Specific Electromagnetic Properties Research Articles

CHARACTERIZATION SUBSOLIDUS SYSTEM STRUCTURE CaO - Al2O3 - CoO – NiO

The paper presents the results of calculations characterizing the elements of the subsolidus structure of the CaO– Al2O3 – CoO – NiO system, which is promising for the production of modified aluminous cements and heterophase materials with a complex of unique properties. Insufficient information about the structure of the four-component phase diagram of a certain multicomponent system makes it difficult to obtain such materials. To predict the phase composition of materials, theoretical studies of the structure of the system were carried out. An analysis of the features of the coexistence of heterophase combinations was carried out, taking into account geometric-topological and statistical characteristics. The technological risks of predicting the phase composition of materials that arise in certain concentration regions of the system under study are shown. Calculations were carried out over the entire temperature range, both up to the melting point of the ternary oxide compound Ca3CoAl4O10 at 1439 K, and in a higher temperature region. Using known methods, the characteristics of eutectics in some sections of the system under study, which is of interest for the technological design of materials, were calculated. The results of calculations of the characteristics of eutectics show that among the analyzed tetrahedra, the minimum eutectic temperature (1367 K) is observed between the oxides of cobalt, nickel, calcium-cobalt aluminate and calcium monoaluminate, which can be realized for the synthesis of heterophase materials with a high content of Ca3CoAl4O10. Such materials have practical application in various industries: lime production; lime binders; corundum abrasives and refractories; high temperature catalysts; ceramics with special electromagnetic properties.

Universal strategy study of applying passive metasurfaces to an intra-DC wireless-optical interconnection

Free-space optical (FSO) communication can reduce the routing complexity of data center networks (DCNs), not only ensuring high-capacity optical switching, but also owning similar flexibility to the wireless connectivity. Presently, mainstream wireless-optical switching units (WOSUs) have adopted serial beam control for unicasting. As a two-dimensional planar structure composed of meta-atoms with special electromagnetic properties arranged in a certain way, a passive metasurface (PMF) has strong parallel beam regulating capability. In this paper, we propose a wireless-optical intra-DC interconnection scheme based on PMFs. Through a real PMF chip, by adjusting the polarization of an incident beam, the power distribution between normal and abnormal reflected beams can be controlled. When both reflected beams are assigned with power, we obtain a pair of beams reflected in parallel, thus simultaneously communicating with two racks. In fact, we can perform 1-to-N (N≥2) multicast by using cascaded PMFs, and 1-to-N means that each source rack can communicate with N destination racks, i.e., a wide communication coverage range. However, the cascaded PMFs may result in huge chip costs and high accumulated power loss. In this paper, we only demonstrate the 1-to-2 communication ability of our PMFs, so the communication coverage may be still limited. Hence, by introducing electrostatic drive to control the PMF rotation, each source rack can achieve a wider communication coverage range than before. As a result, all racks within the coverage range have the ability to establish communication links with the source rack. To this end, we also design a neural network to mimic the PMF rotation, further improving the communication capability between racks. We then propose a DCN-topology reconfiguration algorithm supporting the coexistence of unicasting and multicasting, in order to make real-time decisions on the matching between FSO ports with minimized latency. Finally, we established a proof-of-concept prototype system to demonstrate the parallel beam control of our PMF. The test results show that the angle error is less than 0.1°, satisfying the accuracy requirements of WOSUs, and our PMF always has a good polarization response with the insertion loss of less than 2 dB under various azimuth angles or rotation planes.

Enhancing efficiency of magnetic energy by implementing square-shaped materials adjacent to induction machine windings

This study provides a worthwhile method for increasing the magnetic field energy and induction machine (IM) effectiveness. The coupling between the transmitter and receiver windings in the IM system can be improved by creating materials with specific electromagnetic properties. This added material has altered the magnetic flow as well as the energy of the magnetic field. Eventually, it is possible to calculate the efficiency of the magnetic field, or the ratio of primary to secondary magnetic energy. With the use of two-dimensional finite element analysis, numerical results on five cases with various configurations of a magnetic substance have been produced. This material, which varies in length or breadth, is positioned close to the windings of the transmitter, receiver, or both. Case 3, in which the transmitter generates a magnetic field on the receiver side with a minimum energy of 0.05 J and a maximum energy of 0.015 J, is the ideal material configuration for DC current. Currently, the system efficiency is 0.29 on average. A 1 kHz transmitter's energy is constant under all conditions, but its counterpart's energy fluctuates significantly, with case 5 receiving the most energy. Therefore, case 5 turns into the optimal structural arrangement. It can be inferred that case 5 similarly dominates the other with an efficiency of 0.0026, which is much greater than that of 1 kHz efficiency, while the windings are operating at 1 MHz. This leads to stronger magnetic field coupling and increased power transfer effectiveness.

