Electromagnetic Waves Research Articles

Square-root topological insulator for a dual-band photonic waveguide

We show that square-root topological insulators can be utilized as a platform for dual-band topological waveguides in 2-dimensional photonic crystals. Valley states for each of two frequency band gaps in differently perturbed decorated honeycomb lattices have opposite directions of the phase rotations, revealing opportunities for dual-band unidirectional topological valley transport. The topological valley edge states exist at the boundary between differently perturbed photonic crystals in the two frequency bands. In addition, unidirectional, and robust propagation of electromagnetic waves along the boundary in the two frequency bands are numerically performed. Our work provides extensions of square-root topological insulators to robust, unidirectional, and dual-band photonic waveguides.

Multichannel information transmission via a dual-frequency point space-time coding metasurface

Space-time coding (STC) digital metasurfaces enable dynamic control of nonlinear harmonics. To achieve efficient frequency tuning and harmonic control, we propose a one-bit column-controlled temporal coding dual-frequency point STC digital metasurface. Using a field-programmable gate array (FPGA) to control diode switching, the metasurface is encoded to generate multiple target reflected harmonics as independent information transmission channels. The amplitude intensities of these harmonics are defined as independent binary symbols for transmission. The proposed space-time coding digital metasurface can achieve a phase shift of 180° in its unit structure, with reflectivities above 90% at both operating frequencies. We fabricated the designed metasurface and tested its far-field scattering experimentally. When the incident electromagnetic wave frequency is 4.63 GHz, the predicted results are essentially consistent with the experimental findings.

Improvement of directivity in plasmonic nanoantennas based on structured cubic gold nanoparticles

An array of metallic nanoparticles can diffract or concentrate the incident electromagnetic wave and behave as an antenna. In this paper, the effects of the inner sub-wavelength structure of nanoparticles are studied on the directivity of the plasmonic nanoantenna, which is coated on the output of a waveguide. Three 5*5 element configurations are analyzed: nanocubes, nanoshells, and nanoframes array. Numerical results are obtained using the 3D FDTD technique. The results show that structured nanoantennas can improve the antenna's directivity due to the plasmonic properties and hybridization mechanism. Between the three configurations investigated in the 250–800 nm wavelength range, the nanoshell array exhibits maximum and minimum amounts of its directivity at 321.5 nm and 591 nm, respectively. At 558 nm, nanoframes and nanoshells' arrays show the same amount of directivity, and from the wavelength greater than 558 nm, the nanoframe array has the best performance. The results may help design and fabricate directive optical fiber endcaps.

High-energy Neutrinos from Outflows Powered by the Kicked Remnants of Binary Black Hole Mergers in Active Galactic Nucleus Accretion Disks

Merging of stellar-mass binary black holes (BBHs) could take place within the accretion disks of active galactic nuclei (AGN). The resulting BH remnant is likely to accrete the disk gas at a super-Eddington rate, launching a fast, quasi-spherical outflow (wind). Particles will be accelerated by shocks driven by the wind, subsequently interacting with the shocked disk gas or radiation field through hadronic processes and resulting in the production of high-energy neutrinos and potential electromagnetic (EM) emission. This study delves into the intricate evolution of the shock driven by a merged BH wind within an AGN disk. Subsequently, we calculated the production of neutrinos and the expected detection numbers for a single event, along with their contributions to the overall diffuse neutrino background. Our analysis, which considers various scenarios, reveals considerable neutrino production and possible detection by IceCube for nearby events. The contribution of merged BH winds on the diffuse neutrino background is minor due to the low event rate density, but it can be improved to some extent for some optimistic parameters. We also propose that there could be two neutrino/EM bursts, one originating from the premerger BBH wind and the other from the merged BH wind, with the latter typically having a delay to the gravitational wave (GW) event of around tens of days. When combined with the anticipated GWs emitted during the BBH merger, such a system emerges as a promising candidate for joint observations involving neutrinos, GWs, and EM signals.

