickness of only 2.4 mm. With its multispectral compatibility, the proposed metamaterial has potential applications in stealth and camouflage fields.

Hollow Fe3O4/Fe@C nanocubes for broadband microwave absorption spanning low- and high-frequency bands

Rationally constructing hollow structures with heterogeneous interface is usually an effective strategy to regulate the electromagnetic response behavior for lightweight and strong absorption, but achieving low-frequency and broadband absorption is a major challenge. This work adopts a novel Fe(II)/Fe(III) ions regulation strategy to design and synthesize hollow Fe(OH)X (x = 2, 3) nanocubes, which addresses the disadvantages of time-consuming or using etchant. Subsequently, a unique hollow Fe3O4/Fe@C nanoboxes with adjustable magnetic composition and uniformly coated shell have been successfully synthesized by in-situ carbonization with the assistance of phenolic resin and hydrogen thermal reduction. Notably, the different magnetic components induce the magnetic coupling assembly and play a crucial role in determining its electromagnetic parameters, whereas Fe3O4 contributes to more dipole polarization and stronger low-frequency response characteristics. For Fe3O4@C hollow nanoboxes, the minimum reflection loss (RLmin) is as low as –119.9 dB at 2.3 mm, and extremely wide effective absorption bandwidth (EAB) of 11.4 GHz is achieved spanning low-frequency band of 2.8 ∼ 7.2 GHz and high-frequency band of 11.0 ∼ 18 GHz at 5.0 mm. Surprisingly, the Fe3O4@C also has satisfactory EAB20 (RL＜ –20 dB) reaching 7.1 GHz (14.9 ∼ 18 GHz) at a thin thickness of 1.8 mm. The RLmin of other hollow nanoboxes is also below –30 dB, and the EAB is greater than 9 GHz. This study provides a competitive candidate for efficient microwave absorption in complex frequency bands, especially low-frequency bands.

Fast, non-carbonized, ambient-drying PVA/CNF@GO foam: Towards super-broadband microwave absorption and structural strength enhancement in aramid honeycomb

Lightweight structural/microwave absorption (MA) integrated materials with broadband MA are urgently needed in the aerospace field. In this study, crosslinked PVA/CNF backbone-supported RGO foams were successfully filled into aramid honeycomb structures with significant broadband MA performance and structural enhancement properties through a synergistic strategy of chemical crosslinking, environmental drying and chemical vapor reduction. Flexible tuning of the electromagnetic parameters of the PVA/CNF@GO foam can be achieved by adjusting the number of GO parts. The 30 mm thickness of the PVA/CNF@14GO foam achieves a broadband effective absorption of 13.25 GHz, covering almost all C, X and Ku bands. Microstructural characterization and electromagnetic parameter tests proved that the uniform distribution of RGO was achieved with crosslinked PVA/CNF as the backbone, which resulted in less Debye relaxation and the construction of uniform conductive pathways. Therefore, the PVA/CNF@14GO-filled honeycomb not only enables the composite honeycomb to achieve broadband MA performance, but also achieves a compressive strength of 5.52 MPa, which is an improvement of 262.86 % with respect to that of the pure honeycomb. The obvious overlap of the CST power loss distribution and the electric field distribution region shows that the conductive loss and the 1/4 wavelength interference are the main paths for energy dissipation in the composite of the PVA/CNF@GO-filled honeycomb. The honeycomb-filled PVA/CNF@GO lightweight foams obtained in this chapter have good broadband microwave absorption properties and higher structural strength, which provide important design strategies and practical references for the development of high-performance MA-filled honeycomb structures.

Preparation of a double-layer bionic bamboo structure absorber based on CB/PLA-TPU composites and its broadband microwave absorption characteristics

The study of the mechanical characteristics and microwave absorption capabilities of multifunctional composite materials in complex environments has attracted considerable interest in recent years. Inspired by the structure of bamboo in nature, a novel double-layer microwave absorber structure, a CB/PLA-TPU composite bionic bamboo joint’s structure, was conceived and manufactured for this investigation. This structure ingeniously integrates the load-bearing attributes of bamboo joints with the microwave absorption qualities of CB composites. At the material level, enhancing the CB particle content enhances the matrix's folds and defects, thereby improving its dielectric polarization loss capacity. An effective absorption bandwidth of 3.84 GHz was achieved, with a minimum reflection loss of −60.24 dB at a 2.58 mm thickness and a 9.2 GHz frequency. The bionic bamboo absorber's unit structure is meticulously engineered, with experimental simulations validating its performance. According to the findings, the structure attains a 10.03 GHz broadband absorption and a yield strength of 11.6 MPa. It maintains broadband absorption capabilities above 9 GHz even at oblique incidence angles for TM polar wave (0–60°) and TE polar wave (0–30°). The biomimetic design based on bamboo offers significant potential for engineering applications in stealth technology under adverse conditions.

