Electromagnetic Waves Research Articles

A Semi-amorphous Ti-BDC-derived Ti/C nanocomposite for efficient electromagnetic wave absorption

Electromagnetic (EM) interference presents a crippling risk to both human health and the dependability of technological devices. Due to their diverse advantages, metal-organic framework (MOF) derivatives have received much attention in developing novel EM wave-absorbing materials. Nevertheless, achieving desirable EM wave absorption capabilities in magnetic carbon-based absorbers through deliberate adjustment of MOFs remains a difficult task. In this study, a novel nanoporous carbon material (TiO2/C) has been successfully synthesized by a semi-amorphous material (Ti-BDC), which has excellent EM wave absorption properties. In detail, the minimum reflection loss (RL) of −49.7 dB and broad effective absorbing bandwidth (EAB) of 4.16 GHz can be reached with an absorbent thickness of 2.2 mm. The improved performance is mostly due to the dipole polarization of the functional groups and the even distribution of the nanoparticles, which form a seamless network. This promotes the dissipation of polarization and dielectric energy at the interface. In addition, the TiO2 nanoparticles on the carbon material improve the impedance matching, further enhancing the material's absorption performance.

Nonlinear dynamics driving the conversion of gravitational and electromagnetic waves in cylindrically symmetric spacetime

Nonlinear dynamics driving the conversion of gravitational and electromagnetic waves in cylindrically symmetric spacetime

Synthesis and characterisation of calcium-iron-aluminium nanocomposites for electromagnetic radiation shielding application.

Electromagnetic shielding parameters are crucial to investigate unexplored nanoparticles and their nanocomposites. Herein, calcium-iron-aluminium (Ca: Fe: Al) nanocomposites are synthesised using the simple solution combustion technique. The as-synthesised nanocomposites with various doping concentrations of Al nanoparticles are characterised to study the structural and surface parameters and to confirm the successful formation. Further, the procured Ca: Fe: Al nanocomposites along with various doping concentrations are utilised for electromagnetic shielding applications, and various shielding parameters are calculated. It was confirmed that Ca: Fe: Al nanocomposites are suitable for electromagnetic shielding applications.

Dynamical analysis of a discrete Aihara neuron under a locally active memristor as electromagnetic radiation and its DSP implementation

The study of neuron model under electromagnetic radiation is significant for learning brain principles and treating mental diseases. In this paper, a novel discrete locally active memristor(DLAM) model is designed and its characteristics are investigated thoroughly. Then, the DLAM is used to imitate electromagnetic radiation to stimulate Aihara neuron, called EMR-Aihara neuron model. The equilibrium point of this discrete model is analyzed. Dynamical characteristics are studied by means of phase diagram, iteration sequence, bifurcation diagram, Lyapunov Exponent spectrum(LEs), Kolmogorow entropy(KE) and Spectral Entropy(SE) complexity. With these analysis methods, rich dynamical behaviors and neuron firing patterns are discovered from the EMR-Aihara neuron map, including hyperchaos, chaos and period. In addition, complex multistability and state transition phenomena concerning various attractors and neuron firing modes are observed. This EMR-Aihara neuron map is implemented in digital circuit by DSP platform as well, confirming the physical availability of the model. The EMR-Aihara neuron model can simulate biological neuron under electromagnetic radiation and apply to image encryption.

In Situ Exsolution-Prepared Solid-Solution-Type Sulfides with Intracrystal Polarization for Efficient and Selective Absorption of Low-Frequency Electromagnetic Wave.

The excellent dielectric properties and tunable structural design of metal sulfides have attracted considerable interest in realizing electromagnetic wave (EMW) absorption. However, compared with traditional monometallic and bimetallic sulfides that are extensively studied, the unique physical characteristics of solid-solution-type sulfides in response to EMW have not been revealed yet. Herein, a unique method for preparing high-purity solid-solution-type sulfides is proposed based on solid-phase in situ exsolution of different metal ions from hybrid precursors. Utilizing CoAl-LDH/MIL-88A composite as a precursor, Fe0.8Co0.2S single-phase nanoparticles are uniformly in situ formed on an amorphous substrate (denoted as CoAl), forming CoAl/Fe0.8Co0.2S heterostructure. Combing with density functional theory (DFT) calculations and wave absorption simulations, it is revealed that Fe0.8Co0.2S solid solution has stronger intracrystal polarization and electronic conductivity than traditional monometallic and bimetallic sulfides, which lead to higher dielectric properties in EM field. Therefore, CoAl/Fe0.8Co0.2S heterostructure exhibits significantly enhanced EMW absorption ability in the low-frequency region (2-6GHz) and can achieve frequency screening by selectively absorbing EMW of specific frequency. This work not only provides a unique method for preparing high-purity solid-solution-type sulfides but also fundamentally reveals the physical essence of their excellent EMW absorption performance.

