Reflection Of Electromagnetic Waves Research Articles

Effects of spin-orbit coupling on transmission and absorption of electromagnetic waves in strained armchair phosphorene nanoribbons.

We compute the optical conductivity, both the imaginary and real parts of the dielectric constant, and the optical coefficients of armchair phosphorene nanoribbons under application of biaxial and uniaxial strains. The Kane-Mele model Hamiltonian has been applied to obtain the electronic band structure of phosphorene nanoribbons in the presence of a magnetic field. The effects of uniaxial and biaxial in-plane strain on the frequency behavior of the optical dielectric constant, and the frequency behavior of the optical absorption and refractive index of phosphorene nanoribbons have been studied, in terms of magnetic field, spin-orbit coupling and strain effects. Linear response theory and the Green's function approach have been exploited to obtain the frequency behavior of the optical properties of the structure. Moreover, the transmissivity and reflectivity of electromagnetic waves between two media separated by a phosphorene-nanoribbon layer are determined. Our numerical results indicate that the frequency dependence of the optical absorption includes a peak due to applying a magnetic field. Moreover, the effects of both in-plane uniaxial and biaxial strains on the refractive index of single-layer phosphorene have been addressed. Also, the frequency dependence of the transmissivity and reflectivity of electromagnetic waves between two media separated by armchair phosphorene nanoribbons for normal incidence has been investigated in terms of the effects of magnetic field and strain parameters. Both compressive and tensile strain have been considered for the armchair phosphorene nanoribbons in order to study the optical properties of the structure. In particular, the control of the optical properties of phosphorene nanoribbons could lead to extensive applications of phosphorene in the optoelectronics industry. Also, such a study of the optical properties of phosphorene nanoribbons has further applications in light sensors. Meanwhile, the effects of spin-orbit coupling on the optical absorption and transmissivity of electromagnetic waves in phosphorene nanoribbons could be a novel topic in condensed-matter physics.

Optical meta-cage based on phase gradient metagrating

<sec>How to effectively control the refraction, reflection, propagation and wavefront of electromagnetic wave or light is always one of the advanced researches in the field of optics. In recent years, much effort has been devoted to both theoretical and experimental studies of optical phase gradient metagratings (PGMs) due to the fundamental interest and practical importance of PGMs, such as the generalized Snell’s law (GSL). Typically, the PGMs are constructed as periodic gratings consisting of a supercell spatially repeated along an interface, and each supercell consists of <i>m</i> unit cells, with <i>m</i> being an integer. The key idea of PGMs is to introduce an abrupt phase shift covering the range from 0 to <inline-formula><tex-math id="M2">\begin{document}$2\pi $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M2.png"/></alternatives></inline-formula> discretely through <i>m</i> unit cells to ensure the complete control of the outgoing waves. The phase gradient provides a new degree of freedom for the manipulation of light propagation, which has allowed a series of ultrathin devices to realize anomalous scattering, the photon spin Hall effect, and many other phenomena.</sec><sec>Intuitively, the number of unit cells <i>m</i> in a supercell does not influence the PGM diffraction characteristics, except that a small value of <i>m</i> will lead to a reduced diffraction efficiency. However, some recent studies have shown that the integer <i>m</i> plays a fundamental role in determining the high-order PGM diffractions when the incident angle is beyond the critical angle predicted by the GSL. In particular, for high-order PGM diffractions, <i>m</i> leads to a new set of diffraction equations expressed as</sec><sec> <inline-formula><tex-math id="M3">\begin{document}$ \left\{ {\begin{aligned} &{{k_x} = k_x^t - nG,{\text{ for odd L,}}} \\ &{{k_x} = k_x^r - nG,{\text{ for even L}}{\text{. }}} \end{aligned}} \right. $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M3.png"/></alternatives></inline-formula></sec><sec>In addition to the phase gradient, the integer number of unit cells <i>m</i> in a supercell is another degree of freedom that can be employed to control the light propagation. By the parity of <i>m</i>, the higher-order outgoing wave can be reversed between the anomalous transmission channel and the anomalous reflection channel.</sec><sec>In this work, according to the concept of abrupt phase and the parity-dependent diffraction law in phase gradient metagrating, we theoretically design and study an optical meta-cage. The meta-cage is a periodic structure with one period that contains <i>m</i> different unit cells. Through numerical simulations and rigorous analytical calculations, we find that the ability of meta-cage to trap light is related to the parity of the number of unit cells <i>m</i> in a supercell. Specifically, when the number of unit cells is odd, the point source placed in the meta-cage can perfectly radiate out of the meta-cage without any reflection. On the contrary, when the number of unit cells is even, the point source can hardly radiate out of the meta-cage, and all the energy is localized within the meta-cage. Moreover, such a phenomenon is robust against the disorder. These results can provide new ideas and theoretical guidance for designing new radar radome and photonic isolation devices.</sec>

