Wave Attenuation Properties Research Articles

Interfacical polarization dominant rGO aerogel decorated with molybdenum sulfide towards lightweight and high-performance electromagnetic wave absorber

Lightweight reduced graphene oxide aerogel (rGO) has obtained enormous attention as microwave absorber due to anisotropic characteristics in their structure and electromagnetic parameters. However, the controllable preparation of reduced graphene oxide (rGO) aerogels with tailored multidimensional structure with broadened effective absorption bandwidth is a thorny difficulty. In this paper, rGO aerogel decorated with molybdenum sulfide (rGO/MoS2) with three-dimensional (3D) layered porous structure were synthesized by a two-step hydrothermal method. The unique three-dimensional layered porous structure of graphene aerogel not only effectively avoids the stacking of graphene flake layers, but also provides space for the loading of MoS2 nanosheets. The introduction of MoS2 nanosheets compensates for the imbalance of impedance matching caused by graphene due to the excessive conductivity, and the folded MoS2 nanosheets are uniformly loaded on the graphene lamellae, which is conducive to generate multiple reflections and scattering of electromagnetic waves. Besides, the construction of heterogeneous interfaces strengthens the interfacial polarizability of the composites. As a result, excellent electromagnetic wave attenuation properties were obtained for rGO/MoS2, and the effective absorption bandwidth (EAB) reached 6.56 GHz at 2.1 mm. In addition, the radar cross section (RCS) simulation results further demonstrate the dissipation capability of the composite in practical application scenarios. This paper provides a new idea for the design of lightweight EM wave absorbing materials with broad absorption bandwidth.

Investigating Static and Dynamic Behaviors in 3D Chiral Mechanical Metamaterials by Disentangled Generative Models

AbstractChiral mechanical metamaterials with engineered asymmetric structures have garnered significant interest owing to their potential for manipulating mechanical waves and unconventional mechanical properties. Although several design methodologies have made significant strides in the design and discovery of chiral mechanical metamaterials, 3D designs that incorporate multiple mechanical characteristics remain largely unexplored and the static and dynamic properties of these structures have not received sufficient attention. Here, an innovative approach is introduced for the inverse design of 3D chiral mechanical metamaterials with desired static and dynamic properties, leveraging streamlined shapes to enable a versatile design. By employing conditional generative adversarial networks (c‐GANs), the desired mechanical properties are targeted by focusing on both wave attenuation and stress distribution under compression and shear loading. 3D chiral mechanical metamaterials with additive manufacturing are fabricated to demonstrate the performance of the proposed c‐GAN. Experimental investigations show that the generated structures exhibited a wide range of wave attenuation properties, low stress concentrations, and a variety of stress‐strain curve profiles including nonlinear stiffness, demonstrating their effectiveness in achieving the desired mechanical characteristics. This research offers significant advancements in the on‐demand design capabilities of metamaterials and their applications.

Progressive hollow engineering induced raspberry-like magnetoelectric microspheres via synergistic etching-assembly strategy toward boosted microwave attenuation

Optimizing the electromagnetic (EM) properties of composites through elaborate tailoring of their microstructures has become an attractive research branch, but determining the correlations between morphology, composition, and performance remains challenging. Herein, a novel progressive hollow engineering strategy is proposed for the construction of hollow CuFe Prussian blue analog (CuFePBA, CF) precursors with asymptotic variations of cavities and PBA units based on a synergistic etching-assembly approach, subsequently combined with a polydopamine (PDA) coating and carbothermal process to acquire raspberry-like hollow Cu/Fe/Fe3C@NC (CFC) composites. The proposed approach addresses the drawbacks caused by organic ligand depletion or corrosive agent usage. We then present a systematic investigation of the mechanism by which the progressive hollow engineering-induced concurrent evolution of hollow cavities, phases, defects, and inhomogeneous interfaces contributes to the improvement of the dielectric properties of the CFC samples. An optimal reflection loss (RLmin) of − 65.17 dB at 3.29 mm was realized for the CFC-2 sample and the CFC-3 sample achieved an effective absorption bandwidth (EAB) of 4.4 GHz at an ultra-thin thickness of 1.29 mm. This work reveals the synergistic effects of compositional, interfacial, and defect variations on the EM wave attenuation properties of the composites, and will provide new design inspiration for novel absorbers with modulatable hollow architectures.