Exploring robust microwave absorption properties of functional polyvinyl butyral (PVB) via facile cross-linking and data-driven material discovery

This work introduces a chemically facile approach for synthesizing cross-linked polyvinyl butyral (XPVB) at room temperature, utilizing divinyl sulfone (DVS) as the cross-linking agent. Leveraging data-driven discovery methods, we optimize the DVS concentration to enhance the material's reflection loss (RL) performance, establishing XPVB as a formidable contender in microwave absorption without the need for conventional filler materials. Gaussian Process Regression (GPR) was used in this analysis, the material's development process was streamlined to achieve a high-fidelity predictive model that closely aligns with the observed experimental data. The synergy between our GPR model and the empirical evidence is particularly noteworthy, with the GPR predictions exhibiting exceptional agreement across the investigated frequency range, especially in the Ku-band, where high RL values are crucial. These findings indicate that XPVB exhibits exceptional dielectric properties that translate into an unprecedented absorption bandwidth encompassing the entire Ku-band, paired with strong RL, thereby achieving a significant attenuation of electromagnetic waves even at minimal material thicknesses. The optimized XPVB sample, without any filler addition, delivers an exceptional RL performance. Notably, a 2.4 mm-thick XPVB sample demonstrated an extraordinary RL value of -44 dB with RL≤-10 dB absorption Ku-bandwidth (12.4–18 GHz), showcasing the material's potential as a standalone absorber. This synthesis methodology, combined with the analytical approach, lays the groundwork for further research and development in microwave absorbers and has the potential to significantly impact the fields of defense, telecommunications and self-powered devices by providing a new standard for material performance.

Strong SiC@Carbon nanowire aerogel metamaterials for efficient electromagnetic interference shielding

Lightweight, high-strength and efficient electromagnetic interference shielding materials are in urgent demand for aerospace vehicles such as lunar and Mars rovers. SiC nanowire aerogels exhibit low density, chemical stability, and adjustable dielectric properties, rendering them as ideal candidates for high-performance electromagnetic wave protecting materials. However, developing SiC nanowire aerogels with simultaneous strong mechanical properties and efficient electromagnetic interference shielding performance remains challenging. Herein, a class of strong SiC@carbon nanowire aerogel metamaterials with both mechanical robustness and efficient electromagnetic interference shielding are obtained through microstructure design and compositional optimization. The aerogels with designed meta-structures are fabricated by 3D printing followed with chemical vapor deposition of graphene-like carbon. The optimized compressive strength and Young's modulus of the aerogel metamaterial reach up to 1.581 MPa and 46.230 MPa, respectively, showing an increase of about 50–60 times. It also exhibits an electromagnetic interference shielding effectiveness of 38.39 dB and specific shielding effectiveness of 666.53 dBcm3g−1. These good properties are attributed to the synergistic effects of the hierarchical meta-structure and the SiC@carbon nanowires composite constituents, which provides a feasible pathway toward further design of high-performance electromagnetic interference protection materials.

Terahertz polarization sensing for influenza A virus based on plasmonic metasurface

Terahertz metasurface sensors attract extensive attention for excellent characterisics. However, most existing sensing schemes overlooked the polarization state of electromagnetic waves. Here, we propose a plasmonic metasurface sensor based on the elliptical polarization state of reflected EM wave, which can be used for the sensing of influenza A virus. The sensor achieves the conversion from linear polarization to circular polarization within 1–3 THz. By analysing the electromagnetic field distributions of the resonances at 1.43 THz and 2.16 THz, it can be concluded that the polarization conversion originates from the magnetic dipole. Besides, the sensor can characterize the changes in the complex refractive index of the test sample based on the elliptical polarization state of the reflected wave. The electromagnetic response of the metasurface sensor shows an excellent linear relationship between the rotating direction angle of polarization ellipse and the extinction coefficient (k) of the complex RI of the analyte. Furthermore, we also demonstrate the feasibility of detecting three subtypes of Influenza A viruses (H1N1, H5N2, and H9N2) at 1.39 THz though the elliptical polarization state. This sensing approach does not rely on high-precision broadband scanning, providing an alternative perspective for THz biosensing.