Facile preparation and broadband microwave absorption of multilayered materials based on thin films of reduced graphene oxide

Microwave absorption (MA) materials have received extensive attention for their wide applications in both civil and military areas. However, many MA materials have a large thickness, high filling ratio, and narrow effective microwave absorption bandwidth (Reflection Loss, RL ≤ −10 dB) (EAB), and are prepared by complex processes. In this work, a reduced graphene oxide (RGO) film is prepared for the first time by an approach involving floating-dipping and chemical reduction. Compared with previous micrometers-thick RGO films, the present 200 nm-thick dense RGO film is critical for improving not only the impedance matching but also the capability of the material to attenuate incident microwaves. Based on such a thin RGO film, a multilayered material with a jaaumann structure is constructed with individual RGO layers alternating between low dielectric polyethylene terephthalate (PET) sheets. With the superb impedance matching, multilayer attenuation, and multi-cavity resonance, the present multilayered material can achieve a wide EAB of 13.75 GHz with a minimum reflection loss of −47.69 dB using only 3 layers of RGO films. This study provides a new and simple strategy for the development of layered materials with a thin thickness, low filling ratio, and strong absorption with a wide EAB.

2D/3D structure engineering of dual-phase Mo2C/MoO2-decorated rGO aerogels for electromagnetic waves absorption

The rational design of structure and regulation of composition in micro/nano-scale is of great significance for broadband absorbing properties of lightweight aerogels. Herein, the controllable dual phase Mo2C/MoO2-decorated rGO aerogels are prepared by designing the Mo-rGO precursor, which possesses heterostructure interfaces and three-dimensional structures. The dual-phase of Mo2C/MoO2 was controlled and nanoparticles were dispersed on the surface of graphene. The interconnected rGO sheets construct continuous network for electron transport, which facilitates conduction loss and multiple reflections inside the aerogel. The Mo2C/MoO2 nanoparticles decorated on rGO sheets contribute sufficient interfacial and dipole polarization, and improve the impedance matching and strengthen the loss capacity of electromagnetic waves. The as-prepared Mo2C/MoO2/rGO aerogel exhibits considerable electromagnetic wave absorption performance with a minimum reflection loss of −42.1 dB at 12.5 GHz and an effective absorption bandwidth of 5.6 GHz (10.6–16.2 GHz) at a thin thickness of 2.2 mm with a low density of 9.8 mg·cm−3. This Mo2C/MoO2/rGO aerogel would be a promising material for electromagnetic wave absorption in wide application fields, and it also provides a universal idea for constructing low-density broadband microwave absorption material by structural and composition engineering.

Broadband microwave absorption performance of SrCo2Z hexaferrites with Pr-doping at high-frequency

Rare-earth praseodymium doped Sr3-xPrxCo2Fe24O41 (x = 0.0, 0.1, 0.2, 0.3, and 0.4) hexaferrites were successfully synthesized with sol–gel self-propagating combustion method. The effects of Pr-doping on the crystal structure, morphology, magnetic properties at room temperature, high-frequency electromagnetic properties and microwave absorption (MWA) performance of SrCo2Z hexaferrites are studied in detail. The results indicate that Pr-doping improves saturation magnetization (Ms) and coercivity (Hc) a little and greatly affects the MWA performance of Sr3-xPrxCo2Fe24O41 hexaferrites. The main loss mechanisms in Sr3-xPrxCo2Fe24O41 hexaferrites are magnetic losses as well as slight electrical losses. Sr2.9Pr0.1Co2Fe24O41 hexaferrites exhibit the best MWA performance with the minimum reflection loss of −40.70 dB at 6.32 GHz and the effective absorption bandwidth of 4.16 GHz for the thickness of 4.5 mm. Furthermore, the preparation method of Sr2.9Pr0.1Co2Fe24O41 hexaferrites is facile compared with other heterogeneous MWA materials, indicating a potential application prospect to synthesize MWA materials in GHz band.