Unidirectional guided-wave-driven metasurfaces for arbitrary wavefront control

Metasurfaces are capable of fully reshaping the wavefronts of incident beams in desired manners. However, the requirement for external light excitation and the resonant nature of their meta-atoms, make challenging their on-chip integration. Here, we introduce the concept and design of a fresh class of metasurfaces, driven by unidirectional guided waves, capable of arbitrary wavefront control based on the unique dispersion properties of unidirectional guided waves rather than resonant meta-atoms. Upon experimentally demonstrating the feasibility of our designs in the microwave regime, we numerically validate the introduced principle through the design of several microwave meta-devices using metal-air-gyromagnetic unidirectional surface magneto-plasmons, agilely converting unidirectional guided modes into the wavefronts of 3D Bessel beams, focused waves, and controllable vortex beams. We, further, numerically demonstrate sub-diffraction focusing, which is beyond the capability of conventional metasurfaces. Our unfamiliar yet practical designs may enable full, broadband manipulation of electromagnetic waves on deep subwavelength scales.

Transmissive invisibility cloak using phase gradient metasurfaces

Different from the reflective approach of the carpet cloak designed to conceal surface irregularities on highly reflective surfaces, the transmission invisibility cloak, often capable of achieving perfect invisibility, operates within a transmission geometry. In this configuration, the cloaking mechanism ensures that an object neither reflects nor refracts incoming waves in free space, presenting opportunities for more versatile applications, though with the requirement for intricate designs. This paper introduces a novel methodology for designing a transmissive invisibility cloak, employing a simplified combination structure of two phase-gradient metasurfaces based on the generalized Snell’s law. Initially, we designed a highly transparent metasurface for the millimeter-wave band to yield diverse phase gradients. We confirmed the effectiveness of this metasurface through the observation of abnormal refraction. Then, through a deliberate arrangement of these phase gradients, we construct a transmissive invisibility cloak that guides electromagnetic waves around the cloaked region. Simulations and experimental measurements conducted under plane-wave conditions demonstrate the cloak’s effectiveness and practical applicability. The ensuing comparative investigations of results among free space, uncloaked objects, and cloaked objects validate the expected cloaking effect, offering valuable insights into the design and functionality of transmissive invisibility cloaks.

Hierarchical Magnetic Carbon Nanoflowers for Ultra-Efficient Electromagnetic Wave Absorption.

Porous carbon nanomaterials are widely applied in the electromagnetic wave absorption (EMWA) field. Among them, an emerging flower-like carbon nanomaterial, termed carbon nanoflowers (CNFs), has attracted tremendous research attention due to their unique hierarchical flower-like structure. However, the design of flower-like carbon nanomaterials with different magnetic cores for EMWA has rarely been reported. Herein, a general template method is proposed to achieve a set of high-quality magnetic CNFs, namely Co@Void@CNFs, CoNi@CNFs, and Ni@CNFs. The prepared magnetic CNFs have highly accessible surface area and internal space, rich heteroatom content, multi-scale pore system, and uniform and highly dispersed magnetic nanoparticles, as a result, deliver superior EMWA performance. Specifically, when the thickness is 2.6mm, the Co@Void@CNFs exhibit a maximum refection loss (RLmax) of -56.6dB and an effective absorption bandwidth (EAB) from 8.0 to 12.1GHz covering the whole X band. The CoNi@CNFs have an RLmax of up to -57.6dB and a wide EAB of 5.6GHz at just 1.9mm. For the Ni@CNFs, possess an ultra-broad EAB of 6.1GHz, covering the entire Ku band at 2.0mm. Overall, the hierarchical magnetic carbon nanoflowers proposed here offer new insights toward realizing multifunctional integrated carbon nanomaterials for EMWA.

