Search

With the booming development of electronic information science and 5G communication technology, electromagnetic radiation pollution poses a huge threat and damage to humanity. Developing novel and high-performance electromagnetic wave (EMW) absorbers is an effective method to solve the above issue and has attracted the attention of many researchers. As a typical magnetic material, ferrite plays an important role in the design of high-performance EMW absorbers, and related research focuses on diversified synthesis methods, strong absorption performance, and refined microstructure development. Herein, we focus on the synthesis of ferrites and their composites and introduce recent advances in the high-temperature solid-phase method, sol–gel method, chemical coprecipitation method, and solvent thermal method in the preparation of high-performance EMW absorbers. This review aims to help researchers understand the advantages and disadvantages of ferrite-based EMW absorbers fabricated through these methods. It also provides important guidance and reference for researchers to design high-performance EMW absorption materials based on ferrite. [ABSTRACT FROM AUTHOR]

With the accelerating development of electronic technology, how to effectively eliminate electromagnetic radiation pollution has become a critical issue. Electromagnetic wave (EMW) absorption materials have an irreplaceable position in the field of military stealth as well as in the field of electromagnetic pollution control. In order to cope with the complicated electromagnetic environment, the design of multifunctional and multiband high-efficiency EMW absorbers remains a daunting challenge. In this work, a hierarchical porous molybdenum carbide matrix with a three-dimensional porous structure was designed by salt melt synthesis (SMS) strategy. Furthermore, the relationship between the structure and the impedance matching performance was explored by stepwise modification via ultrathin layered MoS2 nanoflakes. Analysis indicates that the extent of modification of hierarchical porous molybdenum carbide by MoS2 nanoflakes modulates the dielectric performance due to differences in morphology and the introduction of heterogeneous structures, along with a dramatic impact on the impedance matching performance. In particular, the prepared MS/MC/PNC-2 composite exhibits a reflection loss (RL) of -55.30 dB at 2.4 mm, and an ultra-broad effective absorption bandwidth (EAB) of 7.60 GHz is obtained at 2.0 mm. The coordination of structure and component enables the absorber to exhibit strong absorption, wide bandwidth, thin thickness, and multi-band absorption characteristics. Noticeably, the effective absorption performance in the broadband for X and Ku is also satisfying, as well as possessing moderate marine anti-corrosion performance. This study contributes to an in-depth understanding of the relationship between impedance matching and EMW absorber performance and provides a reference for the design of multifunctional, multiband microwave absorbing materials. [ABSTRACT FROM AUTHOR]

Highlights 3D cubic hollow core–shell NiCo2O4@C composites were synthesized. Oxygen vacancies were introduced into the prepared composites. Ultrabroad effective absorption bandwidth of 12.48 GHz was obtained. The absorption performance mechanism of NiCo2O4/C composites was investigated.

As the integration technology for integrated circuit (IC) packaging continues to advance, the issue of electromagnetic interference in IC packaging becomes increasingly prominent. Magnetic materials, acknowledged for their superior electromagnetic absorption capabilities, play a pivotal role in mitigating electromagnetic interference problems. In this study, we employed a liquid-phase reduction method. We prepared three types of cobalt (Co) particles with distinct morphologies. Through variations in the synthesis process conditions, we were able to control the aspect ratio of protrusions on the surface of the Co particles. It was found that the sword-like Co particles exhibit superior electromagnetic wave absorption capabilities, showing a reflection loss value of up to −50.96 dB. Notably, when the coating thickness is only 1.6 mm, the effective absorption bandwidth is extended up to 7.6 GHz. The spatially expansive sword-like Co particles, with their unique structure featuring dipole polarization and interfacial polarization, demonstrated enhanced dielectric and magnetic loss capabilities, concurrently showcasing superior impedance-matching performance. [ABSTRACT FROM AUTHOR]

Highlights: The hierarchical porous structure is regulated by various species of PVP to achieve impedance matching. Interfacial engineering boosts conductivity and constructs a multiband (C, X, Ku) tunable electromagnetic wave absorber. Hierarchical porous molybdenum selenide/epoxy coating exhibits marine anticorrosion capability. Electromagnetic wave (EMW) absorbing materials have an irreplaceable position in the field of military stealth as well as in the field of electromagnetic pollution control. And in order to cope with the complex electromagnetic environment, the design of multifunctional and multiband high efficiency EMW absorbers remains a tremendous challenge. In this work, we designed a three-dimensional porous structure via the salt melt synthesis strategy to optimize the impedance matching of the absorber. Also, through interfacial engineering, a molybdenum carbide transition layer was introduced between the molybdenum selenide nanoparticles and the three-dimensional porous carbon matrix to improve the absorption behavior of the absorber. The analysis indicates that the number and components of the heterogeneous interfaces have a significant impact on the EMW absorption performance of the absorber due to mechanisms such as interfacial polarization and conduction loss introduced by interfacial engineering. Wherein, the prepared MoSe2/MoC/PNC composites showed excellent EMW absorption performance in C, X, and Ku bands, especially exhibiting a reflection loss of − 59.09 dB and an effective absorption bandwidth of 6.96 GHz at 1.9 mm. The coordination between structure and components endows the absorber with strong absorption, broad bandwidth, thin thickness, and multi-frequency absorption characteristics. Remarkably, it can effectively reinforce the marine anticorrosion property of the epoxy resin coating on Q235 steel substrate. This study contributes to a deeper understanding of the relationship between interfacial engineering and the performance of EMW absorbers, and provides a reference for the design of multifunctional, multiband EMW absorption materials. [ABSTRACT FROM AUTHOR]