Study on the electromagnetic properties and microwave absorption properties of Co2Si by non-magnetic metal Cu and Mn single doping

In this study, Co2Si and Co2Si-doped powder materials with different Cu,Mn proportions were prepared by mechanical alloying and thermal sintering. The effects of Cu,Mn doping on the crystal structure, magnetic properties, and microwave absorption properties of Co2Si were investigated. The results showed that all the sample peaks obtained by XRD measurement were consistent with the standard card (ICDD: 98-005-2281) of Co2Si.The Ms values corresponding to 2 wt%, 4 wt%, and 8 wt% Cu doping were 25.79 emu/g, 23.79 emu/g, and 21.75 emu/g, respectively. The saturation magnetization of Co2Si samples doped with 2 at%, 4 at% and 8 at% Mn was 8.26 emu/g, 20.33 emu/g and 14.65 emu/g, respectively.The doping of Cu significantly improved the comprehensive absorption performance of Co2Si alloy, and the lowest reflection loss was obtained when Cu was doped with Co2Si alloy, with an RLmin value of -67.61 dB and an EAB of 2.40 GHz. The comprehensive absorption performance of Mn doped Co2Si was also improved, and the RLmin value of Mn doped with 4 at% was -67.04 dB, and the EAB was 2.39 GHz.This is because that the small Co2-xMxSi (M=Cu,Mn) alloy can produce multiple reflection and scattering effects, which increase the propagation path of the electromagnetic wave and optimize the impedance matching characteristics of the material.

SiC whisker/AgNWs/TPU composite film with asymmetric structure for low‐reflection electromagnetic interference shielding

AbstractThe design and preparation of lightweight and flexible electromagnetic interference (EMI) shielding composites with high efficiency and low reflection are critical to the electronic field. First, silver nanowires (AgNWs) were vacuum filtered on the electrospun thermoplastic polyurethane (TPU) fibrous film. Then, by combining the adhesive with the electrospun silicon carbide nanowhisker (SiCnw) @TPU composite fibrous film, the asymmetric EMI shielding composite films with high electromagnetic shielding efficiency (EMI SE) and low incident power were obtained. The lower AgNWs‐TPU layer provides the primary EMI SE, and the upper SiCnw@TPU fibrous film is used for electromagnetic wave absorption. This unique asymmetric structure, the synergistic effect of SiCnw's particular absorbing function and the excellent conductivity of the AgNWs layer make the film show high overall SE (SET = 55.18 dB). In order to improve the absorption effect of the composite film, the number of layers of SiCnw@TPU was adjusted, resulting in a final reflection coefficient value as low as 0.55. This work proposes a new strategy for developing EMI shielding composite films with high efficiency and low reflection, serving as a reference.

Reconfigurable metamaterial processing units that solve arbitrary linear calculus equations

Calculus equations serve as fundamental frameworks in mathematics, enabling describing an extensive range of natural phenomena and scientific principles, such as thermodynamics and electromagnetics. Analog computing with electromagnetic waves presents an intriguing opportunity to solve calculus equations with unparalleled speed, while facing an inevitable tradeoff in computing density and equation reconfigurability. Here, we propose a reconfigurable metamaterial processing unit (MPU) that solves arbitrary linear calculus equations at a very fast speed. Subwavelength kernels based on inverse-designed pixel metamaterials are used to perform calculus operations on time-domain signals. In addition, feedback mechanisms and reconfigurable components are used to formulate and solve calculus equations with different orders and coefficients. A prototype of this MPU with a compact planar size of 0.93λ0×0.93λ0 (λ0 is the free-space wavelength) is constructed and evaluated in microwave frequencies. Experimental results demonstrate the MPU’s ability to successfully solve arbitrary linear calculus equations. With the merits of compactness, easy integration, reconfigurability, and reusability, the proposed MPU provides a potential route for integrated analog computing with high speed of signal processing.

Liquid Crystal Integrated Dynamic Terahertz Metalenses

AbstractMetasurfaces can freely manipulate the wavefront of electromagnetic waves with the merits of minimization and integration. Dynamic metadevices have continued to be urgently pursued to realize on‐demand functionalities. Among them, dynamic metalenses have attracted particular attention due to their widespread applications, especially in the promising terahertz region. Here, a liquid crystal integrated terahertz metalens with dynamic focusing properties is proposed. Subwavelength silicon columns are specifically designed and set to realize the same lens phase profile for orthogonal linear polarizations, while the rotation of columns additionally introduces a spin‐selective conjugated geometric phase. A photopatterned liquid crystal layer is added to compensate for the geometric phase; therefore, a polarization‐independent single focus is achieved. With a saturated bias applied to the liquid crystal, the phase compensation vanishes; therefore, a spin‐selective bifocal function is realized. When lens and polarization grating profiles are encoded to the geometric phase separately, longitudinal and lateral spin‐dependent focus separations are demonstrated. The metalens can be electrically switched between single‐focus and bifocal functions. The dynamic metalens can be utilized in depth‐of‐field imaging and telecom port selection. The design endows various existing metadevices with dynamic functions.

