Electromagnetic Waves Research Articles

Chiral flat-band optical cavity with atomically thin mirrors.

A fundamental requirement for photonic technologies is the ability to control the confinement and propagation of light. Widely used platforms include two-dimensional (2D) optical microcavities in which electromagnetic waves are confined in either metallic or distributed Bragg reflectors. Recently, transition metal dichalcogenides hosting tightly bound excitons with high optical quality have emerged as promising atomically thin mirrors. In this work, we propose and experimentally demonstrate a subwavelength 2D nanocavity using two atomically thin mirrors with degenerate resonances. Angle-resolved measurements show a flat band, which sets this system apart from conventional photonic cavities. We demonstrate how the excitonic nature of the mirrors enables the formation of chiral and tunable optical modes upon the application of an external magnetic field. Moreover, we show the electrical tunability of the confined mode. Our work demonstrates a mechanism for confining light with high-quality excitonic materials, opening perspectives for spin-photon interfaces, and chiral cavity electrodynamics.

H-CoFe2O4/Ti3C2Tx/BNC Hybrid Aerogels with Modulation Impedance Matching for Electromagnetic Wave Absorption and Health Monitoring.

Given the limitations of single-function electromagnetic wave-absorbing materials (EWAMs) in meeting the evolving demands of complex usage scenarios, there is a growing need for structure-function integrated composites that offer a combination of microwave absorption, human monitoring, and thermal insulation. This study successfully synthesized two-dimensional (2D) Ti3C2Tx MXene via selective etching of Al from the Ti3AlC2 MAX phase. By introducing MXene into a composite of hydroxylated CoFe2O4 nanoparticles (h-CFO NPs) and bacterial nanocellulose (BNC) to modulate the electromagnetic performance of the EWAMs. The optimized electromagnetic parameters and three-dimensional (3D) porous structure achieve enhanced impedance matching of the wave absorber. The h-CFO/BNC/MXene (h-CFO@CM73) hybrid aerogel demonstrates superior electromagnetic wave absorption (EMWA) performance due to the synergistic effects of conductive loss, magnetic loss, interfacial polarization, and dipole polarization, where a minimum reflection loss (RLmin) of -32.66 dB at a thickness of 4.5 mm, an effective absorption bandwidth (EAB) of 10.70 GHz within the test range, and an EMWA efficiency reaching up to 99.92% were realized. Moreover, the hybrid aerogel presents sensitive sensing capabilities, detecting human joint movements, breathing, and vocalizations. Additionally, the developed hybrid aerogels exhibit commendable thermal insulation and infrared camouflage properties. Consequently, the fabricated multifunctional hybrid aerogel has excellent potential for monitoring care of infants, children, and pregnant women.

Interrelation between mechanical and electromagnetic radiation emission parameters with variable notch-width ratios under tensile fracture in silicon steel

Abstract The research investigates the effect of variable notch-width ratios on mechanical and electromagnetic radiation (EMR) parameters during the tensile fracture of silicon steel. The primary purpose is to comprehend the plastic deformation and crack propagation at an atomic level. The mechanical and EMR parameters chosen for analysis were correlated. The EMR energy release rate correlated well with the elastic strain energy release rate. The good fit between the EMR parameters and the plastic zone radius is a novel method to determine the crack growth behaviour of metals. A theoretical model of dislocation predicted the nature of EMR signals at fracture. A reasonable agreement between cross-slip energy with maximum stress at crack instability, the elastic strain energy release rate, and the EMR energy release rate will help assess the dislocation dynamics of metals. The EMR amplitude was sensitive to varying strain rates.

Investigation of electromagnetic wave propagation characteristics across various frequencies in porous media of goaf.