Terahertz metasurface absorbed by both linearly and circularly polarized waves

In recent years, the development of ultrafast laser technology has provided a stable and reliable terahertz source for generating terahertz wave pulses, and the great research progress of terahertz wave has been made. As a new type of two-dimensional artificial metamaterial, metasurface can effectively control the transmission, reflection and polarization of electromagnetic waves, which has attracted the extensive attention. Most of the reported terahertz absorbers so far are based on metasurfaces with linear polarization incidence, and few studies have been conducted on terahertz metasurfaces that can produce efficient absorption at both linear and circular polarization incidence, which limits the practical application areas. Therefore, it is necessary to explore an efficient absorber which can realize both linear polarization and circular polarization. We propose a vanadium dioxide composite metasurface structure. The vanadium dioxide is a typical temperature-controlled phase change material, and its conductivity will undergo a huge mutation in the phase change process. When the temperature is lower than the critical temperature (68 ℃), the vanadium dioxide has high resistivity and good insulation performance. When the temperature is higher than the critical temperature, the resistance changes from high resistance state to low resistance state, showing metal characteristics. By changing the external temperature, the phase of vanadium dioxide is changed, the free switching frequency is achieved and both the linear polarization and circular polarization incident efficient absorption are realized. When the vanadium dioxide is insulated, its conductivity is 0 S/m, the metasurface can absorb left-handed circularly polarized wave at 1.30 THz and reflect the incident right-handed circularly polarized wave, and the circular dichroism is 0.85. When the vanadium dioxide is metallic, its conductivity is 2×10<sup>5</sup> S/m and it possesses linearly polarized incident metasurface, the absorption rate of TE linearly polarized incident wave by metasurface reaches 98.5% at 1.95 THz, and the perfect absorption of terahertz wave is realized. The structure has good wide-angle absorption performance for both TE polarization wave and left-handed circularly polarized wave. This composite metasurface structure can achieve the good absorption effect of terahertz waves with different frequencies and different polarization states. Therefore, the design concept of the composite metasurface structure can be used for designing other metasurface terahertz devices, and also for implementing the terahertz imaging and sensing systems due to different response characteristics to different polarization signals.

Використання НВЧ-радіометрії у побудові медичних приладів для неінвазивної діагностики

Temperature is often used among the information required to diagnose the state of a person’s internal organs, as pathological processes occurring in the human body are usually accompanied by thermal deviations not only on the surface but also inside the body. Modern medicine needs to improve non-invasive methods of measuring temperature deep in the human body for the purpose of early diagnosis and monitoring of various pathological processes. Medical radiothermography, in particular, allows non-invasive determination of the integral deep temperatures of internal organs. The development of modern radiometric equipment involves solving such complex problems as ensuring high sensitivity of devices, matching the antenna to the biological object, ensuring the required penetration depth, and measuring absolute temperature with an error of at least 0.1°C. Given the importance of this problem, this paper demonstrates the approaches to the development of modern radiothermographs that the authors used in the process of creating a device for diagnosing breast temperature abnormalities. The study considers the principles and schemes of construction of radiothermographic devices, requirements to the equipment as a whole, as well as to its main components. The authors conclude that it is optimal to use a modulation-compensation scheme of a radiometer for medical radiothermometry based on the measurement of two parameters: the integrated temperature and the integrated coefficient of reflection of electromagnetic waves from a biological object. A schematic diagram of a prototype radiothermograph, as well as its composition and design, is presented. The approaches to the creation of modern radiothermographs presented in this work should be useful for developers of medical equipment for surgery, otorhinolaryngology, orthopedics, pediatrics, gynecology, etc., where measuring the distribution of patient body temperatures is of diagnostic value.