Highlights: 3D cubic hollow core–shell NiCo2O4@C composites were synthesized. Oxygen vacancies were introduced into the prepared composites. Ultrabroad effective absorption bandwidth of 12.48 GHz was obtained. The absorption performance mechanism of NiCo2O4/C composites was investigated. Cobalt nickel bimetallic oxides (NiCo2O4) have received numerous attentions in terms of their controllable morphology, high temperature, corrosion resistance and strong electromagnetic wave (EMW) absorption capability. However, broadening the absorption bandwidth is still a huge challenge for NiCo2O4-based absorbers. Herein, the unique NiCo2O4@C core–shell microcubes with hollow structures were fabricated via a facile sacrificial template strategy. The concentration of oxygen vacancies and morphologies of the three-dimensional (3D) cubic hollow core–shell NiCo2O4@C framework were effectively optimized by adjusting the calcination temperature. The specially designed 3D framework structure facilitated the multiple reflections of incident electromagnetic waves and provided rich interfaces between multiple components, generating significant interfacial polarization losses. Dipole polarizations induced by oxygen vacancies could further enhance the attenuation ability for the incident EM waves. The optimized NiCo2O4@C hollow microcubes exhibit superior EMW absorption capability with minimum RL (RLmin) of −84.45 dB at 8.4 GHz for the thickness of 3.0 mm. Moreover, ultrabroad effective absorption bandwidth (EAB) as large as 12.48 GHz (5.52–18 GHz) is obtained. This work is believed to illuminate the path to synthesis of high-performance cobalt nickel bimetallic oxides for EMW absorbers with excellent EMW absorption capability, especially in broadening effective absorption bandwidth. [ABSTRACT FROM AUTHOR]

Atomic‐level structural editing is a promising way for facile synthesis and accurately constructing dielectric/magnetic synergistic attenuated hetero‐units in electromagnetic wave absorbers (EWAs), but it is hard to realize. Herein, utilizing the rapid explosive volume expansion of the CoFe‐bimetallic energetic metallic triazole framework (CoFe@E‐MTF) during the heat treatment, the effective absorption bandwidth and the maximum absorption intensity of a series of atomic CoFe‐inserted hierarchical porous carbon (CoFe@HPC) EWAs can be modified under the diverse synthetic temperature. Under the filler loading of 15 wt%, the fully covered X and Ku bands at 3 and 2.5 mm for CoFe@HPC800 and the superb minimum reflection loss (RLmin) of −53.15 dB and specific reflection loss (SRL) of −101.24 dB mg−1 mm−1 for CoFe@HPC1000 are achieved. More importantly, the single‐atomic chemical bonding among Co─Fe on the nanopores is captured by extended X‐ray absorption fine structure, which reveals the formation mechanism of nanopore‐confined vortical dipoles and magnetic domains. This work heralds the infinite possibilities of atomic editing EWA in the future. [ABSTRACT FROM AUTHOR]

Ferrites were among the earliest types of microwave absorbers due to their high magnetic dissipation and low cost. Ferrites, on the other hand, have some disadvantages, such as a low natural resonance frequency (fr), a lack of dielectric loss, and a high density. We effectively generated (SrMnCoFe 10 O 19 /MnCoFe 2 O 4)/SiO 2 samples with hollow microfiber morphologies and most of the effective parameters suggested to overcome these disadvantages and increase the microwave dissipation properties of ferrites. Hard and soft SrMnCoFe 10 O 19 /MnCoFe 2 O 4 hollow microfibers were obtained using sol-gel and electrospinning technology. After heat treatment at 1050 °C for 3 h, the binary ferrites are formed. (Hard ferrite/soft ferrite)/SiO 2 core-shell structures were fabricated by the Stober process, so their microwave absorption performance is greatly influenced by the hard/soft mass ratio and SiO 2 thickness of the sample. The fabricated fibers were characterized by x-ray diffraction (XRD), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FESEM), FTIR spectroscopy, and vector network analyzer (VNA). The single-phase structure of all microfibers was determined by X-ray diffraction (XRD) analysis. The phase formation of the coated microfibers is also elaborated using Fourier transform infrared spectroscopy (FTIR) based on identified chemical bonds. According to the (FESEM) analysis results, the microfibers manufactured have a homogeneous core–shell structure. A vector network analyzer was used to investigate the samples' dielectric constants and microwave absorption properties between 12 and 18 GHz at room temperature. The results showed that when the mass ratio is hard/soft (8: 2) and the mass ratio of ferrite/SiO 2 (1:1), the maximum reflectance loss is −27 dB and the absorption bandwidth is 2 GHz. The magnetic saturation (Ms) was calculated at 43.44 emu/g and the calculated coercivity values (1163.07 Oe) confirm the hard ferrite/soft ferrite/SiO 2 core-shell structures. [Display omitted] [ABSTRACT FROM AUTHOR]