The reliable long-distance transmission of electromagnetic wave signals within goaf is fundamental for the implementation of wireless monitoring and early warning systems for goaf-related disasters. This paper establishes an experimental platform for electromagnetic wave signal transmission within goaf and develops a propagation model for electromagnetic waves in the porous media of goaf. The transmission characteristics of electromagnetic waves at various frequencies within the porous media environment of goaf are investigated through experimental and numerical simulation approaches. The results indicate that the received signal intensity of electromagnetic waves across different frequency bands diminishes with increasing propagation distance in the lossy environment of the goaf. Initially, the decay follows a logarithmic pattern, whereas, at later stages, the attenuation exhibits a gradual and smooth decrease. As the frequency increases, the initial attenuation amplitude of electromagnetic wave intensity rises; however, subsequent attenuation is largely unaffected by frequency, with the later attenuation rate being proportional to porosity. Electromagnetic waves at a frequency of 700 MHz exhibit a low attenuation coefficient under both experimental and simulated conditions, demonstrating superior stability and reliability. This frequency significantly enhances the overall performance of the communication system and is suitable for use as the operational frequency band in wireless sensor networks.

Validation of atmospheric evaporation duct in the eastern Indian Ocean

An atmospheric duct is an anomalous atmospheric structural phenomenon that causes trap refraction in the troposphere to change the propagation paths and ranges of electromagnetic waves, thereby increasing the detection distances of radar and other communications. Atmospheric ducts include evaporation, surface, and elevated ducts. Evaporation ducts are commonly found near the sea surface and can impact electromagnetic wave propagation, radar communication, and livelihood applications at low altitudes. The meteorological environment of the Indian Ocean is complex, and the characteristics of its evaporation duct are still poorly understood. We validate four select atmospheric duct models using the observed evaporation duct height (EDH) in the Indian Ocean and present their spatial as well as temporal characterizations in spring using in situ meteorological variables. The results show that the EDH derived using the Babin model has the lowest bias with the observed value; thus, the Babin model can be used by researchers in the future to study changes to the EDHs in sea areas with similar seasonal conditions. The EDH in the Indian Ocean has diurnal variations, with higher (lower) values during the daytime (nighttime). The EDH has a negative correlation with the relative humidity, and the standard deviation of the EDH is largest when the relative humidity is 90%. The EDH has the maximum value when the wind speed is in the range of 8–14 m/s and when the air–sea temperature difference is zero, i.e., ∆T=Tair−Tsea=0. This study validates four different EDH models in the Indian Ocean, thus broadening our knowledge on the tropical atmospheric boundary layer.

A Review on MXene/Nanocellulose Composites: Toward Wearable Multifunctional Electromagnetic Interference Shielding Application.

With the rapid development of mobile communication technology and wearable electronic devices, the electromagnetic radiation generated by high-frequency information exchange inevitably threatens human health, so high-performance wearable electromagnetic interference (EMI) shielding materials are urgently needed. The 2D nanomaterial MXene exhibits superior EMI shielding performance owing to its high conductivity, however, its mechanical properties are limited due to the high porosity between MXene nanosheets. In recent years, it has been reported that by introducing natural nanocellulose as an organic framework, the EMI shielding and mechanical properties of MXene/nanocellulose composites can be synergically improved, which are expected to be widely used in wearable multifunctional shielding devices. In this review, the electromagnetic wave (EMW) attenuation mechanism of EMI shielding materials is briefly introduced, and the latest progress of MXene/nanocellulose composites in wearable multifunctional EMI shielding applications is comprehensively reviewed, wherein the advantages and disadvantages of different preparation methods and various types of composites are summarized. Finally, the challenges and perspectives are discussed, regarding the performance improvement, the performance control mechanism, and the large-scale production of MXene/nanocellulose composites. This review can provide guidance on the design of flexible MXene/nanocellulose composites for multifunctional electromagnetic protection applications in the future intelligent wearable field.

