Electromagnetic Waves in Canted Magnets

Electromagnetic Environment Associated with Lightning Strikes to Tall Strike Objects

Magnetic wood composite for electromagnetic shielding: Experimental study and machine learning predictions

콘크리트 또는 시멘트 모르타르와 같은 비금속성 재료에서 유전상수와 전도율과 같은 전자기 평가는 특성화 될 수 있으므로 최근 들어 많은 연구가 수행되고 있다. 그러나 이러한 전자기 특성은 수분에 의하여 매우 큰 영향을 받으므로 이에 대한 전자기 거동이 명확하게 이해되어야 한다. 본 논문에서는 5가지 물-시멘트비를 가지는 시멘트 모르타르에 대하여, 포화도 및 전자기 특성 측정이 압축강도와 공극률 평가와 함께 수행되었다. 각각의 포화된 시편은 실내상태에 존치되었으며, 포화도의 변화에 따른 전자기 특성이 분석되었다. 포화상태에서는, 공극률이 높은 시편에서 높은 전자기 특성이 평가되었지만, 이러한 관계는 건조가 진행됨에 따라 반대로 평가되었다. 공극수가 없는 공극에서 전자기 특성이 감소되므로, 물-시멘트비가 낮아질수록 안정적이고 선형적인 전자기 특성 증가를 나타내었다. 한편, 물-시멘트비에 따른 전자기 특성 증가율이 포화도와 함께 제시되었으며, 회귀분석을 통하여 그 상관관계가 도출되었다.

As the basic materials with specific properties, fabrics have been widely applied in electromagnetic (EM) wave protection and control due to their characteristics of low density, excellent mechanical properties as well as designability. According to the different mechanisms and application scenarios on EM waves, fabrics can be divided into three types: EM shielding fabric, wave-absorbing fabric and wave-transparent fabric, which have been summarized and prospected from the aspects of mechanisms and research status, and it is believed that the current research on EM wave fabrics are imperfect in theory. Therefore, in order to meet the needs of different EM properties and application conditions, the structure of fabrics will be diversified, and more and more attentions should be paid to the research on structure of fabrics that meets EM properties, which will be conductive to guiding the development and optimization of fabrics. Furthermore, the application of fabrics in EM waves will change from 2D to 3D, from single structure to multiple structures, from large to small, as well as from heavy to light.

The anomalous Hall effect (AHE) reflects the immense diversity of mechanisms for intrinsic or extrinsic current generation that can be found in the world of magnets. This world offers numerous exciting classes of antiferromagnets, where the anomalous and recently discovered crystal Hall [1] effect as well as the topological Hall effect in non-coplanar antiferromagnets [2] have been studied in the past decades. In this work, we uncover a novel type of Hall effect emerging in generic canted spin systems. Identifying a clear fingerprint of this chiral Hall effect (CHE) in discrete tight-binding models as well as ab-initio calculations is central in establishing a solid understanding of this new phenomenon closely tied to real space topology of magnetic textures. In this study, we provide robust numerical evidence for the CHE in a honeycomb lattice of canted spins and present a material candidate, SrRuO3. We uncover contributions to the Hall conductivity sensitive to the canting angle between neighboring spins which can be directly related to the imprinted vector chirality. Exploring the symmetry properties of the CHE we demonstrate the complex interplay of symmetry, topology and chirality in canted spin systems. **

We numerically compute seismoelectric wavefields generated at a fluid/porous medium interface by an explosive source in the fluid. Our numerical experiments show that electromagnetic (EM) signals accompanying the P, S, and interface waves can be observed at receivers located in the fluid regions near the interface. Such accompanying EM signals are produced by the inhomogeneous EM waves that are generated by the seismic waves at the interface and their amplitudes decrease with the distance from interface. Under the excitation of an explosive source whose strength is within the capability of industry air guns, electric and magnetic fields that accompany the Scholte wave are on the order of 1 μV/m and 0.01 nT, respectively. This means that the EM signals arising from the electrokinetic effect at an ocean bottom are detectable and suggest that it is possible to measure the EM signals during marine seismic explorations to study the properties of the seafloor material. EM signals that accompany the P, S, and interface waves are also observed in the porous medium region near the interface. Component analysis shows that they contain contributions from multiple modes of waves, among which the slow compressional wave contributes significantly to the vertical electric field, leading to a much stronger vertical electric field than the horizontal electric field during the passage of a seismic wave along the interface.

