Multiple Wave Reflections Research Articles

Simultaneously enhancing the EMI shielding performances and mechanical properties of structure–function integrated CF/PEEK composites via chopped ultra-thin carbon fiber tapes and interfacial engineering with MXene

The functionalization of carbon fiber reinforced poly(ether-ether-ketone) (CF/PEEK) structural composites with high electromagnetic interference shielding efficiency (EMI SE) has important engineering application in the fields of aviation and aerospace. However, the simultaneous enhancement of interfacial properties and EMI SE in the CF/PEEK composite remains a significant concern. To address this issue, we have employed a continuous impregnation approach that involved synthesizing PFEEK as a binder and then utilizing mechanical spreading technology to prepare chopped ultra-thin CF tapes as the reinforcement phase. Subsequently, we deposited 2D MXene (Ti3C2Tx) on the CF tape surface to endow the interface properties and EMI SE for the CF/PEEK composites. As a result, when the MXene content was 1.0 mg/ml, the flexural strength, flexural modulus, and interlaminar shear strength (ILSS) of the obtained CF/PEEK composites achieved 17.6 %, 13.3 % and 36.6 % enhancement higher than that of the virgin CF/PEEK composites, respectively, which may be owing to the elevated interfacial properties via the hydrogen bonds, physical entanglement, π-π interactions, and mechanical interlocking with the incorporation of PFEEK and MXene. The optimal ILSS value and specific EMI SE/t value of the CF/PF-M1/PEEK composites can reach 113.7 MPa and 80.8 dB/mm, respectively. The enhancement in the EMI SE can be attributed to the enhancive reflection, the increased polarization losses, and multiple interlayer reflections of EM waves facilitated by the incorporation of MXene and multi ultra-thin CF/PF-MXene layers. This approach resulted in a structure–function integrated CF/PEEK composite, which holds promising application prospects across various cutting-edge domains.

Interfacial metallization in segregated structured PEEK composite for enhanced thermal conductivity and electromagnetic interference shielding1

The increasing integration of electronic devices has created an urgent demand for multi-functional composites with efficient thermal management and electromagnetic interference (EMI) shielding. In this study, a three-dimensional (3D) continuous metal–carbon hybrid thermally/electrically conductive network structure is fabricated by in-situ nickel plating of core–shell structured polyetheretherketone (PEEK) hybrid particles. The hybrid particles realise phonon and electron dual heat-transfer pathways and reduce the interfacial thermal resistance by using metallic Ni nanoparticles to bridge the gap. Furthermore, the interfacial metallization and segregated structure significantly enrich the multiple electromagnetic wave reflection and attenuation mechanisms. The PEEK composites with metallized-segregated structure and filler content of 28.26 vol% exhibit an excellent through-plane thermal conductivity of 6.52 W·m–1·K–1 and an efficient EMI shielding of 91 dB, thus demonstrating their significant potential as multi-functional thermal management materials. The heat-transfer and EMI shielding process of the composites can be visualised using the finite element model, which further proves the effectiveness of the segregated structure and metallization. This simple and efficient strategy is expected to facilitate the manufacture of multi-functional thermal management composites with high thermal conductivity and excellent EMI shielding.

Frequency distribution of different joint slopes containing ceramic soil under seismic wave action

The dynamic response characteristics of high and steep slopes under the action of earthquakes and blasting was focused on, especially the frequency distribution and propagation laws, which are crucial for slope stability assessment. Using stress wave theory as the theoretical basis and advanced FLAC3D numerical simulation technology, we systematically analyze the frequency response of slope under different joint conditions under seismic waves. The nonlinear characteristics of reflected P-wave coefficient and the significant sensitivity of joint to incident wave frequency are revealed when the Angle of incident P-wave changes. The results show that with the increase of the incidence Angle of the incident P-wave, the reflection coefficient of the reflected P-wave decreases slowly at first and then increases sharply to 1.0. The reflection coefficient of the wave at the joint is more sensitive to the frequency of the incident wave. In a biplanar rock mass, multiple reflections of waves between structural planes produce transmitted waves with different time differences.

