Wider Absorption Frequency Research Articles

Core/shell PA6 @ Fe3O4 nanofibers: Magnetic and shielding behavior

One of the main challenges in the reduction of the electromagnetic wave is to develop lightweight absorber material with a wide absorption frequency. Hence, developing shielding materials that could shield electromagnetic radiation to prevent interference is highly desired for protection. The combination between the unique properties of polyamide (PA6) with free surfactant magnetite nanoparticle as core/shell nanofibers (PA6 @ Fe3O4) provides a promising low-cost, environmentally-friendly and electromagnetic shielding properties. Free surfactant magnetite nanoparticles (39 ± 3.5 nm average size) were prepared by the co-precipitation process and incorporated directly into the polyamide solution before the electrospinning technique. The mean average size of the prepared magnetite nanoparticles is compared based on X-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscopy (SEM). The morphology, thermal stability and magnetic behavior of the resultant magnetite nanofibers (150 ± 25 nm average size) were investigated using high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM), respectively. Shielding effectiveness for magnetite polyamide core/shell nanofibers was measured at frequency 30 MHz–1.5 GHz. The results showed that core/shell nanofibers provide not only well-dispersed magnetite nanoparticles in the polyamide matrix but also controllable sized nanofibers with high magnetization. In addition, even with low magnetite loading of 1.7%, the fabricated nanofiber shows high thermal stability with good performance as electromagnetic shielding nanofiber. Therefore, magnetite polyamide core/shell nanofiber could be considered as a promising material for shielding application.

Carbon fiber enhanced mechanical and electromagnetic absorption properties of magnetic graphene-based film

Graphene-based films have attracted much attention as possible candidates for lightweight, wide absorption frequency, high thermal stability, and mechanically strong electromagnetic (EM) absorbers. In this study, colloidal solutions of carbon fiber (CF), Fe3O4 nanoparticles (FeNPs), and reduced graphene oxide (rGO) were used for synthesizing composite films that were first cast and then gradually heated in vacuum for thermal reduction. Compared with FeNPs/rGO film, the as-prepared CF/FeNPs/rGO film with 10 wt% CF exhibited 125% and 100% enhancement in tensile strength and EM interference shielding efficiency, respectively. A minimum reflection loss of −22.18 dB at 10.64 GHz with a matching thickness of 2.0 mm has been attained in the composite containing 50 wt% loading in the wax matrix, and the effective absorption bandwidth with reflection loss values less than −10 dB covered 9.2–12.32 GHz. The results indicated that CF can be considered as promising filler for improving the mechanical properties and microwave absorption capabilities of magnetic graphene-based system and the magnetic graphene-based composites may be used as high-performance EM absorbing materials.

Facile synthesis of Fe3O4/PANI rod/rGO nanocomposites with giant microwave absorption bandwidth

The Fe3O4/PANI rod/rGO nanocomposites were prepared by a new synthesis process, and their microwave absorbing properties were further evaluated. Taking advantage of the synergistic effects of the different components in the nanocomposites and the merits of the proposed synthesis strategies, the Fe3O4/PANI rod/rGO nanocomposites showed excellent microwave absorption performance, especially for obtaining giant absorption bandwidth (ca. 14.6 GHz, <− 10 dB). The work does not only confirm the formation of Fe3O4/PANI rod/rGO nanocomposites with wide absorption frequency range, strong absorption property and lightweight, but also provide a new synthesis process of electromagnetic wave absorbents for large-scale production.

Double peaks of the permeability spectra of obliquely sputtered CoFeB amorphous films

Without applying an in situ magnetic field, soft magnetic Co40Fe40B20 films were successfully deposited onto rotating silicon substrates using the oblique sputtering technique. Different thicknesses could be achieved by controlling the sputtering time. The corresponding static and dynamic electromagnetic properties were then systematically investigated. Interestingly, as the thickness increased from approximately 50 nm to 250 nm, the imaginary part of the permeability spectra of CoFeB films changed from a single peak to double peaks and then to a broad single peak. Ferromagnetic resonance (FMR), crystalline structure and cross-section SEM analyses evidenced that the double peaks of the permeability spectra are attributed to double anisotropies and anisotropic diffusion. The overlapping double FMR peaks provide a wide absorption frequency band over 2 GHz, which is critical for the design of an electromagnetic interference suppressor.

