Reflection Of Electromagnetic Waves Research Articles

Transparent antenna with RCS tunability based on graphene and metasurface in S band

In this paper, we propose a graphene-based radar cross section (RCS) tunable antenna that utilizes metal mesh and graphene, both of which are optically transparent. The graphene sandwich structure is introduced to replace traditional components like diodes, micro-electro-mechanical systems (MEMS), and varactors, acting as an electromagnetic wave controller and significantly simplifying the device's complexity. By applying different voltages, the electrical properties of graphene are altered, enabling the regulation of reflection, transmission, and absorption of electromagnetic waves. This not only modifies the antenna's pattern but also achieves a substantial reduction in out-of-band RCS. The radiation and scattering mechanism of the antenna is carefully elaborated. The numerical and experimental results match well, which validates the effectiveness of the proposed method. The optical transmittance of the device is 27.9% at 550 nm, and the out-of-band RCS reduction is 10.01 dB at 3.83 GHz. The transparent, RCS tunable antenna proposed has significant potential applications in optical and microwave stealth technology.

Investigation on mechanical properties and stealth characteristics of a novel gradient-stitched composite structure

Based on the far field function of electric field, a new glass carbon fiber gradient-stitched structure is proposed and designed in the paper. In the frequency range of 8–28 GHz, the electric field distribution of transverse electric and magnetic field (TEM) waves incident obliquely on the surface of the structure by optimizing the glass fiber fabric units. It is confirmed that the surface has the function of suppressing electromagnetic wave reflection. The electrical performance simulation and testing results of the structure show that the radar cross section (RCS) is reduced by 90% in the frequency range of 12.3–26.5 GHz. In addition, a multi-scale analysis model is established to quickly predict the tensile modulus and strength of the composite material. The strength and modulus reached 26.9 GPa and 403 MPa, respectively. The simulating and testing results of mechanical properties are in good agreement.

Easily manufacture lightweight EPDM/POE/KB foam with high electromagnetic shielding efficiency and high absorption coefficient through chemical foaming

Utilizing foam-structured composite materials for electromagnetic shielding offers several advantages, including lightweight properties, low filler load, and a high absorption coefficient. However, their application in electromagnetic shielding is often limited by relatively lower mechanical performance. This study employed melt blending and chemical foaming processes to fabricate a lightweight EPDM/POE/KB composite foam with favorable mechanical characteristics, heat resistance, and electromagnetic absorbing performance. Significantly, the foam, with a density of 0.195 g/cm³, demonstrates an absorption-dominated shielding mechanism (absorption coefficient of 0.71) and good electromagnetic shielding performance of 20.57 dB in the X-band. The honeycomb structure formed within the material contributes to the multiple reflections of electromagnetic waves. Additionally, the composite foam exhibits excellent flexibility, with a fracture elongation greater than 150 %, alongside tensile and compressive strengths of 1.46 MPa and 0.92 MPa, respectively, demonstrating satisfactory mechanical performance. Furthermore, the composite foam also possesses good thermal stability. The study provides a low-cost and effective method for preparing lightweight, high-absorption coefficient, and excellent mechanical performance electromagnetic shielding foam.

Method for remote measurement of specific conductivity and moisture of subsurface soil horizons

The aim of the research is to develop a radar method for determining the physical and chemical parameters of subsurface soil horizons, providing rapid determination of moisture and specific conductivity in the area of the plant root system. The proposed method is based on a set of Fresnel equations which describe reflection of electromagnetic waves from the interface between dielectric media in vertical and horizontal polarization of the probing signal. For the practical implementation of the method, it is proposed to use two unmanned aerial vehicles that form a bistatic radar system which irradiates the Earth's surface obliquely in order to create the Brewster's effect and increase the fraction of the radio signal reflected from subsurface horizons. The percentage of moisture and the specific conductivity of soil are calculated from the measured values of the imaginary part of the complex permittivity. The required accuracy of moisture and conductivity measurements is achieved by two-step calibration of the measuring device. The values of the moisture content and specific conductivity of soil obtained by radar at a frequency of 469 MHz are in good agreement with the results of measuring these parameters using the soil moisture meter TDR 150 Spectrum Technologies, Inc.

