Wave Absorption Research Articles

Green Strategy for a Large-Format, Superhard, and Insulated Electromagnetic Wave Absorber Inspired by a Natural Feature of a Conch Shell.

Due to the intensification of electromagnetic pollution and energy shortages, there is an urgent need for multifunctional composites that can absorb electromagnetic waves and provide insulation. However, developing low-cost electromagnetic wave-absorbing composites that are lightweight, high strength, heat-insulating, and large-format for special environments remains challenging. Inspired by the conch shell, this article proposes a green strategy of hydration recrystallization self-assembly. Highly biologically active hydroxyapatite (HAP) was used to lock in free water to prevent porous carbon fibers from absorbing a large amount of water. Meanwhile, HAP underwent ion exchange and recombined with hydrated crystals of magnesium oxychloride to form a gelatinous HAP-5 phase crystal. The cementitious HAP-5 phase crystal was interwoven and interlocked with the support skeleton carbon fibers and metal Ni powder to form conch shell composites (Bio-CSC) with multiple interfaces via electrostatic adsorption and metal complexation. This strategy utilized inorganic substances as bridges to uniformly disperse conductive materials such as carbon fibers to construct a conductive network with an enriched interface polarization. The prepared Bio-CSC was composed of multiple heterogeneous interfaces and was lightweight and high strength, with a specific strength increase of 300%. It also provided excellent thermal insulation and electromagnetic wave absorption. Its thermal conductivity was 0.071 W·m-1·k-1, and the lowest RLmin value of -21.88 dB, with a matching thickness of only 1.2 mm. The composites in this study overcame the limitations of traditional absorption materials such as high magnetism and single function and may be used in fields such as building energy conservation and electromagnetic safety.

Synthesis of in situ grown CNTs on MOF-derived Ni@CNT with tailorable microstructures toward regulation of electromagnetic wave absorption performance

Metal-Organic framework (MOF) derivatives have been applied as electromagnetic wave absorption (EMA) materials in recent years. Carbon nanotubes (CNTs) can achieve in situ growth on the surface of MOF derivatives. However, there is limited research on the EMA performance by regulating the morphology of the in situ grown CNTs. In this work, we prepared MOF-derived Ni@carbon nanotubes (Ni@CNT) with controllable length of CNTs by solvothermal and simple one-step pyrolysis method and revealed the CNT growth mechanism. We further investigated the effect of in situ grown CNT morphology on electromagnetic parameters and EMA performance. In situ grown CNTs of similar length on the surface of MOF derivatives lead to similar electromagnetic parameters. When the length of CNTs is short, the relaxation strength (Δε=εs−ε∞) is high, leading to excellent microwave absorption performance. For Ni@CNT-600, the reflection loss of −44.4 dB can be achieved at merely 1.72 mm. Finite element (FE) simulation was used to evaluate the EMA mechanism of different samples by calculating electric field and polarization strength. This work has explored the electromagnetic wave absorption performance from the perspective of microstructural tailoring, helpful for understanding the unique role of the in situ grown CNTs on the surface of MOF derivatives and investigating the ultra-thin electromagnetic wave absorption materials.

Integration of Electrical Properties and Polarization Loss Modulation on Atomic Fe–N-RGO for Boosting Electromagnetic Wave Absorption

HighlightsSingle-atom Fe–N4 sites embedded into graphene were successfully synthesized to exert the dielectric properties of graphene.The absorption mechanisms of metal-nitrogen doping reduced graphene oxide mainly include enhanced dipole polarization, interface polarization, conduction loss and defect-induced polarization.Excellent reflection loss of − 74.05 dB (2.0 mm) and broad effective absorption bandwidth of 7.05 GHz (1.89 mm, with filler loading only 1 wt%) were obtained.