Design of lightweight aircraft trim panel with a high sound transmission loss

The trim panels of aircraft cabin are frequently made up of multilayer materials including a honeycomb, typically in the form of sandwich panels, which have the advantage of being lightweight and space-saving, but lack good acoustic insulation. It has been shown that, for 10% more mass, weights arranged in a fractal pattern in the honeycomb affect the vibratory pattern of a sandwich panel by creating multiple reflections of the bending waves on the inclusions. They thus generate a phenomenon of focusing vibratory waves providing localized modes while attenuating the structure's acoustic radiation. The objectives of this paper are to describe: first, the vibro-acoustic model of an overloaded homogenized bending panel (to mimic a trim panel with a fractal pattern); second, the physical phenomena associated to this concept; third, the impact on the modal behavior and the vibratory and acoustic responses.

Multiple reflection wave detection method based on inversion of multilayer material transfer function

Multiple reflection wave detection method based on inversion of multilayer material transfer function

A Silver Modified Nanosheet Self-Assembled Hollow Microsphere with Enhanced Conductivity and Permeability.

The utilization of sheet structure composites as a viable conductive filler has been implemented in polymer-based electromagnetic shielding materials. However, the development of an innovative sheet structure to enhance electromagnetic shielding performance remains a significant challenge. Herein, we propose a novel design incorporating silver-modified nanosheet self-assembled hollow spheres to optimize their performance. The unique microporous structure of the hollow composite, combined with the self-assembled surface nanosheets, facilitates multiple reflections of electromagnetic waves, thereby enhancing the dissipation of electromagnetic energy. The contribution of absorbing and reflecting electromagnetic waves in hollow nanostructures could be attributed to both the inner and outer surfaces. When multiple reflection attenuation is implemented, the self-assembled stack structure of nanosheets outside the composite material significantly enhances the occurrence of multiple reflections, thereby effectively improving its shielding performance. The structure also facilitates multiple reflections of incoming electromagnetic waves at the internal and external interfaces of the material, thereby enhancing the shielding efficiency. Simultaneously, the incorporation of silver particles can enhance conductivity and further augment the shielding properties. Finally, the optimized Ag/NiSi-Ni nanocomposites can demonstrate superior initial permeability (2.1 × 10-6 H m-1), saturation magnetization (13.2 emu g-1), and conductivity (1.2 × 10-3 Ω•m). This work could offer insights for structural design of conductive fillers with improved electromagnetic shielding performance.

The resonant behavior of airborne standing-wave acoustic levitators based on arrays of ultrasonic transducers

Recently airborne standing-wave acoustic levitation has seen great advances, and its applicability has been broadened due to the development of cavities constructed with arrays of compact ultrasonic sources. Yet, the numerical methods employed to study and predict the pressure distributions inside these cavities do not consider the effect of multiple reflections on the boundaries, hiding their resonant effects. This work presents an analytical, numerical, and experimental study of the effect of multiple reflections inside ultrasonic cavities based on arrays of transducers exhibiting their influence on the pressure amplitudes of focused standing waves. Our numerical results come from a modified version of the Matrix Method to numerically compute the multiple wave reflections of cavities constructed by two opposite arrays of multiple compact sources as boundaries. The correlation between numerical and experimental results reveals that intra-cavity reflections are relevant in focused axisymmetric cavities based on two arrays of multiple ultrasonic sources having a considerable impact on the amplitude of the standing waves and consequently, on the acoustic levitation performance. Thus, intra-cavity reflections must be considered for optimal cavity designs.

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.

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.

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.