Flexible and hydrophobic CoFe-LDH @Co MOF @biomass-derived carbon fabrics for effective near-infrared photothermal conversion and electromagnetic attenuation

Near-infrared (NIR) laser countermeasures firing systems and electromagnetic wave shielding are extremely important in military warfare. Herein, a series of biomass-derived carbon flexible textiles with NIR photothermal conversion and microwave absorption capabilities were created by pyrolysis at temperatures ranging from 700 to 1000 °C. A hydrothermal approach was employed to create 2D CoFe-layered double hydroxides (CoFe-LDH), whose positively charged characteristics were securely attached to the hydroxide clusters on the surface of cotton fibers via electrostatic interaction. Subsequently, the adjustable layer spacing of LDH provides ideal in situ growth sites for metal ions and organic ligands of Co MOF. CoFe-LDH@Co MOF@PDMS cotton-derived carbon textiles (CoFe@PCCF) were successfully made using high-temperature pyrolysis, annealed carbonization, and polydimethylsiloxane curing. The intrinsic light absorption of the interwoven and entangled carbon fibers, combined with the plasmonic resonance of its surface metal particles, promotes photothermal conversion of the material, reduces density, and increases absorption during multiple reflections of electromagnetic waves. Furthermore, its qualities can be optimized and modified by modifying parameters like as carbonization temperature and thickness. As a result, CoFe@PCCF-900 shows the minimum reflection loss (RLmin) of −23.03 dB at 1.6 mm thickness and an effective absorption bandwidth (EAB) of 4.53 GHz. The surface temperature of CoFe@PCCF-1000 reaches 74.5 ℃ after 3 seconds of NIR (980 nm, 200 mW) light, indicating quick and stable photothermal conversion. This work provides an opportunity for laser shooting and electromagnetic attenuation low-cost materials.

Nanocellulose-assisted construction of multi-cavity structured Ti3C2Tx/melamine composite sponges for enhanced electromagnetic interference shielding

The deposition of Ti3C2Tx nanosheets onto an ultralight melamine sponge (MS) holds great appeal for constructing mechanically robust and high-performance electromagnetic interference (EMI) shielding composites. However, the full potential of Ti3C2Tx materials for shielding performance is impeded by the insufficient affinity between Ti3C2Tx nanosheets and MS. Herein, with the assistance of cellulose nanofibers (CNF), large-sized single-layer Ti3C2Tx nanosheets were firmly attached to the MS skeleton and enveloped the pores. The obtained Ti3C2Tx/MS composite sponges exhibit a unique multi-cavity structure. Moreover, hydrophobic modification was applied to the composites through the use of two-component silane coupling agents. The silane-modified multi-cavity structured composite sponges demonstrate significant enhancements in conductivity, mechanical strength, and environmental stability. Particularly, the incorporation of 17 wt% CNF leads to a 29.3 dB increases in shielding efficiency (SE) for the composite sponge. The enhancement can be attributed to the high reflectance of electromagnetic waves due to the highly conductive Ti3C2Tx/CNF cavity-membranes, the multiple internal reflections within the multi-cavity structure, and the improved interfacial polarization loss capability facilitated by the abundance of MXene-CNF interfaces.

Design and Implementation of Different Unit Cells for Reconfigurable Intelligent Surface

Recently, great attention has been given to the idea of a smart environment. It often involves the use of reconfigurable intelligent surfaces (RIS) for the management of electromagnetic wave reflections as the world awaits the emergence of 6G. Changeable intelligent surfaces may enhance the creation of wireless communication. The design and analysis of several unit cell reflections are presented in this work. The first design relies on the Switching Technique which involves switching on and off to acquire the phase as well as the coefficient of reflection to accommodate 6G standards. The unit cells design is configured to operate in the millimeter band and X band. In the second design, the radius of the circular patch was changed to adjustment of the phase and reflection coefficient. The use of Floquet technique is employed in investigating the scattering characteristics of a unit cell's constituent elements based on the assumption that every element consists of an extremely iterating periodic structure. To determine the optimal force reflection and the transformation phase, the return loss alongside reflection phase graphs of each resonant component were examined. The simulation results indicate that the first design exhibits a reflection phase shift range of -180 to 90 and a reflection magnitude over 0.93 at a frequency of 11GHz. In contrast, the second design demonstrates a reflection phase shift range of -135 to 135 and a reflection magnitude surpassing 0.9 at a frequency of 28GHz. The analysis and simulation of the design models were carried out using the CST model.