Ultratough and self‐healable electromagnetic interference shielding materials with sandwiched silver nanowires in polyurethane composite films

AbstractThis study presents a facile self‐healing electromagnetic interference (EMI) shielding composite by sandwiching a layer of silver nanowires (AgNWs) between two layers of self‐healing polyurethane (SPU). The AgNWs layer forms an interconnected conductive network that effectively reflects and absorbs electromagnetic radiation, providing efficient EMI shielding. The SPU layers contribute autonomous healing of mechanical damages and restoring structural integrity and conductive pathways. The composite films exhibit remarkable EMI shielding effectiveness (SE) (up to 64.6 dB), exceptional mechanical toughness (106.4 MJ/m3), and self‐healing capabilities, outperforming conventional shielding materials. The synergy between AgNWs and SPU layers offers lightweight, flexible, tough, and self‐healing properties, making this material highly promising for applications in wearable electronics, aerospace, and automotive industries where durability and long‐term reliability are critical.Highlights Facile fabrication of sandwiched AgNWs layer between SPU films. Sandwiched AgNWs/SPU films with exceptional EMI shielding. AgNWs form conductive networks for efficient EMI shielding. Remarkable mechanical toughness of 106.4 MJ/m3 and self‐healing capability. Potential shielding materials for lightweight, wearable electronics, aerospace.

Large-Depth Ground-Penetrating Radar for Investigating Active Faults: The Case of the 2017 Casamicciola Fault System, Ischia Island (Italy)

We conducted large-depth Ground-Penetrating Radar investigations of the seismogenic Casamicciola fault system at the volcanic island of Ischia, with the aim of constraining the source characteristics of this active and capable fault system. On 21 August 2017, a shallow (hypocentral depth of 1.2 km), moderate (Md = 4.0) earthquake hit the island, causing severe damage and two fatalities. This was the first damaging earthquake recorded on the volcanic island of Ischia from the beginning of the instrumental era. Our survey was performed using the Loza low-frequency (15–25 MHz) GPR system calibrated by TDEM results. The data highlighted variations in the electromagnetic signal due to the presence of contacts, i.e., faults down to a depth larger than 100 m below the surface. These signal variations match with the position of the synthetic and antithetic active fault system bordering the Casamicciola Holocene graben. Our study highlights the importance of employing large-depth Ground-Penetrating Radar geophysical techniques for investigating active fault systems not only in their shallower parts, but also down to a few hundred meters’ depth, providing a contribution to the knowledge of seismic hazard studies on the island of Ischia and elsewhere.

Electromagnetic wave scattering in plasma beam driven waveguides under strong magnetic field

Abstract This work analyzes the scattering of electromagnetic wave in a cold and uniform plasma-filled waveguide driven by an intense relativistic plasma beam under a strong magnetic field. The strong interaction of plasma with electromagnetic waves is the cause of its potential use in different types of waveguides. The Helmholtz's equation governs the boundary value problem which is solved by incorporating the mode matching technique. Invoking the boundary and matching conditions and the derived orthogonality and dispersion relations in this scheme gives an exact solution to the scattering problem. The numerical results shed light on the occurrence of reflection and transmission and flow of power. The power flux is plotted against angular frequency and various duct configurations. The solution is substantiated altogether through the befitting analytical and numerical results. The investigation of this structure reveals not only its mathematical but also the physical features.