Model of time-distance curve of electromagnetic waves diffracted on a local feature in the georadar study of permafrost zone rock layers

In GPR (georadar) studies, one of the most popular procedures for determining electromagnetic waves propagation velocity in a rock mass is the selection of theoretical hyperbolic time-distance curves and subsequent comparison with the time-distance curve obtained from a GPR measurement. This procedure is based on the model of homogeneous medium, but nowadays the subject of GPR study is often inhomogeneous media, such as horizontally layered media characteristic of loose permafrost zone sediments. The paper presents the findings of studying the formation of hyperbolic time-distance curves of georadar impulses in a horizontally layered medium without taking into account the dispersion and absorption of electromagnetic waves. On the basis of geometrical optics laws, formulas were derived to calculate the shape of the hyperbolic lineup of georadar impulses reflected from a local feature in a multilayer frozen rock mass. On the example of a permafrost zone rock mass containing a layer of unfrozen rocks, the effect of the thicknesses of rock layers and their relative dielectric permittivity on the apparent dielectric permittivity resulting from the calculation of the theoretical hyperbolic time-distance curve was shown. The conditions under which it is impossible to determine the presence of a layer of unfrozen rocks from a hyperbolic time-distance curve are also presented. The established regularities were tested on synthetic georadar radargrams calculated in the gprMax software program. The findings of the theoretical studies were confirmed by the comparison with the results of the analysis of the georadar measurements computer simulation data in the gprMax system (the relative error was less than 0.5%).

SiO2-capped ZnO quantum dot based highly sensitive optical fiber humidity sensor with potential applications in human breath monitoring and voice print recognition

This article describes the development and characterization of an optical fiber humidity sensor employing intensity modulation via the evanescent wave (EW) absorption technique. For the development of the sensor, SiO2-capped ZnO quantum dot (QDs) thin film is synthesized over the decladded portion of plastic cladding silica (PCS) fiber via the sol-gel method. A thorough experimental investigation was conducted by varying the thickness of the sensing film to optimize the sensor’s response. The sensing probe with optimized film thickness of 891 nm demonstrates a linear response over 30.5%–92.5%RH with an enhanced sensitivity of 46.2 mV/%RH (0.0138RH−1). Very fast response and recovery times of 2 s and 2.5 s are observed during humidification and dehumidification for the optimized sensing probe. The maximum resolution recorded during the short stability test is ±0.12%RH. Additionally, the proposed sensor demonstrates a very high degree of repeatability, reversibility, and stability. The proposed sensor has also been tested for human breath monitoring and voice print recognition. The result shows the sensor is able to detect minute humidity fluctuations in exhaled air during breathing and speaking.

Hollow core-shell structured Fe3O4@Polypyrrole composites for enhanced electromagnetic wave absorption

Due to the rapid development of electronic devices, the electromagnetic pollution has become increasingly serious. Developing electromagnetic wave absorption (EWA) materials with lightweight, strong absorption capacity and wide effective absorption bandwidth (EAB) becomes a research hotspot. In this work, the hollow-Fe3O4@polypyrrole (HFO@PPy) composites with core-shell structure were successfully synthesized by in situ polymerization method. The electromagnetic parameters could be adjusted by controlling the content of HFO in HFO@PPy. In addition, HFO@PPy composites show both dielectric and magnetic losses. The synergistic effect of both two losses contributes to an enhanced electromagnetic attenuation. The enhanced impedance matching is achieved by the composition (HFO and PPy) and designed unique structure (core-shell and hollow structure). The maximum reflection loss (RL) and EAB are −52.01 dB and 2.72 GHz at 3.1 mm for 60.0 wt% HFO@PPy composites. Therefore, by reasonably regulating the component content and optimizing the structural design, the EWA performance of HFO@PPy composites could be effectively improved, providing a significant inspiration for fabrication of microwave absorbers.

Ultrasound-assisted freeze-drying graphitization process for the fabrication of two-dimensional carbon/Fe3O4 composite aerogels for microwave absorption