In this research, we developed a wideband electromagnetic wave absorber suitable for the X-band frequency by using a unique hybrid nanocomposite structure made of FeWO 4 embellished with Ag 3 PO 4 nanopowders. Simple chemical hydrothermal and microwave-aided hydrothermal procedures were used to successfully produce single-phase spherical-like FeWO4 and FeWO4@Ag3PO4 nanocomposite powders. Using XRD, FTIR, VSM, FESEM, and VNA methods, the phase constituents, morphological, magnetic, and electromagnetic properties of the produced nanocomposite materials were assessed. The resin-based nanocomposite absorber sample allows to obtain a maximum reflection loss of −21 dB with a matching thickness of 1.8 mm at the ferromagnetic resonance of 10.4 GHz with a 3.8 GHz effective absorption bandwidth, which is evaluated using the waveguide technique, when the filler loading percentage reaches 40 wt percent (S40). S40 had superior impedance matching capabilities, a wide effective absorption bandwidth, and a high absorption capacity when compared to other produced absorber samples. The best sample is prepared for free-space testing with the dimension of 200 × 200 mm and an optimum thickness of 1.8 mm, and the results demonstrate a good agreement between the waveguide and free-space technique results. This absorber sample's wideband absorption capacity was attained by adjusting the magneto-electric composition and enhancing the interfacial characteristics brought on by the core-shell construction. In this study, a design approach for efficient microwave absorbers based on a magneto-electric hybrid nanocomposite structure is presented, using waveguide and free-space experimental methods in two different ways. [ABSTRACT FROM AUTHOR]

In this study, the electromagnetic wave absorption properties of woven glass fiber reinforced epoxy composites with Sb2O3 and SnO2 nanoparticles doped mica pigments were investigated. Herein, we synthesized SnO2/mica, Sb2O3/mica, and Sb2O3:SnO2/mica pigments using the sol–gel method. Subsequently, mica pigments filled glass fiber/epoxy composite panels were fabricated with a vacuum assisted resin mold. The phase, crystal, and morphological examinations of particles confirm the deposition of SnO2 and Sb2O3 nanoparticles on the mica surfaces. The electromagnetic wave absorption properties of samples were measured using the S parameters and obtained dielectric data. Sb2O3:SnO2/mica particles display higher complex permittivity and dielectric loss values due to the strong interfacial polarization between conductive nano metal‐oxide shells and mica surfaces. According to the calculated reflection loss values, Sb2O3:SnO2/mica particles exhibit superior electromagnetic wave absorption performance with a minimum reflection loss of −25.62 dB for 2.4 mm thicknesses with effective bandwidth between 9.3 and 12.4 GHz. The S parameters of the prepared structural composites with the size of 30 cm × 30 cm × 3 mm was determined by the free‐space technique using the transmission line technique. According to the S12 parameters, filled glass fiber/epoxy composite containing 25 wt% Sb2O3:SnO2/mica show a minimum reflection loss of −20.426 dB at 8.2 GHz with effective bandwidth between 8.2 and 9.67 GHz. These results indicate that Sb2O3:SnO2/mica‐filled fiber/epoxy composite is an excellent candidate for the practical application of electromagnetic wave absorbers. [ABSTRACT FROM AUTHOR]

Terahertz waves are gathering attention as carrier waves for next-generation wireless communications such as sixth-generation wireless communication networks and autonomous driving systems. Electromagnetic-wave absorbers for the terahertz-wave region are necessary to ensure information security and avoid interference issues. Herein we report a high-performance terahertz-wave absorber composed of a composite of metallic λ-Ti 3 O 5 and insulating TiO 2 nanocrystals (λ-Ti 3 O 5 @TiO 2 ). This material exhibits a strong terahertz-wave absorption with high values for the real (permittivity, ε') and imaginary parts (dielectric loss, ε″) of the complex dielectric constant. Furthermore, the tan(δ) (≡ ε″/ε') values are significantly high, ranging from 0.50 to 0.76 in the frequency range between 0.1 and 1 THz. An ultrathin film with a thickness of 48 μm recorded a reflection loss of -28 dB (99.8% of the terahertz wave is absorbed by the film). A terahertz-wave absorber with such a small thickness has yet to be developed. Not only does the present material exhibit resistance to heat, light, water, and organic solvents, but it can also be economically fabricated to support various applications, including outdoor uses.

In contemporary civilization, the electromagnetic radiation from electronic devices and communication systems has become a substantial pollutant. High-performance electromagnetic absorbers have become a solution for absorbing unwanted electromagnetic waves. This research proposed a lightweight and flexible electromagnetic absorber produced from natural rubber filled with conductive carbon black (CCB) and Fe3O4. The effect of CCB, Fe3O4, and a combination of CCB and Fe3O4 as a hybrid filler on foam morpholog, electromagnetic reflectivity, tensile strength, and compression set properties were investigated. In addition, the effect of the alternating layered structure of CCB and Fe3O4 on electromagnetic absorption was investigated. The results indicated that the composite foam exhibited an interconnected network structure that enhanced the electromagnetic attenuation in the absorber. CCB increased the electromagnetic absorption of the foam, whereas Fe3O4 had less of an effect. The foam filled with the hybrid filler at the CCB/Fe3O4 ratio of 8/2 exhibited excellent electromagnetic absorption. The composite foam had a higher tensile modulus and higher strength compared to neat foam. The addition of CCB decreased the compression set; however, the compression set was improved by the incorporation of Fe3O4. Composite foams filled with hybrid filler can serve as highly efficient electromagnetic absorbing materials. [ABSTRACT FROM AUTHOR]