Bispectral Images of Radar Wideband Objects Characters Interpretation

A methodological approach to the analysis of broadband radar signatures based on the application of the theory of bispectral estimation is presented. The approach involves analyzing the phase relationships of the target scattering centers, providing the more complete account of the information contained in the frequency characteristic of the target compared to the range portrait traditionally obtained using the Fourier transform. Analysis of phase connections allows identifying scattering centers formed as a result of multiple reflections of electromagnetic waves by structural elements of the object of complex shape or by separate close-located objects within the observed scene. The geometric image of the bispectra of the radar broadband object’s signature used for analysis is a hexagon in the coordinates “longitudinal range — longitudinal range,” which allows detecting mutual connections of scattering centers spaced along the direction of the location. The proposed methodological approach was tested using a synthesized frequency characteristic of an abstract multipoint target, as well as based on electrodynamic modeling data of complex backscattering fields. The comparison of the results of identification of scattering centers obtained using a bispectral image, the range portrait and the priori information about the location object indicates the correctness of the proposed methodological approach.

Ultrathin dual-mode orbital angular momentum generated based on dual-polarization coding metasurface

In this paper, an dual-polarization 4-bit coding metasurface is proposed to achieve the flexible manipulation of different polarization electromagnetic wave reflection angles and the generation of dual-mode vortex beams by independent manipulation of orthogonal linearly polarized waves. The proposed metasurface is composed of H-type metal patch, dielectric substrate, and metal grounding layer from top to bottom. To prove the proposed concept, we design and fabricate four coding metasurfaces based on superposition theorem and holographic theory. One of the coding metasurfaces is designed to verify the ability to manipulate the beam angle, and each of the other three coding metasurfaces is designed to carry a vortex beam with different topological charges under orthogonal linearly polarized waves with a central frequency of 24 GHz. The experimental results show that the theoretical design is highly consistent with the simulation results. Therefore, it is verified that our proposed 4-bit dual-polarization coding metasurface has strong and flexible ability to manipulate the beam reflection angle and generate high performance dual-mode vortex beam antenna. Because of the wide application prospect of vortex beam in communication field, we have reason to believe that the proposed ultra-thin dual-mode vortex generator will have potential applications in wireless communication system in the fields of image and microwaves.

A Novel Approach for Radar Passive Jamming Based on Multiphase Coding Rapid Modulation

Electromagnetic controlled surface (ECS) which can regulate the amplitude and phase of electromagnetic wave reflection characteristics has attracted extensive attention in recent years because of its radar stealth effect by reducing the radar cross section (RCS). However, radar detection cannot be avoided only by stealth in the energy field gradually. It is a novel pulse Doppler radar jamming mode proposed in this paper to utilize the self-correlation of radar-transmitted waveforms to result in signal processing and radar detection failure through the rapid time-domain variation of phase coding ECS. In principle, phase modulation alters the intra-pulse characteristics of the original signal and fundamentally interferes with the processing of the radar signal. In this paper, random and periodic phase coding sequences are proposed according to different forms of radar jamming. And through the derivation formula and simulation experiment, the jamming effect under multi-phase modulation is verified. Among them, the target energy is dispersed to the surroundings to form a wide envelope through random coding modulation, which leads to noise barrage jamming. While we use periodic sequence coding modulation, the target is shifted in the range-Doppler domain, causing misplaced coherence on the radar echo and deceptive jamming to the radar. Moreover, the technology can also be widely used in synthetic aperture radar (SAR) imaging, microwave measurement and other remote sensing fields. To further confirm the accuracy and efficiency of the proposed method, multi-parameter contrast experiments and parameter sensitivity analyses are conducted.

Layered polymer composite foams for broadband ultra-low reflectance EMI shielding: a computationally guided fabrication approach.