Terahertz vortex beam generation based on reflective and transmissive graphene metasurfaces

Graphene metasurfaces have substantial potential for generating vortex electromagnetic waves carrying orbital angular momentum (OAM) at terahertz frequencies. In this paper, a deformed H-shaped graphene unit cell is utilized to design a half-space reflective metasurface (with a metal backplane, operating in the reflection mode) and a full-space metasurface (operating in both the reflection and transmission modes) to generate OAM beams. The two structures are intertransformable at the level of physical composition, where one configuration enables efficient anomalous reflection of electromagnetic waves within the 4.6–8.9 THz band, while the other enables uniform modulation efficiency of reflective and transmissive waves within the 5.5–7.0 THz band. Equivalent circuit models have been provided to establish a convenient closed-form mathematical description of the metasurface’s electromagnetic behavior. By performing the near- and far-field simulations, a series of THz vortex generators based on the proposed graphene metasurface are demonstrated. In particular, high-purity reflective and transmissive OAM waves with distinct topological charges are observed. Our study provides a path towards the practical realization of active THz OAM metadevices.

Modeling of electromagnetic wave reflection from wet soil taken into account of dispersion, heterogeneity and surface roughness

Background. Taking into account temperature, soil composition, surface roughness and the dependence of effective dielectric constant on frequency allows a more accurate assessment of soil moisture and other important parameters, which can be used in various fields such as agriculture, geology, ecology and hydrology. Aim. In this work, we calculate the reflection of a linearly polarized electromagnetic wave from wet soil, taking into account such physical factors as heterogeneity of soil structure, surface roughness and dispersion. Methods. Based on a heterogeneous mathematical model of wet soil, taking into account the dispersion of the dielectric constant of water and surface roughness, expressions are derived for the complex reflection coefficients of electromagnetic waves of vertical and horizontal polarization. Results. The model of loose wet soil with the standard deviation of roughness on the surface was chosen as the object of study. An analysis of the frequency and angular characteristics of the modules of the reflection coefficients was carried out at a fixed level of soil moisture. Conclusion. The data obtained as a result of the calculations is a valuable tool for further improving methods of remote sensing of the Earth and contributes to the development of new technologies for monitoring soil parameters using unmanned aerial vehicles, which opens up prospects for more accurate and efficient analysis of the state of land resources and ecosystems.

The Effect of Object Thickness in Numerical Reflectance and Transmittance using Finite Difference Time Domain (FDTD)

The electromagnetic waves could be simulated using finite difference time domain. This simulation method based on Maxwell equations. Here, the fields were spatially discretized along time discretization. This was the basic concept for updating the fields in every time step. Since the reflection and transmission of electromagnetic waves were the basic phenomena for optical studies of the waves in materials, we studied the reflectance and transmittance. In FDTD, the reflection and transmission could be calculated using Fourier transformation. We found that the thickness of the object which was inserted to the system affected the reflection and transmission significantly. If the thickness of the object became thicker, then there also increased the appearance frequency of the reflectance with the similar values. It was also happened to the transmittance.