In situ encapsulation of heterostructures induced microscopic factors to enhance polarization loss of transition metal sulfides microwave absorbers

With the rapid development of modern electronic devices, electromagnetic wave pollution has become increasingly severe. In the field of materials science research, developing superior microwave absorbers holds immense importance. Light-weight carbon nanotube composites are developed for their unique electronic structure and excellent mechanical properties for wide applications in electronics, communication devices, and other specific parts, considering ideal candidates for the preparation of new types of electromagnetic wave absorption materials. This study focuses on embedding Fe7S8/FeS2 heterostructures into nitrogen doped carbon nanotubes through in-situ packaging to optimize interface engineering and improve the electromagnetic wave absorption efficiency of the material. Through pyrolysis and sulfidation processes, we successfully synthesized Fe7S8/FeS2 heterostructures in situ encapsulated within N-doped carbon nanotubes (NCNTs). Fe7S8/FeS2/NCNT shows microwave absorbing ability with a strong absorption (−36.83 dB at 14.08 GHz with a small thickness of 1.6 mm) and a broad effective absorption bandwidth (5.14 GHz). The excellent microwave absorption capability is mainly attributed to the efficient conductive network of NCNTs and the synergistic effect of Fe7S8/FeS2 heterostructures. This not only confirms the potential of transition metal sulfides/NCNTs composites in microwave attenuation applications, but also provides new strategies for the design and development of future microwave absorbers.

Graphene-based tunable broadband metamaterial absorber for terahertz waves

In order to overcome the limitations exhibited by traditional absorbers in electromagnetic wave absorption, such as the extremely narrow absorption bandwidth and uncontrollable absorption results, this paper proposes a novel tunable broadband metamaterial absorber based on graphene. Compared to other terahertz absorbers, the absorber designed in this study exhibits simpler structural design, compact form, thin thickness, efficient absorption performance, and a broader bandwidth. This absorber adopts a three-layer structure, including a patterned monolayer graphene metasurface, a dielectric layer, and a metal substrate. The structure of this patterned graphene consists of four triangular graphene resonators, achieving both high absorption efficiency and maintaining an exceptionally wide absorption bandwidth. The simulation results indicate that at a Fermi energy level Ef of 0.45 eV, the absorber achieves a broadband absorption rate of over 90 % in the 3.287 THz to 5.247 THz frequency range under normal terahertz wave incidence conditions. By analyzing different quantities of the triangular graphene structure on the top of the absorber, we found that the wide absorption bandwidth of the absorber is mainly attributed to the structural coupling of the top-layer graphene in the absorber. Furthermore, through the study of electric field amplitude and current distribution, we stumbled upon that when terahertz waves are incident on the absorber, due to the structural coupling between the graphene layers, electric resonance and magnetic resonance occur within the absorber, resulting in the absorption effect. Finally, through the study of geometric parameters, different polarization angles and oblique incidence angles of the incident waves, as well as different Fermi energy levels of graphene, we discovered that by adjusting the Fermi energy level of graphene, the bandwidth and absorption performance of the absorber can be flexibly tuned. In addition, this absorber exhibits wide-angle absorption characteristics and polarization-insensitive properties, providing potential application prospects in fields such as terahertz thermal imaging and stealth technology.

A Perspective of Fabrication and Applications of MXene–Metal Hybrids

Abstract2D materials with ultrathin structure, high specific areas, and excellent mechanical properties provide potentials to enhance the electrical, mechanical, and chemical properties of metals. In particular, MXene with different compositions, abundant surface terminations, high electrical conductivity has good affinity with some metals such as Al, Li, Na as well as can be uniformly dispersed in the metals. Moreover, the above unique features enable the MXene–metal hybrids with diversified functions. In this review, the current advanced studies in the topic of MXene–metal hybrids are summarized. The properties of MXenes such as mechanical properties, electrical conductivity, wettability, and surface properties of MXenes are first reviewed. Subsequently, different synthetic approaches including physical, metallurgy, electrochemical, and wet‐chemical routes are screened. By harnessing the above unique features, MXene could enhance the electrical, mechanical, and chemical properties of the hybrids, and their application such as energy storage devices, anticorrosion coating, functional structural materials, electromagnetic wave absorption are highlighted. Finally, an outlook on the in‐operando characterization techniques is provided to clarify the strengthening mechanism of MXenes in metals, tailoration of interface between MXenes and metals, and urgent need for industrial‐scale manufacture of MXene–metal hybrids.

