Transmission Of Electromagnetic Waves Research Articles

Frequency selective rasorber based on cross bend resonators for wideband transmission and absorption

Abstract The wideband absorption and transmission of frequency-selective rasorber (FSR) remain a persistent challenge in the application of radar devices. In this article, a novel high performance wideband FSR design based on cross bend resonators (CBR) was proposed. The FSR consists of an upper absorption lossy layer, which offers broad absorption and transmission bands, and a lower bandpass frequency-selective surface (FSS) that enables a highly selective transmission of incident electromagnetic wave. Full wave simulation results showed that this novel design achieves an absorption bandwidth of 83.7% with more than 90% absorptivity in the frequency range of 5.2-12.7 GHz. Furthermore, the passband's fractional bandwidth (FBW) for the insertion loss (IL) less than -3 dB is 33.9%, ranging from 14.9 to 21 GHz, with the minimum IL recorded at 0.69 dB at 17.7 GHz. To further verify the proposed method, a prototype FSR with 10×10 units of 120 mm×120 mm was fabricated and the performance of the FSR was tested. The experiment results were in good agreement with the simulated results, and it showed a significant monostatic radar cross-section (RCS) reduction in the frequency range of 5.3 GHz to 18.3 GHz compared with a metallic plane of the same size.

Structure‐function integrated ZrO2–SiO2 nanocrystalline glass–ceramics achieved by in situ formation of amorphous carbon

AbstractCeramics can be traditionally classified as structural and functional ones. However, the miniaturization and multi‐functionalization of various devices require ceramics to have both structural and functional properties. In this work, we aimed to develop structure‐function integrated ZrO2–SiO2 nanocrystalline glass–ceramics (NCGCs) by in situ formation of homogenously distributed amorphous carbon. By reducing the calcination temperature of carbon‐containing powder, organic carbon groups were partially retained in the powder and they transformed to amorphous carbon in the sintered NCGCs. At micrometer scale, the carbon was homogenously distributed in the NCGCs, avoiding the commonly encountered agglomeration problem of carbon fillers. The effects of carbon on the microstructure, mechanical properties, wear resistance, and dielectric properties of the NCGCs were investigated. Results showed that the in situ formed amorphous carbon was homogenously distributed in the ZrO2 nanocrystallites. Meanwhile, the amorphous carbon strongly bonded with the ZrO2–SiO2 NCGCs. Only a small amount of carbon was combusted even after annealing at 1000°C for 3 h. The formation of amorphous carbon led to an improvement of nanohardness and wear resistance of the NCGCs, while slightly reducing Young's modulus and flexural strength. The electromagnetic wave transmission performances were improved due to the formation of amorphous carbon. The current study paves a new way for developing structure‐function integrated glass–ceramics through in situ formation of carbon. The prepared structure‐function integrated ZrO2–SiO2 NCGCs have great potential to be used as radome and antenna windows of aerospace aircrafts that work in harsh environment.

Exact closed forms for the transmittance of electromagnetic waves in one-dimensional anisotropic periodic media

In this work, we obtain closed expressions for the transfer matrix and the transmittance of electromagnetic waves propagating in finite one-dimensional anisotropic periodic stratified media with an arbitrary number of cells. By invoking the Cayley–Hamilton theorem on the transfer matrix for the electromagnetic field in a periodic stratified media formed by N cells, we obtain a fourth-order recursive relation for the matrix coefficients that defines the so-called Tetranacci polynomials (TPs). In the symmetric case, corresponding to a unit-cell transfer matrix with a characteristic polynomial where the coefficients of the linear and cubic terms are equal, closed expressions for the solutions to the recursive relation, known as symmetric TPs, have recently been derived, allowing us to write the transfer matrix and transmittance in a closed form. We show as sufficient conditions that the 4×4 differential propagation matrix of each layer in the binary unit cell, Δ , a) has eigenvalues of the form ±p1 , ±p2 , with p1≠p2 , and b) its off-diagonal 2×2 block matrices possess the same symmetric structure in both layers. Otherwise, the recursive relations are still solvable for any 4×4 matrix and provide an algorithm to compute the Nth power of the transfer matrix without carrying out explicitly the matrix multiplication of N matrices. We obtain analytical expressions for the dispersion relation and transmittance, in closed form, for two finite periodic systems: the first one consists of two birefringent uniaxial media with their optical axis perpendicular to the z-axis, and the second consists of two isotropic media subject to an external magnetic field oriented along the z-axis and exhibiting the Faraday effect. Our formalism applies also to lossy media, magnetic anisotropy or optical activity.