Multiple relaxation behaviors are promising for broad frequency band and strong electromagnetic wave (EMW) absorption based on polarization‐controlled electromagnetic (EM) attenuation. However, rational selection of materials and structure manipulation through tunable substitution or phase control are challenging toward optimization of EMW absorption. Herein, bi‐metallic organic frameworks (B‐MOFs) with various morphologies are employed as EMW absorbers. Remarkably, the polar units can be enhanced by introducing Ni‐metal nodes into the Cu‐coordinated MOFs, rendering the B‐MOFs with self‐polarized properties and consecutive multifrequency EMW absorption behaviors. The maximum reflection loss of acetylene black (ACET) filled NiCu‐MOFs can reach –40.54 dB together with a wide bandwidth (<‐10 dB) of 5.87 GHz at a thickness of 2.5 mm. As a counterpart of the Ni/Cu/C derivatives, significantly increased broad band absorption (6.93 GHz) and multifrequency absorbing and polarization characteristics are also maintained in bimetal coexisting carbonized architectures as prepared by calcination of CuNi‐MOFs. This work demonstrates that the performance of effective absorbing frequency band can be enhanced in multi‐metallic organic frameworks‐based architectures, and paves a novel avenue for developing broadband and strong EMW absorbers. [ABSTRACT FROM AUTHOR]

Abstract Phase engineering is an important strategy to modulate the electronic structure of molybdenum disulfide (MoS2). MoS2-based composites are usually used for the electromagnetic wave (EMW) absorber, but the effect of different phases on the EMW absorbing performance, such as 1T and 2H phase, is still not studied. In this work, micro-1T/2H MoS2 is achieved via a facile one-step hydrothermal route, in which the 1T phase is induced by the intercalation of guest molecules and ions. The EMW absorption mechanism of single MoS2 is revealed by presenting a comparative study between 1T/2H MoS2 and 2H MoS2. As a result, 1T/2H MoS2 with the matrix loading of 15% exhibits excellent microwave absorption property than 2H MoS2. Furthermore, taking the advantage of 1T/2H MoS2, a flexible EMW absorbers that ultrathin 1T/2H MoS2 grown on the carbon fiber also performs outstanding performance only with the matrix loading of 5%. This work offers necessary reference to improve microwave absorption performance by phase engineering and design a new type of flexible electromagnetic wave absorption material to apply for the portable microwave absorption electronic devices.

The feasibility of beam-shaping of a Ku-Band horn as a transmitting (Tx) antenna by mounting two different versions of lenses which are kind of Fresnel Zone Plates (FZP) is studied. The designed and fabricated geometrical structures offer a simpler approach building Fresnel Zone Plates by using an electromagnetic wave absorber and diffractive optic material. The diffractive optic material, paraffin, forms a set of alternating open and opaque annular zones on a flat surface, based on the design principles of Fresnel Zone Plates. An electromagnetic wave absorber covers the top surface of the formed paraffin, but not including the grooves. Thereafter, the Fresnel Zone plates are suitably attached in front of the transmitter horn antenna, located in the far-field region of a receiving antenna. The half-power beam-widths for the horn antenna (unloaded) and with two types of lenses are investigated. The results indicate that Fresnel zone plate structures can play a role suppressing side lobes in H-plane so that the effective radiation is to be significantly concentrated.

In order to overcome the problems caused by electromagnetic pollution, the design and development of high-performance microwave absorbers is urgently required. In this work, a hierarchical ZnFe 2 O 4 @MnO 2 @RGO composite was successfully fabricated via a facile and rapid hydrothermal method. Its unique core-shell structure and synergistic effect between multiple components are beneficial for electromagnetic wave absorption. The morphology, elemental composition, microstructure and microwave absorption characteristics were systematically studied. With a filler loading of 20 wt%, the composite presents a minimum reflection loss (R Lmin) of −46.7 dB and an effective absorption bandwidth (EAB) as wide as 5.2 GHz at a thickness of 2.5 mm. The superior absorption ability profits from a special microstructure, good impedance matching, multiple attenuation features, interfacial polarization, and the synergistic effect of dielectric and magnetic loss. Consequently, this work lays a foundation for the design of high-performance electromagnetic wave absorbers with multicomponent heterogeneous structures. [ABSTRACT FROM AUTHOR]

VB‐Group transition metal disulfides (TMDs) are considered excellent materials for electromagnetic wave (EMW) absorption because of their good conductivity and abundant active sites located at their edges and substrates, as compared with VIB‐Group TMDs. Herein, for the first time, EMW absorbers based on VB‐Group NbS2 nanosheets by using a facile one‐step solvothermal method are successfully prepared. The minimum reflection loss (RLmin) can reach up to 43.85 dB with an effective absorption bandwidth of 6.48 GHz (11.52–18.00 GHz). The remarkable EMW absorption performance can also be reflected in the tunable frequency bands (C‐, X‐, and Ku‐bands), which is achieved by adjusting the contents of materials. Furthermore, the influence of the content of 2H‐phase and 1T‐phase in NbS2 on the EMW absorption performance is systematically investigated. The hierarchical hollow‐sphere structure of NbS2 promotes dielectric loss and the multiple reflection and absorption of EMW, and enhances the impedance matching and synergistic attenuation ability. This work demonstrates that the bottleneck of effective absorbing frequency band of single‐component dielectric EMW absorbing materials could be broken through, and paves a novel path towards developing broadband absorbing materials in EMW absorption. [ABSTRACT FROM AUTHOR]