Multi-heterogeneous interfaces boost dielectric polarization in PBA-derived Co/MnO@NC ternary composites for electromagnetic wave absorption

The elaborate construction of multi-component composites has been deemed as a promising strategy to enhance dielectric polarization response capability in the preparation of highly efficient microwave absorbers. However, the rational design and integration of homogeneous composites with diverse components continues to pose a great challenge. Herein, we propose a straightforward self-assembly-carbonization strategy for fabricating Co/MnO@NC ternary composites derived from CoMn-Prussian Blue Analogous precursors, featuring enriched heterogeneous interfaces and balanced magneto-electric coupling synergy. The ternary composites effectively introduce diverse dissipation mechanisms, including interfacial polarization behavior originated from the constructed heterogeneous interfaces, dipole polarization relaxation triggered by atomic defects, and optimized magnetic loss ability from well-dispersed metallic Co species. Benefiting from these advantages, the Co/MnO@NC composites demonstrate superior electromagnetic wave absorption performances, with a minimum reflection loss value of −61.37 dB at the thickness of 3.5 mm and effective frequency absorption bandwidth of 6.32 GHz, covering the full Ku-band. Furthermore, power loss density and radar cross-section simulations validate that the Co/MnO@NC ternary composites possess exceptional microwave signal attenuation abilities, with a maximum radar cross-section reduction value of up to 27.98 dBm2 at 0°. Such outstanding absorption properties exceed those of most currently reported ternary composites and exhibit significant potential to replace conventional ferromagnetic-based absorbers. This work offers a straightforward strategy to fabricate ternary composites with excellent electromagnetic wave attenuation properties and sheds novel insights into the dissipation mechanisms.

All-Around Electromagnetic Wave Absorber Based on Ni-Zn Ferrite.

Exploring a convenient, scalable, yet effective broadband electromagnetic wave absorber (EMA) in the gigahertz (GHz) region is of high interest today to quench its expanding demand. Ni-Zn ferrite is considered as a potential EMA; however, their performance study as a scalable effective millimeter-length absorber is still limited. Herein, we investigated EM wave attenuation properties of Ni0.5Zn0.5Fe2O4 (NZF) samples substituting Mn ion in place of Fe3+ as well as Zn2+ within a widely used frequency range of 0.1-9 GHz. Through composition optimization, Ni0.5Zn0.4Mn0.1Fe2O4 (NZM0.1F) EMA demonstrates excellent microwave absorption performance accompanied by simultaneous maximum reflection loss (RL) of -50.2 dB and wide BW of 6.8 GHz (with RL < -10 dB, i.e., attenuation >90%) at an optimum thickness of 6 mm. Moreover, the attenuation constant significantly increases from ∼217 to 301 Np/m with Mn doping. The key contribution arises from magnetic-dielectric properties synergy along with enhanced dielectric and magnetic losses owing to cation chemistry and site occupation in spinel NZF. In addition, porosity is induced in the system by a controlled two-step heat treatment process that promotes total loss with multiple internal reflections of the EM wave. Furthermore, RL is simulated by varying incident EM wave angles for the NZM0.1F sample displaying its angle insensitivity up to 50°. Our results reveal NZM0.1F as a futuristic environment-friendly microwave absorber material that is suitable for practical high-frequency applications.

Elastic Wave Propagation Control in Porous and Finitely Deformed Locally Resonant Nacre-like Metamaterials.

Recent studies have shown that the mechanical properties of bioinspired periodic composite materials can be strongly influenced by finite deformation effects, leading to highly nonlinear static and dynamic behaviors at multiple length scales. For instance, in porous periodic nacre-like microstructures, microscopic and macroscopic instabilities may occur for a given uniaxial loading process and, as a consequence, wave attenuation properties may evolve as a function of the microstructural evolution, designating it as metamaterials. The numerical outcomes provide new opportunities to design bioinspired, soft composite metamaterials characterized by high deformability and enhanced elastic wave attenuation capabilities given by the insertion of voids and lead cores.

