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To achieve highly efficient electromagnetic wave absorber, elaborately designing magnetic–dielectric Co@TiO2 microspheres with core–shell configuration are successfully constructed through a facile sequential process of liquid phase reduction–sol–gel–annealing. Owing to the core–shell configuration and the synergistic effect among magnetic and dielectric components, the annealed sample shows outstanding electromagnetic wave absorption (EMA) in X and Ku band. Impressively, a maximum reflection loss (RLmax) is reached –56.6 dB at a coating thickness of 2.3 mm with corresponding effective absorption bandwidth (EAB10) of 7.2 GHz (including 65% of Ku band and 82.5% of X band), much stronger than those of as-prepared Co (EAB10 of 1.6 GHz, RLmax of 14.6 dB) and pristine Co@TiO2 (EAB10 of 2.9 GHz, RLmax of 16.3 dB). An EAB10 covering completely the whole X and Ku band could be obtained by controlling the thickness only from 2.0 mm to 2.5 mm. The composites have both outstanding RL and wide EAB10 with the thin coating thickness, reinforcing that fabricating core–shell configuration composites is an efficient strategy to boost the EMA efficiency.

Designing and preparing hollow nanomaterials is one of the most feasible ways to obtain the high-performance electromagnetic wave absorber. To this end, Metal–organic frameworks (MOFs), featuring regular crystalline structures with coordinated metal nodes and organic linkers, have won the widespread attention. Here, the recent progress in the study of MOFs-derived hollow materials for electromagnetic wave absorption are summarized and discussed. Some remarkable examples in the synthesis of hollow structures from MOFs precursors are illustrated in terms of the preparation methods and structural architectures. Thereafter, their characteristics and advantages as electromagnetic wave absorber are analyzed and demonstrated. Finally, it summarizes the current achievements, limitations, and urgent challenges, and provides some views on potential solutions and possible future trends.

High-entropy alloy/polypyrrole (HEA/PPy) composites were synthesized by magnetic stirring at room temperature. The crystal structures, surface morphologies and electromagnetic parameters were analysed. The experimental results show that the composites with 12 ml PPy content present excellent microwave absorbing properties due to the interface loss and good impedance matching. The minimum reflection loss is − 45.28 dB, which is achieved when the thickness is 2.40 mm, and the effective bandwidth is 6.64 GHz. The HEA/PPy composites develop high-efficiency HEA-based electromagnetic wave absorber and have promising for application.

With the development of electronic communication technology, the issues of electromagnetic (EM) wave pollution have become increasingly prominent, and the requirements for EM wave absorbing materia...

Nanostructured microwave absorbing materials attract researchers because of their ability to combat electromagnetic (EM) pollution generated by high-speed electronic gadgets without interrupting ga...

A novel electromagnetic wave absorber of three-dimensional carbon networks decorated with CoFe2O4 nanoparticles (3DC/CoFe2O4) was prepared through a simple freeze-drying method followed by a high-t...

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. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00646-y., 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. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00646-y.

Ellipsoidal Fe3O4 @ C nanoparticles decorated fluffy structured graphene nanocomposites were synthesized. The effect of the magnetic nanoparticle content on the microwave absorption properties was studied. As electromagnetic wave absorber, we researched the electromagnetic absorption properties of the composites that were composed of the prepared nanocomposites and paraffin with a filler loading of 80 wt% paraffin. The results showed that the nanocomposites with suitable magnetic nanoparticle showed a maximum reflection loss of − 55.02 dB at 14.8 GHz with a coating thickness of 1.5 mm; and the bandwidth less than − 10 dB reached 5.44 GHz. The microwave absorption mechanism of the ellipsoidal Fe3O4 @ C nanoparticles decorated fluffy structured graphene nanocomposites mainly came from the effect of the fluffy structure, multiple reflections, interfacial polarization, magnetic loss and dielectric loss.

A new broadband electromagnetic wave absorber based on a periodic surface and a method to increase its absorption bandwidth is proposed. The proposed absorber structure shows broadband characteristics, and its bandwidth is improved by generating additional resonances through a reasonable approach. To provide an understanding of the logical design procedure, an analytical method to determine the sheet resistance and new equivalent circuit models for analysing the impedance are both presented. From the analysis, it is shown that the exact range of the sheet resistance corresponding to the desired absorption level can be efficiently estimated for the resonance of the structure. For the verification of this approach to obtain an efficient design, as well as the functionality of both the absorber and the proposed method, experimental results are demonstrated along with analytical and computational results. The final measured results using the proposed method show a broadband reflectivity response, with a fractional bandwidth of approximately 93% below −10 dB and a bandwidth increase of 17%.