Protein purification with light via a genetically encoded azobenzene side chain

Affinity chromatography is the method of choice for the rapid purification of proteins from cell extracts or culture supernatants. Here, we present the light-responsive Azo-tag, a short peptide comprising p-(phenylazo)-L-phenylalanine (Pap), whose side chain can be switched from its trans-ground state to the metastable cis-configuration by irradiation with mild UV light. Since only trans-Pap shows strong affinity to α-cyclodextrin (α-CD), a protein exhibiting the Azo-tag selectively binds to an α-CD chromatography matrix under daylight or in the dark but elutes quickly under physiological buffer flow when illuminating the column at 355 nm. We demonstrate the light-controlled single-step purification – termed Excitography – of diverse proteins, including enzymes and antibody fragments, without necessitating competing agents or harsh buffer conditions as normally applied. While affinity chromatography has so far been governed by chemical interactions, introducing control by electromagnetic radiation as a physical principle adds another dimension to this widely applied separation technique.

Transient electromagnetic sources can detect solitary black holes in Milky Way galaxy

Abstract The Milky Way galaxy is estimated to host up to a billion stellar-mass solitary black holes (BHs). The number and distribution of BH masses can provide crucial information about the processes involved in BH formation, the existence of primordial BHs, and the interpretation of gravitational wave (GW) signals detected in LIGO-VIRGO-KAGRA. Sahu et al. recently confirmed one solitary stellar-mass BH in our galaxy using astrometric microlensing. This work proposes a novel mechanism to identify such BH by analyzing the frequency and damping of the quasi-normal modes of GW generated from the interaction of the BH and EM wave originating from a transient electromagnetic (TEM) source. The incoming EM waves distort the curvature of a BH, releasing GWs as it returns to a steady state. Using the covariant semi-tetrad formalism, we quantify the generated GWs via the Regge-Wheeler tensor and relate the GW amplitude to the energy of the TEM. We demonstrate that isolated BHs at a distance of 50 pc from Earth can be detected by LIGO A+ and 100 pc by Cosmic Explorer/Einstein Telescope. Additionally, we discuss the observational implications for orphan afterglows associated with GRBs, highlighting the potential for further discoveries.

A Broadband and Wide-Scanning Dual-Polarized Dipole Array with Low Profile

This study presents a novel methodology for designing a planar broadband wide-scanning dual-polarized array using tightly-coupled dipoles and wide-angle impedance matching. By etching the S-shaped gaps between the dipoles and incorporating shorting vias with defected ground structures, we demonstrated that all radiation elements can be arranged on a single-layer substrate. Additionally, we introduced a thin printed circuit board (PCB) layer with two-dimensional periodic structures for impedance matching at wide scan angles. Leveraging high permittivity and constrained electromagnetic waves, we realized zero-scan blindness within this band. The aperture consisted of only two PCB layers, with a total profile of approximately 0.091λlow, where λlow represented the free-space wavelength at 6 GHz. A 3 × 4 dual-polarized array was fabricated and measured to validate the proposed approach. The measured active voltage standing wave ratio for one embedded array element surpassed 2.2 over 6–18 GHz. By enabling the orthogonal dipoles at the edge of the array to be mutually coupled using an additional metal patch, the active S11 for the edge cells exceeded −8.8 dB over 6.9–18 GHz. The measured patterns were in good agreement with simulations over 6–18 GHz, with the array exhibiting good radiation performance over ±60° in the E- and H-planes.

Intelligent Recognition of Road Internal Void Using Ground-Penetrating Radar

Internal road voids can lead to decreased load-bearing capacity, which may result in sudden road collapse, posing threats to traffic safety. Three-dimensional ground-penetrating radar (3D GPR) detects internal road structures by transmitting high-frequency electromagnetic waves into the ground and receiving reflected waves. However, due to noise interference during detection, accurately identifying void areas based on GPR-collected images remains a significant challenge. Therefore, in order to more accurately detect and identify the void areas inside the road, this study proposes an intelligent recognition method for internal road voids based on 3D GPR. First, extensive data on internal road voids was collected using 3D GPR, and the GPR echo characteristics of void areas were analyzed. To address the issue of poor image quality in GPR images, a GPR image enhancement model integrating multi-frequency information was proposed by combining the Unet model, Multi-Head Cross Attention mechanism, and diffusion model. Finally, the intelligent recognition model and enhanced GPR images were used to achieve intelligent and accurate recognition of internal road voids, followed by engineering validation. The research results demonstrate that the proposed road internal void image enhancement model achieves significant improvements in both visual effects and quantitative evaluation metrics, while providing more effective void features for intelligent recognition models. This study offers technical support for precise decision making in road maintenance and ensuring safe road operations.