Analysis and Design of Microwave Absorbers Combining Surface Wave Attenuation and Reflection Bandwidth Properties

Analysis and Design of Microwave Absorbers Combining Surface Wave Attenuation and Reflection Bandwidth Properties

On the wave attenuation properties of seagrass meadows

The wave attenuation properties of seagrass meadows were investigated in a flume facility using dynamically-scaled models of seagrass exposed to regular long crested waves. Experiments were conducted for 66 wave conditions and with four plant densities; waves were measured with eight resistance wave gauges. The data collected represent the most-comprehensive dataset of its kind. They reveal that the wave attenuation coefficient KD of a seagrass meadow reaches a uniform value after a distance of approximately 1.5–3 times the water depth from the meadow start and that both KD and the drag coefficient Cd depend significantly on the plant density. An improved model of KD based on the work of Lei and Nepf (2019) is proposed that takes into account the effects of the solid volume fraction of the plant model through a correction on Cd and that of plant density via an effective vegetation frontal area av−e. The effective vegetation frontal area is described as a power law of the roughness density λf. The model, which was validated with the data of KD obtained from the laboratory experiments described herein, displays an excellent agreement with data from the literature. It can predict KD accurately also for cases whereby the maximum wave orbital excursion is comparable with the blade length, despite this condition violates the model’s assumptions. This work provides a comprehensive dataset and a new model that can be used to improve the prediction of wave attenuation of seagrass meadows.

Organosilane waste-derived SiCnws/SiOC composites with enhanced electromagnetic wave absorption performance

SiCnws/SiOC nanowires composites with a 3D network structure, exhibiting enhanced electromagnetic microwave absorption properties, were synthesized using carbothermal reduction. The solid precursor, organosilane waste, was employed, enabling cost-effective and environmentally friendly production. The structure and morphology of SiCnws/SiOC nanowires composites were extensively investigated by XRD, SEM, TEM, XPS spectra, and Raman spectra. Moreover, the composite demonstrated superior electromagnetic wave absorbing properties, including wide effective absorption bandwidth (EAB) of 2.73 GHz, strong minimum reflection loss (RLmin) of −52.66 dB, and thin thickness of 2.40 mm. These excellent electromagnetic wave attenuation properties stem from the synergistic strategy of dielectric and conductive losses, resulting from the unique 3D network heterostructural architecture. This work not only offers improved EMW absorption solutions but also contributes to waste recycling and resource recovery.

Enhanced electromagnetic wave attenuation performance of hierarchical Fe3O4/N-doped carbon nanosheets by heterointerface engineering

The dielectric-magnetic composites with a unique structure are regarded as promising materials for addressing the issue of electromagnetic wave pollution. Herein, a series of hierarchical Fe3O4/N-doped carbon nanosheets (Fe3O4/HNCS) composites with adjustable electromagnetic wave attenuation (EMWA) properties were successfully fabricated by adjusting the proportion of iron source and carbon using a simple combination of molten salt and solvothermal methods. Among all the composites, the Fe3O4/HNCS-0.25 exhibits the strongest reflection loss (RL) value of − 52.08 dB with an ultra-thin thickness of 1.4 mm, corresponding to an effective absorption bandwidth (EAB) of 4.16 GHz. Furthermore, the Fe3O4/HNCS-0.20 achieves a maximum EAB value of 4.4 GHz, obtained at a thickness of 1.4 mm. The superior EMWA performances originate from excellent impedance matching, synergy between dielectric and magnetic loss, and unique hierarchical structure. This study presents a straightforward and environmentally friendly method for fabricating high-performance dielectric-magnetic EMWA materials with an ultra-thin matching thickness.

Electromagnetic wave absorption properties of porous carbon nanocomposite prepared by explosion method derived from energetic CuFe-MOF

