Characteristics Of Electromagnetic Waves Research Articles

Application of terahertz time-domain spectroscopy and chemometrics-based crested porcupine algorithm in identification of different medicinal parts of Angelica sinensis

ObjectiveAngelica sinensis is one of the commonly used Chinese herbal medicine in traditional Chinese medicine clinic, exhibits different pharmacological characteristics due to variations in the content of active ingredients in its head, body, and tail. Therefore, research on the identification methods of different medicinal parts of Angelica sinensis is of great practical significance. Terahertz Time-Domain Spectroscopy (THz-TDS) technology is widely used in the field of nondestructive testing because of its unique electromagnetic wave characteristics. This study explores the feasibility of combining THz-TDS with chemometrics to identify different medicinal parts of Angelica sinensis. MethodsBy comparing the spectral response characteristics of different parts of Angelica sinensis to various optical parameters, the absorption coefficient spectrum in the 0.6–3.0 THz range was selected, and three types of feature extraction algorithms, namely, joint Competitive Adaptive Reweighted Sampling (CARS), Uninformative Variable Elimination (UVE), and Successive Projections Algorithm (SPA), were used to establish the classification models of Extreme Learning Machine (ELM), Random Forest (RF), and Support Vector Machine (SVM) in turn, and optimize the models by using the crown porcupine algorithm (Crested Porcupine Optimizer (CPO) to optimize the model. ResultsThe research results indicate that the CPO optimizer significantly improved the classification accuracy of the models, with the accuracy of the ELM, RF, and SVM models increasing by 4.36%, 1.11%, and 12.22%, respectively. The SPA-CPO-SVM model exhibited the best overall performance, achieving accuracies of 96.11% and 97.96% on the prediction and training sets, respectively, while the number of input features was only 5% of the total feature set. ConclusionThe results show that the fully joint feature extraction strategy and optimization algorithm can play a powerful synergistic effect in model construction, confirming the feasibility of THz-TDS technology to correctly identify different medicinal parts of Angelica sinensis, and providing an important reference for the application of terahertz technology in the identification of Chinese herbal medicines.

Continuous manipulation of electromagnetic radiation based on ultrathin flexible frequency coding metasurface

The physical characteristics of electromagnetic waves are combined with digital information in coding metasurfaces. Coding metasurfaces enable precise control of beams by flexibly designing coding sequences. However, achieving continuous multivariate modulation of electromagnetic waves on passive flexible coded metasurfaces remains a challenge. Previous passive coding metasurfaces have a fixed phase difference between adjacent coding units throughout the operating frequency band, and when the coding pattern is defined, the coded metasurface can only achieve a single electromagnetic function. Our proposed frequency coding metasurface units vary linearly in phase difference over the operating frequency band with different phase sensitivities. Frequency coding metarsurfaces enable a wide range of tunable and versatile electromagnetic energy radiation, without introducing any active devices and changing the coding pattern. As a demonstration of the concept, we have shown theoretically and numerically that frequency coding metasurface can achieve successive transformations of electromagnetic functions, including multi-beam generation, anomalous deflection and diffuse scattering. In addition, beam sweeping function is achieved by means of spatially non-periodically distributed frequency coding metasurface. When the frequency of the incident wave is changed, the deflection angle of the beam is also changed. In addition to the tunability of properties, research on coding metasurfaces has tended to be limited to rigid materials. Flexible coding metasurfaces have potential applications in microwave antennas, radar and aircraft. The passive flexible frequency coding metasurfaces provide a novel approach to manipulating electromagnetic waves with increased design flexibility. This promises applications in microwave antennas, radar, aircraft, and satellite communications.

Study on human brain protection from electromagnetic radiation of mobile phone by plasma

The propagation characteristics of electromagnetic waves (EMW) in plasma with the plural dielectric properties (real and imaginary parts of the relative dielectric constant) were investigated in the virtual human brain (VHB) model by the full-wave solution. Simulation results indicate that the value of the electric and magnetic field amplitude of EMW with the frequency of 5 GHz and the value of specific absorption ratio within VHB can be reduced by more than 60% and 80%, respectively. After the secondary absorption of the plasma layer, the reflected wave amplitude is attenuated by 33.066 dB. The amplitude attenuation of EMW from 2.45 to 6 GHz can be exceeded 10 dB. Compared to the traditional absorbing materials for the electromagnetic protection, the plasma layer, as an absorbing medium, possesses wide frequency characteristics. These results have important reference value for reducing the high-frequency electromagnetic radiation to VHB.

