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In this study, flower sphere alumina was synthesized autonomously by hydrothermal and annealing processes. The in situ polymerization of polypyrrole on the surface of alumina at low temperatures based on the principle of component synergy has enabled the construction of a core–shell structure for Al2O3@ppy materials, resulting in excellent electromagnetic wave absorption properties. The effect of the addition of alumina and the morphology of the materials on the microwave absorption properties of Al2O3@ppy composites was also discussed. Various methods are used for the characterization of the material. The Al2O3@ppy composites were effective in matching thicknesses of 2.5 mm with a minimum reflection loss (RL) of − 65.8 dB at a frequency of 11.52 GHz and a maximum effective absorption bandwidth (EAB) of 5.6 GHz at a matched thickness of 2.0 mm. The results show that Al2O3@ppy composites can provide a reference for EMW absorber material research. [ABSTRACT FROM AUTHOR]

For electromagnetic wave-absorbing materials, organic-derived carbon materials and metal sulfides are highly preferred. In this paper, ZnS/C microsphere composites were prepared using calcination and hydrothermal method. The carbon microsphere material derived from d-xylose was used as a substrate, and zinc sulfide was grown on its surface, thus enhancing the interfacial polarization loss of the material. Considering the defects that originate from within the carbon microspheres and the excellent conductive properties, the composite material involved dipole polarization and conduction losses. These loss mechanisms are coordinated with the optimum impedance match obtained by adjusting the addition of carbon microspheres, resulting in the RLmin value of − 44.86 dB and the EABmax of 5.68 GHz for the ZnS/C microsphere composite. [ABSTRACT FROM AUTHOR]

To explore a type of high-performance microwave absorber with lightweight and thin thickness, the flowerlike γ-AlOOH hollow spheres decorated with multi-walled carbon nanotubes (MWCNTs) were fabricated by a facile hydrothermal method. The microscopic morphology characterization showed the γ-AlOOH microspheres consisted of a hollow inner core and a shell made of numerous flakes. The γ-AlOOH/MWCNTs composites exhibited excellent microwave absorption performance with the reflection loss of − 49.8 dB at 11.1 GHz and effective absorption bandwidth of 4.56 GHz (from 13.44 to 18 GHz) at a thickness of 1.5 mm, which covered almost the entire X band. Furthermore, the unique microstructure of γ-AlOOH exerted a considerable effect on the obtained microwave absorption capacity of the composites, leading to interfacial polarization, multiple reflections, and scattering of electromagnetic wave. Meanwhile, the suitable MWCNTs additive amount played a crucial role in the improvement of impedance matching, conduction loss, and dipole polarization, which benefit the performance of microwave absorption. It is expected that the flowerlike hollow spheres structure in our work can provide a method of designing the novel microwave absorbers. [ABSTRACT FROM AUTHOR]

In this study, two MWCNTs@ZnO/NiO composites, TS-A and TS-B, were synthesized through two methods, respectively, and a series of microscopic morphology characterization and electromagnetic test were performed. Microstructure characterization results suggested that TS-A dispersed well with hierarchical and porous structure, while TS-B grew unevenly as a result of tight bound. Electromagnetic tests show that the unique hierarchical and porous structure was key to the superior absorption performance of TS-A over TS-B, and played an important role in optimizing impedance matching and enhancing dielectric loss. The minimum reflection loss of TS-A reached − 46.65 dB at the thickness of 3.3 mm and the frequency of 3.58 GHz, and the EAB reached 3.89 GHz at the thickness of 1.5 mm. The above results indicate that the synthesis of hierarchical and porous structure is one of the effective ways to enhance the electromagnetic wave absorption ability of materials. [ABSTRACT FROM AUTHOR]

A novel Al@reduced graphene oxide (Al@RGO) composite was designed and synthesized by a one-step hydrothermal method. We investigated the effect of the graphene on the microwave absorbing properties and infrared emissivity of composites. The crystal structure, microscopic morphology, infrared emissivity and electromagnetic parameters of the prepared samples were characterized by XRD, FESEM, TEM, XPS, dual band infrared emissometer and vector network analyzer. TEM and SEM show that the thin Al sheet is uniformly wrapped by RGO with a crumpled surface. Functionalized RGO and surface cation-modified Al sheets are tightly compounded through an electrostatic interaction. The oxygen content and defect from RGO as polarization center endows the material with enhanced molecular polarization and dipole polarization effect. The Al sheet is well coated with RGO, enhancing interface polarization and impedance matching. The minimum reflection loss (RL) of optimized Al@RGO composites is − 46.11 dB at 13.68 GHz under the coating thickness of only 2 mm. The bandwidth below − 10 dB can reach 4.88 GHz (11.52–16.4 GHz). Al sheet is a suitable base material for both microwave absorption and infrared stealth. The Al@RGO composites exhibit excellent infrared stealth ability, and their lowest infrared emissivity is 0.62. Thus, Al@RGO composites show potential application for both electromagnetic wave absorption and infrared stealth. [ABSTRACT FROM AUTHOR]