Constraining gravitational wave velocities using gravitational and electromagnetic wave observations of white dwarf binaries

Abstract Although the general theory of relativity (GR) predicts that gravitational waves (GWs) have exactly the same propagation velocity as electromagnetic (EM) waves, many theories of gravity beyond GR expect otherwise. Accurate measurement of the difference in their propagation speed, or a tight constraint on it, could be crucial to validate or put limits on theories beyond GR. The proposed future space-borne GW detectors are poised to detect a substantial number of galactic white dwarf binaries (GWDBs), which emit the GW as semi-monochromatic signals. Concurrently, these GWDBs can also be identified as optical variable sources. Here we proposed that allocating a GWDB’s optical light curve and contemporaneous GW signal can be used to trace the difference between the velocity of GW and EM waves. Simulating GW and EM wave data from 14 verification binaries (VBs), our method constrains propagation-originated phase differences, limiting the discrepancy between the speed of light (c) and GW (cGW). Through the utilization of LISA’s design sensitivity and the current precision in optical observation on GWDB, our study reveals that a four-year observation of the 14 recognized VBs results in a joint constraint that confines Δc/c (Δc = cGW − c) to the range of −2.1 × 10−12 and 4.8 × 10−12. Additionally, by incorporating this constraint on cGW, we are able to establish boundaries for the mass of the graviton, limiting it to mg ≤ 3 × 10−23 eV/c2, and for the parameter associated with local Lorentz violation, $\bar{s}_{00}$, constrained within the range of $-3.4\times 10^{-11}\le \bar{s}_{00}\le 1.5\times 10^{-11}$.

Porous-multilayered Ti3C2Tx MXene hybrid carbon foams for tunable and efficient electromagnetic wave absorption

The rapid development of modern wireless communication technology makes electromagnetic wave pollution increasingly serious, necessitating the development of high-performance electromagnetic wave-absorbing materials. This study introduces a Ti3C2Tx MXene hybrid carbon foam (HCF) that exhibits a tunable and efficient electromagnetic wave absorption performance. The HCF features a porous, multilayered structure, which enhances its multi-reflection properties, and a heterogeneous interface between the carbon foam and MXene boosting its dielectric loss. By regulating the content of MXene, the ratio of polarization loss to conduction loss can be regulated to achieve better impedance matching. As a result, the HCF demonstrated superb electromagnetic wave absorption performance with RLmin = −72.25 dB and EABmax = 6.55 GHz. Furthermore, the minimum absorption frequency domain could be tuned within 8–14 GHz by varying the MXene content. The performance in radar wave absorption and electromagnetic-thermal conversion (ramp rate 85.81 °C/s from RT to 200 °C) proves that HCF is an efficient and reliable electromagnetic wave absorber, suitable for radar technology, microwave heating, and communication systems applications.

Bimetallic two-dimensional metal-organic frameworks nanosheets derived bimetallic@C composite materials for effective electromagnetic wave absorption

The development of information technology has resulted in serious environmental pollution and health concerns due to electromagnetic wave radiation. There is a necessity to develop electromagnetic wave absorbers with strong absorption, wide bandwidth, thin thickness, light weight, and environmental friendliness. In this study, a series of Ni4Cux@C composite materials was synthesized through a simple coprecipitation and pyrolysis process. The morphology and absorption properties of the composite materials were precisely tuned by adjusting the ratio of the bimetallic Ni and Cu. The Ni4Cux@C two-dimensional nanosheets were designed to possess a high specific surface area and abundant porous structure, thus optimizing impedance matching. Its strong dielectric loss capability is collectively contributed to the excellent graphitization degree and multiple polarizations. Additionally, the dispersion of NiCu alloy nanodisks within the carbon matrix leads to the aggregation of a large number of free space charges at the heterogeneous interface, inducing the formation of interfacial polarization. The well-designed Ni4Cu2@C composite materials exhibit outstanding electromagnetic wave absorption capabilities, with the optimal reflection loss reaching -74.9 dB, and the maximum effective absorption bandwidth reaching 6.8 GHz (2.9 mm). This work provides an important research foundation for the rational design of a new generation of two-dimensional bimetallic electromagnetic waveabsorption materials.