PISC-Net: A Comprehensive Neural Network Framework for Predicting Metasurface Infrared Emission Spectra.

Multifunctional metasurfaces have exhibited extensive potential in various fields, owing to their unparalleled capacity for controlling electromagnetic wave characteristics. The precise resolution is achieved through numerical simulation in conventional metasurface design methodologies. Nevertheless, the simulations using these approaches are inherently computationally costly. This paper proposes the Physical Insight Self-Correcting Convolutional Network (PISC-Net), which enables rapid prediction of infrared radiation spectra of metasurfaces with remarkable generalization capacity. In contrast to preceding prediction networks, we have enhanced the cognitive ability of the network to recognize physical mechanisms by designing parameter-communication modules and integrating a priori knowledge grounded in the parameter association mechanism. Additionally, we proposed an effective strategy for constructing data sets that facilitate precise tuning of absorption bands in the entire spectral range (3-14 μm) and serves to reduce the costs associated with data set development. Transfer learning is employed to obtain precise predictions for large-period metasurfaces from limited data sets. This approach demonstrates that a network trained exclusively on simulation data could predict experimental outcomes accurately, as proved by the comparative analysis between simulation, experimental testing, and prediction results. The average mean square error is less than 4%.

Design and Development of Metasurface Materials for Enhancing Photodetector Properties.

Recently, metasurface-based photodetectors (metaphotodetectors) have been developed and applied in various fields. Metasurfaces are artificial materials with unique properties that have emerged over the past decade, and photodetectors are powerful tools used to quantify incident electromagnetic wave information by measuring changes in the conductivity of irradiated materials. Through an efficient microstructural design, metasurfaces can effectively regulate numerous characteristics of electromagnetic waves and have demonstrated unique advantages in various fields, including holographic projection, stealth, biological image enhancement, biological sensing, and energy absorption applications. Photodetectors play a crucial role in military and civilian applications; therefore, efficient photodetectors are essential for optical communications, imaging technology, and spectral analysis. Metaphotodetectors have considerably improved sensitivity and noise-equivalent power and miniaturization over conventional photodetectors. This review summarizes the advantages of metaphotodetectors based on five aspects. Furthermore, the applications of metaphotodetectors in various fields including military and civil applications, are systematically discussed. It highlights the potential future applications and developmental trends of metasurfaces in metaphotodetectors, provides systematic guidance for their development, and establishes metasurfaces as a promising technology.

Simulation of ideal blackbody based on multi-space boundary condition in FDTD

Abstract Investigation shows that it is difficult to solve the electromagnetic field surrounding an ideal blackbody using the analytic method. To solve this problem, the simulation method should be adapted, and the Maxwell function should be expanded to multi space. In this paper, a multi space simulation scheme of finite difference time domain (FDTD) and a multi space boundary condition (MSBC) are proposed for the simulation of an ideal blackbody. Compared with the traditional absorbing boundary condition (ABC) or perfectly matched layer (PML), which can only be assigned in the outermost layers of the simulation space, the proposed MSBC is simpler and can be arranged inside the computing space. Numerical simulation shows that MSBC has good electromagnetic wave absorption performance and can simulate the ideal blackbody accurately. At the same time, the simulation results also show some interesting characteristics of electromagnetic waves around the ideal blackbody.

A study on the structural, magnetic, and electromagnetic wave absorption properties of CoFe2O4@MWCNT nanocomposites