An energetic heteronuclear metal–organic framework (MOF), denoted as {[CuIIFeIII3O(tza)6(H2O)3]·Cl·(NO3)2·4H2O}n (CuFe-MOF), was successfully synthesized and characterized using various techniques, including single-crystal X-ray diffractometry (XRD), powder X-ray diffractometry (PXRD), and scanning/transmission electron microscopy (SEM/TEM). The compound crystallized in the P63m space group, forming an infinite 3D cationic network composed of [Fe3O(tza)6]+ clusters and Cu2+ ions. Subsequently, we transformed CuFe-MOF into porous carbon nanocomposites, C/Cu/Fe3N/Fe4N/Fe3O4/CuFe2O4, using an explosion method. We then investigated the electromagnetic wave (EMW) attenuation properties and mechanisms of the carbon nanocomposite. Notably, the synthesized C/Cu/Fe3N/Fe4N/Fe3O4/CuFe2O4 composite material demonstrated exceptional EMW absorption. At a low frequency of 4.1 GHz with a thickness of 5.0 mm, it achieved a minimum reflection loss (RL) of −47.7 dB. Even at a high frequency of 17.8 GHz and a thickness of 1.5 mm, the minimum RL reached −41.8 dB. Moreover, this material exhibited a wide effective absorption bandwidth (EAB; RL ≤ −10 dB) spanning 14.9 GHz (3.1–18 GHz) for thicknesses between 1.0 and 5.5 mm. These attributes position the carbon composite as a strong candidate for absorption applications within the Ku, X, and C bands, making it suitable for both military and civilian usage. Our mechanistic analysis suggests that the excellent absorption performance of C/Cu/Fe3N/Fe4N/Fe3O4/CuFe2O4 results from a combination of mechanisms, including electrical and magnetic loss. This research introduces an innovative approach for the fabrication of high-performance carbon composite materials via the explosive method, utilizing multinuclear energetic materials.

The In Situ Preparation of Ni-Zn Ferrite Intercalated Expanded Graphite via Thermal Treatment for Improved Radar Attenuation Property.

The composites of expanded graphite (EG) and magnetic particles have good electromagnetic wave attenuation properties in the centimeter band, which is valuable in the field of radar wave interference. In this paper, a novel preparation method of Ni-Zn ferrite intercalated EG (NZF/EG) is provided in order to promote the insertion of Ni-Zn ferrite particles (NZF) into the interlayers of EG. The NZF/EG composite is in situ prepared via thermal treatment of Ni-Zn ferrite precursor intercalated graphite (NZFP/GICs) at 900 °C, where NZFP/GICs is obtained through chemical coprecipitation. The morphology and phase characterization demonstrate the successful cation intercalation and NZF generation in the interlayers of EG. Furthermore, the molecular dynamics simulation shows that the magnetic particles in the EG layers tend to disperse on the EG layers rather than aggregate into larger clusters under the synergy of van der Waals forces, repulsive force, and dragging force. The radar wave attenuation mechanism and performance of NZF/EG with different NZF ratios are analyzed and discussed in the range of 2-18 GHz. The NZF/EG with the NZF ratio at 0.5 shows the best radar wave attenuation ability due to the fact that the dielectric property of the graphite layers is well retained while the area of the heterogeneous interface is increased. Therefore, the as-prepared NZF/EG composites have potential application value in attenuating radar centimeter waves.

Elastic wave dispersion in layered media with suture joints: influence of structural hierarchy and viscoelasticity

Suture joints contribute to the exceptional combination of stiffness, strength, toughness and efficient load bearing and transmission of many biological structures like the cranium or ammonite fossil shells. However, their role in the attenuation of vibrations and effect on dynamic loads is less clear. Moreover, the self-similar hierarchical geometry often associated with suture joints renders its treatment with standard numerical approaches computationally prohibitive. To address this problem, this paper investigates the dynamic response of periodic layered media with suture joints using an analytical approach based on material homogenization. A general trapezoidal suture geometry is considered together with the fundamental ingredients of hierarchy and viscoelasticity. The Spectral Element Method and Bloch theorem are used to derive the dispersion relation and band diagram of the system, including propagating and evanescent dispersion modes. A strong influence of the suture morphology and material properties emerges, and the analysis reveals an important advantage of adding hierarchy, i.e. the possibility of simultaneously obtaining wider bandgaps and their shift to higher frequencies. A synergy between hierarchy and structure is also observed, providing superior levels of wave attenuation. These findings suggest a possible design concept for bioinspired devices with efficient and tailorable wave attenuation properties.