Multi‐Scale Design of Metal–Organic Framework Metamaterials for Broad‐Band Microwave Absorption

AbstractThe development of nanocomposite microwave absorbers is a critical strategy for tackling electromagnetic pollution. However, challenges persist regarding material stability and achieving broadband absorption. Herein, a novel multi−scale design approach for metamaterial absorbers is proposed. First, a series of bimetallic (cobalt and copper) semiconductive metal–organic framework (SC−MOF) crystals with atomically resolved structures are successfully prepared to serve as building blocks for metamaterials. By simply adjusting the concentration ratio of the two ions, the controllable preparation of crystal morphology can be achieved. This enables to precisely tune the absorption peak and bandwidth range of the SC−MOF, resulting in excellent EMW absorption performance (effective absorption bandwidth: 6.16 GHz, minimum reflection loss: −61 dB). Based on this, printable inks are further constructed by encapsulating the SC−MOF in polydimethylsiloxane and 3D‐printed multi−layered metamaterial absorbers based on woodpile porous architecture. The metamaterial absorber demonstrates a near‐perfect absorption in the microwave spectrum (with a bandwidth of 11.33 GHz), closely matching theoretical simulations. This multi−scale design approach, combining precise MOF materials construction with topological structure design, offers new insights for the development of broadband microwave absorbers.

Reduced graphene oxide/nonwoven fabric filled honeycomb composite structure for broadband microwave absorption

The prevalence of electromagnetic pollution in daily life has led to a rapid escalation in the demand for high-performance electromagnetic absorption and protection materials. Herein, a composite material consisting of reduced graphene oxide (RGO)/nonwoven absorbent was prepared and filled into honeycomb structures. The single-layer nonwoven/honeycomb composite, with a thickness of 5 mm, demonstrates an effective absorption bandwidth (reflection loss ≤ −10 dB) reaching 12.1 GHz (5.9 GHz–18 GHz) and a minimum reflection loss of −37 dB. This is attributed to the synergistic absorption effects of conduction loss, interfacial scattering, dielectric relaxation, and multiple scattering losses. Furthermore, the bilayer composite structure demonstrates the capability to achieve full band absorption of 2 GHz–18 GHz with a thickness of only 10 mm, giving carbon materials a thin and lightweight absorption effect. In addition, the composite materials exhibit excellent mechanical properties. This study presents a new idea for the design and manufacture of broadband, lightweight, and high-performance microwave absorbers, which holds significant potential in the field of electromagnetic pollution prevention and absorption.

Constructing honeycomb structured metastructure absorber based on FeSiAl@CeO2 flakes for ultra-broadband microwave absorption

Due to the limitations of the Kramers-Kronig relationship, how to achieve ultra-wide effective absorption bandwidth remains a challenge for typical magnetic-dielectric absorbers. In the present work, we have explored the possibility of obtaining ultra-wide absorption bandwidth in FeSiAl composites with help of efficient electromagnetic (EM) simulation software-Computer Simulation Technology (CST). Flaky FeSiAl powders covered by CeO2 have been prepared, in which EM parameters can be tuned by filling ratio of FeSiAl/CeO2 in FeSiAl/CeO2-paraffin composites. The filling ratio has an effect on impedance matching and EM parameters by the arrangement of particles in the paraffin. The composite with 30 wt% flaky FeSiAl/CeO2 achieves an effective absorption bandwidth (EAB) of 6.48 GHz and the optimal microwave absorption efficiency of 1499.3 dB GHz/(wt%⋅m) at 1.9 mm. Integrated with a macroscale honeycomb structural design, the FeSiAl/CeO2 composites based metastructure exhibits broadband microwave absorption with an EAB of 14.224 GHz covering from 3.776 GHz to 18 GHz and reflection loss of-65.61 dB at 8.5 GHz. The excellent performances of the designed absorber are ascribed to multiple loss by integrating EM parameters of flaky FeSiAl/CeO2 and the geometry parameters of honeycomb metasrtucture. The present work makes flaky FeSiAl/CeO2 composites possible to achieve broadband microwave absorption.

