Electromagnetic Absorption Applications Research Articles

Switchable and tunable terahertz metamaterial absorber based on graphene and VO2 resonator with ultra-broadband and multi-band absorption

Vanadium dioxide (VO2) and graphene have been combined to create new design possibilities for high-performance metamaterial devices, which offer an alluring foundation for electromagnetic absorption applications. The structure under investigation, which is based on patterned graphene-vanadium dioxide and metamaterial absorbers, is capable of achieving both broadband and multi-band absorption. Also, the offered structure is tunable and switchable in the proposed wide-band range. We theoretically suggest a switchable and tunable graphene and VO2 resonator-based Broadband and Multi-band terahertz (THz) metamaterial absorber. The proposed absorber can achieve more than 99% absorption while operating in multi-band absorption mode at 2.26, 6.68, and 7.71 THz. Moreover, it can achieve absorption of more than 90% when operating in broadband mode, which has a bandwidth of 8.74 THz within the frequency range of 2.76–11.5 THz. In the 3.12–11.01 THz frequency band, this absorption percentage is 98%. The absorption spectra can be tailored by altering the chemical potential of the graphene layer and the conductivity of VO2. The suggested absorber also has a wide incidence angle insensitivity. As a result, the suggested absorber can be considered a good choice for various THz frequency range applications.

Temperature-dependent dielectric properties of p-n heterojunction diodes based on hydrothermally synthesized ZnO nanostructures

In this study, the effect of coating p-Si substrates with a pure ZnO layer using the hydrothermal reaction method on the dielectric parameters was reported. The studied dielectric properties of the ZnO/p-Si structure include dielectric constant (ε′), dielectric loss (ε″), ac electrical conductivity (σ AC), and real and imaginary electrical modulus (M′, M″). These properties were investigated using experimental capacitance-frequency (C-f) and conductivity-frequency (G-f) measurements in a frequency range of 20 Hz-1 MHz and a temperature range of 300-420 K. Experimental results show that dielectric parameters are strongly frequency- and temperature-dependent. The dielectric constant showed an increase of about 11 times in the investigated temperature range. At the same time, AC electrical conductivity increased with increasing frequency and temperature. In addition, the electrical modulus was examined, and peaks were observed in M″ values. It was observed that the peaks shifted to the high-frequency region with the increase in temperature. The activation energies were also calculated from the conductivity parameters and a decrease was observed in the activation energies as the frequency increased. Regardless of temperature and frequency, the higher dielectric loss of the fabricated diode compared to its dielectric constant can be advantageous for certain heating or electromagnetic absorption applications.

Computational evaluation of absorption characteristics of ceramic-based auxetic materials in X-band frequency range

This research study investigates the absorption capabilities of ceramic-based auxetic metamaterials within the X-band frequency range, emphasising their potential application in stealth technology. Four distinct auxetic topologies have been chosen for this purpose: star, re-entrant, anti-tetrachiral, and missing-rib/cross-chiral while maintaining an equal cross-sectional area for comparison analysis. A computationally efficient homogenisation scheme based on the variational asymptotic method is used to evaluate the effective properties of these auxetics. The absorption spectra are then obtained by evaluating scattering matrices using these effective properties. The influence of auxetics out-of-plane thickness, incidence and polarisation angles on the proposed ceramic absorber’s absorption spectra is evaluated. One of the interesting observations is the identical absorption capabilities of star and missing-rib/cross-chiral geometries despite their distinct architectures. The star and missing-rib/cross-chiral based absorbers achieved a maximum absorption of 99.99% or a minimum reflection loss (RL) of −40 dB with a thickness of 3.50 mm. The RL is less than −10 dB (the standard for an electromagnetic (EM) absorber) for all incidence angles less than 70∘. The findings of this study hold significant potential for the advancement of ceramic-based auxetic metamaterials in EM absorption applications within the aerospace industry.

Conjugate ferrocene polymer derived magnetic Fe/C nanocomposites for electromagnetic absorption application

Coordination bonds are relatively unstable compared to covalent bonds, and common carbon-based absorbing material precursors are bonded in the form of coordination bonds. In this work, we have introduced ferrocene units into conjugated microporous polymers (CMP) in one step by Suzuki reaction. By adjusting the proportion of ferrocene units, a series of magnetic Fe-C nanocomposites (Fe-P-XC) derived from conjugated ferrocene polymers without heteroatom doping (N, S, P, etc.) were formed. The Fe-P-2C composite has good absorption properties with minimum reflection loss at 4.4 GHz (-58.66 dB) and effective absorption bandwidth (EAB) of 6.28 GHz at 2.4 mm (11.72–18 GHz). Compared with the precursor materials formed by coordination bonds, the present work reveals the electromagnetic wave absorption mechanism of carbon-based materials without heteroatom doping through a simple and effective strategy.