Because of their low density, high electrical conductivity, and distinctive structure, magnetic nanoparticles have been used in conjunction with dielectric materials like carbon nanotubes in a number of studies on electromagnetic wave absorption. This paper describes the preparation of cobalt ferrite-multi-walled carbon nanotube (CoFe2O4@MWCNT) nanocomposites (NCs) at varying weight ratios for use in X and Ku-band electromagnetic wave (EMW) absorbing coatings. Investigations were also conducted on their structural, magnetic, and dielectric properties. Using the nitrate-citrate method, cobalt ferrite nanoparticles (NPs) having the chemical formula CoFe2O4 (CF) were first successfully produced. Then, carbon nanotubes (MWCNT) were mixed with cobalt ferrite NPs under different weight ratios to form CF@MWCNT NCs. The following are the methods used to determine the crystal structure of the samples: X-ray diffraction (XRD) measurements; scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) attached; Fourier transform infrared spectroscopy (FT-IR); magnetic properties determined by vibrating sample magnetometer (VSM); and room temperature dielectric properties investigated by vector network analyzer (VNA). CF@MWCNT NCs were extensively described and prepared in five distinct weight ratios. Under the thickness of d = 2.18 mm, sample EM5 exhibited the best reflection loss (RL) under the X band of all the samples, measuring −54.29 dB. Under the Ku band, sample EM5, which has a thickness of d = 1.18 mm, exhibited the best RL, measuring −53.42 dB. A method for creating magnetic @dielectric NCs with adjustable parameters and electromagnetic wave characteristics is presented in this work.

Analysis of electromagnetic wave characteristics of heterogeneous plasma sheath based on the ZT-DGTD

Analysis of electromagnetic wave characteristics of heterogeneous plasma sheath based on the ZT-DGTD

Recent Advances in Terahertz Manipulations Using C‐Shape‐Split‐Ring‐Resonator Metasurfaces (Review)

AbstractMetasurfaces have garnered significant interest owing to their inherent advantages over traditional optical components in manipulating electromagnetic waves unconventionally. Among the fundamental building blocks of metasurfaces, C‐shaped‐split‐ring resonators (CSRRs) have emerged as a highly promising option, enabling strong resonances and precise control over various characteristics of electromagnetic waves, such as phase, amplitude, and polarization. This review aims to showcase recent advancements in CSRR metasurfaces for manipulating THz waves, particularly focusing on both passive and active methods employed for controlling THz waves using single‐layer and multi‐layer CSRR metasurfaces. Moreover, this review will provide valuable insights into potential research directions in this rapidly evolving field.

Influence factors and mechanism of backscattering characteristics of electromagnetic waves in a single layer plasma tube array

A single-row plasma tube array (PTA) experimental system is established to improve the backscattering attenuation of a metal plate covered by a plasma tube array. The backscattering test system is utilized in a microwave anechoic chamber to examine the effects of gas composition, pressure, tube diameter, and discharge power on the backscattering attenuation of a metal plate using a plasma tube array. The electron density is obtained via microwave diagnosis. The backscattering attenuation mechanism in different frequency bands is revealed via numerical simulation. The results show that the reasonable selection of PTA parameters achieves strong attenuation in different frequency bands. The strong attenuation frequency bands of Ar–Hg PTA are in low frequency (1.5–3.5 GHz) and high frequency (13–17 GHz), while that of Ne–Hg discharge is in medium frequency (6.4–11.7 GHz). When the pressure is 0.5 and 1 Torr, the PTA shows a low, medium, and high multi-band distribution for the backscattering strong attenuation region. The backscattering strong attenuation region shows a low and high dual-band distribution, while the pressure is 2–4 Torr. As the tube diameter increases, the strong attenuation region maintains the dual-band, but it changes from low and high frequency bands to medium frequency (6-12 GHz), where the backscattering attenuation mechanism is collisional absorption when the frequency of plasma electron oscillation is close to that of electro-magnetic waves. The backscattering attenuation mechanism in the low frequency band involves the periodic structure of PTA generating local surface plasmon to absorb electromagnetic waves.

Application and testing technology of new road materials in highways

Abstract In the face of annual highway construction and highway maintenance projects, traditional road materials and road testing technology are difficult to meet the current highway construction needs. Based on this research background, the article first discusses the three-dimensional ground-penetrating radar nondestructive testing technology, analyzes the detection principle from the fluctuation equation of electromagnetic wave, the propagation characteristics of electromagnetic wave, and the propagation speed in the medium, and specifically analyzes its detection performance and application in the detection of the thickness of the structural layer. Finally, some sections of the Shanzhan Expressway are chosen as test objects and test experiments are designed and implemented. The test results show that the strength of the road material with water water-reducing agent increases compared to the material without water water-reducing agent. By using red mud instead of cement, road materials can have a relatively high strength. Therefore, using red mud as a substitute for conventional materials is entirely feasible and can save costs. The cracking rate of the highway was reduced by using the “leaching recycled” material, and the small cracks of less than 2mm were basically sealed, while the cracks of more than 2mm were alleviated. There is no water seepage on the pavement at 28 points of the 7 sections tested, so the “leaching regeneration” material has a better waterproof effect on the highway pavement.