Microfluidic Metasurface with Constant Absorption Efficiency Throughout the Ku Band

AbstractMetasurfaces with designable electromagnetic parameters are ideal candidates for broadband and tunable microwave absorbers. Water‐based metasurface microwave absorbers have been demonstrated to exhibit ultra‐broadband and near‐unity absorption. However, a broadband microwave absorber with constant and designable efficiencies remains a challenge due to stringent impedance‐matching conditions over a large frequency region. In this work, a design paradigm of microfluidic metasurface absorbers is proposed to regulate absorption efficiency over a wide frequency range. As an example, microfluidic metasurface absorbers are demonstrated with constant absorption efficiency over the Ku band, which is designable from 61.8% to 99.9%. The broadband metasurface absorbers have the advantages of easy fabrication, low cost, and optical transparency, making them highly promising for applications in fields like electromagnetic shielding, active camouflage, electromagnetic pollution control, and wireless communications.

Preparation of morphology- controllable γ-AlOOH/RGO composites and broadband microwave absorbers

Preparation of morphology- controllable γ-AlOOH/RGO composites and broadband microwave absorbers

Ni/Porous Carbon-Based Composite Derived from Poplar Wood with Ultrabroad Band Microwave Absorption Performance

Electromagnetic wave (EMW) absorbers and electromagnetic shielding materials have attracted much attention in recent years. In this paper, Ni/wood-based porous carbon (WPC) composite material was prepared via morphology genetic method by using nickel chloride and poplar as raw material, The experimental results show that the microwave absorbing properties of the materials are related to the pyrolysis temperature, when the pyrolysis temperature settle at 700 °C, the minimum reflection loss of WPC-Ni can reach-60.4 dB with the thickness of 2.93 mm. Moreover, the effective absorption bandwidth has been greatly broadened up to 7.3 GHz when the thickness is 2.63 mm. The reason for such excellent wave absorbing performance is that the introduction of magnetic particles Ni and WPC-Ni regular straight channels improve impedance matching, the heterogeneous interface of Ni/ wood increases the polarization loss of electromagnetic waves. It is believed that this work can provide a new idea for the preparation of low-cost and high-efficiency broadband microwave absorber.

Construction core–shell BCN@PANi composites with broadband microwave absorption performance

Construction core–shell BCN@PANi composites with broadband microwave absorption performance

Broadband and Tunable Microwave Absorption Properties from Large Magnetic Loss in Ni–Zn Ferrite

AbstractHighly effective electromagnetic (EM) wave absorber materials with strong reflection loss (RL) and a wide absorption bandwidth (EBW) in gigahertz (GHz) frequencies are crucial for advanced wireless applications and portable electronics. Traditional microwave absorbers lack magnetic loss and struggle with impedance matching, while ferrites are stable, exhibit excellent magnetic and dielectric losses, and offer better impedance matching. However, achieving the desired EBW in ferrites remains a challenge, necessitating further composition design. In this study, impedance matching is successfully enhanced and EBW in Ni–Zn ferrite is broadened by successive doping with Mn and Co , without incorporation of any polymer filler. It is found that Ni0.4Co0.1Zn0.5Fe1.9Mn0.1O4 material exhibits exceptional EM wave absorption, with a maximum RL of −48.7 dB. It also featured a significant EBW of 10.8 GHz, maintaining a 90% absorption rate (RL < −10 dB) for a thickness of 4.5 mm. These outstanding properties result from substantial magnetic losses and favorable impedance matching. These findings represent a significant step forward in the development of microwave absorber materials, addressing EM wave pollution concerns within GHz frequencies, including the frequency band used in popular 5G technology.

Fabrication of nitrogen-doped reduced graphene oxide/tricobalt tetraoxide composite aerogels with high efficiency, broadband microwave absorption, and good compression recovery performance

The fabrication of advanced graphene-based microwave absorbing materials with thin thickness, wide bandwidth, strong absorption strength, and low filling ratio remains a huge challenge. In this paper, nitrogen-doped reduced graphene oxide/tricobalt tetraoxide (NRGO/Co3O4) composite aerogels were synthesized by a three-step method of solvothermal reaction, high-temperature calcination, and hydrothermal self-assembly. The results showed that the attained NRGO/Co3O4 composite aerogels had a unique three-dimensional porous network structure, extremely low bulk density, and good compression recovery. Furthermore, the effect of the addition amounts of flower-like Co3O4 on the complex dielectric constant and microwave absorption properties of NRGO/Co3O4 composite aerogels was investigated. When the addition amount of Co3O4 was equal to 15 mg, the prepared binary composite aerogel showed the strongest absorption strength of –62.78 dB and a wide absorption bandwidth of 5.5 GHz at a thin thickness of 2.13 mm and a low filling ratio of 15 wt.%. It was worth noting that the maximum absorption bandwidth could reach 6.32 GHz (11.68–18 GHz, spanning the entire Ku-band) at a thickness of 2.24 mm. In addition, the possible microwave absorption mechanism of NRGO/Co3O4 composite aerogels was also proposed. Therefore, this paper will provide a new and simple strategy for preparing RGO-based porous nanocomposites as lightweight, efficient, and broadband microwave absorbers.