Post-consumer plastics/CoxMn3–xO4 spinels derived Co/MnO@carbon nanotube composites towards advanced electromagnetic absorbents

Waste plastics and electromagnetic radiation pollution have been two serious issues that largely affect our environment. How to solve them in a single approach is a social and scientific challenge. In this work, advanced Co/MnO@carbon nanotube composite (Co/MnO@CNTs) absorbents were prepared via pyrolysis-catalysis conversion of face masks as post-consumer plastic waste with multi-scale designed CoxMn3–xO4 spinel pre-catalysts. The (nano)structure (e.g., MnO-carbon and Co-carbon hetero-interface), composition, and graphitic degree of the Co/MnO@CNTs absorbents were facilely controlled by varying the catalytic reaction temperature and the composition of spinel pre-catalysts. By constructing multi-loss mechanisms (e.g., magnetic loss, conductive loss, interface polarization loss, and defects-induced polarization loss), the largest effective absorption bandwidth (EAB) of the Co/MnO@CNTs/wax composites can reach as wide as 5.28 GHz at a thickness of 1.7 mm. When the content of the Co/MnO@CNTs absorbents is 17 wt%, the EAB and minimal reflection loss (RLmin) achieves 5.04 GHz and −38.1 dB, respectively. This work is based on a sustainable and cost-effective feedstock as well as an innovative method for the large-scale production of advanced CNTs-based materials in electromagnetic absorption application.

Hyper-crosslinked Conjugated Microporous Polymers with Increased Micropores Promotes Confining Polymerization for Electromagnetic Absorption Application

Hyper-crosslinked Conjugated Microporous Polymers with Increased Micropores Promotes Confining Polymerization for Electromagnetic Absorption Application

Highly Performant Electromagnetic Absorption at the X Band Based on Co@NCS/Ti3C2Tx Composites

Electromagnetic waves at the X band (8.2-12.4 GHz) play significant roles in military applications such as radar, satellite, and wireless communication. However, within this band range, the developed performance of electromagnetic absorption (EMA) is still unsatisfied, and it is hard to settle the corresponding problems on radar stealth and electromagnetic pollution. Herein, we demonstrate a state-of-the-art EMA property of -82.6 dB at 8.24 GHz with 2.57 mm thickness and 30 wt % paraffin filling ratio. For this purpose, an optimal Co@NCS/Ti3C2Tx composite is prepared by an electrostatic self-assembly approach through compelling Co-loading of nitrogen-doped carbon sheets (Co@NCS) derived from the pyrolysis of ZIF-67 (CoZn) with 2D Ti3C2Tx MXene nanosheets. Experimental results show that the highly efficient EMA performance of this Co@NCS/Ti3C2Tx composite originates from the large surface area for multiple reflection and electromagnetic wave scattering, from abundant defects sites for dipole and interfacial polarization, and from the optimizing impedance matching by the combination of Co magnetic nanoparticles and conductive NCS/Ti3C2Tx composite. These results confirm that the as-fabricated composites possess scientific and practical values for EMA applications at the X band, paving the way for developing highly performant electromagnetic absorbers toward specific microwave bands.

Old molybdenum blue for new application: {Mo 72X 30}/PANI/MWCNTs (X = Fe, V) ternary coaxial cable-like fibers for superior electromagnetic wave absorption

The systematic design of heterointerfaces has been a topic of considerable attention in electromagnetic absorption applications. For the first time, molybdenum blue/polyaniline/multiwalled carbon nanotubes ({Mo₇₂X₃₀}/PANI/MWCNTs, X = Fe, V) ternary coaxial cable-like fibers are systematically designed and synthesized via host–guest electrostatic and synergistic effect and employed as exceptional electromagnetic wave absorbers. The coaxial cable-like structure features an abundance of heterointerfaces between layers, which improves dipole polarization and interface polarization effect, and regulates conductive loss. In addition, the inclusion of polyoxometalates boosts magnetic losses dominated by eddy current losses and improves impedance matching. The optimal {Mo₇₂V₃₀}/PANI/MWCNTs exhibit higher electromagnetic wave absorption (−48.12 dB) at a thinner thickness (2.3 mm). At a thickness of 2.5 mm, {Mo₇₂Fe₃₀}/PANI/MWCNTs exhibit the maximum effective absorption bandwidth (6.16 GHz). In addition to expanding our understanding of the effect of heterointerfaces on electromagnetic absorption, this study demonstrates the potential utilization of polyoxometalate functional molecules in the electromagnetic wave absorption field.