Special Issue on the Progress and Application of Electromagnetic Materials

Electromagnetic materials refer to materials that can manipulate electromagnetic waves, which can control the amplitude, phase, polarization, spectrum, and other characteristics of electromagnetic waves [...]

Analysis of electromagnetic wave applications and development

With the continuous advancement of science and technology, the variety of technological products around our lives has also increased, and many of them use the characteristics of electromagnetic waves. In order to make people better understand the relevant characteristics of electromagnetic waves, this article will systematically introduce the basic theory, classification, application and related safety issues of electromagnetic waves. Electromagnetic waves not only have a wide range of applications in daily life, such as communications, remote sensing and other fields, but also play an important role in military and medical fields. Although electromagnetic waves bring many conveniences, there are also certain safety risks. Therefore,understanding the nature and application of electromagnetic waves to better protect our health and promote scientific and technological progress is important. In addition, for the limitations and shortcomings of electromagnetic wave applications, It is also crucial to explore potential development directions, in order to achieve comprehensive and efficient electromagnetic wave applications in the future.

Observation of photonic Peierls transition for manipulating microwave in metallic diaphragm-array periodic structures

Peierls transition that modifies electronic band structure has attracted intensive attention in solid state physics. In the present work, we report that a photonic analog of Peierls transition has been observed in a 1-D triangular metal diaphragm array, where the photonic bandgap structures have been designed at will by adjusting periodically metal diaphragm positions. It is shown by the numerical analysis that the transmission and radiation effect of the present periodic metal structure designed through the Peierls transition rule exhibits the behavior significantly different from an original periodic structure with each unit cell containing a metal diaphragm. The near- and far-field measurement results are in good agreement with our theoretical simulation. The present effect of photonic Peierls transition can serve as a working mechanism for designing new types of guided wave devices. It can be seen that the photonic Peierls transition would be one of the simplest ways for modifying the transport characteristics of electromagnetic waves in periodic structures.

IQ-Impaired Wireless-Powered Modify-and-Forward Relaying for IoT Networks: An In-Depth Physical-Layer Security Analysis

With the large-scale commercialization of 5G networks, the era of Internet-of-Things (IoT), which is oriented towards the internet-of-everything (IoE), is coming. Under the circumstance, reliable and secure communication are the great challenges for future wireless network because of the broadcasting characteristics of electromagnetic wave. Physical layer security (PLS) is an effective way to ensure secure communication by exploiting random nature of fading channels. Motivated by this, we investigate PLS of the wireless-powered cooperative multi-relaying for IoT networks in the presence of eavesdropper with the estimation errors of channel (EEC) and imbalance between in-phase and quadrature-phase (IIQ). Specifically, the relays can be charged by the source with the aid of energy harvesters, and a novel more secure modify-and-forward (MF) relay protocol is proposed. For further improving energy efficiency and reducing extra interference, the K-th superior relay selection scheme is proposed since some best ones are not available due to some scheduling or failure. Based on the system under study, we derive the analytical expressions for the outage probability (OP), intercept probability (IP) and secrecy outage probability (SOP) to evaluate the reliable and secure performance of this consideration system. Particularly, we then analyze the asymptotic behaviors of the OP, IP and SOP, respectively. Through computer simulation, we show that: i) With EEC, the error floors of the OP and SOP are of presence; ii) Multiple relays lead to better OP and SOP performance; and iii) IIQ improves the security and is detrimental to the system reliability.

Analysis of electromagnetic waves reflected by re-entry plasma sheath based on CSO-FDTD

A transmission model of terahertz waves in the plasma sheath is established based on a cascaded finite time domain difference method and analyzed the transmission characteristics of electromagnetic waves under the action of an external magnetic field and collision frequency. The flow field around the hypersonic aircraft is simulated and the characteristics of the flow field as the altitude changes of the aircraft are analyzed based on the flow field distribution of the RAM-C (Rapid Attenuation Measurement) vehicle. The results show the transmission characteristics of terahertz waves in plasma that will be affected by flight height, plasma parameters, external magnetic field, and collision frequency. In addition, under the action of an external magnetic field and the different collision frequency, the transmission characteristics of the left-handed terahertz wave will be improved. The application of the magnetic field will introduce an absorption peak in the right-handed terahertz wave, and it will move to the high frequency direction with the increase of the magnetic induction intensity.