Broadband electromagnetic wave absorption properties of RGO cement-based composite

In this study, a cement-based composite was prepared using reduced graphene oxide (RGO) as a raw material via an ethanol liquid-phase mixing pre-dispersion process. The microstructure of cement-based composites with varying RGO contents was discussed, and a systematic investigation was conducted into the electromagnetic wave absorption (EWA) performance of RGO-cement composites within the frequency range of 2–18 GHz. The results indicate that the RGO content significantly impacts its wave absorption performance. Notably, at an RGO content of 3.0 wt%, the wave absorption performance experiences substantial enhancement. For instance, the minimum reflection loss (RLmin) of −48.33 dB at 8.9 GHz with a coating thickness of 2.6 mm is achieved, while an effective absorption bandwidth (EAB) of 5.02 GHz is attained with a thickness of only 1.6 mm, covering nearly the entire Ku-band. The incorporation of high specific surface area RGO into cement materials results in abundant interface polarization losses and additional electromagnetic wave transmission paths, effectively boosting the EWA performance. Consequently, these materials exhibit significant potential for applications in the field of electromagnetic wave shielding.

Joint waveform design and resource allocation strategy for cognitive radar target situation awareness

AbstractTraditional radar systems use fixed patterns and constant electromagnetic wave transmission to illuminate targets, but they often do not effectively use prior information about targets and consume significant radar resources. Cognitive radar has emerged as a way to improve resource efficiency and address these shortcomings. A joint waveform design and resource allocation strategy for cognitive radar that incorporates target situational awareness is proposed. This method integrates the interacting multiple model algorithm and the Unscented Kalman Particle Filter to achieve target situation awareness as prior knowledge. By combining the target attitude and the frequency response function of the target radar cross section at different time points in the prior knowledge, a joint beam control and power allocation strategy is formulated and transformed into an optimization problem. In addition, a cognitive pulse‐to‐pulse frequency agile waveform design method is proposed to support multiple target tracking under complex motion models. Simulation experiments demonstrate the effectiveness of this approach in obtaining accurate target situation information, achieving beam control, and optimizing power allocation. The designed waveforms can enhance radar target detection performance and improve low probability of intercept characteristics by adjusting the pulse repetition interval. This method has significant technical value.

Bounding Volume Hierarchy-Assisted Fast SAR Image Simulation Based on Spatial Segmentation

In order to improve the simulation efficiency under the premise of ensuring the fidelity of synthetic aperture radar (SAR) simulation images, we propose a BVH-assisted fast SAR image simulation method based on spatial segmentation. The beam scanning model is established based on RD imaging geometric relation, and the bounding volume hierarchy (BVH) algorithm is used to assist in obtaining the time-varying latticed radiation and shadow areas within the radar beam, combining them with the real-time position of the sensors to complete the simulation of the electromagnetic (EM) wave transmission. The ray tracing algorithm is used to calculate the multiple backscatter fields of EM waves, including various material properties of the target surface. The SAR spatial traversal is adopted to spatially segment the latticed radiation area, and the compute unified device architecture (CUDA) kernel function is designed using the echo matrix cell method to make each cell of the target echo matrix as a subfield of the backscattering field, and the position of the echo matrix cell is traversed to obtain the target backscattering field. The target simulated echo is processed by the range Doppler (RD) imaging algorithm to obtain the SAR-simulated image. The simulation results show that compared with a CPU single-thread simulation, the simulation speed of the proposed method is significantly improved, and the SAR simulation image has high structural similarity with the real image, which fully verifies the effectiveness of the proposed method.

Electromagnetic telemetry signal denoising: An interference elimination via parameter estimation

Electromagnetic telemetry has emerged as a promising technique for the real-time acquisition of downhole data. However, the transmission of electromagnetic waves through the formation encounters attenuation, leading to a weakened received signal at the surface, typically registering at the microvolt level. The growing presence of surface electrical equipment in well-site environments has engendered heightened electromagnetic interference, thus deteriorating the signal-to-noise ratio (SNR) of received signals. The conventional linear filtering method can effectively eliminate the electromagnetic interference at the wellsite, but it has no effect on the low frequency interference close to the carrier frequency, especially the common low-frequency pulse interference (LPI) and power line interference (PLI). To mitigate the adverse effects of surface noise, we propose a nonlinear processing method based on parameter estimation algorithms. Generally, the proposed method entails reconstructing the interference by accurate parameter estimation and subtracting it from the received signal, aiming to enhance the SNR of the received signal. Simulation data and real noise data collected in the field are processed to verify the effectiveness of the proposed method. The results demonstrate the superiority of this approach over traditional filtering techniques in effectively eradicating surface interference.