In situ etching by released proton in aniline polymerization to form network VO2 doped polyaniline composites with variable infrared emissivity for electromagnetic absorption application

In situ etching by released proton in aniline polymerization to form network VO2 doped polyaniline composites with variable infrared emissivity for electromagnetic absorption application

Constructing ohmic contact on hollow carbon nanocages to enhance conduction loss enabling high-efficient microwave absorption

Metal organic frameworks (MOFs) derived carbon materials have attracted much attention as hopeful electromagnetic microwave absorbents. However, the poor impedance matching and high filler content severely limited its electromagnetic absorption application. The introduction of hollow structural engineering is beneficial to improving microwave absorption performance. Herein, we designed and constructed Ni-incorporated hollow N-doped carbon nanocages (Ni/NCNs) to reveal interfacial charge transfer in electromagnetic wave attenuation. The hollow carbon structure facilitates impedance matching, highly dispersive Ni nanoparticles not only build a dense magnetic coupling network but also generate a series of Ohmic contact heterogeneous interfaces with hollow NCNs, extremely accelerating the charge transfer and enhancing conduction loss. Thanks to hollow structure, optimized impedance matching, and abundant Ohmic contact heterogeneous interfaces, the Ni50/NCNs exhibit a minimum reflection loss of −57.3 dB. The results demonstrate that Ni50/NCNs composites have great potential to be considered efficient electromagnetic wave materials, and the designed Ohmic contact heterogeneous interfaces pave the way in the study of electromagnetic wave absorption mechanisms.

Reactive polymeric ligand mediated one-pot synthesis of hybrid magnetite nanospheres for enhanced electromagnetic absorption

The facile preparation of magnetite nanostructures with diverse electromagnetic (EM) loss pathways is highly essential for their practical application in EM absorption. In this work, we have synthesized a reactive polymer (polyarylene ether, PAE) containing multiple polar groups, which has been employed as structure-directing agent to enable one-pot fabrication of PAE@Fe3O4 hybrid nanospheres. Systematic characterization demonstrated that the fine morphology, crystal structures, surface charge and magnetic properties of the obtained hybrid nanospheres were highly dependent on the loading content of polymer ligand. Furthermore, thanks to the metal-ligand bonding between Fe3O4 and PAE, several electromagnetic loss pathways, including multiple polarization, improved impedance matching and intrinsic magnetic response, have been synergistically unified in the obtained PAE@Fe3O4 hybrid nanospheres. Consequently, the optimized PAE@Fe3O4 hybrid nanospheres exhibited a maximum reflection loss of −56.7 dB and effective absorption bandwidth of 3.9 GHz, which was respectively enhanced by 41% and 63% compared with pristine Fe3O4 nanospheres. Basically, the current work opens a new way to fabricate high performance magnetite-based EM absorbers that can be easily dispersed in various polymer matrixes, which is of great interest for the development of flexible electromagnetic radiation controlling devices.

High-Density Anisotropy Magnetism Enhanced Microwave Absorption Performance in Ti3C2Tx MXene@Ni Microspheres

Two-dimensional materials, especially the newly emerging MXene, have attracted numerous interests in the fields of energy conversion/storage and electromagnetic shielding/absorption. However, the inherently inevitable aggregation and absence of magnetic loss of MXene considerably limit its electromagnetic absorption application. The introduction of magnetic component and favorable structural engineering are the alternatives to improve the microwave absorption (MA) performance. Herein, we report a spheroidization strategy to assemble double-shell MXene@Ni microspheres, where the commonly lamellar MXene are reshaped into three-dimensional microspheres that provide the substrate for oriented growth of Ni nanospikes. Whereas this structural feature offers massive accessible active surfaces that effectively promote the dielectric loss ability, the introduction of magnetic Ni nanospikes enables the additional magnetic loss capacity. Benefiting from these merits, the synthesized 3D MXene@Ni microspheres exhibit superior MA performance with the minimum reflection loss value of -59.6 dB at an ultrathin thickness (∼1.5 mm) and effective absorption bandwidth of 4.48 GHz. Moreover, the electron holography results reveal that the high-density anisotropy magnetism plays an important role in the improvement of MA performance, which provides an insight for the design of MXene-based materials as high-efficient microwave absorbers.