Optimizing the Electromagnetic Wave Absorption Performances of Designed Co3Fe7@C Yolk-Shell Structures.

Due to the increasing demand for military and commercial applications, magnetic metal-based core@shell nanostructures have attracted extensive attention in the field of electromagnetic wave (EMW) absorption materials. To further improve the overall performance, herein, an effective strategy is designed to fabricate Co3Fe7@C yolk-shell structures by using (Co0.9Fe0.1)Fe2O4@phenolic resin core@shell structures as precursors. The structure parameters, including the size of the CoFe alloy cores, the thickness of the carbon shell, and the void between the core and the shell, can be tailored by controlling the reaction conditions. It is demonstrated that the EMW absorption properties of the as-prepared Co3Fe7@C yolk-shell structures are closely related to their structure parameters. The optimized Co3Fe7@C yolk-shell structure shows excellent EMW absorption performance, the strongest reflection loss (RL) is up to -35.3 dB at 9.1 GHz with the matching thickness of 2.0 mm, and the effective bandwidth (RL < -10 dB) can reach 8.4 GHz (9.6-18 GHz) with a thickness of only 1.5 mm. It is revealed that the excellent performances stem from the unique yolk-shell structure as well as the complementarities and synergies between the dielectric loss and the magnetic loss. By rational designing, the magnetic metal alloy@carbon yolk-shell structures will be convinced to have the potential as novel high-efficiency EMW absorption materials with lightweight, low thickness, wide absorption frequency, high stability, and strong absorption characteristics.

Porous materials for sound absorption

Abstract With the rapid urbanization and fast growth of transportation, noise pollution has become one of the most serious environmental problems in front of the people worldwide, it usually causes various disorders and greatly affects the work efficiency and living standards of human beings. Reducing noise by using sound absorption materials is an important approach to lessen the harm of noise pollution. As the most abundantly used materials, porous materials combine the properties of lightweight, wide absorption frequency range and highly sound absorption ability, and they hold great potential in the field of sound absorption. In this review, the recent progress in the design and fabrication of porous sound absorption materials is summarized and highlighted. This review covers the introduction of the sound absorption mechanism and evolution of prediction models for porous sound absorption materials, and the research and development of the design concepts and fabrication of sound absorption foams and fibrous sound absorption materials. The review concludes with some perspectives and outlook for the porous sound absorption materials.

Metasurface with multi-sized structure for multi-band coherent perfect absorption.

We demonstrate that multi-band coherent perfect absorption can be achieved at infrared frequencies by a metasurface in which four-sized columnar metal patches are separated by a dielectric layer in a unit cell. The absorption bandwidth is enhanced by three times compared with single-band absorption while high absorbance is maintained. The coherent perfect absorption is polarization-independent and can be independently modulated at each resonant frequency by tuning the phase difference of two coherent incident beams. Moreover, the resonant frequency is sensitive to the radius of the columnar patch, and thus a wide coherent perfect absorption frequency range can be obtained by adjusting the radius. Through optimizing the structural parameters, nearly perfect absorption at oblique incidence for both TE and TM polarizations are achieved. The optimized metasurface can be used as a beamsplitter at oblique incidence.