We propose a class of invisible slab cloaks based on the embedded optical transformation. The designed slab structures will guide the incident electromagnetic (EM) waves to propagate around the cloaked objects inside the slabs. Such EM waves will return to their original propagation directions without any distortions. We show that there are no singular values in the EM parameters of the slab cloaks and they could be realized using metamaterials. General formulations of the inhomogeneous and anisotropic permittivity and permeability tensors are derived for the slab cloaks using linear and nonlinear optical transformations. Numerical simulations based on the finite element method have been performed to confirm the design and analysis. The potential application of the slab cloak is a new type substrate for integrated circuits, which will protect the devices inside from the interference of EM waves but not disturb their EM properties.

Soft transduction technology is rapidly adopting soft active elastomer-based minimum energy structures because of their distinctive programmable shape-morphing characteristics. For effective device design, an understanding of the nonlinear dynamic behavior is crucial as they often experience time-dependent motion while operating. Moreover, there has been an increasing scientific interest in enhancing the actuation performance of soft active elastomers by imparting particle reinforcements. This article provides a theoretical framework for investigating the nonlinear dynamics of smart composite elastomer-based minimum energy structures (SCEMES) with the provision of non-aligned electric and magnetic fields, leading to an actively programmable pre-stretch paradigm. Unlike conventional actuators, the proposed SCEMES is made up of a polymer that has electro-magnetic properties and is filled with appropriate fillers with specific volume fractions. An electromagneto-viscoelastic model is developed here to predict actuator behavior and investigate the effects of particle reinforcement on equilibrium and actuated configurations. Besides strengthening the polymer, particle reinforcement is observed to enhance the equilibrium angle achieved by the structure with enhanced functionality. The proposed nonlinear dynamic model is extended to investigate a number of critically influential parameters, including shear modulus ratio of fiber to matrix, frame bending stiffness, membrane pre-stretching, and electro-magnetic loading with time-dependent DC and AC modes of actuation. The results reveal that the combined electro-magnetic actuation enhances the actuation range significantly. The attained tip angle of the actuator increases appreciably when the magnetic and electric fields are applied mutually perpendicular to each other, indicating that the direction of applied magnetic field governs the attained actuated configuration. Further, particle reinforcement enrichments result in a depletion in oscillation amplitudes and an increase in excitation frequencies under the AC actuation mode. The efficient semi-analytical framework presented here would be crucial in developing new actuators, smart devices and soft robots for a variety of advanced engineering and medical applications.

Au nano-tetradecapods with well-defined morphology and controllable branches are synthesized, and their tunable optical and electromagnetic properties are systematically investigated.

In order to increase the magnetic loss for electromagnetic(EM) wave absorption, the soft magnetic <TEX>$Fe_{73}Si_{16}B_7Nb_3Cu_1$</TEX>(at%) alloy strip was used as the basic material in this study. The melt-spun strip was pulverized using an attrition mill, and the pulverized flake-shaped powder was crystallized at <TEX>$540^{\circ}C$</TEX> for 1h to obtain the optimum grain size. The Fe-based powder was mixed with 2 wt% <TEX>$BaTiO_3$</TEX>, <TEX>$0.3{\sim}0.6$</TEX> wt% carbon black, and polymer-based binders for the improvement of electromagnetic wave absorption properties. The mixture powders were tape-cast and dried to form the absorption sheets. After drying at <TEX>$100^{\circ}C$</TEX> for 1h, the sheets of 0.5 mm in thickness were made by rolling at <TEX>$60^{\circ}C$</TEX>, and cut into toroidal shape to measure the absorption properties of samples. The characteristics including permittivity, permeability and power loss were measured using a Network Analyzer(N5230A). Consequently, the properties of electromagnetic wave absorber were improved with the addition of both <TEX>$BaTiO_3$</TEX> and carbon black powder, which was caused by the increased dielectric loss of the additive powders.