Core/Shell Structured Ni/Fe3O4 Composites with Enhanced Electromagnetic Absorption Performances

Core/shell structured Ni/Fe3O4 composites with grain sizes of 200–800 nm were synthesized by using a hydrothermal method. The phase structure, morphology, magnetic and electromagnetic absorption properties of the as-prepared samples were characterized by various analysis techniques. Experimental results revealed that spinel Fe3O4 was in situ deposition on the surface of Ni spheres through electrostatic interactions. Moreover, the Ni/Fe3O4 mass ratios had a significant influence on the electromagnetic absorption performances. When the mass ratio of Ni/Fe3O4 was 1:1, the composites reached an outstanding reflection loss (RL) of [Formula: see text]48.06[Formula: see text]dB at 12.96[Formula: see text]GHz with a thin thickness of 1.8[Formula: see text]mm. Meanwhile, the effective absorption bandwidth was 5.36[Formula: see text]GHz (10.72–16.08[Formula: see text]GHz), covering the X and Ku bands. The enhanced electromagnetic absorption performance of core/shell structured Ni/Fe3O4 composites as compared to pure Ni, may be attributed to the multiple interfacial polarization, magnetic exchange coupling resonance and optimal impedance matching. Consequently, core/shell structured Ni/Fe3O4 composites would be promising candidates for a wider range of electromagnetic absorption applications.

Carbon encapsulation of MoS2 nanosheets to tune their interfacial polarization and dielectric properties for electromagnetic absorption applications

Electrical conductivity and interfacial polarization are two crucial factors that affect the electromagnetic absorption (EMA) performance of dielectric semiconductors.

One-dimensional MnO@N-doped carbon nanotubes as robust dielectric loss electromagnetic wave absorbers

Dielectric loss materials exhibit appealing ability for electromagnetic wave attenuation due to their tunable permittivity, favorable stability and light weight. Herein, MnO@N-doped carbon nanotubes with adjustable carbon layer are synthesized by thermal decomposition of pyrrole on the surface of MnO2 nanotubes for electromagnetic absorption application. The morphology, composition, internal defects, conductivity and electromagnetic parameters of the composites are fully investigated. By using ANSYS software to simulate the electric field distribution in the material under the excitation of alternating electromagnetic field, the polarization behavior is analyzed in depth. The combination of MnO and carbon endows the composites with enhanced dielectric loss capacity and better impedance matching. The MnO@N-doped carbon composites achieve an optimal absorption intensity of −62.8 dB at 2.4 mm and a broad effective absorption bandwidth of 5.4 GHz with the thickness of 2.5 mm. The facile synthesis method and the superb EMW absorptivity make the tubular core-shell MnO@N-doped carbon composites a promising EMW absorber, and we believe this study will provide new strategies for designing novel dielectric EMW absorbers in the future.

Rational construction of MXene/Ferrite@C hybrids with improved impedance matching for high-performance electromagnetic absorption applications

Sandwiched MXene/Ferrite@C (Ti3C2Tx/Fe3O4@C) hybrids have been successfully obtained by assembling MXene with Fe3O4@C nanoparticles derived from Fe-MOFs. The MXene/Ferrite@C hybrids achieved an excellent microwave absorption performance with a RLmin of −45.5 dB, an effective absorbing bandwidth of 3.5 GHz and a thin thickness of 1.6 mm. Therefore, the sandwiched MXene/Ferrite@C hybrids are expected to be powerful candidates for high performance electromagnetic microwave absorbers.