Lightweight thermoplastic polyurethane/multi-wall carbon nanotube foams with a continuous gradient cell structure for electromagnetic interference shielding

With the rapid development of portable microelectronic devices, materials with tunable electromagnetic shielding (EMI) performance and comfort of use have become urgently necessary. A lightweight, conductive thermoplastic polyurethane/multi-walled carbon nanotube (TPU/MWCNT) composite foam with a continuous gradient cell structure has been developed to impede electromagnetic wave reflection induced by excessive impedance mismatch. The continuous gradient distribution of cell structure and conductivity provides the TPU/MWCNT composite foams with distinct shielding effects of electromagnetic waves in both front and back gradient directions. The maximum front absorption coefficient (A) reached 0.93, which is higher than any foam with a uniform cell size within the cell size range of the gradient composite foams. At the same time, the gradient composite foams possess the characteristics of lightweight, high elasticity, and extensibility. The weight was decreased by 67.27–85.45 %, the elastic recovery ratio of compression reached 95 %, and the toughness was also excellent. Numerical simulation of the gradient foam model was conducted using CST Microwave Studio to uncover the gradient asymptotic dissipation mechanisms. The lightweight and stretchable continuous gradient foams show great promises for the next-generation portable electronic devices that generate no radiation pollution.

Polarization conversion and lateral shifts in multilayered structure with finitely-gapped topological surface states

Abstract The polarizatison conversion and the Goos–Hänchen (GH) shifts of the reflected electromagnetic wave for the multilayered structure made of topological insulator (TI) layers with finite surface energy gap are investigated. The transfer matrix formalism is adopted to analyze the reflection of electromagnetic wave through the multilayered structure, and the influences of surface energy gap, thickness and number of the TI layers are discussed. We find that maximum polarization conversion rate can be obtained with appropriate surface energy gap of TI, and within a certain range of finite energy gap, the polarization conversion effect is stronger than that for the case under the infinite surface energy gap limit. Greater polarization conversion rate for TI with small surface energy gap can be found than that for TI with larger energy gap in some range of layer numbers. At large incident angles the GH shifts vary considerably with the layer number for TI with relatively larger energy gap. Result of the combined influence of surface energy gap and layer number shows that, there exists both the positive and negative enhancement peaks of the GH shifts, and for smaller energy gap, fewer TI layers are required to obtain the transition between positive and negative GH shifts.

Efficient broadband sea urchin-like Fe3O4@C electromagnetic wave absorbing materials

The development of electromagnetic wave absorbing materials is crucial for various applications. Carbon materials and ferrite materials were recognized as ideal candidates of absorbing agents due to their respective dielectric loss and magnetic loss capabilities. In this study, Fe3O4@C were prepared using hydrothermal carbonization coupling method. The microstructure and morphology of Fe3O4@C were studied using SEM, TEM, XRD and TG. The results showed that Fe3O4@C exhibited a hollow sea urchin-like structure. The molar ratio of carbon to iron sources in the raw materials significantly influenced the crystal structure of the product. The growth mechanism of sea urchin-like Fe3O4@C was proposed. The carbon content in Fe3O4@C increased with the increase of molar ratio of glucose and iron (III) sulfate. The Fe3O4@C with carbon content of 31.10 % exhibited optimal absorption performance, with a minimum reflection loss of −57.1 dB at a matching thickness of 5.10 mm and effective absorption bandwidth (EAB) of 4 GHz. Electromagnetic parameters and absorption performance could be adjusted by varying the molar ratio of glucose and iron (III) sulfate. The unique sea urchin-like structure enhanced multiple reflection of electromagnetic waves. Interface polarization, conductivity loss and synergistic effect between carbon and Fe3O4 also contributed to the favorable absorption properties.

Controllable construction of hollow Fe3O4/Ag particles for microwave absorption and photocatalysis

Hollow metallic composite particles are widely used in microwave absorption and catalysis due to their unique cavity structures, and favorable physical and electromagnetic properties. In this work, we propose an approach to prepare highly dispersed Fe3O4/Ag composite particles with a hollow structure using water-soluble green template method combined with in-situ growth process. The as-prepared cubic Fe3O4/Ag composite particles with an average size of 3.19 μm of hollow Ag and 11.65 nm of Fe3O4 coating on the surface were used as fillers for preparing microwave absorption epoxy resin films, showing a minimum reflection loss of −62.37 dB at 16.63 GHz with 7.5 mm thickness. An effective absorption bandwidth of 4.80 GHz can be observed in the frequency bands of 4.70–6.09 and 14.59–18.00 GHz. This mechanism is attributed to the internal cavity of the Fe3O4/Ag particles realizing multiple reflections of electromagnetic waves, and the synergistic effect of Fe3O4 and Ag. Moreover, this perspective is confirmed by their photocatalytic performance. The Fe3O4/Ag particles achieve a high photocatalytic degradation efficiency of 99.84% for Congo red dye within 30 min of light exposure and maintain a value of 96.62% after 6 cycles, demonstrating an outstanding reusability.