Progress on microwave absorption materials with core-shell structure

Microwave absorber is a kind of functional material, which can absorb electromagnetic (EM) wave effectively and then convert EM energy into thermal energy or make EM wave dissipate by interference. The researches of microwave absorbers are important to satisfy the need of electromagnetic interference in daily life and industrial production, also meet the application requirements of stealth technology in military. Nowadays, the rapid increase in the use of telecommunications equipment, digital systems, and fast processors result in the increasing demand for the development of novel high-efficient microwave absorbers with light weight, thin thickness, wide absorption frequency, and strong absorption characteristics. The structures of microwave absorber are found closely related to the absorption properties. In recent years, many research institutions including our research group, found that the core-shell structure has good absorption performance. The core-shell structured nanocomposites, which combined functionalities of cores and shells, show great potential for significant effect on broadening the absorption spectrum and increasing the absorption intensity because of the complex impedance material matching, interface polarization and multi structure interface scattering. For example, the combination of magnetic materials (e.g., Fe3O4, Co, Ni) and dielectric materials (e.g., TiO2, SnO2, carbon nanotubes) in one entity may take advantages of both the magnetic and dielectric materials, which then can be used as high-performance microwave absorbers. It is well known that Fe3O4, which have been widely used as microwave absorbers because of low cost and strong absorption characteristics usually suffer from ease of oxidation at high-tempera- ture and relatively narrow absorption frequency bandwidth at applied frequency range. While, the magnetic nanoparticles encapsulated within carbon-nanotube composites and Fe3O4/TiO2 core/shell nanotubes were found with lower reflection loss and wider absorption frequency range than single-component absorbers. Meanwhile, remarkable progress has been made in the study of the absorbing mechanism of core-shell structure absorbing materials, which is a great contribution to the design of new structures to meet the new demands of absorbing materials. For example, the particle shapes and grain sizes of magnetic absorbents are of importance for high performance microwave absorbing materials, which are well known. However, research into the relationships among microstructure, electromagnetic property, and microwave absorption performance is rarely reported, especially from the influence of microcosmic magnetism distribution on microwave absorption performance is still lacking previously. While, based on the micro-magnetic investigation via electron holography and Lorentz microscopy, the micromagnetic analysis of the absorber provides a series of direct evidences regarding the effect of grain size on the microcosmic magnetic property, which was important for the further comprehension of the microwave absorption mechanism and new insight into the microstructure design strategy. Other researches, which focus on the influence of cores or shells to absorption performance, are also meaningful to absorption mechanism explanation. The development of science and technology has never stopped the demand for high performance microwave absorbing materials. It is still a difficult but meaningful task for absorbers practical applications to design microwave absorption materials with minimal coating thickness, even light weight, ultra-wide bandwidth, stronger absorption and higher heat-resistance characteristics

Direct Growth of Edge‐Rich Graphene with Tunable Dielectric Properties in Porous Si3N4 Ceramic for Broadband High‐Performance Microwave Absorption

AbstractHigh‐performance graphene microwave absorption materials are highly desirable in daily life and some extreme situations. A simple technique for the direct growth of graphene as absorption fillers in wave‐transmitting matrices is of paramount importance to bring it to real‐world application. Herein, a simple chemical vapor deposition (CVD) route for the direct growth of edge‐rich graphene (ERG) with tailored structures and tunable dielectric properties in porous Si3N4 ceramics using only methyl alcohol (CH3OH) as precursor is reported. The large O/C atomic ratio of CH3OH helps to build a mild oxidizing atmosphere and leads to a unique structure featuring open graphite nanosteps and freestanding nanoplanes, endowing the ERG/Si3N4 hybrid with an appropriate balance between good impedance matching and strong loss capacity. Accordingly, the prepared materials exhibit superior electromagnetic wave absorption, far surpassing that of traditional CVD graphene and reduced graphene oxide‐based materials, achieving an effective absorption bandwidth of 4.2 GHz covering the entire X band, with a thickness of 3.75 mm and a negligibly low loading content of absorbents. The results provide new insights for developing novel microwave absorption materials with strong reflection loss and wide absorption frequency range.