Research progress and practical application of magnetic composite absorbing materials

The update and iteration of communication technology, the continuous emergence of new electronic devices, smart home appliances and new energy vehicles, and the widespread use of military electromagnetic technology have caused serious electromagnetic radiation problems. Nanomagnetic materials have special electromagnetic properties and become the continuous research object of absorbing materials, especially in the development of low-frequency absorbing materials. This paper reviews the theoretical basis and research status of nanomagnetic materials in low-frequency absorbing materials and composite absorbing materials that are "thin, light, wide, and strong". In addition, the basic research is aimed at realizing the final application, and this paper also summarizes the application status of the absorbing agent in practical application.

Application of DNA molecules in nature- inspired technologies: a mini review

The DNA molecule is considered as an object of nature-like technologies, with the focus on the special electromagnetic properties of DNA-like helices. This is the difference from the traditional approach to the DNA molecule as the repository of genetic information. DNA-like helices are regarded as artificial micro-resonators, or “meta-atoms,” exhibiting both dielectric and magnetic properties, that are equally pronounced. The article presents methods for creating spatial structures directly from DNA molecules, as well as from DNA-like helices. It is shown that the design of metamaterials and metasurfaces should be carried out considering the special electromagnetic properties of DNA-like helices. This will make it possible to obtain the required properties of metamaterials and metasurfaces and achieve advantages over other types of artificial structures.

Effects of Gd doping on microwave absorption properties and mechanism for CaMnO3 perovskites

ABO3 type perovskite oxides have been widely studied due to their unique structure and special electromagnetic properties. CaMnO3 is well known for its excellent thermoelectric performance and temperature stability. In this paper, Ca1-xGdxMnO3 (x = 0, 0.1, 0.2, 0.3, 0.4) perovskites were comprehensively studied by first-principles calculations and experimental characterizations on their crystal structure and electromagnetic properties to finally elaborate the microwave absorption mechanism. It is found that Gd doping significantly enhances the dielectric polarization effects, resulting in better electromagnetic wave absorption performance than undoped CaMnO3. Especially for CG2MO perovskite, its reflection loss and bandwidth below −10 dB at 2–18 GHz reaches −31.9 dB and 3.3 GHz approximately, exhibiting excellent microwave absorption property. Moreover, the microwave absorption mechanism of CGMO perovskites involves various modes of conductive loss, resonance loss, multiple reflection and scattering as well as the polarization phenomenon including interfacial polarization, dipole polarization and defect polarization. Among them, polarization effects and conductive loss contributes the most to the microwave absorption performance.

A prediction method for the screening current induced field in HTS magnets based on time series models

Due to their special electromagnetic properties, high temperature superconducting (HTS) conductors have become a potential solution for ultra-high field magnet and energy storage applications. However, the screening current induced field (SCIF) has been demonstrated to be the main limitation of high field HTS magnets in actual applications. Based on time series models, this paper presents a prediction method of SCIF to support the design and application of HTS magnets. First, we analyze the data characteristics of the SCIF hysteresis loop. The simulated dataset is prepared for two typical magnet structures: single pancake and solenoid. Then, time series models are proposed for the SCIF prediction. Through intuitive analysis and evaluation metrics, the training performance of time series models is confirmed. After a discussion of hyper-parameters and dimension reduction, the optimized prediction performance is obtained for the SCIF hysteresis loop. In conjunction with the iterative prediction mode, we finally achieve a feasible and effective prediction method of SCIF for HTS magnets. This will provide a tool and research strategy to support the general finite element method.