Shape and non-shape unified isogeometric optimal design for extremal band gaps

A unified shape and non-shape design optimization for lattice structures is performed to obtain extremal band gaps in an isogeometric computational framework, which uses the same NURBS basis functions as used in CAD description. Using a precise numerical model in both response and shape sensitivity analyses, enhanced response and sensitivity can be obtained, which leads to a precise optimal design. A plane wave propagation in infinite periodic lattice is analyzed within a representative unit cell using the Bloch theory with periodic boundary conditions. The ligaments of lattice structures are modeled using geometrically exact beams whose cross-sectional area and configuration are regarded as design variables, which are parameterized by the NURBS basis functions. The design variables are controlled by a mathematical programming algorithm with efficient adjoint design sensitivity. The obtained optimal lattice structures of triangular, squared, hexagonal, and Kagomé structures are fabricated using a 3D printing machine to be validated by physical experiments. Through harmonic response analysis and physical experiment for the optimal and the original designs, the wave attenuation properties are compared to demonstrate the validity of the obtained optimal design.

Temperature effects on wave attenuation properties of metamaterials: Bandgap drift

The bandgap properties of phononic crystals and acoustic metamaterials have been investigated far and wide due to their potential application in vibration and noise reduction devices. The factors affecting the bandgaps including the material parameters and structural parameters were widely discussed, while there are few papers about the effect of temperature on the bandgap properties. In this paper, the influence of temperature on bandgap characteristics of metamaterial devices is studied theoretically and numerically. Since the elastic constants of some materials are affected by temperature, the bandgap drift phenomenon caused by temperature is displayed visually in the one-dimensional spring-mass system. Based on one-dimensional spring-mass metamaterials, the temperature-dependent theoretical formulations for calculating the dispersion relationships are derived and the effective mass equations related to temperature are also deduced to illustrate the negative effective mass density properties. Finally, the vibration attenuation properties and the directional transmission characteristics of two metastructures at different temperatures are performed to manipulate elastic wave field by temperature. This study could provide some insight into the use of acoustic metamaterials in extreme environments and provides a new approach for elastic wave field manipulation.

Construct of CoZnO/CSP biomass-derived carbon composites with broad effective absorption bandwidth of 7.2 GHz and excellent microwave absorption performance

Biomass-carbon materials have excellent electromagnetic wave attenuation properties, which is one of the essential factors for developing ultra-thin matched-thickness, and high-performance microwave absorption materials. This study reports a two-step procedure consisting of carbonization and subsequent in-situ growth for preparing a wrinkle-like multilayer biomass-derived composites with magnetic Co particles and ZnO particles (CoZnO/C-X). The synergistic effect of a wrinkle-like multilayer structure and Co and ZnO particles, as well as the existence of many heterogeneous interfaces in the composites structure, and efficiently creates multiple scattering and reflections, which gives the composites the strong microwave absorption properties. The minimum reflection loss value (RLmin) of CoZnO/C-X reaches − 54.90 dB with a thickness of 1.8 mm, and the effective absorption bandwidth (lower than − 10 dB) is 7.2 GHz covering from 10.8 GHz to18.0 GHz with matching thickness of 2.0 mm. Furthermore, the reasonable dielectric/magnetic losses, optimized impedance matching and enhanced polarization loss play an indispensable role among improving microwave absorption performance. Thus, this result provides a good potential method for preparation of magnetic particle/metal oxide/biomass-derived carbon microwave absorbing structural materials.

Thermodinamically-consistent dynamic continualization of block-lattice materials

Lattice-like materials featuring periodic planar tessellation of regular rigid blocks connected by linear elastic interfaces and chiral or achiral properties are considered. The chirality results from a uniform rotation of the blocks with respect to their centroidal joining line and leads to interesting auxetic and dispersive acoustic behaviors. The governing equations of the discrete Lagrangian model are properly manipulated via the novel enhanced continualization scheme in such a way to obtain equivalent non-local integral and gradient-type higher-order continua. Based on the formal Taylor series expansion of the integral kernels or the corresponding pseudo-differential functions accounting for shift operators and proper pseudo-differential downscaling laws, the proposed enhanced continualization technique allows formulating homogeneous non-local continuum models of increasing orders, analytically featured by characteristic non-local constitutive and inertial terms. The enhanced continualization shows thermodynamic consistency in the definition of the overall non-local constitutive tensors, as well as qualitative agreement and quantitative convergent matching of the actual complex frequency band structure. The theoretical findings are successfully verified though the study of wave dispersion and attenuation properties as referred to a representative tetrachiral geometry.