Enhanced microwave absorption properties and mechanism of core/shell structured magnetic nanoparticles/carbon-based nanohybrids

An efficient scheme was designed to selectively synthesize different categories of core/shell structured magnetic nanoparticles/carbon-based nanohybrids such as Fe3O4/C and Fe/helical carbon nanotubes (HCNTs) through the decomposition of acetylene directly over Fe2O3 nanotubes by controlling the pyrolysis temperature. The measured electromagnetic parameters indicated that the Fe/HCNT nanohybrids exhibited enhanced microwave absorption properties, which may be related to their special structures. The optimum reflection loss (RL) could reach −47.1dB at 17.39GHz with a matching thickness of 1.39mm. The absorption bandwidth with the RL values below −20dB was up to 11.59GHz. Moreover, based on the obtained results, the possible enhanced EM absorption mechanisms were also discussed in detail. The results show excellent microwave absorption materials that are lightweight, have strong absorption and a wide absorption frequency band may be realized in these nanohybrids.

Investigation of FeCo–Ti–O nanogranular films with tunable permeability spectrum

A series of soft magnetic nanogranular FeCo–Ti–O films with different Ti contents were fabricated on Si substrates by co-sputtering. By adjusting the Ti content, it appears that the imaginary part of the permeability spectra of FeCo–Ti–O films changes from a single peak to double peaks then to a single peak. Frequency conversion ferromagnetic resonance (FMR) analysis evidences that double FMR peaks can be found in all three films, which were attributed to local anisotropy or two magnetic phases embedded in amorphous TiOx matrix. Structural and temperature dependent resistivity analysis support such three component microstructure. The overlapping double FMR peaks provide a wide absorption frequency band over 3 GHz, which is critical for the design of electromagnetic interference suppressor.

Synthesis of lightweight, hierarchical cabbage-like composites as superior electromagnetic wave absorbent

Three-dimensional (3D) hierarchical cabbage-like carbonaceous materials (Fe/CCMs-X, X means treating temperature) have been successfully prepared employing combinatorial processes of cobalt-assisted hydrothermal carbonization (HTC) of furfural and subsequent iron salt impregnation and thermal treatment. This new absorbent was characterized using powder X-ray diffraction (XRD), N2 adsorption–desorption isotherms, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM) techniques. The maximum reflection loss (RL) of Fe/CCMs-500 reached −22.9dB, and the effective absorption bandwidth (RL⩽−10dB) was 4.32GHz (7.76–9.84GHz and 11.20–13.44GHz) corresponding to an absorber thickness of 2.5mm, a low loading amount of iron (6.83%) component and high carbon content (69.8%), clearly demonstrating its wide absorption frequency range and strong absorption ability. It is thus believed that the newly synthesized Fe/CCMs-500 can serve as light-weight electromagnetic wave absorbent and can be potentially used in practice.

Hierarchical composites of polyaniline nanorod arrays covalently-grafted on the surfaces of graphene@Fe3O4@C with high microwave absorption performance

Abstract Two kinds of hierarchical structures of graphene@Fe 3 O 4 @C@PANI (polyaniline) nanorod arrays were prepared by covalently and noncovalently grafting PANI nanorod arrays to the surface of graphene@Fe 3 O 4 @C, respectively. The measured electromagnetic parameters show that the bonding form between PANI nanorod arrays and graphene@Fe 3 O 4 @C have significantly effect on microwave absorption properties of graphene@Fe 3 O 4 @C@PANI nanorod arrays hierarchical structures, and the formation of covalent bond between PANI nanorod arrays and graphene@Fe 3 O 4 @C in hierarchical structures exhibits significantly enhanced microwave absorption performance. The maximum reflection loss is up to −44.2 dB at 11.4 GHz and the absorption bandwidth with a reflection loss below −10 dB ranges from 9.7 to 15.5 GHz with a thickness of 3 mm. Therefore, the high microwave absorption performance with lightweight and wide absorption frequency band can be realized by fabricating graphene-based hierarchical structures using covalent bond interaction.