Cationic pre-insertion interlayer engineering of manganese dioxide for highly efficient electromagnetic wave absorption

Interlayer engineering of two-dimensional structural materials provides unique advantages for tuning the electromagnetic properties of metal oxides, injecting unlimited energy into the design of advanced two-dimensional metal oxide electromagnetic wave absorbers. In this study, Manganese dioxide intercalated with alkali metal ions was prepared by a simple molten salt method. The pre-intercalation of ions not only enhances the polarization loss at the heterogeneous interface between cations (point sites) and manganese dioxide (face sites) but also alters the energy band structure of manganese oxide and enhances its electrical conductivity, which in turn enhances the conductive loss of the manganese dioxide. Due to the synergistic effect of multiple polarizations and conductive losses, NaMO exhibits superb electromagnetic wave absorption properties and an effective absorption bandwidth of 5.36 GHz at thinner matched thicknesses. In addition, the RCS simulation result further verifies the excellent electromagnetic wave absorption capability of NaMO. Under the positive incidence of electromagnetic waves, the electromagnetic wave reflection intensity of the metal plate coated with NaMO is effectively reduced. Finally, this work establishes a new way to modulate the electromagnetic properties.

Overcoming the Incompatibility Between Electrical Conductivity and Electromagnetic Transmissivity: A Graphene Glass Fiber Fabric Design Strategy.

Conventional conductive materials such as metals are crucial functional components of conductive systems in diverse electronic instruments. However, their severe intrinsic impedance mismatch with air dielectric causes strong reflection of incident electromagnetic waves, and the resulting low electromagnetic transmissivity typically interferes with surrounding electromagnetic signal communications in modern multifunction-integrated instruments. Herein, graphene glass fiber fabric (GGFF) that merges intrinsic electrical and electromagnetic properties of graphene with dielectric attributes and highly porous macrostructure of glass fiber fabric (GFF) is innovatively developed. Using a novel decoupling chemical vapor deposition growth strategy, high-quality and layer-limited graphene is prepared on noncatalytic nonmetallic GFF in a controlled manner; this is pivotal to realizing GGFF with the desired compatibility among high conductivity, low electromagnetic reflectivity, and high electromagnetic transmissivity. At the same sheet resistance over a wide range of values (250-3000 Ω·sq-1), the GGFF exhibits significantly lower electromagnetic reflectivity (by 0.42-0.51) and higher transmissivity (by 0.27-0.62) than those of its metal-based conductive counterpart (CuGFF). The material design strategy reported herein provides a constructive solution to eliminate the incompatibility between electrical conductivity and electromagnetic transmissivity faced by conventional conductive materials, spotlighting the applicability of GGFF in electric heating scenarios in radar, antenna, and stealth systems.

Preparation and electromagnetic waves absorption performance of hibiscus-like CuS/SiC NWs@PANI in the GHz band

With the increasing demand for electromagnetic (EM) waves absorbing materials in communication, military, and electronic devices, the exploration of lightweight, wideband, and highly absorptive materials in the GHz frequency range has become urgent. This article presents a successful synthesis of hibiscus-like copper sulfide (CuS)/silicon carbide nanowires (SiC NWs) @polyaniline (PANI) composite material using a combination of hydrothermal and in-situ polymerization techniques. With a filling amount of only 25 wt% of CuS/SiC NWs@PANI in the paraffin transmissive matrix, the material exhibits a minimum reflection loss (RLmin) of −31.6 dB at a thickness of 2.1 mm, while providing an effective absorption bandwidth (EAB) of 4.5 GHz. As the filling amount increases to 35 wt%, the RLmin drastically reduces to −41.38 dB at a thickness of 2.3 mm. The CuS particles exhibit a unique multi-layered asymmetric hibiscus-like structure, which greatly enhances the reflection of EM waves. The conductive polymer PANI, forming a coating layer at the interface with CuS and SiC NWs, effectively enhances the conductive loss. The collaborative interactions among the components in the ternary composite material significantly boost the EM waves absorption performance. This article offers valuable insights into the preparation and real-world application of absorbent materials with distinctive microstructures, thus opening up new avenues for the design of composite absorbing materials.