Study of the relaxation time for the polarization mechanism in SiO2–SiC/B4C nanowires with broadband absorption of microwave

SiO2-supported SiC/B4C (SiO2–SiC/B4C) nanowires were synthesized by using SiO2@C nanospheres, amorphous B powders and catalyst Ni(NO3)2·6H2O as raw materials, and exhibited remarkable microwave absorbing characteristics. The minimum reflection loss of the SiO2–SiC/B4C nanowire/paraffin composite reaches −41.33 dB with an effective absorption bandwidth up to 9.69 GHz. The broadband microwave absorption of SiO2–SiC/B4C nanowires is attributed to the synergistic effect of interfacial polarization relaxation and conduction loss. While conductive loss dominates at low frequencies within 2–8 GHz, polarization loss caused by the heterogeneous interfaces plays an important role at high frequencies, especially between 10 and 16 GHz. The movement of the polarization relaxation peaks to lower frequencies in the composites is further investigated by modeling the relaxation process as a rotating sphere in a viscous fluid. The linear relationship between relaxation time and conductivity indicates that the conductivity is an important factor that affects the electromagnetic wave (EMW) absorption performance not only on the impedance matching and attenuation constant of the materials, but also regulates the relaxation time, and this result provides a new idea for exploring the absorption mechanism of EMW absorbing materials.

Yolk-shell construction of Co0.7Fe0.3 modified with dual carbon for broadband microwave absorption

The rational and effective combination of multicomponent materials and the design of subtle microstructure for efficient microwave absorption are still challenging. In this study, carbon-coated CoFe with heterogeneous interfaces was space-restricted in the void space of hollow mesoporous carbon spheres through a facile approach involving electrostatic adsorption and annealing, and a high-performance microwave absorber (MAs) (denoted as Co0.7Fe0.3@C@void@C) was successfully prepared. The heterostructure, three-dimensional lightweight porous morphology, and electromagnetic synergy strategy enabled the Co0.7Fe0.3@C@void@C material with yolk-shell structure to exhibit surprising microwave absorption properties. When the annealing temperature and filler loading were 550° C and 15 wt%, respectively, the composites exhibited an effective absorption bandwidth (EAB) of 7.16 GHz at 2.48 mm and a minimum reflection loss of −24.1 dB at 2.11 mm. A maximum EAB of 7.21 GHz at 2.37 mm could be achieved for the composite prepared with an annealing temperature of 650° C. In addition, radar cross-section experiments demonstrated, the potential practical applicability of Co0.7Fe0.3@C@void@C. This work expands a new avenue to develop high-performance and lightweight MAs with ingenious microstructure.

Divalent metal-ions blowing strategy achieved 3D luffa aerogels heterostructure for lightweight broadband microwave absorber

Explicitly, effective dispersion configuration and hierarchical network construction are two practicable measures to develop the broadband and lightweight absorbers. Based on the newly developed sugar blowing art, 3D Luffa aerogels heterostructure have been successfully developed through metal ion assisted caramel blowing (MCB) strategy. The Luffa foam hierarchical configuration with those dielectric, magnetic, and porous interfaces can be all achieved. Such hierarchical 3D lightweight aerogels are facilitated to building effective impedance matching networks (2.4 wt%) and exhibit an optimized polarization relaxation. Thus, the effective absorbing bandwidth (EAB) of the Luffa aerogel can be broadened up to 8.0 GHz. Moreover, the MCB strategy can be applicable to a wide range of divalent metal ions (Co2+, Ni2+, Mn2+, Zn2+ et al.). This study provides a new method for efficient synthesis of aerogel network structures and opens a way to realize lightweight and broadband electromagnetic wave absorbing (EWA) materials.