Reflective linear polarization converter with multimode, dual band and high efficiency

Abstract A thin, dual-band, highly efficient linear polarization converter based on a multi-mode metasurface was proposed. The high-efficiency manipulation of polarization states of electromagnetic waves in dual-band frequencies was achieved by utilizing a diagonally etched metasurface as a square joined by a ring. The metasurface transforms incident linearly polarized (LP) waves into cross-polarized LP waves at various frequencies. Numerical simulations reveal that the metasurface operates efficiently in the bands from 7.724 GHz to 8.192 GHz and 13.142 GHz to 15.95 GHz, with a polarization conversion rate (PCR) of 95% in both bands. To validate the theoretical analysis and simulation results, a model is fabricated and measured. The experimental results confirm that the proposed metasurface successfully achieves dual band-and dual-mode polarization conversion, showing reasonable consistency of theoretical and simulated findings. This converter can optimize the signal performance by clarifying polarized radio waves.

Alloy Element Adjustment and Heat Treatment Combination in Enhancing Electromagnetic Wave Absorption Properties of FeCoNiCu Medium Entropy Alloy

Alloy Element Adjustment and Heat Treatment Combination in Enhancing Electromagnetic Wave Absorption Properties of FeCoNiCu Medium Entropy Alloy

Modulating the γ-ray Protection Properties of Melanin via a Highly Conjugated Catechol Structure.

Melanin is a dark pigment found in many organisms that interacts with various forms of electromagnetic radiation, such as X-rays, γ-rays, and Ultraviolet visible light, providing protection against radiation damage to the host. The mechanism by which melanin protects against ionizing radiation involves dissipating energy around the cell nucleus to form a perinuclear cap. Additionally, melanin reacts with the free radicals produced by the radiolysis of water, quenching reactive oxygen species. In this study, we introduced a conjugated monomer, hexahydroxytriphenylene (HHTP), which has a rigid planar structure, into selenomelanin. The aim was to increase the physical shielding ability of selenomelanin while increasing its free radical content. Our findings indicated that incorporating HHTP molecules into selenomelanin effectively increased the unpaired electron content of selenomelanin and protected immortalized human keratinocyte (HaCaT) cells from 10 Gy γ-rays exposure. Additionally, eumelanin supplemented with HHTP molecules demonstrated excellent biocompatibility and offered similar protection to HaCaT cells exposed to 10 Gy γ-rays at high concentrations. This study is important for optimizing the functionality of melanin through the modulation of its conjugated structure.

Artificial Photothermal Nociceptor Using Mott Oscillators.

Bioinspired sensory systems based on spike neural networks have received considerable attention in resolving high energy consumption and limited bandwidth in current sensory systems. To efficiently produce spike signals upon exposure to external stimuli, compact neuron devices are required for signal detection and their encoding into spikes in a single device. Herein, it is demonstrated that Mott oscillative spike neurons can integrate sensing and ceaseless spike generation in a compact form, which emulates the process of evoking photothermal sensing in the features of biological photothermal nociceptors. Interestingly, frequency-tunable and repetitive spikes are generated above the threshold value (Pth =84mWcm-2) as a characteristic of "threshold" in leaky-integrate-and-fire (LIF) neurons; the neuron devices successfully mimic a crucial feature of biological thermal nociceptors, including modulation of frequency coding and startup latency depending on the intensity of photothermal stimuli. Furthermore, Mott spike neurons are self-adapted after sensitization upon exposure to high-intensity electromagnetic radiation, which can replicate allodynia and hyperalgesia in a biological sensory system. Thus, this study presents a unique approach to capturing and encoding environmental source data into spikes, enabling efficient sensing of environmental sources for the application of adaptive sensory systems.