We theoretically investigate a circuit analog approach to integrate graphene and metamaterial in electromagnetic wave absorber design. In multilayer graphene-metamaterial (GM) absorbers, ultrathin metamaterial elements are theoretically modeled as equivalent loads which attached to the junctions between two transmission lines. Combining with the benefits of tunable chemical potential in graphene, an optimized GM absorber is proposed as a proof of the circuit method. Numerical simulation results demonstrate the effectiveness of the circuit analytical model. The operating frequency of the GM absorber can be varied in terahertz frequency, indicating the potential applications of the GM absorber in sensors, modulators, and filters.

This paper presents a robust design approach that not only optimizes the absorption efficiency of an electromagnetic wave absorber over a wide bandwidth, but also reduces the sensitivity of the optimized performance to a number of hard-to-control variables. The optimizable object is a planar multilayer electromagnetic absorber. The important design variables are identified, and the influence of each variable on the performance is analyzed. A robust design of the absorber is realized by employing the signal-to-noise ratio of the absorption efficiency.

This paper proposes a method of designing EM absorber panels under oblique incident waves. TM and TE wave reflection characteristics of the absorber panel show its anisotropy under oblique incidence. By using the wire array sheet proposed this paper, TM and TE reflection coefficients in oblique incidence can be matched at almost the same frequency range.

A wide-band ferrite fin electromagnetic wave absorber panel for a precast curtain wall has been developed for multi-pass interference reduction in urban communication systems. The ferrite fin structure is designed to obtain a wide-band characteristic from the parameter survey of the fin structure. The characteristics are measured using mock-ups of the precast curtain wall with a time-domain method. Results indicate that the proposed absorber panel suppresses reflection < -14 dB in the frequency band 88.6 - 916.6 MHz for the incident angle of 30 degrees and 80.0 - 987.4 MHz for that of 60 degrees. The absorber panel can be applied to the TV ghost problem and other communication systems in both VHF and UHF bands.

In this paper, a complex nonstandard finite-difference time-domain (CNS-FDTD) method is proposed in order to simulate wave propagation in lossy media. To clarify the characteristics of the method, expressions for the numerical propagation constant and the stability condition are derived. It is found that the CNS-FDTD method is much more accurate and stable than the conventional finite-difference time-domain (FDTD) method. The method is applied to the analysis of a fin ferrite electromagnetic wave absorber with a periodic structure., application/pdf

Mg–Ni–Zn ferrites powders with various compositions were synthesized by the combustion reaction of Fe 2 O 3 + x MgO+ y NiO+(1− x − y )ZnO+FeMg x Ni y Zn 1− x − y Fe 2 O 4 in order to develop a high-performance electromagnetic wave absorber in the VHF/UHF region. The reaction mechanism includes the gas–solid reaction among the iron (Fe) and various oxides such as NiO, ZnO, MgO. A neutron diffraction analysis revealed that the final compositions are Mg 0.5 Ni 0.05 Zn 0.52 Fe 2 O 4 and Mg 0.4 Ni 0.21 Zn 0.39 Fe 2 O 4 . The lattice parameters are a =0.839379 and 0.839355 nm, respectively ( χ 2 =3.14 0.5 Ni 0.05 Zn 0.52 Fe 2 O 4 amount to 5318 A/m, 10.18, 0.81 Wb/m 2 kg and 0.015 m 3 /kg, respectively. Similar results for Mg 0.4 Ni 0.21 Zn 0.39 Fe 2 O 4 are 7802 A/m, 14.97, 1.43 Wb/m 2 kg and 0.018 m 3 /kg, respectively.

The purpose of this paper is to demonstrate the electromagnetic wave absorption characteristics of powder-type magnetic wood by changing the mixing ratios for the Mn-Zn ferrite and Ni-Zn ferrite powder. The results show that the matching frequency of the electromagnetic wave absorption characteristics can be controlled by changing the mixing ratios of the magnetic materials and the thickness of the board. We obtained electromagnetic wave absorption of close to 20 dB over the 2.5 GHz-6.2 GHz frequency range. The powder-type magnetic wood boards used in these experiments satisfy JIS standards for wood surface materials in terms of bending strength and deflection. The results from our studies can be used to design indoor powder-type magnetic wood wave absorbers for a specified absorption frequency.