Tunable chiral photonic cavity based on multiferroic layers.

Realization of externally tunable chiral photonic sources and resonators is essential for studying and functionalizing chiral matter. Here, oxide-based stacks of helical multiferroic layers are shown to provide a suitable, electrically-controllable medium to efficiently trap and filter purely chiral photonic fields. Using analytical and rigorous coupled wave numerical methods we simulate the dispersion and scattering characteristics of electromagnetic waves in multiferroic heterostructures. The results evidence that due to scattering from the spin helix texture, only the modes with a particular transverse wavenumber form standing chiral waves in the cavity, whereas all other modes leak out from the resonator. An external static electric field enables a nonvolatile and energy-efficient control of the vector spin chirality associated with the oxide multilayers, which tunes the photonic chirality density in the resonator.

Ultra‐broadband electromagnetic wave absorption of ceramic composite coating by atmospheric plasma spraying

AbstractDy doped ceramic material of Ba4Fe2.6Dy1.4Nb8O30 with the tetragonal black bronze structure was synthesized by solid‐state reaction at 1300°C. The composite powders of Ba4Fe2.6Dy1.4Nb8O30/FeSiAl with good flowing were prepared by spray drying using the powders slurry. The obtained composite powders were then plasma sprayed to fabricate coating. The microstructure and absorption characteristics of electromagnetic wave (EMW) of the coating materials are investigated. Results show that the composite powders significantly remain the phase stability during atmospheric plasma spraying and adsorbing heredity of EMW for the coating. The coating powders have excellent EMW absorption with the minimum reflection loss of −48.20 dB at the thickness of 3.5 mm. Also, the coating powders display the maximum effective absorption bandwidth of 6.24 GHz at the thickness of 1.5 mm, which covers the X‐band. Moreover, the coating was found to have a certain EMW absorption performance at high temperature of 700°C. The Ba4Fe2.6Dy1.4Nb8O30 ceramic material with low thermal conductivity ensured the electromagnetic absorption capacity of the coating at high temperature. The Ba4Fe2.6Dy1.4Nb8O30/FeSiAl ceramic composite materials could have the potential applications as the high temperature EMW absorber.

Specific Features of the Angular Distribution of Electromagnetic Radiation of the Kerr Black Hole

By analyzing algebraically special solutions of the Maxwell equations in the Kerr space-time, we obtain the exact expressions for the polarization characteristics of electromagnetic waves emitted from the vicinity of a black hole. We revealed the asymmetry of dependence of the ellipticity angle on the polar angle for the fundamental mode and the first harmonics of polarized radiation. This creates a basis for the new method of evaluation of the intrinsic angular momentum of the Kerr black hole. It is shown that the existence of singular points of the solution in a local orthonormal frame is a consequence of the Poincaré–Brouwer theorem.

Effects of High-collision Plasma on Radiation Protection of Human Brain

Objective: The purpose of this paper is to find a reasonable composite structure of electromagnetic protection device, especially the distribution characteristics of plasma parameters and operation conditions. Methods: Due to its high collision frequency, the high-pressure discharge plasma can be usedas a filling medium to take the electromagnetic protection effect. The strategies and algorithmsare presented to solve the propagation characteristics of electromagnetic wave (EMW) in plasma with complex dielectric constant. When the real and imaginary part of permittivity are of the same order of magnitude, the imaginary part value will impact on the feature of plasma dielectric constant, also affect the behavior of propagation of EMW. The propagation process of EMW in virtual human brain (VHB) model is investigated by finite difference time domain method. By optimizing the layout of plasma layer and air layer, an effective phase regulator is constructed, and the reflected wave amplitude is greatly reduced. Results: The simulation results show that plasma makes the amplitude of the electromagnetic fields in VHB decrease to different degrees. their maximum average decrease is about 25% and the corresponding reduction of SAR value is more than 40% in the frequency range of 1.8-3.6GHz. Conclusion: The existence of plasma can make the scalp and muscle possess the excellent performance in resisting the incident of EMW, so that the amplitude of the electromagnetic field inside the brain body is small, so as to effectively protect the brain tissue. These research results have good reference value and engineering applicability for the structure design of protection equipment with high frequency of EMW.