Magnetic Fe3O4 materials have received attention from researchers due to their significant wave absorption potential, but there are limitations to their efficient electromagnetic wave absorption and lightweight applications. Combining materials with dielectric properties to optimize the performance of Fe3O4 has become one of the research directions. In particular, carbon nanomaterials, such as graphene, show great application prospects in the field of microwave absorption due to their physical properties. To improve the impedance mismatch issue of graphene, researchers consider combining it with magnetic nanoparticles. Commercial applications require materials that are cost-effective, easy to produce, and environmentally sustainable, driving research on novel 2D carbon materials. In this study, 2D carbon materials were prepared by ultrasound-assisted freeze-drying/graphitization process using polymers as precursors, which simplifies the preparation process and avoids the use of expensive sacrificial templates and catalysts. The 2D carbon materials prepared by this method were used as the dielectric component in the wave-absorbing composites, and the nano effect was utilized to significantly improve the microwave absorption properties of the materials. The maximum reflection loss of the prepared graphite nano-aerogel reaches −84.16 dB and the EAB reaches 3.74 GHz. In addition, by adding Fe3O4 nanoparticles and applying an ultrasonic field for dispersion in the freeze-drying process, the nanoparticle agglomeration is effectively prevented, which provides a simple and efficient pathway for the preparation of nanocomposites.

Absorption of electromagnetic waves by cylindrical surface plasmon resonance

Abstract The absorption characteristics of cylindrical surface plasmon resonance (CSPR) have been studied. We demonstrated that a single plasma column with CSPRs can achieve high absorptivity at the plasmon frequency. We also studied the effects of plasma density and collision frequency on the absorptivity. As both of them increase, the corresponding absorptivity tends to increase first and then decrease, but with different reasons. Such manifestation is explained by analyzing transmission and reflection spectra in both cases, as well as magnetic field distribution patterns at the frequency of plasmon. On the one hand, the increase in plasma density leads to the enhancement of plasmons, improving transmittance; On the other hand, the increase in collision frequency leads to a weakening of plasmons and an increase in reflectivity. Finally, we investigated the absorption characteristics of plasmons in the plasma photonic crystals (PPCs) structure and overcame the absorption attenuation caused by the increase in plasma density by increasing the number of plasma columns. Meanwhile, the absorption generated by surface plasmon resonance is not affected by the lattice constant of PPCs. The research has shown that efficient absorption can be achieved using CSPR, resulting in extremely high absorptivity when using fewer plasma columns. Finally, we verified the absorption ability of CSPRs through experiments.

Interface-driven microwave absorption enhancement in Mn-optimized Co2FeAl1-xMnx Heusler alloys

To address the urgent need for efficient and stable electromagnetic wave absorbing materials for electromagnetic interference (EMI) protection, we synthesized Co2FeAl1−xMnx Heusler soft magnetic alloys using a high-energy planetary ball milling method. We comprehensively analyzed their structural characteristics, surface morphology, magnetic properties, and electromagnetic parameters to explore their potential in electromagnetic wave absorption. The results show that incorporating manganese (Mn) significantly changes the alloys' crystal structure, surface morphology, and magnetic properties, greatly enhancing their wave absorption performance. The Mn doping specifically alters the surface morphology, which plays a crucial role in influencing the wave absorption characteristics of the Heusler alloys. When the Mn content increased to 25 %, the sample exhibits superior wave absorption, achieving the maximum reflection loss of −44.83 dB at 13.68 GHz with a thickness of 1.5 mm and an effective absorption bandwidth of 5.52 GHz. With a significant increase in the aspect ratio and noticeable changes in surface morphology, the sample with 75 % Mn content shows exceptional performance with an effective absorption bandwidth of 5.68 GHz, representing the highest effective absorption bandwidth in single-phase Heusler alloys. The Mn doping strategy effectively improves the material's impedance matching by adjusting its permittivity and permeability, facilitating multiple polarization relaxation mechanisms and significantly enhancing the alloys' electromagnetic wave absorption efficiency. Our study provides detailed experimental data for optimizing the electromagnetic wave absorption characteristics of Heusler alloys, verifies their practical application potential, and paves the way for developing new high-performance electromagnetic wave absorbing materials.