The development of layered polymer composites and foams offers a promising solution for achieving effective electromagnetic interference (EMI) shielding while minimizing secondary electromagnetic pollution. However, the current fabrication process is largely based on trial and error, with limited focus on optimizing geometry and microstructure. This often results in suboptimal electromagnetic wave reflection and the use of unnecessarily thick samples. In this study, an input impedance model was employed to guide the fabrication of layered PVDF composite foams. This approach optimized the void fraction (VF) and the thickness of each layer to achieve broadband low reflection. Moreover, hybrid heterostructures of SiCnw@MXene were incorporated into the PVDF composite foams as an absorption layer, while the conductive PVDF/CNT composite foams served as a shielding layer. Directed by theoretical computations, we found that combining 2.2 mm of PVDF/SiCnw@MXene composite foam (50% VF) and 1.6 mm of PVDF/CNT composite yielded EMI shielding effectiveness of 45 dB, with an average reflectivity (R) of 0.03 and an effective absorption bandwidth of 5.54 GHz (for R < 0.1) over the Ku-band (12.4-18 GHz). Importantly, the corresponding peak R was only 0.000017. Our work showcases a theoretically guided approach for developing absorption-dominant EMI shielding materials with broadband ultra-low reflection, paving the way for cutting-edge applications.

Measuring the reflection of electromagnetic waves from foam structures of varied foaming ratio

A specific multi-frequency technique for measuring the reflectivity of constantly collapsing foam structures of varied initial foam ratio is developed. A measuring and computing complex implemented the technique is used. It operates in the microwave range from 38 to 52 GHz. Dynamic foam structures with an initial foaming ratio of 55, 108, and 156 units in the form of flat-layered foam samples with a fixed thickness are under measurement. It is shown that the use of foam structure covering allows to reduce the reflection of electromagnetic waves from metal surfaces significantly. The obtained measurement results confirm the possibility of measuring dynamic foam structures, and this technique makes it possible to separate reflections from the front and back faces of the samples, which is very important for the study of the syneresis processes of the foaming liquid and the destruction of foam structures. The results are useful for studying the radiophysical characteristics of foams and for developers of new foaming agents for various applications where electromagnetic waves are used.

Morphology controllable urchin-shaped bimetallic nickel-cobalt oxide/carbon composites with enhanced electromagnetic wave absorption performance

The microscopic morphology of electromagnetic wave absorbers influences the multiple reflections of electromagnetic waves and impedance matching, determining the absorption properties. Herein, the urchin-shaped bimetallic nickel-cobalt oxide/carbon (NiCo2O4/C) composites are prepared via a hydrothermal route, whose absorption properties are investigated by different morphologies regulated by changing calcination temperature. A minimum reflection loss (RLmin) of -75.26 dB is achieved at a matching thickness of 1.5 mm, and the effective absorption bandwidth (EAB) of 8.96 GHz is achieved at 2 mm. Multi-advantages of the synthesized NiCo2O4/C composites contribute to satisfactory absorption properties. First, the interweaving of the needle-like structures increases the opportunities for scattering and multiple reflections of incident electromagnetic waves, and builds up a conductive network to facilitate the enhancement of conductive losses. Second, the carbon component in the NiCo2O4/C composites enhances the interfacial polarization and reduces the density of the absorber. Besides, generous oxygen vacancy defects are introduced into the NiCo2O4/C composites, which induces defect polarization and dipole polarization. In summary, the ternary coordination of components, defects and morphology led to outstanding electromagnetic wave absorption, which lightened the path for improving the electromagnetic wave absorption property and enriching the family of NiCo2O4 absorbers with excellent performance.

Magnetic Porous Carbon Composites for Efficient Electromagnetic Wave Absorption

Biomass carbon composites have the shining points of lightweight, economy, harmlessness, and large specific surface area, casting on them great development prospects in terms of excellent wave absorbing properties. Herein, a facile route to fabricate magnetic porous with a special spongy structure for its great contribution to microwave absorption is reported. It is endowed with a strong absorption capacity and a wide absorption band. The 3D spongy structure and uniform distribution of magnetic Co particles can promote defect polarization, interface polarization, and dipole polarization, which are conducive to scattering and reflection of electromagnetic waves (EMW) in the absorbing body. The magnetic Co particles can enhance the magnetic loss on the one hand and harmonize the impedance matching on the other hand. The minimum reflection loss can reach −54.7 dB. The effective absorption bandwidth at 2.1 mm can reach 7.61 GHz, almost covering the X and Ku bands. This proposed strategy provides more possibilities for the application of biomass microwave absorbers with lightweight and broadband properties.