Stochastic Resonance in Graphene Bilayer Optical Nanoreceivers

Graphene, a 2-D sheet of carbon atoms, is believed to have diverse application areas ranging from medicine to communications. A novel application is using graphene as a photodetector in optical communications due to its superior optical and electrical properties such as wide and tunable absorption frequency range and high electron mobility. Noise, which is especially significant in nanoscale communications, is mostly seen as an adversary. Stochastic resonance (SR) is the performance enhancement of a system due to incorporation of noise. It is shown that the excess noise in nanocommunications can be used to improve the performance of a graphene bilayer photodetector system with hard threshold decoder, when received signals are subthreshold. SR arises due to the nonlinear nature of the hard decoder. First, the SR effect due to the background ambient noise and intentional light noise is analyzed. An approximate inverse signal-to-noise ratio expression is derived, which maximizes the mutual information. The effect of frequency on the mutual information is also investigated, and it is shown that the higher frequencies are more preferable for noise limited regimes. Later, the case with the intentional noise added to the top gate is investigated. It is shown that significant mutual information improvements are achieved for subthreshold signals, due to the multiplicative stochastic terms arising from the nonlinear graphene bilayer characteristics, i.e., the exponential dependence of photocurrent on the gate voltages. All the analytical results are verified with extensive simulations.

Synthesis and Enhanced Electromagnetic Wave Absorption Properties of Fe3O4@ZnO Mesoporous Spheres

ABSTRACTMesoporous Fe3O4 nanoparticles coated with ZnO nanocrystals were successfully synthesized by a simple solution method at low temperature. The transmission electron microscopy analysis indicates that the mesoporous Fe3O4 nanoparticles are monodispersed with a mean diameter of 160 nm and the thickness of ZnO layer is 15 nm approximately. The porosity of the products was further substantiated by the nitrogen (N2) sorption measurement. The N2 adsorption-desorption isotherm curve can be identified as type IV, which is a characteristic of mesopores. Electromagnetic (EM) wave absorption properties of the as-prepared Fe3O4@ZnO mesoporous spheres-wax composites were investigated at a room temperature in the frequency range of 0.5∼18 GHz. Interestingly, the Fe3O4@ZnO mesoporous spheres exhibit an enhanced EM wave absorption due to the mesoporous structure. The multiple absorbing mechanisms result from the interface polarization induced by the special core/shell and mesoporous structures as well as dipole polarization of both Fe3O4 and ZnO. The results demonstrate that the Fe3O4@ZnO mesoporous spheres are attractive candidates for a new kind of EM wave absorption materials with wide absorption frequency band.

Quaternary Nanocomposites Consisting of Graphene, Fe3O4@Fe Core@Shell, and ZnO Nanoparticles: Synthesis and Excellent Electromagnetic Absorption Properties

This paper presents for the first time a successful synthesis of quaternary nanocomposites consisting of graphene, Fe(3)O(4)@Fe core/shell nanopariticles, and ZnO nanoparticles. Transmission electron microscopy measurements show that the diameter of the Fe(3)O(4)@Fe core/shell nanoparitcles is about 18 nm, the Fe(3)O(4) shell's thickness is about 5 nm, and the diameter of ZnO nanoparticles is in range of 2-10 nm. The measured electromagnetic parameters show that the absorption bandwidth with reflection loss less than -20 dB is up to 7.3 GHz, and in the band range more than 99% of electromagnetic wave energy is attenuated. Moreover, the addition amount of the nanocomposites in the matrix is only 20 wt %. Therefore, the excellent electromagnetic absorption properties with lightweight and wide absorption frequency band are realized by the nanocomposites.

Absorbing Properties of Composite Material Plates of Multi-Layer Absorbing Structure

Microwave absorbing material is currently being more and more widely applied in the world. However, conventional absorbent coating material cannot fulfill the complex current requirements of science and technology to have a wide absorption frequency band, and high absorption. This paper describes composite material plates with a multi-layer absorbing structure designed according to impedance-matching and attenuation principles, producing two- and three-layer absorbing structures. Twelve samples were made, containing graphite powder and manganese dioxide at varying concentrations. The results show that in the frequency range 8-18 GHz, the peak absorption of double-layer samples is -12.3dB, the effective bandwidth (R &lt; -10 dB) is 1.8GHz. The absorption peak of three-layer samples is -18 dB, and the effective bandwidth (R &lt; -10 dB) is 8GHz. The findings of this research are useful in improving the absorption bandwidth of absorbing material.