Construction of a 3D spider web structure with spherical Ho2O3 wrapped by carbon nanofibers for high-efficiency microwave absorption and corrosion protection

Reasonable composition control and microstructure design are the effective ways to realize multi-functional high-performance absorbing materials. In this work, a three-dimensional (3D) spider web structure was designed by the electrospinning and high temperature carbonization technology, where Ho2O3 spheres were wrapped by carbon nanofibers. Herein, the spherical Ho2O3 were surrounded by layers of carbon nanofibers (spider silk), which were like the preys inside the spider's web. This unique bionic structure working in conjunction with the tuned components enables the as-prepared composites with improved impedance matching and enhanced loss capacity. The superior electromagnetic wave absorption performance was obtained as the minimum reflection loss of −61.37 dB at 2.90 mm and the maximum effective absorption bandwidth of 6.88 GHz (11.12–18 GHz) at 2.64 mm. At a thickness of 3.44 mm, the effective absorption bandwidth is 4.80 GHz (8–12.80 GHz), covering the entire X-band. At the same time, the composite soaked in the corrosive medium for 7 days owns a low corrosion current density (10−4 ∼10−6 A cm−2) and a high polarization resistance (105∼107 Ω), which exhibits the obvious anticorrosion ability. This work designs a specific spider web structure with high-performance microwave absorption and corrosion protection.

Mesoporous carbon spheres modified with atomically dispersed iron sites for efficient electromagnetic wave absorption

Carbon materials have obtained some achievements in electromagnetic wave (EMW) absorption owing to their excellent electrical conductivity and low density. However, poor impedance matching and high electrical conductivity limit their EMW absorption properties. Metal single atoms absorbers have garnered considerable attention in EMW absorption, largely due to the high metal availability and special coordination structure, but the modulation of the EMW absorption properties still needs to be improved. Herein, atomically dispersed Fe sites embedded into the N-doped mesoporous carbon spheres (Fe–SAs/NC) were synthesized through a facile coordination-assisted polymerization assembly strategy without acid leaching treatment. Benefitting from abundant mesoporous structure, the Fe–SAs/NC displays large specific surface area (339 m2 g−1) and optimized impedance matching, which results in an effective reduction of the absorber density. The homogeneously dispersed Fe single atoms (Fe–SAs) on the carbon skeleton lead to the improvement in conduction and dipole polarization losses of Fe–SAs/NC, which endows Fe–SAs/NC with exceptional EMW absorption properties. Experimental results indicate that Fe–SAs/NC displays desirable EMW absorption properties with the minimal reflection loss of −52.5 dB at 2.8 mm and the effective absorption bandwidth of 4.8 GHz. The study provides valuable insights for the development of carbon materials modified with atomically dispersed metal sites to achieve high-efficient EMW absorbers.

A pattern design strategy for microwave-absorbing coding metamaterials with tortuosity and connectivity

Microwave absorption presents a challenge for the design of metamaterials, which is critical for the stealth and electromagnetic compatibility. To address this, a novel design strategy for patterns is proposed to enhance the wave absorption, which is tortuosity and connectivity. Utilizing the carbon ink composite and genetic algorithm, multi-layer coding metamaterials (MCMs) are designed to satisfy diverse engineering specifications, with reflectivity tests confirming their efficacy. Temperature alternation experiments simulate frequent environmental changes, and the absorptivity of MCMs is compared to evaluate their resilience. This approach ensures the designed MCMs maintain performance and stability under variable thermal conditions, offering a robust solution for advanced applications.

Improved Interfacial Interactions by Core-Shell CoFe2O4@SiO2 Composites to Enhance the Ability of Corrosion Resistance and Electromagnetic Wave Absorption.

With the rapid development of science and technology, stealth and anti-corrosion activities in oceans have attracted widespread attention. This study successfully prepares CoFe2O4@SiO2 with a core-shell structure. This core-shell structure endows the CoFe2O4@SiO2 with good impedance matching and interfacial polarization. Thus, the CoFe2O4@SiO2 exhibits an excellent electromagnetic wave absorption performance with a minimum reflection loss of -45.16dB. Moreover, the CoFe2O4@SiO2 exhibits an excellent dispersion ability in epoxy. The corrosion resistance of the CoFe2O4@SiO2/epoxy is enhanced. After 60 days of immersion, the low-frequency impedance modulus of the CoFe2O4@SiO2/epoxy is still >109Ωcm2. The CoFe2O4@SiO2 realize the dual functions of stealth and anti-corrosion, which provide ideas for developing marine stealth applications.