At a bearing manufacturing plant, a large quantity of grinding sludge is discharged from finish machining process. The microstructure of this sludge is a fiber form which entangles naturally. Raw sludge is not an electromagnetic wave absorber because of its conductivity. The sludge was therefore ground into minute particles by a mechanical alloying method (MA). An electromagnetic wave absorber was then produced using MA-treated bearing grinding sludge for magnetic loss factor. These electromagnetic wave absorbers had practical efficiency at Blue Tooth frequency (2.45 GHz) and ETC frequency (5.8 GHz).

Ni-Zn ferrite films 0.2-1.2 μm in thickness were prepared by spraying a reaction solution of FeCl2(+FeCl3)+NiCl2+ZnCl2 (pH = 6.95) and an oxidizing solution of NaNO2 + CH3COONH4 (+NH3) simultaneously onto spinning glass substrates at a substrate temperature of 90°C. Films with a thickness of 0.48 μm deposited by the conventional spin-spray method using only Fe2+ as iron ions exhibited a high permeability μ' of 42 and a high magnetic resonance frequency fr of 650 MHz. This was 5 times as high as the value for Ni-Zn ferrite bulk. Film plated by adding NH3 to an oxidizing solution and film deposited by using a mixture of Fe3+(10%) and Fe2+(90%) as iron ions exhibited higher fr values of 900 MHz and 1.2 GHz, respectively. Since not only the real part μ' but also the imaginary part μ'' had large values of about 30 at 1 GHz, the films prepared in this study will be applicable to rf inductors as well as wave absorbers for suppressing EMI in the quasi-microwave range exceeding 1 GHz.

No detailed analysis has been available on the return loss characteristics of a pyramidal electromagnetic wave absorber. Therefore, an approximate analysis method for the pyramidal absorber has not been established in a rigorous sense. In this paper, the return loss characteristics for the normal incident on the pyramidal absorber are derived by the numerical simulation based on the spatial network method. Also, as an approximate method for the wave absorber that can approximate the obtained results well, a method called the synthesized capacitance model is proposed. By comparison of the numerical results by the two methods, it is found that the approximate results by the synthesized capacitance model provide more accurate results than those by the previous approximate models. Further, by means of the synthesized capacitance model for the normal incidence, the oblique incidence characteristics of the TE wave were computed and the results agreed well with the measured data.

A design chart for the fabrication of an electromagnetic wave absorber was constructed. The design chart consists of the matching boundaries, which enclose the complex permeability values satisfying |/spl Gamma/|/spl les/0.1. The area inside of the boundary represents over 20 dB attenuation. The secant method was employed to compute the matching boundary values corresponding to 20 dB attenuation. In addition to the matching boundary which is determined by the theoretical equations, several restrictions due to the fabrication process were examined. Based on the study on the effects of the variance of the thickness and permittivity on the electromagnetic wave absorbing characteristics, a means to exclude such effects was also included in the proposed design method. Among the six variables required to construct the design chart, the effect of /spl epsiv//sub r/' was investigated in the range of 5-30 at 9.45 GHz. The effect of /spl epsiv//sub r/" was not considered. >

A novel ferrite grid electromagnetic wave absorber composed of sintered ferrite is proposed. Based on the condition that the return loss should be above 20 dB at 30 MHz, its wideband characteristics for suppressing reflections compared to a single-layer absorber are demonstrated by computer simulation. Calculating the return loss by varying the geometrical parameters of the ferrite grid, an optimum structure is determined which gives the maximum frequency band. In addition, it is found that the return loss of the grid absorber is impaired by an air gap between the ferrite and conductor. Moreover, the operating characteristics of the grid absorber are demonstrated by experimental models.

Fin electromagnetic wave absorbers are proposed in which the sintered ferrite plates are placed in the direction perpendicular to the electric field of the incident electromagnetic field. By numerical calculations, it is shown that this structure has a broadband reflection suppressing characteristic. The characteristics of the absorbers in terms of the structural parameters of the absorber and ferrite permeability are shown, and it is found that the optimum structure of the absorber for a broadband operation depends on the permeability of the ferrite. Further, by means of the model experiment, the broadband characteristics of the proposed absorber are demonstrated.