[Display omitted] Absorbing materials can convert electromagnetic wave (EMW) energy into heat and other energy and dissipate it. Carbon materials can attenuate EMW by generating large conduction losses due to their high conductivity. The introduction of low dielectric materials can improve impedance matching caused by high conductivity. However, the density of materials compounded with carbon materials is too large, which affects the overall density of composite materials. Therefore, this problem is solved by matching melamine foam with ZIF-67. As an ultra-light material, the melamine foam-based carbon material can significantly reduce the density of composite materials, and its developed three-dimensional structure can cause multiple scattering of EMW. The large specific surface area and evenly distributed metal oxides obtained after annealing of ZIF-67 can provide ultra-low-density carbon materials and abundant interfacial polarization to further attenuate EMW. So far, the methods of self-growing materials on the surface of melamine foam have not been reported. We prepared a 500 nm Co 3 O 4 nanosheet/carbon foam (CF) composite material coated on the surface by a two-step method. The sample had a maximum reflection loss of −46.58 dB at 10.72 GHz, and an effective absorption bandwidth (EAB) of 5.4 GHz. This research provides a new idea for the growth of porous materials on the surface of melamine foam-based carbon materials. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) carbon-based materials have attracted growing attention in the field of electromagnetic wave absorption applications. However, their high conductivity results in high dielectric constant, leading to impedance mismatching, and this characteristic finally weakens their electromagnetic wave absorption performance. In this work, 3D carbon foam (3DCF) was successfully prepared by calcining the melamine foam as the carbon framework precursor under N 2 atmosphere. Subsequently, 1T-2H MoS 2 nanosheets were uniformly assembled on the surface of the 3DCF skeleton through a solvothermal process. The diameter of the 3DCF skeleton was about 1 μm and the thickness of the 1T-2H MoS 2 on the surface was about 150 nm. The 3D network brings in many advantages for microwave attenuation, including numerous conductive pathways, excellent impedance matching and multi-polarization processes. The composites exhibited a maximum reflection loss (RL max) of −45.88 dB at 10.2 GHz with the thickness of 2.2 mm, and the effective absorbing bandwidth (E AB) was as wide as 5.68 GHz, implying their superb microwave absorption behavior. This work is believed to offer a strategy for the design of efficient 3D electromagnetic wave absorbers with low density in the future. [ABSTRACT FROM AUTHOR]

Highlights: A facile one‐step hydrothermal method for producing gram‐scale 1T@2H-MoS2 by imbedding the guest molecules and ions was developed. The influence of different MoS2 phase for electromagnetic absorbing properties was explored by analyzing electromagnetic parameters of 1T/2H MoS2 and 2H MoS2 with 50%, 40%, 30%, 20%, 15%, and 10% filler loading. Taking the advantage of 1T/2H MoS2, the flexible CF@1T/2H MoS2 was also synthesized to mind the request of flexible portable microwave absorption electronic devices.Phase engineering is an important strategy to modulate the electronic structure of molybdenum disulfide (MoS2). MoS2-based composites are usually used for the electromagnetic wave (EMW) absorber, but the effect of different phases on the EMW absorbing performance, such as 1T and 2H phase, is still not studied. In this work, micro-1T/2H MoS2 is achieved via a facile one-step hydrothermal route, in which the 1T phase is induced by the intercalation of guest molecules and ions. The EMW absorption mechanism of single MoS2 is revealed by presenting a comparative study between 1T/2H MoS2 and 2H MoS2. As a result, 1T/2H MoS2 with the matrix loading of 15% exhibits excellent microwave absorption property than 2H MoS2. Furthermore, taking the advantage of 1T/2H MoS2, a flexible EMW absorbers that ultrathin 1T/2H MoS2 grown on the carbon fiber also performs outstanding performance only with the matrix loading of 5%. This work offers necessary reference to improve microwave absorption performance by phase engineering and design a new type of flexible electromagnetic wave absorption material to apply for the portable microwave absorption electronic devices. [ABSTRACT FROM AUTHOR]

The feasibility of beam-shaping of a Ku-Band horn as a transmitting (Tx) antenna by mounting two different versions of lenses which are kind of Fresnel Zone Plates (FZP) is studied. The designed and fabricated geometrical structures offer a simpler approach building Fresnel Zone Plates by using an electromagnetic wave absorber and diffractive optic material. The diffractive optic material, paraffin, forms a set of alternating open and opaque annular zones on a flat surface, based on the design principles of Fresnel Zone Plates. An electromagnetic wave absorber covers the top surface of the formed paraffin, but not including the grooves. Thereafter, the Fresnel Zone plates are suitably attached in front of the transmitter horn antenna, located in the far-field region of a receiving antenna. The half-power beam-widths for the horn antenna (unloaded) and with two types of lenses are investigated. The results indicate that Fresnel zone plate structures can play a role suppressing side lobes in H-plane so that the effective radiation is to be significantly concentrated. [ABSTRACT FROM AUTHOR]