Effect of SiC doping on microwave absorbing properties of ball-milled carbonyl iron/MoS2 composites

Using MoS2 to prepare novel composite absorbing coatings is an effective strategy to enhance electromagnetic wave absorption. In order to explore the preparation process of large-scale preparation of MoS2 composite absorbing materials, a Fe/MoS2/SiC laminated composite absorbing material was prepared by high-energy ball milling method to realize the absorption of electromagnetic waves. By adjusting the proportion of SiC, SiC, MoS2 and Fe were ball-milled at room temperature for 20 h, and the dielectric properties were improved to achieve good absorbing effect. The microstructure and properties of the materials were measured by XRD, SEM, Raman, XPS, HRTEM, VSM and VNA. The results show that the doping of appropriate amount of SiC reduces the interplanar spacing of MoS2 and increases the edge points, which increases the conductivity of MoS2. MoS2 reduces the number of layers and increases its size and area, which improves the dielectric properties of Fe/MoS2 and optimizes the electromagnetic parameters of the composites. When the ratio (mole) of SiC, Fe and MoS2 is 3:6:2, the best electromagnetic wave absorption effect is obtained, the lowest electromagnetic wave reflection loss is −72.98 dB, and the best bandwidth is 3.04 GHz when the matching thickness is 6.53 mm.

Genome engineering of materials based on Ce doping, high-performance electromagnetic wave absorber for marine environment

Traditional microwave absorbing materials (MAM) are difficult to meet the current increasingly complex electromagnetic environment, MAM began to functionally integrated development to meet the needs of diversified applications. For the high humidity and high salt spray environment of the ocean, the development of electromagnetic absorber integrating microwave absorption (MA) and corrosion protection functions is imminent. In this work, high-quality genes were screened through materials genome engineering, and in-situ doping strategies of Ce gene were designed to synergistically enhance MA properties using composition modulation and structure modulation, the effective absorption bandwidth (EAB) of composite material WC@FCC1 can reach 5.62 GHz at an ultra-thin thickness of 1.66 mm. Thanks to the unique 4f orbital mechanism of Ce element, CeO2 is endowed with excellent redox property, forming an oxide protective film on the surface, which prevents the entry of external corrosive media. The excellent corrosion protection performance of the composite material has been verified through electrochemical testing and molecular dynamics simulation. This work provides new design ideas for high-performance MAM, as well as new strategies and insights for functionally integrated electromagnetic absorber.

LaFe-MOFs derivatives with different compositions for boosting low-frequency and broadband electromagnetic wave absorption

To achieve low-frequency and broadband electromagnetic wave absorption (EMWA), building excellent metal-organic frameworks (MOFs)-derived EMWA materials is critical but remains challenging. In this research, La2O3/La2O2CN2/Fe/N-doped carbon (LFC) composites with different compositions were synthesized by adjusting the La3+ content to tune the electromagnetic parameters. As the La3+ content increased, the EMWA performance showed a trend of first increasing and then decreasing. As a result, LFC-2 achieved a minimum reflection loss (RLmin) value of −60.82 dB at a thickness of 2.60 mm when the molar ratio of La3+ to Fe3+ was 1: 1, along with an effective absorption bandwidth value of 5.76 GHz (9.84–15.60 GHz) at 2.29 mm. Moreover, the EMWA performance of LFC-3 at low-frequency (4.08 GHz) was enhanced when the La³⁺ to Fe³⁺ molar ratio was 2: 1, with an RLmin value of −47.47 dB. Comprehensive characterizations suggested that the formation of the La2O2CN2 phase played an indispensable role in optimizing impedance matching and enhancing magnetic loss and dielectric loss. In addition, La3+ had a high coordination number, which effectively regulated the electromagnetic parameters. Concurrently, radar cross-section simulation results confirmed the outstanding EMWA capability of the LFC coating. This work proposed a strategy for LaFe-MOFs derivatives, shedding light on the foundation for designing more efficient low-frequency and broadband absorbent materials.