Noncontact elasticity measurement of hydrogels in a culture dish using reverberant optical coherence elastography

Estimating the elasticity of hydrogel phantoms in a cell culture plane is important for understanding the cell behavior in response to various types of mechanical stimuli. Hence, a noncontact tool for measuring the elastic properties of hydrogel phantoms in such three-dimensional cell cultures is required. A well-known method to determine the mechanical properties of hydrogels is the transient wave method. However, due to the multiple reflections of waves from the boundaries, a bigger cell culture plane or multiple directional filters may be required. In this study, we utilized reverberant shear wave elastography, which is based on the autocorrelation principle, to evaluate the shear wave speed in hydrogel samples within a culture dish. Numerical simulations were performed first to confirm the validity of the reverberant elastography method. Subsequently, we used this method to measure the wave speeds in hydrogel phantoms with different concentrations. Shear rheology tests were also performed, and their results were found to be in good agreement with the measured shear wave speeds. The proposed method could be useful for measuring the elasticity of tissues in tissue engineering applications in an inexpensive and noncontact manner.

Preparation of MOFs-derived Ni/NPC materials and absorption properties

In order to solve the problems of electromagnetic pollution, it is urgent to prepare excellent microwave absorbing materials. A solvent-thermal method is employed to synthesize the precursor Ni-MOF-74, followed by carbonization treatment at different temperatures to prepare Ni/NPC material with a porous carbon encapsulation structure. The results indicate that, with the variation of carbonization temperature, the absorption performance of Ni/NPC composite material reaches its optimum at 700 ℃. At a frequency of 17.36 GHz, the minimum reflection loss is −38.4 dB, and the effective absorption bandwidth is 2.61 GHz (15.39–18 GHz). Studies on the absorption mechanism reveal that multiple reflections of electromagnetic waves, interface polarization losses, and resonance are the main contributing factors to the enhancement of absorption performance.

Porifera-Inspired Lightweight, Thin, Wrinkle-Resistance, and Multifunctional MXene Foam.

Transition metal carbides/nitrides (MXenes) demonstrate a massive potential in constructing lightweight, multifunctional wearable electromagnetic interference (EMI) shields for application in various fields. Nevertheless, it remains challenging to develop a facile, scalable approach to prepare the MXene-based macrostructures characterized by low density, low thickness, high mechanical flexibility, and high EMI SE at the same time. Herein, the ultrathin MXene/reduced graphene oxide (rGO)/Ag foams with a porifera-inspired hierarchically porous microstructure are prepared by combining Zn2+ diffusion induction and hard template methods. The hierarchical porosity, which includes a mesoporous skeleton and a microporous MXene network within the skeleton, not only exerts a regulatory effect on stress distribution during compression, making the foams rubber-like resistant to wrinkling but also provides more channels for multiple reflections of electromagnetic waves. Due to the interaction between Ag nanosheets, MXene/rGO, and porous structure, it is possible to produce an outstanding EMI shielding performance with the specific surface shielding effectiveness reaching 109152.4dBcm2 g-1 . Furthermore, the foams exhibit multifunctionalities, such as transverse Joule heating, longitudinal heat insulation, self-cleaning, fire resistance, and motion detection. These discoveries open up a novel pathway for the development of lightweight MXene-based materials with considerable application potential in wearable electromagnetic anti-interference devices.

Highly effective EMI shielding composites for 5G Ka-band frequencies

Reliable electromagnetic interference (EMI) shielding is essential to secure communications, protect components, and ensure efficient 5G network operation as these technologies expand. In this investigation, we propose a composite material that demonstrates remarkable EMI shielding efficacy, particularly within the Ka-band frequency range (26–40 GHz). This material is practical for industrial fabrication because it can be readily produced by integrating carbonyl iron powder (CIP) and carbon fabric (CF) into a polydimethylsiloxane matrix. It achieves a high shielding effectiveness of at least 120 dB within the Ka-band range, which can be further increased to an ultra-high level of 160 dB by adjusting the CF content. Electromagnetic analyses reveal that this enhanced shielding efficiency is due to the synergistic interplay between multiple reflections of incident EM waves within the CF structure and the excellent EM wave absorption properties of CIP. This composite material not only enhances EM shielding efficiency but also provides enhanced mechanical strength and thermal conductivity, rendering it a practical choice for EM shielding applications in the 5G Ka-band frequency range.