Analytical Solution for Transient Thermal Behavior of Two Semisolids With Contact Resistance and Interfacial Heat Generation

Abstract The problem of two dissimilar semi-infinite solids at different initial temperatures brought into contact has a well-known simple analytical solution. In this work, this problem is reexamined with the additional simultaneous complications of both contact resistance and surface heat generation. While contact resistance is always present to some degree due to surface asperities or oxidation layers, heat generation at the contact interface can also occur in certain situations. These situations can occur in applications such as ultrasonic welding or arise in situations involving electromagnetic radiation passing through an optically transparent medium, but dissipating as heat at an interface with an opaque material that is in contact with the transparent material. In this paper, an analytical solution to the unsteady conduction problem is developed that accounts for both contact resistance and interfacial heat generation. The solution confirms that the initially warmer object rapidly decreases in temperature in the vicinity of the interface as heat flows into the cooler object and the heat generated at the interface preferentially flows to the cooler material. After a short time, however, the temperatures of both materials at the interface increase in temperature above even the initial temperature of the initially hotter material. An experiment was performed that verified the analytical solution.

Electron Dynamics Associated With Advection and Diffusion in Self‐Consistent Wave‐Particle Interactions With Oblique Chorus Waves

AbstractChorus waves are intense electromagnetic emissions critical in modulating electron dynamics. In this study, we perform two‐dimensional particle‐in‐cell simulations to investigate self‐consistent wave‐particle interactions with oblique chorus waves. We first analyze the electron dynamics sampled from cyclotron and Landau resonances with waves, and then quantify the advection and diffusion coefficients through statistical studies. It is found that phase‐trapped cyclotron resonant electrons satisfy the second‐order resonance condition and gain energy from waves. While phase‐bunched cyclotron resonant electrons cannot remain in resonance for long periods. They transfer energy to waves and are scattered to smaller pitch angles. Landau resonant electrons are primarily energized by waves. For both types of resonances, advection coefficients are greater than diffusion coefficients when the wave amplitude is large. Our study highlights the important role of advection in electron dynamics modulation resulting from nonlinear wave‐particle interactions.

Blind Source Separation of Electromagnetic Signals Based on Swish-Tasnet

Blind Source Separation of Electromagnetic Signals Based on Swish-Tasnet

Super-resolution by converting evanescent waves in microsphere to propagating waves and light transmitted from its surface to nano-jet

The electro-magnetic (EM) waves transmitted through a thin object with fine structures is observed, by microsphere located above the thin object. The EM radiation transmitted through the object produces both evanescent waves, which include information on the fine structures of the object (smaller than a wavelength), and propagating waves which include the large image of the object (with dimensions larger than a wavelength). The super-resolutions are calculated by using Helmholtz equation. According to this equation, evanescent waves have an imaginary component of the wavevector in the z direction, leading the components of the wavevector, in the transversal directions, to becomes very large, so that the fine structures of the object can be observed. Due to the decay of the evanescent waves, only a small region near the contact point, between the thin object and the microsphere is effective for producing the super resolution effects. The image with super-resolution can be increased by a movement of the microsphere over the object, or by using arrays of microspheres. Both propagating and evanescent waves arrive at the inner surface of the microsphere. A coupling between the transmitted EM waves and resonances produced in the dielectric sphere, possibly obtained by Mie method, leads to product of the EM distribution function with the transfer function. While this transfer function might be calculated by Mie method it is possible also to use it as an experimental function. By Fourier transform of the above product we get convolution between the EM spatial modes and those of the transfer function arriving at the nano-jet, which leads the evanescent waves to become propagating waves, with effective very small wavelengths, and thus increase the resolution.

Coherent radiation of an electron bunch colliding with an intense laser pulse

We study the conditions for coherent radiation of an electron bunch driven by a counterpropagating strong pulsed electromagnetic plane wave. We derive the spectrum of the coherent radiation and show that it is emitted backward with respect to the laser propagation direction and has a very narrow angular spread. We demonstrate that for a solid density plasma coherent radiation extends to frequencies up to hundreds of keV, thereby enhancing the low-frequency part of the spectrum by many orders of magnitude. Our analytical findings are tested with three-dimensional particle-in-cell simulations of an electron bunch passing through a laser pulse, clearly demonstrating how the coherence can essentially modify the observed radiation spectrum. Published by the American Physical Society 2024

V-Based MXene/MAX Heterostructure Composites with Enhancing Dielectric Loss for Broadband Microwave Absorption.