The titanite-based ceramics with nominal composition CaTi1−xNb4x/5SiO5 (0 ≦ x ≦ 0.2) in which part x of Ti sites are occupied with Nb, showed a remarkable jump of the complex relative permittivity at x = 0.025 compared with that at x = 0 at 110 GHz. Real part increased from 22.5 to 39, and the imaginary part from 4 to 14 (tangent delta from 0.18 to 0.36). Non-reflection condition is fulfilled in both cases when 0 < x < 0.0125, d/λ0 = 0.05 and x = 0.2, d/λ0 = 0.045, where d is thickness of the plate sample and λ0 is the wavelength of incident electromagnetic wave. The dominant dielectric dispersion may occurr due to difference of ionic polarization between Ti4+ and Nb5+ ions relative to O2− ions, which becomes inactive and saturates at x = 0.025. From the measurement of the lattice parameters, a, b, c, and the angle β, characterizing monoclinic crystal structure, this saturation may have close correlation with some structural rearrangement of constituting atoms, Ti and Nb in CaTi1−xNb4x/5SiO5. [ABSTRACT FROM AUTHOR]

• Composite was prepared by coordinate combination to improve the agglomeration phenomenon. • The impedance matching of composites was optimized by constructing mesoporous structures and regularized surface structures. • The absorption mechanism of the composite was explained by analyzing electromagnetic parameters and microscopic morphology. • The reflection loss and effective absorption bandwidth of the composites are −48.5 dB and 4.52 GHz, respectively. Biomass carbon has been widely studied as an electromagnetic wave-absorbing material in recent years due to its wide range of material sources, natural porous structure, and other advantages. Herein, a series of magnetic lignin-based carbon composites have been prepared as electromagnetic wave absorbers using carboxylation lignin as an organic ligand and Fe, Co as a metal ion. The bimetallic to coordinate combination with carboxylation lignin improved the agglomeration phenomenon, optimized mesoporous structure, and the pore distribution of the material compared to monometallic. This lignin-based FeCo@C had an abundant interfacial, mesoporous structure, dielectric, and magnetic loss capability. When the ratio of Fe and Co was 1:1, the reflection loss value of −48.5 dB at 12.3 GHz, and the effective absorption bandwidth achieved 4.52 GHz with a thickness of 2.5 mm. In short, this work provided a new direction for the preparation of renewable and high-performance lignin-based electromagnetic wave absorber materials. [ABSTRACT FROM AUTHOR]

Electromagnetic (EM) wave has become an integral part of this electronics dominated era with extensive application in wireless communication, health care, and military applications. This has led to the development of EM wave absorbers for camouflaging the military warheads from the enemy radar tracking systems. The development of these absorbers requires considerable resources viz. time, energy, raw materials and cost. This creates a need for selection of a better absorber from the existing ones rather than the development of a new one to save the valuable resources. The judicious selection of an efficient microwave absorber requires ranking the existing absorbers based on selection criteria. For the first time, an attempt has been made to apply the concept of multi-criteria decisionmaking methods viz. VIKOR and TOPSIS in ranking the microwave absorbers. Core-shell materials provides enhanced EM wave attenuation owing to their hierarchical composite structure which provides a better approach to tune the dielectric and magnetic properties of the composite for obtaining good impedance matching resulting into enhanced absorption. In the present work, magnitude of minimum reflection co-efficient value, absorber thickness, deviation from the central frequency (i.e. 10 GHz) and -10 dB bandwidth have been selected as the criteria for judiciously selecting suitable core-shell based EM wave absorbers in 2-18 GHz. The selected criterion has been assigned distinct weights using Analytic Hierarchy Process (AHP). The AHP derived weights have been employed in TOPSIS and VIKOR analysis for the absorbers ranking and selection. [ABSTRACT FROM AUTHOR]

Associated with the unique structure and superior properties of zeolitic imidazolate frameworks (ZIFs) of Co-based metal-organic frameworks (MOFs), we synthesized the MWCNTs@carbonaceous CoO composites of a 3D interconnected network using multi-walled carbon nanotubes (MWCNTs) as decoration through the wet chemical and pyrolysis method. Due to the mutual coordination between proper magnetic loss and strong dielectric loss together with perfect impedance match, the MWCNTs@carbonaceous CoO composites exhibit the maximal reflection loss (RL) value of −50.2 dB with 1.84 mm thickness at 14.3 GHz, absorbing bandwidth (RL ≤ −10 dB) of 13.2 GHz (4.8–18 GHz) with respect to 1.0–4.0 mm thickness range. More importantly, the content of composites added to paraffin matrix is merely 10 wt%. In addition, the synergistic effect between CoO NPs and MWCNTs is also beneficial to the highly efficient electromagnetic (EM) wave absorption of the composites. Therefore, the obtained CoO NPs/MOF-derived composites with lightweight and thin performance can be an attractive candidate of the EM wave absorptive materials. Unlabelled Image • MWCNTs@carbonaceous CoO composite is prepared via wet chemical and pyrolysis method. • The composite can reach −50.2 dB at 14.3 GHz with the thickness of 1.84 mm. • The composite exhibits a bandwidth of 13.2 GHz at RL ≤ −10 dB in the range of 1.0–4.0 mm. • The composite shows a good performance of impedance match. [ABSTRACT FROM AUTHOR]