3D printed PEEK/CF nanocomposites metamaterial for enhanced resonances toward microwave absorption and compatible camouflage

The stealth materials for future weapons and equipment need to operate within the radar working band, be lightweight, easy to process, and compatible with infrared stealth. Integrating all these characteristics poses a significant challenge. This work utilizes poly (ether-ether-ketone)/carbon fibers (PEEK/CF) composite materials and employed reverse-guided manufacturing through simulation design. Incorporating a grid structure within the pyramid metamaterial enables electromagnetic wave reflecting multiple times in various directions. By optimizing the important interaction between dielectric properties of the materials structures，the Pyramid Grid Filled Metamaterial enables broadband electromagnetic wave absorption (<-10 dB, 8–18 GHz), weak angular dependence (5- 45o incidence), polarization insensitivity, radar cross section (RCS) reduction (reduction over 10 dB between θ = −60° and 60°), and infrared camouflage performance. The PGF metamaterial of 180◊180 mm2, weighs only 103.1 g at a thickness of 9 mm. This work paves a way for the design the radar infrared compatible composite metamaterials.

Multispectral compatible anti-reconnaissance strategy: Implementing a modulation system integrating visible light-hyperspectral-radar wave

To tackle the challenges of multi-spectral reconnaissance technology, a pioneering anti-reconnaissance device that integrates visible-light, hyperspectral, and microwave radar functionalities has been developed for the first time. By oxidative polymerization method to create a core–shell Fe3O4@polyaniline composite material for the counter electrode. This design optimized impedance matching, achieving wideband radar wave absorption up to 10.5 GHz (reflection loss < -10 dB). The core–shell structure enhanced specific surface area, improving charge exchange and electrochemical performance to meet stringent counter electrode requirements. And, constructed a frequency-selective metal electrode based on metamaterial principles, complementing the radar wave absorption capabilities of the counter electrode material. Additionally, synthesized an asymmetric viologen molecule as the working electrode, mimicking vegetation color transitions from green to yellow while preserving hyperspectral characteristics and radar wave absorption properties. To enhance hyperspectral compatibility without compromising radar wave absorption or color dynamics, we developed a cross-linked polyvinyl alcohol/hydroxyethyl cellulose film based on biomimetic principles. The device can switch between yellow and green under voltages of 0 or −1.2 V, with both states exhibiting a spectral similarity to foliage exceeding 0.95 and an effective bandwidth reaching 13.44 GHz. The integration of these three functionalities allows the device to operate independently without interference.

Excellent C-band microwave absorption properties of Ni@nitrogen-doped porous carbon nanocomposite via polymer bubbling technique

Nitrogen-doped porous carbon nanocomposites are highly sought-after materials for electromagnetic wave absorption due to their unique combination of electrical and magnetic properties. However, achieving optimal absorption performance within the critical C-band (4–8 GHz) frequency range remains a significant challenge. Ni@NPC nanocomposites, synthesized through the polymer bubbling technique, demonstrated exceptional microwave absorption (MWA) performance in the C-band. These materials exhibited a reflection loss (RL) of −65.20 dB at a thickness of 4.8 mm. When carbonized at 600 °C, a thickness of 2.0 mm achieved an effective absorption bandwidth (EAB) of 5.74 GHz. The remarkable absorption performance is ascribed to the combined effect of their porous composition and the addition of nitrogen dopants, which efficiently foster various microwave attenuation processes. Furthermore, the material’s effectiveness in real-world applications was evaluated using computer simulation technology (CST). This work highlights the potential of the one-pot fabrication method for developing high-performance MWA materials with practical applications.

Dual-channel asymmetric absorption-transmission properties based on plasma metastructures-photonic crystals

In this paper, a kind of plasma metastructures-photonic crystals (PMPC) structure is proposed to investigate the absorption and transmission properties of electromagnetic waves (EWs) incident from opposite directions. The results show that the PMPC can achieve a dual-channel asymmetric absorption-transmission (AAT) phenomenon. At an operating bandwidth (OB) of 2.15∼2.85 GHz, EWs are absorbed in the forward incidence and transmitted in the backward case, and a relative bandwidth (RB) with forward absorption above 0.9 is 28.0%. On the contrary, at an OB of 7.07∼7.67 GHz, EWs can be transmitted in the forward propagation and absorbed in the backward case with a RB of 8.1%. Moreover, the effects of parameters such as applied magnetic field, incident angle, and tilt angle on AAT performance are investigated separately. The proposed dual-channel tunable AAT will further extend the application of asymmetric devices in the fields of optical communication and optical transmission.