Simplistic framework of single-pixel-programmable metasurfaces integrated with a capsuled LED array

Coding metasurfaces can manipulate electromagnetic wave in real time with high degree of freedom, the fascinating properties of which enrich the metasurface design with a wide range of application prospects. However, most of the coding metasurfaces are designed based on external excitation framework with the wired electrical or wireless light control devices, thus inevitably causing the interference with electromagnetic wave transmission and increasing the complexity of the metasurface design. In this work, a simplistic framework of single-pixel-programmable metasurfaces integrated with a capsuled LED array is proposed to dynamically control electromagnetic wave. The framework fully embeds the photoresistor in the meta-atom, controlling the LED array to directly illuminate the photoresistor to modulate the phase response. With this manner, the complex biasing network is transformed to the universal LED array, which means the physical control framework can be transformed to a software framework, and thus the functions of the metasurface can be freely manipulated by encoding the capsuled LED array avoiding mutual coupling of adjacent meta-atoms in real time. All the results verify that the far-field scattering pattern can be customized with this single-pixel-programmable metasurface. Encouragingly, this work provides a universal framework for coding metasurface design, which lays the foundation for metasurface intelligent perception and adaptive modulation.

Effects of air-entraining agents and glass powder on the electromagnetic wave transmission and mechanical performances of sulfoaluminate cement

This study prepared a sulfoaluminate cement with high electromagnetic wave transmission performance by adding air entraining agent and glass powder and revealed the related mechanism. The test results showed the air-entraining agents and glass powder cannot affect the type of hydration products of the sulfoaluminate cement. The addition of the air-entraining agents and glass powder reduced the dielectric constant of the SAC while increasing the magnetic permeability. The air-entraining agents and glass powder increased the transmittance with a maximum value of 60.2 %, illustrating the electromagnetic wave transmission performance of the sulfoaluminate cement could be improved. The electrical resistivity of the sulfoaluminate cement with the air-entraining agents and glass powder did not change significantly because the air-entraining agents increased the electrical resistivity and the effect of the glass powder was the opposite. The strengths of the sulfoaluminate cement with the air-entraining agents and glass powder decreased.

Non-destructive testing of reinforced concrete structures using sub-terahertz reflected waves

Terahertz (THz) and sub-terahertz (sub-THz) waves are unexplored waves between the infrared and microwave ranges. This range features unique characteristics of both light resolution and electromagnetic wave transmission. Sub-THz waves are part of attractive new diagnostic methods for inner objects because they are safer than normal non-destructive inspection methods involving high energy, such as X-rays. In this study, a novel non-contact and non-destructive inspection method for reinforced concrete (RC) structures using sub-THz reflection imaging is proposed to inspect the deterioration of inaccessible damaged RC structures. The results of this study confirmed that the proposed sub-THz imaging method can detect cracks and voids in concrete, as well as in metals inside or behind the concrete, based on differences in reflectance. In addition, the camera-based measurement system makes real-time on-site field measurements possible.

Molecular interface anchoring in PI-b-PDMS/SiO2@BN block copolymer foams for flexible, ultra-low dielectric, and enhanced terahertz communication performance

In the context of the future sixth-generation (6G) communication system, the development of multi-functional materials with ultra-low dielectric permittivity (Dk) and ultra-low dielectric loss (Df) is of paramount importance for the design of terahertz (THz) frequency electromagnetic wave transmission devices. In this work, polyimide-block-polydimethylsiloxane (PI-b-PDMS copolymer, PIC) material with low Dk, high flexibility and high supercritical fluid foaming ability was fabricated via copolymerization. Additionally, core–shell SiO2@BN nanofillers were synthesized by condensing tetraethyl orthosilicate (TEOS) on hexagonal boron nitride (BN) nanofiller surface. Subsequently, flexible polyimide/SiO2@BN foam was fabricated via supercritical N2 foaming. The resulting PIC/SiO2@BN nanocomposites exhibit exceptional flexibility and impressive thermal resistance (thermal decomposition temperature 472.2 °C). Notably, the incorporation of core–shell SiO2@BN nanofillers leads to the formation of a molecular interface anchoring structure through hydrogen bonding effect. This structure effectively reduced the mobility of the flexible PIC polymer chains on the SiO2@BN nanofiller surfaces. Consequently, the porous PIC/SiO2@BN materials show a low shrinkage ratio, low dielectric property (Dk = 1.21, Df = 0.012 at 1 THz), excellent THz transmission rate (91.4 %) and long distance 6G THz signal coverage (125.99 m). Furthermore, porous PIC/SiO2@BN materials show superior flame-retardant and thermal infrared stealth properties.