Abstract The dielectric-dielectric composite (SRGA) for electromagnetic absorber was fabricated via integrating Ag(I)-Schiff base coordination compounds (SSBCC) with three-dimensional reduced graphene aerogel (3D-rGA) powders. SRGA showed excellent electromagnetic wave absorption properties in terms of reflection loss, absorption band width and absorber thickness. Specially, when the mass ratio of SSBC to 3D-rGA powders was 1:3 (SRGA-25), the maximum value of reflection loss at 2 mm was up to −63.82 dB and the effective frequency bandwidth of 6.28 GHz (10.16–16.44 GHz) at 2.5 mm can be obtained. The mechanism investigation of electromagnetic wave absorption for SRGA showed that the enhanced electromagnetic wave absorption was ascribed to enhanced polarization loss derived from good 3D-conductive-network units of 3D-rGA, abundant interfaces caused by the media heterostructure due to the introduction of SSBCC and the good impedance matching condition. And 3D-rGA based materials might be put into practical application only in powder state due to the very low strength of the buck state. Therefore, the investigation on SRGA in our contribution is considered to be an actual performance evaluation of the materials based on three-dimensional graphene for microwave attenuation. This work also provided a method for fabricating excellent graphene-based electromagnetic wave absorbers by simply mixing a suitable dielectric lossy material, e.g. SSBCC. Graphical abstract Image 1 Highlights • The preparation method of SRGA through mixing components is simple. • 3D-rGA powers overcome the limitation of low strength of graphene aerogel. • Schiff base enhances dielectric properties and makes SRGA good impedance matching. • The max RL at 2 mm is up to −63.82 dB and the effective bandwidth reaches 6.28 GHz. [ABSTRACT FROM AUTHOR]

In this study, a novel electromagnetic (EM) wave absorbing composite sandwich structure and its application process are proposed. The composite sandwich can be applied to the outer part of structures as a final surface treatment through a secondary bonding process, and this covers all the surface components that illuminate the incident EM waves. This process improves the structural material properties of the original components and their durability against the environment in contrast to EM wave absorbing paint or patch. With the help of EM wave absorbing characteristics and continuous impedance of the composite sandwich structures, the EM signals from reflection, diffraction, and scatter decrease effectively. The outer skin of the composite sandwich includes a resistive periodic patterned sheet prepared using printed electronics, and a low-dielectric foam is adopted as the core material. This composite is designed based on the equivalent circuit theory and is subsequently fabricated. The EM characteristics are tested after application on an aircraft skin structure through a secondary bonding process. The measurement of reflection loss and image processing of the reflected signal show that this composite and application process decrease the EM wave reflections from the original structure significantly. [ABSTRACT FROM AUTHOR]

Abstract In the present study, an electromagnetic (EM) wave absorber was fabricated with a multi-walled carbon nanotube (MWNT)-incorporated cement composite and the absorbing capability of the absorber was assessed. To disperse MWNTs in a cement matrix, composites were fabricated under a low flow condition of the fresh mixture, and silica fume (SF) was added to explore the influence of SF addition on MWNT distribution. The electrical conductivity of the composite was evaluated to examine the MWNT distribution and the complex permittivity was determined to study the EM characteristics of the composite. The conductivity results demonstrated that SF addition of 10 wt% led to the greatest enhancement. Meanwhile, the absorber was designed on the basis of complex permittivity at a frequency point of 9.4 GHz, and SF0-M1.0 type (no SF addition and MWNT content of 1.0 wt%) and SF10-M0.6 type (SF content of 10 wt% and MWNT content of 0.6 wt%) were employed. The experimental assessment of the absorbing capability demonstrated that the −10 dB bandwidths of SF0-M1.0 and SF10-M0.6 type absorbers were 2.5 GHz and 3.2 GHz, respectively. In addition, the absorbing capability derived from the experimental work was compared and validated by means of computational simulation work. [ABSTRACT FROM AUTHOR]

Copyright of Electronic Components & Materials is the property of Electronic Components & Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Display omitted] • A facile method to prepare Co@CNs with core-shell porous structure by heat treatment of Z@P nanocomposites. • The RL min of Co@CN-60 is −59.08 dB at 17.66 GHz with a thickness of only 1.7 mm. • The effective absorption bandwidth is broadened ranging from 15.19 to 9.41 GHz (5.78 GHz) when the thickness is 2.3 mm. • The porous core-shell structure of Co@CN-60 not only consume the EMW, but also improve the impedance matching. N-doped porous core-shell nanocomposite is considered to be a competent candidate for the absorbing of electromagnetic wave (EMW). In this work, polydopamine (PDA) wrapped ZIF-67 (Z@P) precursors with the core-shell structure were obtained through ZIF-67 triggered dopamine self-polymerization. After high-temperature pyrolysis treatment, the N-doped graphitized carbon layers wrapped cobalt (Co@CNs) absorber with porous structure was obtained, which exhibited high efficiency and adjustable EMW absorbing properties. The minimum reflection loss (RL min) of Co@CN-60 approached −59.08 dB at 17.7 GHz with a thickness of 1.7 mm. The effective absorption bandwidth (EAB) reached 5.8 GHz with a corresponding thickness of 2.3 mm. Besides, the RL min of Co@CN-90 reaches −44.07 dB at 14.5 GHz (thickness 2.0 mm), and the EAB is 5.9 GHz. Therefore, the porous core-shell Co@CNs nanocomposite is expected to be a promising EMW absorption material. [ABSTRACT FROM AUTHOR]