Ultralight Ti3C2Tx-derivative chrysanthemum-like Na2Ti3O7/Ti3C2Tx MXene quantum dots 3D/0D heterostructure with advanced microwave absorption performance

As an outstanding representative of two-dimensional materials, newly emerged Ti3C2Tx MXene has aroused widespread attention in the field of microwave absorption (MA). However, the high conductivity of Ti3C2Tx MXene is prone to lead to impedance mismatch, and the attenuation performance of incident electromagnetic waves in the Ti3C2Tx matrix needs to be further improved. To address these issues, Ti3C2Tx MXene quantum dots (MQDs) were applied in the field of MA for the first time, and combined with Ti3C2Tx derivative chrysanthemum-like Na2Ti3O7 to prepare Na2Ti3O7/MQDs composites with 3D/0D heterostructure. Compared with Ti3C2Tx MXene bulks and nanosheets, Ti3C2Tx MQDs possess larger specific surface area and richer surface-active groups and defects, which are more favorable for interfacial polarization and dipole polarization, while the moderate conductivity of Ti3C2Tx MQDs is conducive to impedance matching. The unique chrysanthemum-like Na2Ti3O7/MQDs with 3D/0D heterostructure generates abundant heterointerfaces to promote the increase of interfacial polarization, achieves a rational combination of different conductive materials to optimize impedance matching, and facilitates multiple reflections of electromagnetic waves among numerous nanowires in the chrysanthemum-like structure. Benefiting from the good impedance matching and the synergistic effect of multiple loss mechanisms, Na2Ti3O7/MQDs composites show excellent MA performance with a minimum reflection loss of −48.28 dB at a thickness of 2.6 mm. Simultaneously, the effective absorption bandwidth comes up to 6.38 GHz at 2.5 mm thickness. This study demonstrates the potential of MQDs as efficient microwave absorbers and points out the direction for a wide application of various MQDs in the field of MA.

Peculiarities of spectral reflectance of fractions with sizes from 20 to 5,000 microns in soil samples

By the example of arable horizon samples taken from three soil types (sod-podzolic, gray forest, and leached chernozem) the peculiarities of electromagnetic waves reflection from their different particle size fractions were studied. The extraction of fractions by dry sieving was carried out using Retsch AS 200 BASIC equipment. As a result, 14 fractions ranging in size from less than 20 microns to more than 5,000 microns were isolated. Spectral reflectance was determined for each fraction and for the soil sample before sieving in the electromagnetic wave range from 350 to 2,500 nm using a SR-6500 field spectroradiometer (Spectral Evolution, USA). Analysis of similarities and differences in the obtained spectral reflectance curves of individual fractions was carried out using their visual analysis, the method of similarity dendrogram construction, as well as regression analysis between light reflectance and fraction particle size. It was confirmed that at a more detailed level of analysis compared to the one carried out by other researchers earlier, the general patterns of light reflectance of the samples do not change. A higher reflection of waves by thinner fractions and a lower reflection by more coarse fractions are observed. At the same time, spectral reflection curves for individual fractions are out of the general pattern, the level of intensity of local extremes of the curves’ changes. This confirms the difference of the material composition, which forms the color of soils, of these fractions from others. The color of the mixed sample is a spectral mixture of colors of its separate fractions. Presumably, this is the main reason for such a phenomenon as change of spectral reflectivity of open surface of soils under the influence of atmospheric precipitation.