Ultra‐wideband electromagnetic interference shielding properties of parallel expanded graphite/Fe3O4 composites

AbstractThe rapid development of electronic devices in various fields has stimulated an increased demand for electromagnetic interference (EMI) shielding materials working in ultra‐wideband frequencies of gigahertz. However, the aggregation problem and single attenuation mechanism severely limit the broadband shielding applications of nanomaterials. To address these challenges, a novel composite of parallel expanded graphite (EG) embedded in the densified Fe3O4 matrix is designed and successfully synthesized through the in situ chemical coprecipitation followed by pressure sintering. This unique structure creates heterogeneous interfaces by combining the conductive EG and magnetic Fe3O4. The significant dielectric and magnetic loss then arise from conduction and polarization loss, as well as the eddy current and resonance effects. The multiple reflections of electromagnetic waves between the oriented EG sheets further cause the “absorb–reflect–reabsorb” effect that prolongs the propagation paths and enhances the dissipation of electromagnetic waves. Based on these multiple mechanisms over an ultrawide range of frequencies (8.2–40 GHz), the EG/Fe3O4 composites exhibit exceptional EMI shielding performance, with an average shielding effectiveness of 29.3 dB, indicating the potential for multifunctional EMI shielding applications.

Tying Shock Features to Impact Conditions: The Significance of Shear Deformation During Impact Cratering

AbstractImpact cratering is associated with extreme physical conditions with temperatures and pressures far exceeding conditions otherwise prevailing at the surfaces of terrestrial planets. As a consequence, shock‐metamorphosed rocks contain unique deformation features such as planar deformation features in quartz, high‐pressure mineral polymorphs and melted rock. While the physical conditions of formation for impact‐induced melting following the highest pressure and temperature conditions is relatively well understood, aspects of the formation of melt‐veins in otherwise seemingly relatively low shock material has been the topic of discussion. In a new study, Hamann et al. (2023, https://doi.org/10.1029/2023JE007742) are able to largely reproduce the current classification of progressive shock metamorphism of felsic rocks using a modern experimental set up that eliminates multiple shock wave reflections at sample containers and excavation and ejection of target material. Importantly, however, they find that shear deformation results in the formation of melt veins at pressures as low as 6 GPa. The authors recover stishovite in melt veins formed at low‐moderate (<18 GPa) shock pressure, lower than most previous studies. These results have bearing on our understanding of the conditions of progressive shock metamorphism at terrestrial impact structures. However, since the results are similar to data obtained from experiments on basaltic rocks, the results also have broader implications for understanding the shock histories of meteorite parent bodies. Hamann et al. show the importance of experimental impact cratering for bridging the gap between observations in shocked rocks from terrestrial impact structures, in meteorites, and in returned samples, and their formational conditions.

Polymer blend templated hierarchical porous composites with segregated structure and enhanced electromagnetic interference shielding performance

AbstractConductive network built by less conductive filler is vital for high‐performance conductive polymer composites. Herein, porous ultrahigh molecular weight polyethylene (UHMWPE)/poly(vinylidene fluoride) (PVDF) blends filled with multi‐walled carbon nanotubes (MWCNT) were fabricated, where poly(lactic acid) (PLA) and polymethyl methacrylate (PMMA) were served as sacrificial template. An interconnecting conductive network is formed based on the UHMWPE segregated structure and PVDF co‐continuous structure in porous UHMWPE/PVDF/MWCNT (UFC) composites. The UFC composites demonstrate a low electrical percolation threshold (0.25 wt%) due to the segregated/co‐continuous structure. Porous UFCs exhibit higher electromagnetic interference shielding effectiveness (EMI SE) than their compact counterparts. The blend‐templated porous structure enhances the EMI SE of composites because a well‐dispersed and densely packed MWCNT network is formed around the polymer particles, facilitating the multiple reflections of electromagnetic waves inside the composites. This effort provides a facile way for preparing high‐performance shielding materials by controlling the hierarchical structure and conductive filler distribution.Highlights Hierarchical porous structure was constructed by blend sacrificial templating method. Carbon fillers are exclusively distributed at blend interface, forming the segregated structure. Porous composites exhibit better shielding performances than their solid counterparts.