In this work, Al@MWCNTs (multi-walled carbon nanotubes) composites were prepared by a one-step hydrothermal method. The effects of the morphology and mass ratio of Al@MWCNTs on microwave absorption were studied. The Al@MWCNTs were also found to participate in infrared emissivity. A large number of MWCNTs were interconnected and interspersed between Al sheets, forming a conductive network. As the mass ratio of MWCNTs in the composite was increased, the microwave absorption performance became stronger, and the infrared emissivity remained excellent. When the mass ratio of MWCNTs:Al was 3:20, the minimum reflection loss of the composite at 10.88 GHz was − 39.24 dB, and the effective absorption bandwidth below − 10 dB were 3.04 GHz (9.2–12.24 GHz), the matching thickness was 2 mm, and the infrared emissivity was only 0.67. In this paper, Al powder, a composite material with low infrared emissivity, was creatively used to achieve the superior material bifunctional absorption of MWCNTs, providing a novel and effective way to design other excellent bifunctional materials in the future. [ABSTRACT FROM AUTHOR]

SnO/α-FeO@RGO composites were prepared through a solvothermal method. The phase structure, morphology, and electromagnetic (EM)-wave-absorbing properties of the as-prepared samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and vector network analyzer. Results indicated that the remarkable EM wave absorption properties of the samples resulted from the interaction between lamella-structured reduced graphene oxide and semiconductor-heterostructured SnO/α-FeO. The optical reflection loss calculated from the measured complex permittivity and permeability was −44.33 dB at 12.64 GHz. Meanwhile, the Fe/Sn molar ratio in the composites was 6:1, and the coating thickness was 2 mm. The bandwidth below −10 dB was 4.4 GHz (10.80-15.20 GHz). Therefore, SnO/α-FeO@RGO could serve as a high-performance EM-wave-absorbing material. [ABSTRACT FROM AUTHOR]

α-FeO/SnO@polyaniline composites were prepared by combining a hydrothermal reaction and an emulsion polymerization process. The sizes of α-FeO and SnO particles dispersed into PANI were 80-120 and 8 nm, respectively. The structure, morphology, and electromagnetic (EM) parameters were characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and vector network analysis. To achieve the absorption of different EM bands, the EM wave absorption properties of α-FeO/SnO@PANI composites with different stannic oxide content were investigated according to transmission line theory. Polarizations and multiple reflections in the composite absorber play a key role in EM wave absorption. The α-FeO/SnO@PANI composites exhibited high EM absorption capacity and an optimal reflection loss of −50.3 dB at 9.9 GHz with thickness of 2.7 mm. Moreover, the composite could reach an effective absorption bandwidth (below −10 dB) from 7.84 to 12.08 GHz. Thus, the synthesized composites are suitable candidates for highly efficient EM wave absorption in the entire X-band. [ABSTRACT FROM AUTHOR]

In this study, Zn-doped Fe3O4 nanoparticles were successfully synthesized by a facile solvothermal method in the presence of sodium dodecyl sulfate (SDS). The morphology, magnetic properties and electromagnetic wave absorbing properties of these materials were characterized. Results showed that Zn played a significant role in the formation of Zn-doped Fe3O4. With the protection of SDS, highly dispersed Fe3O4 nanoparticles were obtained. The nanoparticle size decreased after Zn doping, and the dispersity deteriorated with increasing Zn doping concentration. Zn-doped Fe3O4 exhibited excellent electromagnetic wave absorbing property, which resulted in magnetic loss and dielectric loss at an appropriate doping concentration. The minimum reflection loss (RL) was approximately dB at 16.9GHz. As the coating layer thickness increased to 4.0mm, the bandwidth was approximately 5.0GHz corresponding to RL below dB, which nearly covered the entire S band (2-4GHz) and C band (4-8GHz). The peak frequency of RL and the number of peaks matched the quarter-wave thickness criteria. It was believed that the Zn-doped Fe3O4 could be a potential electromagnetic wave absorbing material in S and C bands. Zn-doped Fe3O4 nanoparticles were synthesized by a facile solvothermal method. Zn2+ plays a key role in the formation of Zn-doped Fe3O4. The as-synthesized Zn-doped Fe3O4 exhibited excellent electromagnetic wave absorbing property, as the coating layer thickness at 4.0mm, the bandwidth was approximately 5.0GHz corresponding to RL below −10dB, which covered nearly the entire S band (2-4GHz) and C band (4-8GHz). [ABSTRACT FROM AUTHOR]