본 논문에서는 W-Band(75 GHz~110 GHz) 주파수 대역에서 전파특성 분석을 위한 샘플홀더 제작을 위하여 수행되었다. 먼저 도파관 내에서 전파의 전파이론을 정립하고 재료정수 측정기법을 도출하였다. 그리고 밀리미터파 W-band에 알맞은 도파관형 샘플홀더를 설계 및 제작하고 RAM 샘플을 이용하여 재료정수 및 전파흡수능을 측정하여 분석하였다. 분석결과 샘플시료 특성을 정확하게 측정할 수 있음을 확인하였으며, 향후 이 측정 샘플홀더는 W-band 대역 전파특성 분석을 위해 매우 유용하게 쓰일 수 있을 것이다. In this paper, fabrication of sample holder was studied for an analysis of electromagnetic(EM) wave property in W-band(75 GHz~110 GHz). First of all, a propagation theory of EM wave was considered in the rectangular waveguide, and measurement technique was suggested for analysis of characteristics. A sample holder using in W-band was designed and fabricated, and used for analysis of material property and absorption ability using RAM samples. As a result, the sample holder test was verified exactly for measuring EM wave property of RAM sample. In the future, the proposed sample holder would like to be used for the EM wave property analysis in W-band.

EM waves absorption properties of nitrogenous porous carbon derived from PANI fiber clusters carbonization

This paper focuses on the characterization of the electromagnetic (EM) properties of textiles (polar fleece, cotton, denim, polyester, and polyamide-elastane) and study of their impact on the performance of a wearable antenna. EM properties are measured by the cavity perturbation method, and it is found that the textile materials exhibit low values of complex relative permittivity between 1. $2+i0.002$ and 1. $9+i0.1$. A hexagonal-shaped monopole antenna with a substrate from polar fleece and high body-antenna isolation (front-to-back ratio 31 dB) is designed to serve the performance baseline. Additionally, prototypes on cotton, denim, polyester, and polyamide-elastane substrates are simulated, fabricated, and measured. Results show that radiation efficiency, gain and directivity decrease with increasing dielectric losses in the textile substrate. Further numerical investigations reveal that each of these five textile antennas achieves stable on-body performance in the frequency range of 2.4 to 2.5 GHz when it is placed on a flat phantom.

We propose a broadband measurement method for measuring the electromagnetic (EM) properties of metamaterials in the 1–6 GHz frequency range. For this experimental technique, an original adjustable height strip transmission-line was developed that makes it possible to characterize metamaterials with different volumes and different numbers of unit cells. Therefore, it was possible to assess the influence of the number of unit cells in a sample on the measured constitutive parameters (complex permittivity and permeability). This study enabled us to define the criterion of the representative elementary number of cells. This criterion must be satisfied in practice in order to determine the microwave behavior for the sample under test in as close as possible to an infinite medium, whose EM properties can only be determined from simulations. Experimental and theoretical results for split ring resonator-type metamaterials are presented, compared, and discussed.

The development of UHF RFID technology has reached significant performance advancement in the last 20 years. Both tags and readers are now improved with better sensitivity levels providing a potential for achieving greater tag read ranges. However, the performances of the technology are also limited by complexity and electromagnetic (EM) properties of the environment in which the system operates. The aim of this contribution is to evaluate how well the state-of-the-art UHF RFID systems behave in an actual retail store environment rather than in a controlled anechoic setting. An extensive empirical study is performed and data for the performance analysis are collected from both a commercial reader and an USRP-based sniffer. It is shown that physical and MAC layer should be considered cooperatively in order to improve the overall system performance. Specifically, although the tag responsiveness depends on the products&#x2019; EM properties as well as the number of products and their relative position in the basket, still the appropriate reader mode of operation can ensure a reliable and stable reading process. For the item identification and localization in the smart IoT stores, the EM properties of retail products should be taken into account in the data classification.