Design and optimization of multiarray antenna operating in terahertz (THz) band for in-vivo nanonetworks

In-body antennas have specific electromagnetic properties and are surrounded by materials such as muscle, fat tissue, and skin. The goal of this research is to examine some of the existing antenna optimization approaches and to optimize the gaps between the multiarray antenna's parts. Another main goal of this research is to construct an optimized antenna and compare its performance to that of a non-optimized multiarray antenna. The terahertz spectrum is employed in the antenna design, which has applications in different In-Vivo nanonetworks. The bandwidth used is in the range of 0.1–10 THz which is suitable to be operated in the human body. In the present work, a terahertz patch antenna, 2 × 1 array antenna, and 2 × 2 multiarray antenna are designed and simulated on CST Studio Suite 2019 software which operate at 0.3 THz. The proposed 2 × 2 multiarray antenna has dimensions of 784×524×5μm3 having a patch of annealed copper and Rogers RO3210 lossy (ɛr=10.8) as substrate. The results obtained for the proposed multiarray antenna show a significant improvement from the single patch antenna in terms of gain. After the successful simulation of antenna ANN algorithm would be applied in order to obtain MSE values to get an optimized value of gain of an Antenna.

Tunable broadband terahertz metamaterial absorber based on vanadium dioxide

The special electromagnetic properties of metamaterials have contributed to the development of terahertz technology, and terahertz broadband absorbers for various applications have been investigated. The design of metamaterial absorbers with tunability is in a particularly attractive position. In this work, a tunable broadband terahertz metamaterial absorber is proposed based on the phase transition material vanadium dioxide (VO2). The simulation results show that an excellent absorption bandwidth reaches 3.78 THz with the absorptivity over 90% under normal incidence. The absorptivity of the proposed structure can be dynamically tuned from 2.7% to 98.9% by changing the conductivity of VO2, which changes the structure from a perfect reflector to an absorber. An excellent amplitude modulation with the absorptivity is realized. The mechanism of broadband absorption is explored by analyzing the electric field distribution of the absorber based on impedance matching theory. In addition, it also has the advantage of polarization and incident angle insensitivity. The proposed absorber may have a wide range of promising applications in areas such as terahertz imaging, sensing, and detection.

Large-scale preparation of electrically conducting cellulose nanofiber/carbon nanotube aerogels: Ambient-dried, recyclable, and 3D-Printable

This work demonstrates an ambient-dried and non-chemical cross-linking way of preparing functional aerogels from cellulose nanofibrils (CNFs) and carbon nanotubes (CNTs), constructing aerogel pore walls with sufficient mechanical properties by cycling freeze-thawing to cross-linking CNFs and CNTs. During the process, a novel dual-networks interpenetrating strategy is constructed benefiting from the tubular dispersion of CNFs and CNTs, enabling the creation of hybrid dual-networks of hydrophobic and hydrophilic nanofibers. As a result, aerogels with tunable densities (0.0519 g cm−3), high specific surface area (157.24 m2 g−1), and good conductivity (30.95 S cm−1) can be prepared. Besides, the aerogels can be easily recyclable due to the absence of chemical crosslinking. Various shaped and structural characteristics of the aerogels can be adjusted through 3D printing or mold, behaving a large-scale production future (diameter of aerogel up to 8.68 cm). To demonstrate their use in various applications, the aerogels show high specific electromagnetic shielding properties (440.9 dB cm3 g−1) and can be used as a free-standing electrode for loading active materials (e.g., MnO2), exhibiting excellent energy storage properties (551 F g−1). More than that, this method can be applied to other nanofibers (ANF, PI, etc.), and even more diverse structures are expected to be obtained.

Biogenic ferroxides derived from Leptothrix bacteria for applications in electronics, biomedicine and biotechnology

The present work is focused on studying by-products derived from the metabolism of bacteria of the Leptothrix genus, which are among the first described microorganisms associated with the iron cycle in nature. The products of their metabolism are nanostructured biogenic iron oxides in the form of precipitating powders and sheath structures. The sheath structures can be considered as an organic matrix in which inorganic crystallites are discretely dispersed. We used X-ray diffraction, magnetic measurements, light microscopy and scanning electron microscopy to characterize biogenic products formed in a silicon iron glucose peptone medium under laboratory conditions. The studies showed a lack of significant differences between the naturally obtained and the artificially synthesized biogenic sheaths, i.e., an adequate laboratory technological process had been developed. From the point of view of nanoelectronics application, these biogenic by-products are unique because they are biocompatible, have specific electromagnetic properties and are potential candidates for various applications in biomedicine and electronics.