Construction of Hierarchical Yolk-Shell Co/N-Dope C@void@C@MoS2 Composites with Multiple Heterogeneous Interfaces toward Broadband Electromagnetic Wave Absorption.

The synthesis of materials with a multicomponent hierarchical structure is an essential strategy for achieving high-performance electromagnetic wave (EMW) absorption. However, conventional design strategies face challenges in terms of the rational construction of specific architecture. In this study, we employ a combined space-restricted and hierarchical construction strategy to surface-plant MoS2 nanosheets on yolk-shell structural carbon-modified Co-based composites, leading to the development of high-performance Co/NC@void@C@MoS2 absorbers with advanced architecture. The surface-planted MoS2 nanosheets, the Co/NC magnetic yolk, and the dielectric carbon shell work together to enhance the impedance matching characteristics and synergistic loss capabilities in the composites. Experimental results indicate that Co/NC@void@C-700@MoS2 exhibited the best absorption performance with an effective absorption bandwidth of 7.54 GHz (at 2.05 mm) and a minimum reflection loss of -60.88 dB (at 1.85 mm). Furthermore, radar cross-section simulation results demonstrate that Co/NC@void@C-700@MoS2 effectively suppresses the scattering and transmission of EMWs on perfect electric conductor substrates, implying its superior practical application value. This study provides inspiration and experimental basis for designing and optimizing EMW absorption materials with hierarchical yolk-shell architecture.

Design and Development of Metamaterial Absorber for IoT Applications

Microwave absorbers are efficient design structures that enhance electromagnetic shielding and reduce electromagnetic wave interference. It dissipates an incident electromagnetic wave by converting it into other forms of energy, thereby preventing the electromagnetic wave's reflection and/or transmission. A novel electromagnetic metamaterial dual-band microwave metamaterial absorber for IoT application is proposed in this manuscript. The proposed absorber has an excellent absorption rate, above 98% and 99% at 2.4 and 5.1 GHz, respectively. The structure, designed over FR-4 material, provides negative permittivity and permeability. The Nicolson Ross Weir (NRW) method investigates metamaterial properties. An array of (3 × 3) unit cell absorbers is designed, developed, and tested; simulated and measured results are in good agreement.

Thermal controlled multi-functional metasurface for freely switching of absorption, reflection, and transmission.

Metasurfaces have garnered significant attention in recent years due to their substantial electromagnetic (EM) wave manipulation capabilities. However, most previously documented metasurfaces have been limited to controlling just a single EM wave mode, encompassing transmission, reflection, or absorption. Such limitations have impeded the broader applications of metasurfaces. To address this issue, this study introduces a multi-functional metasurface (MFM) in the utilization of Ge2Sb2Te5 (GST), vanadium dioxide (VO2), and graphene. This novel design enables real-time control over the transmission, absorption, and reflection of EM waves as necessitated through thermal control, allowing for seamless transitions from complete transmission to complete reflection. Furthermore, this configuration achieves extensive broadband perfect absorption, spanning up to 1.83 THz. The optical response mechanism of this MFM across distinct operational modes is meticulously analyzed through electric field distribution. Remarkably, this proposed MFM exhibits polarization insensitivity and maintains good optical performance even under conditions of wide-angle incidence. With the ability to switch to different operating modes according to the needs of different environments, the proposed MFM has the potential to be used in a wide range of scenarios, including radar stealth, wireless communications, and military search.