Flexible multilayer MXene/Polyimide composite film with excellent electromagnetic interference shielding and photothermal conversion performance

The development of flexible, thin, multifunctional materials represents a strategic advancement for the creation of next-generation wearables that offer both electromagnetic shielding and thermal management. This study introduces the fabrication of a multilayer MXene/polyimide (MXene/PI) composite film, demonstrating significant electromagnetic shielding effectiveness (EMI SE) and photothermal conversion efficiency through a layer-by-layer casting technique. When the MXene content is 29.7 wt%, the alternating multilayer MXene/PI composite film can reach a high EMI SE of 23.3 dB at 0.26 mm thickness, and when the MXene content is 45.7 wt%, the EMI SE can reach a maximum of 40.7 dB, which has a significant advantage over other materials. This superior performance exceed that of alternative materials, owing to the multilayer MXene construction that magnifies electromagnetic wave reflection losses. Furthermore, the film displays a rapid and sensitive photothermal response under laser irradiation, achieving temperatures up to 93°C at a 0.5 W/cm2 density. Impressively, at 0.4 W/cm2, it maintains a stable long-term saturation temperature over 40 cycles, showing its potential in applications such as photothermal sensors, personal heating, and muscle protection.

Effect of glass powder on mechanical properties and electromagnetic transmission properties of high alumina cement paste

The mechanical properties and electromagnetic transmission properties of high alumina cement (HAC) paste with different glass powder (GP) contents were investigated in this paper. The effects of hydration phase, unhydrated phase, GP phase and pore phase on the dielectric properties of HAC paste were quantitatively analyzed. The results show that the strength, fluidity and setting time of HAC paste decrease with the increase of GP replacement rate. The real part, imaginary part and loss angle tangent of dielectric constant decrease. The addition of GP leads to a reduction in reflectivity and absorptivity of electromagnetic waves in the paste, while increasing transmittivity.Furthermore, the real part of the dielectric constant of each phase in the HAC paste follows the order: hydration product phase > unhydrated phase > GP phase > pore phase. With an increase in GP content, the real part of the dielectric constant of the hydration product phase increases. Finally, based on the results of vector network analysis (VNA), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), the reasons for the changes of mechanical properties and electromagnetic properties of HAC paste under different GP replacement rates were analyzed from the aspects of phase composition, pore distribution and microstructure.

Radar absorbing properties of different size carbon nanotube reinforced polymer composites

Carbon nanotubes (CNTs), which have a diameter on the nanometer scale, are tube-like materials composed of carbon and graphite sheets. Carbon nanotubes play an important role in many fields such as nanotechnology, electronics, optics and material science due to their superior properties such as high elasticity, high thermal conductivity, low density and being more chemically inert. In this study, the use of carbon nanotubes in radar absorbing materials (RAM) to reduce the reflection of electromagnetic waves was investigated. In this sense, by using a polymeric composite structure reinforced with carbon nanotubes, a material with unique properties such as solid absorption, low weight/thickness and cost-effectiveness has been produced, minimizing the reflection of electromagnetic waves. For this purpose, carbon nanotubes with different particle sizes of 8 nm, 30–50 nm and 48–78 nm were blended with polyester at the ratio of 1%. The resulting composites were characterized using a Network analyzer in the frequency range of 8–12 GHz. According to the results obtained, it was observed that radar absorption increased with increasing particle size. It has been determined that by changing the particle sizes of carbon nanotubes in composites, the absorption bands can be adjusted to suit different applications in different frequency bands.