Reconfigurable Particle Swarm Robotics Powered by Acoustic Vibration Tweezer.

Inspired by natural swarms such as bees and ants, various types of swarm robotic systems have been developed to work together to complete tasks that transcend individual capabilities. Autonomous robots controlled by collective algorithm and colloidal swarms energized by external field have been designed in an attempt to emulate collective behaviors in nature. However, either sophisticated hardware designs or active agents with special electromagnetic properties and microstructural designs are needed. Here, for the first time, we create a swarm robotic system that can make any granular materials an active swarm robot by acoustic vibration tweezer. It should be noted that the particles energized by only one vibration generator are ordinary sand without any microstructural design. Therefore, it is the simplest and lowest cost swarm robot. Particles can display a solid-like aggregate, which is capable of robustly carrying and transporting an object that is about 1 million times heavier than a single particle. Moreover, through the cooperation of two swarm robots, we can achieve cooperative transport of a stick with a length of 1000 times the diameter of a single particle. The particle robot can move in a fluid-like amorphous group, which can change its own shape to adapt to the surrounding environment, thus having a strong environmental adaptability. Besides, it can move quickly (about 600 times the particle diameter per second) in a discrete state. Within one certain particle system, the particle swarm robot can emulate diverse biomimetic collective behaviors through navigated locomotion, multimode transformation, and cooperative transport.

Analysis of Microwave Transmission Characteristics of Toroidal Plasma Array Photonic Crystal

In this paper, a new type of ring-shaped plasma photonic crystal structure is proposed. The influence of the structure parameters on the photonic band gap is calculated by simulation. At the same time, the application possibility of the structure change transmission mechanism is discussed. The use of photonic crystals to achieve tunable forbidden bands is the focus of current research in the field of electromagnetics, and plasmas have been widely used in photonic crystal structures in recent years because of their special electromagnetic properties, density changes with frequency. In addition to studying the band gap regulation of photonic crystals by plasma frequency, it is also an important direction to explore the effects of different plasma photonic crystal shapes and periodic structure parameters on the mechanism of microwave transmission.

Topology optimization based methods and the realization programs for designing microstructures of patched metamaterials with prescribed electromagnetic properties

This paper aims to establish a design tool to design the metamaterial microstructures with specific electromagnetic properties easily and conveniently, including the design methods of metamaterial microstructures and the corresponding program codes. For the patch type microstructure and several typical metamaterials (such as the single-negative metamaterials with specific negative permeability, left-handed metamaterials with specific material constants at the prescribed frequency; single negative metamaterials and left-handed metamaterials in prescribed frequency bands), the topology optimization models, solving schedules and corresponding implementation program codes for microstructure design are presented in detail. Several typical metamaterial microstructures with different design requirements are designed concretely. The results illustrated the correctness and validity of the design methods and the corresponding program codes. The designing method proposed and the program codes developed in this paper provide an effective tool for the design of metamaterial microstructure with specific function for the designers.

Synthesis of Iron-Containing Preceramic Polymer and Preparation of Fe/Si/C Ceramics via Precursor-Derived Method

Iron-containing SiC ceramics have low specific resistivity and excellent electromagnetic properties. In this work, hyperbranched polyferrocenylsilane as the precursor of Fe/Si/C ceramics was prepared by the reaction of ferrocenyl dilithium, dichlorodimethylsilane and trichloromethylsilane. The ceramization process of the preceramic polymer from organic to inorganic was then investigated. Precursor microspheres were prepared by emulsion method, which were then pyrolyzed to obtain Fe/Si/C ceramic microspheres.The composition, structure and morphologies of the precursor and ceramics were characterized by 1H-NMR, FT-IR, TG-MS, XRD, SEM and EDS. Experimental results showed that the hyperbranched precursor was successfully synthesized, the pyrolytic process of which started at 350 °Cand almost completed above 600 °C. There was crystalline transformation from Fe5Si3 to Fe3Si as the sintering temperature increased from 1000 °C to 1400 °C. Moreover, the crystalline phase of β-SiC appeared at 1400 °C. Precursor microspheres were prepared by emulsion method. Porous ceramic microspheres were obtained after the precursor microspheres being sintered at 1400 °C, which can be applied in gas adsorption and catalyst supports.