Analysis of the Electromagnetic Wave Transmission Characteristics in Inhomogeneous Plasma Based on an Equivalent Circuit Model

Analysis of the Electromagnetic Wave Transmission Characteristics in Inhomogeneous Plasma Based on an Equivalent Circuit Model

Reconfigurable and Programmable Space Channels for Non‐Reciprocal Electromagnetic Transmissions by Active Metasurfaces

AbstractThe Control of spatial electromagnetic (EM) waves has always been an attractive prospect, especially with the emergence of metasurfaces, which introduce additional manipulating methods and degrees of freedom. In this paper, a design is proposed to realize reconfigurable and programmable space channels for non‐reciprocal transmissions of EM waves through the use of active metasurface. The layout of the chessboard pattern is preferred for constructing the metasurface, which is composed of two kinds of meta‐atoms. One type of meta‐atom is independently controlled for the transmission gain, attenuation, and phase shift, while the other type is independently controlled for the transmission attenuation and phase shift only. The use of power amplifiers (PAs) to achieve transmission gain in the meta‐atoms can actualize the performance of non‐reciprocal transmissions. The programmable operations of phase shift and attenuation in meta‐atoms can dynamically establish varied spatial channels. A prototype of the active metasurface is fabricated and measured. In the measurements, multiple types of reconfigurable and programmable non‐reciprocal transmission channels are observed clearly, verifying the validity of the proposed method.

Formation of photonic band gaps by direct destructive interference.

We study a photonic band gap (PBG) material consisting of multiple waveguides. The multiconnected waveguides provide different paths for direct wave interference within the material. Using coaxial cables as waveguides, we are able to tune the PBG of the material. Using direct destructive interference between different paths of the waveguides, we experimentally observe a kind of PBG which is quite different from the traditional PBG that is caused by scattering in dielectrics with inhomogeneous refractive indices. Particularly, this newly observed PBG has an extremely strong wave attenuation, making electromagnetic (EM) waves in the PBG cannot even pass through one unit cell under certain conditions. We also systematically investigate the transmission of EM waves in our PBG materials and discuss the mechanism of band gap formation. Our results provide a new insight to develop new band gap materials for photons and phonons.

Electromagnetic wave propagation in cylindrical photonic crystals with engineered disorder effects

In this study, the manipulation of engineered disorder effects in cylindrical photonic crystals is examined, with a focus on the influence of three varied types of disorder effects on the transmission spectra near the first five photonic band gaps of CPCs. The investigation employed the basic (ABA)N model, where A and B depict two isotropic dielectrics, and N is the number of periods. The impact of the disorder on the CPCs is analyzed and discussed in detail. In addition, the disorder-induced localization and delocalization of the electromagnetic waves are measured by the inverse participation rate and disorder-to-order energy ratio. These results are analyzed numerically. Based on this, the intrinsic connection between the defined parameters and the mechanism of disorder-influenced structure switching between the localized and transmitted states is investigated. All the above phenomena and findings might lead to a new understanding of electromagnetic wave transmission and localization in micro and nano-optical devices.

Simulation of Electromagnetic Waves with Sinusoidal Pulses on Metal through the Finite Difference Time Domain (FDTD) Method

Understanding electromagnetic wave physical phenomena in three dimensions can be challenging. This research aims to create a model for how electromagnetic waves travel through a three-dimensional medium. One of the best ways to visualize this type of electromagnetic wave is Finite-Difference Time-Domain (FDTD). The simulation results revealed that the properties of the dielectric material and conductivity affect the shape of the sinusoidal pulse propagation, where the electromagnetic wave experiences reflection and transmission. The properties of the material influence the electric and magnetic fields in various ways, affecting the interaction between the transmitted and reflected waves. This interaction is influenced by several factors, such as permeability, and leads to either constructive or destructive interference.

Multi-Functional Reconfigurable Intelligent Surfaces for Enhanced Sensing and Communication.

In this paper, we propose a reconfigurable intelligent surface (RIS) that can dynamically switch the transmission and reflection phase of incident electromagnetic waves in real time to realize the dual-beam or quad-beam and convert the polarization of the transmitted beam. Such surfaces can redirect a wireless signal at will to establish robust connectivity when the designated line-of-sight channel is disturbed, thereby enhancing the performance of wireless communication systems by creating an intelligent radio environment. When integrated with a sensing element, they are integral to performing joint detection and communication functions in future wireless sensor networks. In this work, we first analyze the scattering performance of a reconfigurable unit element and then design a RIS. The dynamic field scattering manipulation capability of the RIS is validated by full-wave electromagnetic simulations to realize six different functions. The scattering characteristics of the proposed unit element, which incorporates two p-i-n diodes have been substantiated through practical implementation. This involved the construction of a simple prototype and the subsequent examination of its scattering properties via the free-space measurement method. The obtained transmission and reflection coefficients from the measurements are in agreement with the anticipated outcomes from simulations.