A polarization- and angle-insensitive broadband tunable metamaterial absorber using patterned graphene resonators in the terahertz band

The emerging material of graphene has resulted in new options for the design of metamaterial devices with excellent performances, offering an attractive platform for electromagnetic absorption applications. To date, researches on patterned graphene-based metamaterial absorbers (MAs), have focused on achieving broadband absorption while maintaining many excellent properties. Here, we propose a broadband tunable MA with a perfect absorption based on a novel design of the combination of cross- and square-shaped graphene sheets. Numerical simulation results show that the bandwidth of the proposed broadband MA reaches 2.76 THz with the absorptivity greater than 90% for both the transverse electric (TE) and transverse magnetic (TM) modes, which exceeds most of broadband absorption results achieved by MAs in previous studies. A numerical analysis employing the equivalent circuit model for the designed structure is conducted to determine the influence of the structural parameters on the absorptivity and optimize the parameters. Results show that impedance matching is achieved between the input impedance and the free-space impedance at the absorption band. Detailed numerical simulations are conducted to calculate the surface loss density, electric field, and surface currents to obtain an understanding of the high absorption mechanism. Also, the designed MA exhibits excellent properties, such as tunability, polarization independence, incident angle insensitivity and outstanding tolerance to changes in the structural parameters, suggesting that the proposed absorber is a promising candidate for various applications in the terahertz band.

Novel binary cobalt nickel oxide hollowed-out spheres for electromagnetic absorption applications

Novel binary cobalt nickel oxide Co1.29Ni1.71O4 hollowed-out spheres have been successfully synthesized via a facile hydrothermal method with a further calcination process. The phase, crystal structure, morphology, and electromagnetic (EM) and EM wave absorption properties were characterized in detail. We find that as the temperature increases, the ionic mobility in the spinel structure will increase, leading to lattice disorder and an increase in the concentration of oxygen vacancy, which will improve the dielectric loss and EM wave absorption capacity of the material. The minimum reflection loss (RLmin) of the sample calcined at 500 °C reached up to −50.7 dB with a matching thickness (d) of 1.6 mm, and the corresponding effective absorption bandwidth (fE, RL < −10 dB) was 4.84 GHz. The sample calcined at 550 °C also showed excellent EM wave absorption properties, and the corresponding RLmin, fE, and d were −44.5 dB, 5.13 GHz, and 2.0 mm, respectively. We are confident that the spinel Co1.29Ni1.71O4 will become an excellent candidate for a new generation of high-efficiency EM wave absorbing material.

Graphene anchored with super-tiny Ni nanoparticles for high performance electromagnetic absorption applications

This paper reports a facile strategy for one-step synthesis of graphene anchored with super-tiny (< 5 nm) nickel nanoparticles (graphene@Ni) with high perfomance microwave absorption. The phase structure, morphology and magnetism of graphene@Ni were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM), respectively. The magnetic Ni nanoparticles with 2.45 nm in average size are densely anchored on the surface of graphene. The electromagnetic characteristics of graphene@Ni compounds were measured by vector network analyzer using a coaxial line method in the frequency range of 1–18 GHz. The reflection loss (RL) of graphene@Ni reaches − 53.92 dB at 9.5 GHz with a thickness of 2.8 mm, and the maximum effective absorption bandwidth with RL values lower than − 10 dB is 5.44 GHz covering from 11.45 to 16.89 GHz at a thickness of 2.1 mm, showing that both of the RLmin and absorption bandwidth for graphene@Ni are obviously enhanced with thinner thickness compared to pure Ni NPs and graphenes. The real RL of graphene@Ni modified aramid fabrics/bismaleimide composite laminate is also measured for comparison, which is basically consistent with simulated results of graphene@Ni. Therefore, the graphene@Ni compounds have advantage in practice for high performance microwave absorption applications.

Reduced Graphene Oxide-Wrapped Super Dense Fe3O4 Nanoparticles with Enhanced Electromagnetic Wave Absorption Properties.

The efficient preparation of electromagnetic wave absorbing materials with low density and excellent electromagnetic wave absorption remains a considerable challenge. In this study, reduced graphene oxide (RGO) wrapped Fe3O4 nanoparticles (NPs) were synthesized based on one-step reaction by the reduction of graphene oxide (GO), and the generation of super-fine Fe3O4 NPs was achieved. The phase structure, chemical composition, micromorphology, and magnetism were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM), respectively. The electromagnetic characteristics were evaluated on a vector network analyzer by the coaxial line method. The results showed that super-fine Fe3O4 NPs with an average size of 6.18 nm are densely distributed on the surface of graphenes. The RGO/Fe3O4 nanocomposites exhibited excellent microwave absorption properties with a minimum reflection loss (RL) of up to −55.71 dB at 6.78 GHz at 3.5 mm thickness and the highest effective absorption bandwidth with RL values exceeding −10 dB is 4.76 GHz between 13.24 and 18 GHz at 1.7 mm thickness. This work provides a concise method for the development of RGO supported super dense Fe3O4 nanocomposites for high performance electromagnetic absorption applications.