Electromagnetic wave absorption performance is strictly dependent on attenuation and impedance matching, which are directly influenced by the ratio of MXene/MAX in the multilayer structured MXene/MAX composites. However, there is still a challenge to achieve collaborative optimization of dielectric loss and impedance matching by precisely regulating the proportional relationship of MXene/MAX. Herein, V-based MXene/MAX heterostructure composites with different V2C/V2AlC ratios were successfully synthesized by rationally controlling the temperature and time of the hydrothermal reaction. Experimental results indicated that V2C-100 °C-1 harvested the balance between reduced impedance matching and enhanced dielectric losses, which was attributed to the mildly enhanced conduction loss and polarization loss. The first principles indicated that abundant electrons migrate from the V atoms of the MXene to the C atoms of the MAX phase. The charge redistributed and accumulated at the interface, exciting the increase in the dielectric loss of V2C-100 °C-1. As a result, the V2C-100 °C-1 heterostructure composite had an excellent electromagnetic absorption effect with a minimum reflection loss of -50.06 dB and a wide effective absorption bandwidth of 4.0 GHz (12.72-16.72 GHz). This work provides a valuable experience for the development of efficient MXene-based microwave absorbing materials.

Research on Food Preservation Based on Antibacterial Technology: Progress and Future Prospects

The nutrients present in food are not only prone to a series of physicochemical reactions but also provide conditions for the growth and reproduction of foodborne microorganisms. In recent years, many innovative methods from different fields have been introduced into food preservation, which extends the shelf life while maximizing the preservation of the original ingredients and properties of food. In this field, there is a lack of a systematic summary of new technologies emerging. In view of this, we overview the innovative methods applied to the field of food preservation in recent 3 years, focusing on a variety of technological approaches such as antimicrobial photodynamic therapy based on nanotechnology, electromagnetic radiation sterilization based on radiation technology, and antimicrobial peptides based on biomolecules. We also discuss the preservation mechanism and the application of the different methods to specific categories of products. We evaluated their advantages and limitations in the food industry, describing their development prospects. In addition, as microorganisms are the main causes of food spoilage, our review also has reference significance for clinical antibacterial treatment.

Robust Electrothermal Switching of Optical Phase‐Change Materials through Computer‐Aided Adaptive Pulse Optimization

Electrically tunable optical devices present diverse functionalities for manipulating electromagnetic waves by leveraging elements capable of reversibly switching between different optical states. This adaptability in adjusting their responses to electromagnetic waves after fabrication is crucial for developing more efficient and compact optical systems for a broad range of applications, including sensing, imaging, telecommunications, and data storage. Chalcogenide‐based phase‐change materials (PCMs) have shown great promise due to their stable, nonvolatile phase transition between amorphous and crystalline states. Nonetheless, optimizing the switching parameters of PCM devices and maintaining their stable operation over thousands of cycles with minimal variation can be challenging. Herein, the critical role of PCM pattern as well as electrical pulse form in achieving reliable and stable switching is reported on, extending the operational lifetime of the device beyond 13000 switching events. To achieve this, a computer‐aided algorithm that monitors optical changes in the device and adjusts the applied voltage in accordance with the phase transformation process is developed, thereby significantly enhancing the lifetime of these reconfigurable devices. The findings reveal that patterned PCM structures show significantly higher endurance compared to blanket PCM thin films.

Volume-Metallization 3D-Printed Polymer Composites.

3D printing polymer or metal can achieve complicated structures while lacking multifunctional performance. Combined printing of polymer and metal is desirable and challenging due to their insurmountable mismatch in melting-point temperatures. Here, a novel volume-metallization 3D-printed polymer composite (VMPC) with bicontinuous phases for enabling coupled structure and function, which are prepared by infilling low-melting-point metal (LM) to controllable porous configuration is reported. Based on vacuum-assisted low-pressure conditions, LM is guided by atmospheric pressure action and overcomes surface tension to spread along the printed polymer pore channel, enabling the complete filling saturation of porous structures for enhanced tensile strength (up to 35.41MPa), thermal (up to 25.29Wm-1K-1) and electrical (>106Sm-1) conductivities. The designed 3D-printed microstructure-oriented can achieve synergistic anisotropy in mechanics (1.67), thermal (27.2), and electrical (>1012) conductivities. VMPC multifunction is demonstrated, including customized 3D electronics with elevated strength, electromagnetic wave-guided transport and signal amplification, heat dissipation device for chip temperature control, and storage components for thermoelectric generator energy conversion with light-heat-electricity.