Zn ferrite/multi-walled carbon nanotubes (Zn ferrite/MWCNTs) composite were prepared by one-pot hydrothermal method. Their crystal structure, morphology, composition, magnetic properties, and electromagnetic-wave (EM-wave) absorption performance were measured by X-ray powder diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, vibrating sample magnetometry, and vector network analysis. Results indicated that Zn ferrite particles were distributed on MWCNTs surface with agglomeration, and MWCNTs crucially affected the magnetic properties of Zn ferrite/MWCNTs composite. Compared with Zn ferrite, Zn ferrite/MWCNTs composite showed low addition amount, low coating thickness, and enhanced EM-wave absorption performance. With 60 wt% addition amount and 1.5 mm coating thickness, the minimum reflection loss of Zn ferrite/MWCNTs composite was −42.6 dB at 12.1 GHz. The enhanced EM-wave absorption performance was mainly ascribed to the increased interfacial polarization and dielectric loss that resulting from the introduction of MWCNTs. The result illustrated that the introduction of MWCNTs into magnetic materials can enable the efficient design of excellent EM-wave absorbers with low addition amount and coating thickness. [ABSTRACT FROM AUTHOR]

The development of heterojunction composite materials with excellent electromagnetic wave absorption performance is emerging as an effective means to address the hazardous electromagnetic waves. Here, two types of Cu 9 S 5 @VO 2 microspheres with different morphologies were designed. The Cu 9 S 5 @VO 2 microspheres were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and vector network analyzer. Results show that the minimum reflection loss (RL min) of unique lamellar-flower Cu 9 S 5 @VO 2 sphere reaches −56.98 dB, and the wide effective absorption bandwidth (EAB) is 6.88 GHz at only 2.5 mm thickness due to the synergistic effect of multiple loss mechanisms. Radar simulated radar cross section (RCS) results show a reduction of 16.56 dBm2. The design engineering of the phase interface on the material surface can functionalize the material surface properties, introduce lattice defects and polarization behavior, and improve the microwave absorption performance of the material. This work enriches the use of copper sulfide-based functional composites in microwave absorption with high-performance microwave absorbers by designing microscopically controllable, simple processes and heterojunction design. The morphology regulation strategy was realized by simple hydrothermal method, and the bi-semiconductor heterojunction Cu 9 S 5 @VO 2 composites with unique morphology, obvious lattice defects and synergistic effects of multi-polarization behavior were finally designed. Lamella-flower-like Cu 9 S 5 @VO 2 microspheres exhibit high-performance electromagnetic wave absorption with broadband and could effectively achieve radar stealth effect. [Display omitted] • The bi-semiconductor heterojunction, lattice defects and multi-polarization behavior were designed. • Cu 9 S 5 @VO 2 composites with different morphologies were prepared to enrich the application of Cu 9 S 5 in microwave absorption. • Cu 9 S 5 @VO 2 microspheres exhibit high-performance electromagnetic wave absorption and could achieve radar stealth effect. [ABSTRACT FROM AUTHOR]

Three Ni/C composites with different morphologies were prepared by changing nickel salt using a hydrothermal method and high-temperature pyrolysis. Results show that material defects, nitrogen doping, heterointerface, conductive network, and magnetic effect optimize impedance matching, resulting in the synergistic effect of conductivity loss, polarization loss, multiple scattering, and magnetic loss. The reflection loss of the sample prepared using nickel nitrate is − 44.2 dB at 11.84 GHz and 2.4 mm thickness, and the effective absorption bandwidth is 5.2 GHz. In addition, radar cross section simulation demonstrates the excellent performance of the material in practical applications. Thus, the sample prepared using nickel nitrate is a candidate material for radar stealth and electromagnetic wave absorption. [Display omitted] • Preparation of Ni/C composites with different morphology by controlling nickel source. • The synergistic effect of dielectric loss and magnetic loss optimizes impedance matching. • The RL min achieved − 44.2 dB and EABmax was 5.84 GHz. • The RCS contribution of Ni/C composites in far field is simulated by CST. [ABSTRACT FROM AUTHOR]

Sheet aluminum powder was used as the substrate and aniline as the polymer monomer, to design novel Al/PANI composites via in-situ polymerization, which exhibited high electromagnetic wave absorption properties and low infrared emissivity. These unique bifunctional composite were systematically characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, IR-2 dual-band emission rate measuring instrument and vector network analyzer. The calculated results showed that the maximum reflection loss value of Al/PANI composite reached −46.09 dB at 14.56 GHz with a film thickness of only 1.0 mm. Meanwhile, the infrared emission rate of the composite was 0.55. The excellent electromagnetic absorption performance may be ascribed to its superior conductivity and unique structure. The merits of as-synthesized composites with high-performance microwave absorbing properties and low infrared emissivity indicate the potential use of Al/PANI composites in the applicable stealth fields. • Al/PANI composites have both microwave absorption performance and low infrared emissivity ability. • Al/PANI composites were prepared by a facile in-situ polymerization method. • The microwave absorption performance and infrared emissivity of the composites can be adjusted by the amount of polyaniline. • The minimum reflection loss of Al/PANI composite achieve −46.09 dB at 14.56 GHz. • The lowest infrared emissivity of Al/PANI composite can reach up to 0.55. [ABSTRACT FROM AUTHOR]