Effective Multi-Layered Structure Design with Carbon-Based Hybrid Polymer Nanocomposites Using Evolutionary Algorithms

Electromagnetic wave-absorbing materials (EMAMs) and structures are crucial in aerospace and electronic communications due to their ability to absorb electromagnetic waves. The development of materials that are lightweight, sustainable, and cost-effective, exhibiting high-performance absorption across a broad frequency spectrum, is therefore important. However, homogeneous electromagnetic absorbing materials require assistance to meet all these criteria. Therefore, developing multi-layer absorbing coatings is essential for enhancing performance. The present study uses 21 different composites of varying weight fractions of polypropylene, graphene nanoplatelets, and multiwall carbon nanotubes nanocomposites to develop multi-layer absorbing materials and optimize their performance. These multi-layer carbon polymer nanocomposites were meticulously constructed using evolutionary algorithms like Non-sorted Genetic Algorithm-II and Particle Swarm Optimization to achieve ultra-broadband electromagnetic wave absorption capabilities. Among the designed electromagnetic absorbing materials, a two-layer model, i.e., 1.5 wt% MWCNT/PP/epoxy with a thickness of 1.052 mm and 2.7% GNP/PP/epoxy with a thickness of 4.456 mm totaling 5.506 mm, was identified as optimal using NSGA-II. The structure has exhibited exceptional absorption performance with a minimum reflection loss of −21 dB and a qualified bandwidth extending to 4.2 GHz. PSO validated and optimized this structure, confirming NSGA-II’s efficiency and effectiveness in quickly obtaining optimal solutions. This broadband absorber design combines the structure design and material functioning through additive manufacturing, allowing it to absorb well over a wide frequency range.

Construction of 1D Molecular Conductive Wires Through a Polarized Gene Weaving Strategy for Efficient Electromagnetic Wave Absorption.

The growing threat of electromagnetic pollution has become a pressing safety concern. Metal-organic framework (MOF) derivatives are considered ideal candidates for mitigating electromagnetic radiation. However, due to the limitations imposed by complex post-processing and disruption of pristine crystal structures, the mechanisms of electromagnetic wave absorption remain unclear, let alone achieving atomic-level regulation in MOF derivatives. Moreover, research on MOF-based electromagnetic wave absorbers (EMWA) has predominantly focused on 2D and 3D structures, leaving 1D MOFs largely unexplored. To address these challenges, a bottom-up polarization gene weaving strategy is proposed to integrate polarizable conjugated groups, thieno(3,2-b)thiophene (TBTT), into two types of conductive MOFs by fine-tuning self-assembly conditions. As expected, both MOFs exhibited strong natural polarization effects. Among them, the 1D linear coordination mode of CuTBTT-1D demonstrated enhanced charge carrier mobility and geometric effects compared to the 2D structure, CuTBTT-2D. The synthesized 1D molecular polarization wire, with a thickness of 2.2mm, achieved ultra-high reflection loss (-77dB) and super-wide absorption bandwidth (6.52GHz). Its performance surpasses that of all known MOF-based EMWAs. This study provides a valuable strategy for the rational design of next-generation 1D MOF EMWA with atomic precision.