Change of transmission characteristics of FSSs in hybrid composites due to residual stresses

The frequency selective surface (FSS) embedded hybrid composite materials have been developed to provide excellent mechanical and specific electromagnetic properties. Radar absorbing structures (RASs) are an example material that provides both radar absorbing properties and structural characteristics. The absorbing efficiency of an RAS can be improved using selected materials having special absorptive properties and structural characteristics and can be in the form of multi-layers or have a certain stacking sequence. However, residual stresses occur in FSS embedded composite structures after co-curing due to a mismatch between the coefficients of thermal expansion of the FSS and the composite material. In this study, to develop an RAS, the thermal residual stresses of FSS embedded composite structures were analyzed using finite element analysis, considering the effect of stacking sequence of composite laminates with square loop (SL) and double square loop (DSL) FSS patterns. The FSS radar absorbing efficiency was measured in the K-band frequency range of 21.6 GHz. Residual stress leads to a change in the deformation of the FSS pattern. Using these results, the effect of transmission characteristics with respect to the deformation on FSS pattern was analyzed using an FSS Simulator.

Polarization conversion of reflected electromagnetic wave from topological insulator

Based on the special electromagnetic properties of a 3D strong topological insulator (TI), we discuss, theoretically, the reflection of electromagnetic wave at the interface between a dielectric and a TI, and focus on the polarization conversion between the incident field and reflected field. Two cases, linear polarization and elliptical polarization at oblique incidence are considered. We derive the conditions required for the complete polarization conversion from incident s polarization into reflected p polarization, and vice versa. Furthermore, elliptical polarization incidence also can be modulated to linear or circular polarization after reflection, under special conditions, and the corresponding reflectivity can approach 1. All these special polarization behaviors originate from the intrinsic topological magnetoelectric coupling response in TI. This work provides promising applications of TIs on polarized devices and the polarization splitters.

Evaluation of a nanostructured microwave absorbent coating applied to a glass fiber/polyphenylene sulfide laminated composite

The rapid coating of composites with absorbing paints yields materials that can absorb microwave radiation and still have approximately the same specific mass of the original composites. The use of paints with specific electromagnetic properties together with carbon- nanotube-based materials allows the production of structural materials of interest to the aeronautical industry. Thus, the objective of this study was to produce and characterize the electromagnetic properties of a material consisting of a microwave absorbing coating (carbon nanotubes and polyurethane) applied to a laminated composite made with polyphenylene sulfide and glass fiber. The attenuation of microwaves (8 to 12 GHz) incident on this material was evaluated using the waveguide technique to determine whether this material can be used as an absorbing structural material. The results show that the material absorbs up to 90% of the energy of the incident microwave, indicating that the material is an efficient absorber of microwave radiation.

Directional Coupler Based on Metamaterial Square Csrr Shape

Metamaterials are artificial structures that can be designed to exhibit specific electromagnetic properties that are not in the nature. In this paper, we design a directional coupler, based on the theory of the split-ring resonators (SRRs), and the complementary SRR (CSRRs). The experiments and simulations of the directional coupler are based on the theory of the square structure (and not based on the circular structure) of the SRR and CSRR. The advantage of this circuit is that the area of the coupling is great as regards to the coupler based on the circular structure. The results of simulation and measurement with the miniature structures show the backward-wave phenomenon of the left-handed (LH) material.

Electromagnetic surface and line sources under coordinate transformations

Although the analysis of electromagnetic sources in the context of coordinate transformations and the implications for transformation optics have been discussed in the literature, a correct formulation that includes surface and line currents has not been reported. Here we derive how surface and line currents behave under coordinate transformations and validate the analysis through numerical validation of a specific example. This analysis enables transformation optics to be applied to problems that include singular source distributions, which is often the case for practical radiating systems and antennas, to make a given current distribution produce the same fields as a different current distribution by surrounding it with a material with specific electromagnetic properties.