Исследование влияния интерференции в кювете на поглощение газа, измеренное с использованием метода нестационарной ТГц спектроскопии

Cell is the important part of the terahertz (THz) spectrometer designed to study the chemical composition of multicomponent gas mixtures, since it is used for supporting the optimal pressure of the gaseous sample. However, the reflection of electromagnetic waves from the cell windows leads to standing-wave interference, which can distort the measured spectrum. Mathematical modeling of the impact of the interference on the measured spectrum was carried out in the paper. The cell was treated as a Fabry-Perot cavity with infinite flat dielectric mirrors. Diffraction of electromagnetic waves, as well as the frequency dependences of the source power and the detector sensitivity, was taken out of the scope of the considered model. The two effects of the interference were described. The interference not only determined the slow frequency dependence of the cell transmission spectrum, but also affected the profile of the gas absorption lines reconstructed from the cell spectrum in accordance with the Bouguer-Lambert-Beer law. Both the processing of the measured spectrum and the setup calibration required for accurate quantitative measurements could be complicated by the effects. However, methods of modulation and non-stationary spectroscopy enabled to eliminate the first effect, they were possibly ineffective to eliminate the second one. Presumably, the detected distortion of the contour of the absorption lines was caused by a shift in the interference pattern and, accordingly, a change in the reflection coefficient of the cell due to the anomalous dispersion of the sample. The correlation of the distortions with the derivatives of the transmission spectrum of the empty cell was revealed. The obtained results could be used to develop algorithms for calibrating the measuring setup and processing experimental data.

Evaluation of Air-Cavities behind Concrete Tunnel Linings Using GPR Measurements

The primary objectives of this study are to investigate the interference of ground penetrating radar (GPR) signals with air-cavities behind concrete linings subjected to three experimental parameters (GPR antenna frequency, thickness of concrete lining, and thickness of air-cavities), and their effects on the evaluation of important engineering parameters (thickness of concrete, and length and thickness of air-cavities) for tunnel structure inspection using GPR. For these purposes, first, a concrete model specimen is fabricated in the laboratory, which simulates air-cavity defects with various thicknesses (0 mm, 30 mm, 100 mm, 200 mm, and 300 mm) behind concrete with four different thicknesses (100 mm, 200 mm, 300 mm, and 400 mm) in tunnel structures. Second, a series of GPR survey is performed on the fabricated concrete model specimen using three ground-coupled GPR antennas with nominal center frequencies of 400 MHz, 900 MHz, and 1600 MHz. Third, a practical signal interpretation method is proposed to evaluate air-cavities in concrete tunnel linings subjected to the three experimental parameters. It is demonstrated that the cross-correlation analysis is effective for identifying air-cavities behind concrete, and for characterizing the length of the air-cavities. In addition, the thicknesses of air-cavities are estimated by a new approach in this study, measuring the apparent time delay of partially overlapped electromagnetic wave reflections within air-cavities. The results in this study provide a fundamental basis to improve GPR signal interpretation techniques for the evaluation of air-cavities behind concrete tunnel linings.

Multifunctional Nd2O3/CNFs Composite for Microwave Absorption and Anti-Corrosion Applications

To improve the limitations of traditional microwave absorbing materials (MAMs), such as high density and narrow absorption bandwidth, neodymium oxide/carbon nanofiber (Nd2O3/CNF) composites were successfully prepared by electrospinning technology combined with a high-temperature carbonization process. The three-dimensional network structure of CNFs provides a path for conducting electromagnetic waves, and its porous structure also increases the multiple reflections of electromagnetic waves in the composite fibers, which significantly attenuates the energy of electromagnetic waves. Additionally rare-earth elements have a unique electronic arrangement on the 4f electron layer. The addition of Nd2O3 can turn the dielectric constant of Nd2O3/CNF and optimize the impedance matching. Also, Nd2O3 nanoparticles (Nd2O3–NPs) resulted in numerous of heterojunction surfaces and introduced the magnetic loss mechanism. Under the combined action of the double loss mechanism, the minimum reflection loss of Nd2O3/CNF composite fiber is −66.7 dB at 9.36 GHz, and the effective absorption bandwidth is 4.4 GHz (7.68–12.08 GHz). The radar cross section simulation results also prove that the composite fibers exhibit strong consumption of electromagnetic waves. Additionally, the excellent flexibility and anticorrosion properties of the composite fibers make them satisfy the multifunctional requirements of MAMs.