Since ferrites are electromagnetic wave absorbing materials of composition-dependent resonance type, useful frequency ranges are typically narrow. In the present study, laminated electromagnetic wave absorbers composed of ferrite-ferrite or ferrite-dielectric layers were constructed to improve electromagnetic wave absorbing properties. When ferrites of different composition and thickness were layered, center frequency of the laminated ferrite could be changed over a range of values lying between the center frequencies of each ferrite. Compared with monolithic ferrites, ferrite-dielectric laminates exhibited broader frequency ranges with 20 dB or more attenuation. >

The effect of substitutional elements (Ti, Sc, Zr, Ti0.5M0.5, Zr0.5M0.5, Sn0.5M0.5 (where M = Co, Ni, Zn, Mn, Mg, Cu)) on the natural resonance frequency of Barium M-type hexagonal ferrite (BaFe12O19) was investigated, with the aim of finding a material suitable for use as a microwave absorber in the GHz range. It was found that the anisotropy field (HA) decreases with increasing amounts of substitutional element, which leads to the natural resonance frequency (fr) and the matching frequency (fm) shifting to lower values. Some Ti0.5M0.5 substituted samples exhibited values of fr within the 1 to 20 GHz range, and the minimum reflection loss (R. L. ) for these samples was found to be less than -20dB. In particular, because of their large values of magnetic loss ((μ") =4.6 and μ" =4.0), the BaFe9(Ti0.5Mn0.5)3O19 and BaFe9.5(Ti0.5Mn0.5)2.5O19 samples had small matching thicknesses (dm) of 0.58mm and 0.53mm, with matching frequencies (fm) of 12.35GHz and 15.75GHz, respectively. Therefore, it may be concluded that Barium M-type ferrite is a candidate for use as a microwave absorber in the GHz range.

The conditions for perfect absorption under oblique incidence in a single-layer homogeneous absorber backed by a perfectly conducting plate are derived in this article. The cases corresponding to the two types of polarization of the incidence-wave, perpendicular polarization (TE) and parallel polarization (TM), are discussed, respectively. Some conclusions and curves are given. © 1993 John Wiley & sons, Inc.

A thin tapered absorber is described that is capable of effecting wide band absorption of electromagnetic waves at oblique incidence. The absorption mechanism for the taper is shown to be inherently wide band and seems not to be constrained by the bandwidth/reflectivity limitations that apply to thin planar materials. Predicted reflectivity data for the tapered absorbing layer are shown.

An electromagnetic wave absorber for a small sized conducting sphere is designed by applying the Newton-Raphson method to the eigenfunction series solution for a coated conducting sphere. The parameters for the perfect absorbing condition are the constitutive parameters and the thickness of coating for a given radius of conducting sphere. The wave absorber designed by this method exhibits a superior absorption performance to that designed using flat plate absorber theory.

Ferrite, a ferromagnetic material in the form of sintered ferrite and rubber ferrite, is used for electromagnetic-wave absorbers. However, there is a certain limit to reducing the thickness of the electromagnetic wave absorber using ferrite. For obtaining thin rubber-ferrite electromagnetic-wave absorbers, carbon is added to them and their electromagnetic-wave absorbing characteristics are examined. The results show that the thickness can be reduced to about 30 percent by adding the order of 1 to 10 percent (volume ratio) of carbon to ferrite. The reduction of the thickness of the absorber also reduces its weight. The mixing of carbon is highly effective in reducing the weight of the absorber, since the specific gravity of carbon is smaller than ferrite. This paper presents the electromagnetic-wave absorption characteristics of carbon-added rubber ferrite.

An electromagnetic wave absorber utilizing ferrite or rubber ferrite composed of ferrite powder and rubber is described. In our investigation, the existence of a matching frequency f/sub m/ and a matching thickness t/sub m/ has been found. The terms f/sub m/ and t/sub m/ mean that the ferrite which is backed with a conducting plate can be a perfect absorber only under the conditions that the frequency of the incident wave is f/sub m/ and that the thickness of the ferrite is t/sub m/.Each ferrite has two matching frequencies f/sub m1/, f/sub m2/, (f/sub m1

A broad band electromagnetic wave absorber in GHz frequency range was newly developed by two-layer construction. Each layer operates as a low-impedance resonator and an impedance transformer. For the low-impedance resonator design, a ferrite/resin mixture incorporated with short metal fibers is used. The electromagnetic wave absorber presented in this paper has a broader operation bandwidth, nearly 50 % in relative bandwidth (bandwidth more than 20 dB absorption/center frequency), than the operation bandwidth for a conventional ferrite absorber. Broadband characteristics are achieved in oblique incidence, up to nearly 45 degrees of incident angle.

A general solution for perfect absorption under normal incidence in a single-layer homogeneous absorber backed by a perfect conductor is derived considering both electric and magnetic losses. Design curves and equations are given for the lowest-order or minimum-thickness solutions, and its possible use in the design and fabrication of practical absorbing materials is also illustrated.