Microwave Attenuation Studies of Polypyrrole-SWCNT Nanocomposite Films for Improved EMI Shielding

In the process of finding stable, lightweight, broadband, cost-effective and improved electromagnetic interference (EMI) shielding material, electromagnetic wave attenuation properties of polypyrrole (PPy)—single-walled carbon nanotube (SWCNT) nanocomposite hybrid films were investigated in X-band region (8.2–12.4 GHz) and reported in the present work. The incorporation of SWCNT as a nanofiller in polymer matrix exhibits enhanced EMI shielding performance as compared to pure polymer films. The substantial values of dielectric loss with good impedance matching contribute to improvement in EMI shielding performance. It is found that with an increase of SWCNT loading in polymer matrix from 0 wt% to 5 wt%, nanocomposite films display a gradual increase in AC conductivity and total shielding effectiveness. The maximum total shielding effectiveness of 32.10 dB and minimum reflection loss of −45.54 dB with a wide bandwidth of 3.1 GHz, were obtained for 5 wt% CNT loading. The present results revealed that the prepared nanocomposite films are appropriate materials for lightweight, broadband EMI shields for radar and stealth applications.

The Emerald Tutu: Floating Vegetated Canopies for Coastal Wave Attenuation

Nature-based solutions (NBS) have been broadly defined in coastal resilience as the restoration of natural environments or as civil infrastructure with natural elements, with examples ranging from marsh restoration and new oyster beds to artificial reefs and living shorelines. The multiplicity of NBS types makes it difficult to quantify and model their effectiveness as a whole in coastal flood reduction and environmental co-benefits. Specific types of NBS operate under a variety of physical and ecological regimes: oyster beds care about the benthic environment and can be modeled as bed roughness elements, while living shorelines are a combination of emergent/submerged vegetation elements located in the dynamic swash zone. As such, NBS cannot be investigated as a monolith and their evaluation will be intervention-specific. Here, we present the evaluation of an engineered NBS called the Emerald Tutu, a series of interlinked vegetated mats which leverage known physical and ecological properties of marsh environments and combine them in networked formats for rapid deployment around shoreline environments. The Tutu takes inspiration from marsh canopies, but aims to transport the physical protection of these canopies to urban areas using the wave attenuation properties of floating vegetation elements and network effects. Prototype Tutu units were deployed in the OH Hinsdale Wave Lab at Oregon State University in summer 2021 to test the physical efficacy of the mat networks. The results show the effect of network arrangement, mat canopy size, and Tutu unit density on wave attenuation. We show how these results can be used to design the Tutu for a variety of coastal environments, and discuss the impact of submerged vegetation dynamics on Tutu effectiveness and what research gaps remain for the implementation of these kinds of engineered NBS.

Static mechanical properties and stress wave attenuation of metaconcrete subjected to impulsive loading

To mitigate shock wave propagation, a conventional engineered aggregate (EA) consisting of solid core coated with relatively soft material was designed to be tuned at targeted frequencies based on the local resonance mechanism. Previous studies demonstrated that metaconcrete consisting of conventional engineered aggregates (EAs) exhibited favourable attenuation performance of impulsive loading effects on structures. However, it was also found that the existence of the soft coating on conventional EA caused a reduction in the compressive strength of metaconcrete. In this study, a new type of EA by adding a relatively stiff shell outside the soft layer of the conventional EA was developed to overcome the issue of strength reduction whilst keeping its favourable wave attenuation properties. Quasi-static mechanical properties of metaconcrete consisting of conventional and newly developed EAs were examined through standard compression tests. The dynamic responses of the cylindrical metaconcrete specimens subjected to non-destructive and destructive impulsive loadings were also tested to investigate its wave attenuation capacity. The failure processes and the failure modes of metaconcrete made of different types of EAs under destructive tests were compared. It was found that adding a stiffer shell to the conventional EAs can improve the mechanical properties of metaconcrete while still keeping its good performance in mitigating stress wave propagation under both destructive and non-destructive loads.