Quiet Places

Designed to stop the reflection of sound or electromagnetic waves, anechoic chambers are essential to today's consumer electronics testing. CET&amp;D surveys some of the most silent spaces on Earth.

Cellulose nanofiber/MXene/FeCo composites with gradient structure for highly absorbed electromagnetic interference shielding

Conductive polymer composites (CPCs) had attracted tremendous attention in the field of electromagnetic interference (EMI) shielding. However, these materials encountered an intrinsic contradiction between high EMI shielding effectiveness (EMI SE) and low electromagnetic waves reflection. Herein, an excellent EMI SE and low electromagnetic waves reflection composite film with a controllable magnetic-conductive dual gradient structure was constructed using cellulose nanofiber (CNF), MXene, and FeCo by layer-by-layer vacuum filtration method. Benefiting from the synergy of the transition layers and reflection layer with gradient structure, the composite film exhibited favorable impedance matching, abundant loss mechanism, and efficient EMI shielding ability, resulting in absorption dominated shielding characteristic. In addition, the gradient structure facilitated the “absorb-reflect-reabsorb” process when electromagnetic waves were transmitted into the composite film. The obtained CNF/MXene/FeCo-G composite film possessed a remarkable EMI SE of 58.0 dB and the reflection coefficient (R) as low as 0.61. It was proven that the electromagnetic waves absorbing ability can be enhanced by thickening the transition layers, and the EMI SE was improved with the thickening of the reflection layer. Therefore, this work provided a facile strategy to prepare high EMI SE materials with low reflection, which had a good application prospect as the new-generated smart electronic devices.

Efficient microwave absorption with Vn+1CnTx MXenes

The availability of MXenes and other two-dimensional conductive nanomaterials with tunable surface chemistry has reshaped the field of electromagnetic protection. However, the high electrical conductivity and low dielectric loss of titanium-based MXenes lead to strong reflection of electromagnetic waves, even when combined with polymers to form composites. Here, we report on the ability of vanadium-based MXenes to provide broadband microwave absorption. Polyurethane composites with ∼2 wt % V n+1 C n T x can absorb 90% of electromagnetic waves covering the entire X band. In addition, pure V n+1 C n T x films of submicrometer thickness can provide effective electromagnetic interference shielding. The free electron transport, surface terminations, native defects, and layers arrangement in composites have profound effects on electronic and dielectric properties of V n+1 C n T x MXenes. This study points toward a new frontier for development of thin and highly absorbing MXene-based electromagnetic protection materials. • Polyurethane composites with ∼2 wt % V n+1 C n T x absorb >90% of microwaves in X band • 600-nm-thick V n+1 C n T x films provide effective electromagnetic interference shielding • The native defects and surface groups affect the microwave absorption behavior Han et al. report that vanadium-based MXenes (V 2 CT x and V 4 C 3 T x ) can provide broadband microwave absorption with ultralow filler loading in polymer matrix. The free electron transport, surface terminations, native defects, and layers arrangement significantly affect electronic and dielectric properties of V n+1 C n T x MXenes.

Multi-hierarchy heterostructure assembling on MnO2 nanowires for optimized electromagnetic response

One-dimensional (1D) nanomaterials allow reflection of electromagnetic (EM) waves due to large anisotropy and aspect ratio. It is still a challenge to optimize the impedance matching characteristic for strong EM dissipation of 1D nanomaterials. Herein, we propose a strategy of incorporating two-dimensional (2D) layered double hydroxides (LDHs) sheets with 1D nanowires to reinforce interactions with EM waves. Wherein, 1D MnO2 nanowires are used to support the LDH nanosheets, which facilitates the EM waves capture and impedance matching characteristics. Moreover, the heterogeneous interfaces and vacancies contributes to the polarization loss as well. As a consequence, the minimum reflection loss (RLmin) of MnO2@ZnCoNi-LDHs demonstrates −56.3 dB at 2.4 mm and the broad effective absorption bandwidth (fE) reaches 4.56 GHz at 2.1 mm. This heterogeneous structure assembly strategy can be served as a reference for refining the absorption performance of 1D EM absorbers.