High-speed terahertz communication with graphene-based time-modulated low-bit phase coding metasurfaces: A novel architecture for enhanced performance

Coding metasurfaces have revolutionized electromagnetic device development by enabling precise electromagnetic wave manipulation. While spatial phase modulation alone offers significant capabilities, its limitations to comprehensive control and optimal functionality are evident. As a result of recent advancements, joint amplitude-phase coding approaches have been explored using different techniques in order to enhance performance. However, such methods often result in complex structures due to the combining of various modulation techniques within meta-atoms. Addressing this challenge, this paper proposes a novel architecture for terahertz (THz) communication utilizing low-bit coding metasurfaces featuring simplified meta-atoms. Our approach introduces a coding unit cell based on graphene, combined with time-modulated coding, to enable phase and amplitude control for different harmonics. As a proof-of-concept application, we demonstrate the effectiveness of our technique in multimode vortex communication. Moreover, we show secure hologram communication by using our proposed design within the THz frequency regime. By enhancing wavefront shaping flexibility through a straightforward approach, this work lays the foundation for next-generation devices, particularly in high-speed macroscale and nanoscale communication networks.

A Study on a Compact Double Layer Sub-GHz Reflectarray Design Suitable for Wireless Power Transfer

The paper presents a novel small-footprint varactor diode-based reconfigurable reflectarray (RRA) design and investigates its power reflection efficiency theoretically and experimentally in a real-life indoor environment. The surface is designed to operate at 865.5 MHz and is intended for simultaneous use with other wireless power transfer (WPT) efficiency-improving techniques that have been recently reported in the literature. To the best of the authors’ knowledge, no RRA intended to improve the performance of antenna-based WPT systems operating in the sub-GHz range has been designed and studied both theoretically and experimentally so far. The proposed RRA is a two-layer structure. The top layer contains electronically tunable phase shifters for the local phase control of an incoming electromagnetic wave, while the other one is fully covered by metal to reduce the phase shifter size and RRA’s backscattering. Each phase shifter is a pair of diode-loaded 8-shaped metallic patches. Extensive numerical studies are conducted to ascertain a suitable set of RRA unit cell parameters that ensure both adequate phase agility and reflection uniformity for a given varactor parameter. The RRA design parameter finding procedure followed in this paper comprises several steps. First, the phase and amplitude responses of a virtual infinite double periodic RRA are computed using full-wave solver Ansys HFSS. Once the design parameters are found for a given set of physical constraints, the phase curve of the corresponding finite array is retrieved to estimate the side lobe level due to the finiteness of the RRA aperture. Then, a diode reactance combination is found for several different RRA reflection angles, and the corresponding RRA radiation pattern is computed. The numerical results show that the side lobe level and the deviation of the peak reflected power angles from the desired ones are more sensitive to the reflection coefficient magnitude uniformity than to the phase agility. Furthermore, it is found that for scanning angles less than 50°, satisfactory reflection efficiency can be achieved by using the classical reactance profile synthesis approach employing the generalized geometrical optics (GGO) approximation, which is in accord with the findings of other studies. Additionally, for large reflection angles, an alternative synthesis approach relying on the Floquet mode amplitude optimization is utilized to verify the maximum achievable efficiency of the proposed RRA at large angles. A prototype consisting of 36 elements is fabricated and measured to verify the proposed reflectarray design experimentally. The initial diode voltage combination is found by applying the GGO-based phase profile synthesis method to the experimentally obtained phase curve. Then, the voltage combination is optimized in real time based on power measurement. Finally, the radiation pattern of the prototype is acquired using a pair of identical 4-director printed Yagi antennas with a gain of 9.17 dBi and compared with the simulated. The calculated results are consistent with the measured ones. However, some discrepancies attributed to the adverse effects of biasing lines are observed.

Generating grid double-scroll attractors from magnetized SC-CNN and its application in image encryption

Cellular neural network has attracted widespread attention due to its easy hardware implementation and general application in information processing. In this paper, a new memristive State-Controlled-CNN (MSC-CNN) model is established by introducing two novel flux-controlled memristors into a three-cell network, where one of which simulates the electromagnetic radiation and the other characterizes the coupling weight. The present MSC-CNN can generate multi-double-scroll attractors (MDSAs) in one direction or grid multi-double-scroll attractors (GMDSAs). Stability analysis shows that each asymptotically stable equilibrium point of the memristors serves as index-1 saddle-focus in the MSC-CNN, which induces the corresponding connecting bond orbits between two scrolls. Thus, the number of GMDSAs can be flexibly adjusted by varying the number of the asymptotically stable equilibrium points of the memristors. Moreover, the memristive coupling strength also controls the number of MDSAs. Through numerical simulations, complex dynamic behaviors such as extreme multistability and amplitude control are also observed. Then, an image encryption scheme based on the proposed MSC-CNN is designed from the application perspective. Finally, a microcontroller-based hardware system is implemented to verify the effectiveness of numerical simulations.