W-type Sr-hexaferrites, Sr 0.75 Ca 0.25 Zn 2- x Co x Fe 16 O 27 (0.0 ≤ x ≤ 2.0), were synthesized, and their magnetic and electromagnetic (EM) wave absorption properties were investigated. As x increased from 0.0 to 2.0, the saturation magnetization value increased and reached a maximum at x = 1.25, followed by a decrease, while the magnetic anisotropic field (H ani) decreased and showed a minimum at x = 1.0, then increased again. The variation in H ani could be controlled by adjusting the value of x , which also changed the ferromagnetic resonance (FMR) frequency and enabled control over the frequency band of EM wave absorption. It is demonstrated that the EM wave absorption is primarily controlled by imaginary part of permeability (μ") induced by FMR. Composite of the W-type hexaferrite-epoxy (10 wt%) with x = 0.75–2.0 showed a broad-band EM wave absorption in the 1–18 GHz range, while the composites with x = 0–0.4 showed it in the 26.5–40 GHz. The x = 1.25 sample satisfied RL < − 10 dB in the 7–17 GHz range with a thickness of 2.1 mm, while x = 0.3 sample satisfied RL < − 10 dB in the 27–39 GHz with a thickness of 0.8 mm. Sr 0.75 Ca 0.25 Zn 2- x Co x W is a very promising material for tunable wideband EM wave absorbers in 1–40 GHz range. • H ani of Sr 0.75 Ca 0.25 Zn 2- x Co x W could be controlled by Co-doping level x , which also changed the FMR frequency. • EM wave absorption is primarily controlled by μ" induced by FMR. • Sr 0.75 Ca 0.25 Zn 2- x Co x W-epoxy composites exhibited tunable and broad-band EM wave absorption within 1–40 GHz range. [ABSTRACT FROM AUTHOR]

Two-dimensional nanomaterial MXene Ti 3 C 2 T x with excellent electrical conductivity has received extensive attention in the electromagnetic wave (EMW) absorption field. However, the excessively high permittivity of Ti 3 C 2 T x is not conducive to impedance matching and the absorption of EMW. Considering the low permittivity and mesoporous structure of MOF, in this work, Co/La-MOF were in situ growth on the surfaces of Ti 3 C 2 T x by a facile co-solvothermal method. The obtained Co/La-MOF anchored on Ti 3 C 2 T x (Co/La-MOF/Ti 3 C 2 T x) composite exhibits low density with excellent EMW absorption performance. Co/La-MOF/Ti 3 C 2 T x -2 (Co2+/La3+ mass ratio of 16:3) shows the minimum reflection loss of − 44.15 dB at 4.00 GHz with the effective absorption bandwidth of 3.67 GHz in the frequency range of 14.03–17.70 GHz under 1.3 mm. In addition, the electromagnetic absorption mechanism of Co/La-MOF/Ti 3 C 2 T x was also investigated. It provides an effective strategy for the preparation of a novel absorber with high EMW absorbing performance. • Two-dimensional Ti 3 C 2 T x MXene and Co/La-MOF with porous structure were synthesized by in-situ growth method. • Co/La-MOF/Ti 3 C 2 T x exhibits an excellent electromagnetic absorption performance. • The RL min of Co/La-MOF/Ti 3 C 2 T x is − 44.15 dB at 4.00 GHz under 4.5 mm, the EAB is 3.67 GHz under 1.3 mm. • EMW absorption performance of samples can be regulated by adjusting the Co2+/La3+ mass ratio. [ABSTRACT FROM AUTHOR]

Polyaniline (PANI)-coated Y 3 Fe 5 O 12 (YIG)/CoFe 2 O 4 (CFO) hybrid composites were synthesized via sol-gel and oxidative polymerization methods to achieve advanced microwave absorption properties. The structural, morphological, magnetic, and microwave absorption characteristics of the resulting samples were analyzed by performing X-ray diffraction (XRD), scanning electron microscopy (SEM), vibration sample magnetometer (VSM), and vector network analyzer (VNA). XRD results revealed that CFO and YIG have cubic crystal structures with Fd3m and Ia3d space symmetry, respectively, with an average crystallite size of 35.3 nm and 42.9 nm. The Ferro/ferrimagnetic signals were detected from the ferrite samples' room temperature magnetic hysteresis loops. The incorporation of PANI and YIG into the composites resulted in a decrease in their magnetic saturation (M s) and coercive field (Hc) values. VNA measurements demonstrated that nearly all samples achieved 90% absorption (≤−10 dB) of incident electromagnetic waves throughout the X -band frequency range. The minimum reflection loss (RL min) value reaches − 47.34 dB at 8.14 GHz, with an effective bandwidth of 4.00 GHz, covering the entire X -band and beyond. These impressive absorption characteristics suggest that the manufactured composites possess potential as viable candidates for defense applications conducted at X -band frequency. [Display omitted] • PANI/[YIG x /CFO 1−x ] hybrid composites were synthesized by in-situ polymerization of aniline followed by the sol-gel route. • All manufactured samples, except PYC06, absorb 90% of incident EMW through X-band frequency. • The RL min value is found as − 47.34 dB at 8.14 GHz with effective bandwidth of 4.00 GHz (entire X-band) for PYC02 sample [ABSTRACT FROM AUTHOR]