Tunable directional radiation and reception based on magneto-optical photonic crystal waveguides

Abstract We have proposed a magneto-optical photonic crystal (MOPC) waveguide that can not only realize highly directional radiation but also work as an electromagnetic (EM) wave receiver. This waveguide consists of a square MOPC and a covering layer of Al2O3 PC tilted at 45° that allows for the penetration of EM waves. Due to the broken time-reversal symmetry caused by an external magnetic field, there exists a unidirectional leaky topological edge state within the photonic bandgap. Such the leaky edge state transmits unidirectional and radiates into the air simultaneously, leading to a broadside radiation beam with a low half-power beam width of less than 4°. More importantly, the radiation direction of the beam can be tuned over a wide angular range by adjusting the operation frequency or the magnetic field strength. Besides, this designed waveguide can also act as a tunable receiver for capturing incident EM waves effectively. These results have potential for various practical applications, such as antennas and sensors.

Accounting for the Different Propagation Velocities for the Focusing and Time–Depth Conversion in a Layered Medium

This contribution deals with the focusing and time–depth conversion of GPR data in a two-layer scenario. In a layered scenario, the different propagation velocities of the electromagnetic waves in different layers can induce distortion in the reconstruction. In particular, it is not possible, with common data processing, to achieve the focusing of both the targets embedded in the upper and deeper layers at the same time. We will present a strategy for mitigating this problem. The strength points of this strategy are its simplicity and the fact that it only requires a commercial code for the GPR data processing plus some steps easily implementable through a homemade code. This work extends a contribution of the same authors at the 20th International GPR conference held in Chanchung, China, in June 2024, and the conclusions are updated with three-dimensional numerical results, including depth slices determined directly in the spatial domain. Both numerical and experimental data will be shown.

Raman intensity enhancement of Raman active and forbidden modes induced by naturally occurred hot spot at GaAs edge

Abstract Edge structures are ubiquitous in the processing and fabrication of various optoelectronic devices. Novel physical properties and enhanced light-matter interactions are anticipated to occur at crystal edges due to its broken spatial translational symmetry. However, the intensity of first-order Raman scattering at crystal edges has been rarely explored, although the mechanical stress and edge characteristics have been thoroughly studied by the Raman peak shift and the spectral features of the edge-related Raman modes. Here, by taking GaAs crystal with a well-defined edge as an example, we reveal the intensity enhancement of Raman-active modes and the emergence of Raman-forbidden modes under specific polarization Raman configurations at the edge. This is attributed to the presence of hot spot at the edge, due to the redistributed electromagnetic fields and electromagnetic wave propagations of incident laser and Raman signal near the edge, which are confirmed by the finite-difference time-domain simulations. Spatially-resolved Raman intensity of both Raman-active and Raman-forbidden modes near the edge is calculated based on the redistributed electromagnetic fields, which quantitatively reproduce the corresponding experimental result. These findings offer new insights into the intensity enhancement of Raman scattering at crystal edges and presents a new avenue to manipulate the light-matter interactions of crystal by manufacturing various types of edges and to characterize the edge structures in photonic and optoelectronic devices.

Local Charge Regulation in Selenides via High‐Entropy Engineering to Boost Electromagnetic Wave Absorption

AbstractLocal charge modulation is an effective method to improve the polarization loss and electromagnetic (EM) absorption characteristics. However, the use of conventional means (doping, defects, heterojunction surfaces) remains singular and limited in achieving local charge modulation. Surprisingly, lattice distortions induced by high‐entropy engineering can intrinsically regulate local charge states and improve EM wave absorption performances. Herein, a series of selenides with enhanced configuration entropy are designed and prepared to improve polarization loss capacity. Due to the different radii of the mixed ions and the Jahn‐Teller distortion effect, the local charge of the selenides is effectively modulated by the presence of defects and strong lattice distortions inside the lattice. Uneven distribution of charge at defects and formation of boundaries promotes defect‐induced polarization and interface polarization, respectively. Compared to single NiSe2, high‐entropy (NiFeCuCoMn)Se2 with an entropy value of 1.53R has more severe lattice defects and suitable impedance matching properties, exhibiting good EM absorption properties both in the absorption intensity and respond frequency. Tailoring the local charge density via an entropy strategy paves a new way for the high‐performance EM absorption materials.