Honeycomb-like bamboo powders-derived porous carbon with low filler loading, high-performance microwave absorption

Nowadays, the problem posed by electromagnetic wave pollution to electronic devices and biological systems is of serious concern. To create a microwave absorber, component and structural modulation is crucial. Biomass-derived porous carbon is a potential material for microwave absorption applications due to the characteristics of lightweight, high specific surface area, and significant dielectric loss. In this study, by examining the impact of various KOH concentrations on the pore structure, bamboo powders with an 80-mesh size were used as a raw material to create honeycomb-like bamboo powders-derived porous carbon (BPDPC) materials. The activation mechanism of the BPDPC material is also explained. Based on the electromagnetic parameters, the sample BPDPC-4 impregnated with 4 mol/L KOH has a maximum effective absorption bandwidth (RL ≤ −10 dB) of 4.76 GHz at a matching thickness of 2.0 mm, covering 11.54–16.30 GHz and a minimum reflection loss (RLmin) of −40.99 dB at a matching thickness of 2.2 mm at 5 wt% ultra-low filler loading. Due to polarization loss, conduction loss, and the mutually beneficial effects of multiple electromagnetic wave reflection and scattering, the superior wave absorption performance is explained. This work also serves as a reference for investigating porous carbon generated from biomass.

Tough, stretchable dual-network liquid metal-based hydrogel toward high-performance intelligent on-off electromagnetic interference shielding, human motion detection and self-powered application

The stretchable conductive materials with adjustable electromagnetic interference (EMI) shielding performance and other multifunctional integrated applications are remarkably desirable and challenging in flexible electronics. However, the existing stretchable materials often suffer from the decay of EMI shielding performance during the stretching process, which limits their practical applications. Meanwhile, it remains a great challenge to construct materials with ordered porous frameworks as integrated shielding devices. Incorporating porous structure will generate abundant interior surfaces/interfaces, facilitating multiple reflections of incident electromagnetic waves (EMWs). Herein, we employ ultrasound method to modify liquid metal (LM) with carbon nanotubes (CNTs), and further utilize an UV in-situ polymerization method to fabricate CNT@LM/polyacrylamide/gelatin (LMCPG) dual network hydrogel elastomer. The LMCPG hydrogel elastomer possesses high strength and durability, and its tensile strength reaches 117 kPa at 1033% strain owing to the high strength of the rigid network and the beneficial deformation ability of the flexible network. Deformable CNT@LM droplets elongate randomly during stretching process, which facilitates establishing more conductive paths. The EMI shielding capacity of the stretched elastomer can be controlled, achieving an intelligent on-off behavior, which exhibits a 211% increase at 200% strain in EMI shielding effectiveness (SE) compared with the undeformed state. Moreover, the LMCPG elastomer shows a significant triboelectric performance, which can provide power supply for flexible electronic devices, achieving an uninterrupted monitoring of the human body motion by devices. Therefore, as a flexible electronic material, it can offer a facile solution to achieve intelligent multifunctional integrated EMI shielding materials.

Sandwich structure electromagnetic interference shielding composites based on Fe3O4 nanoparticles/PANI/laser-induced graphene with near-zero electromagnetic waves transmission

High-performance electromagnetic interference (EMI) shielding materials with flexible and lightweight characteristics are still a hot research direction, which will be highly promising in many application fields. In this work, laser-induced graphene (LIG) as the top and bottom layer, and binary composites of co-precipitated Fe3O4 NPs and in-situ chemical polymerized PANI (FePA) functioned as the intermediate layer is assembled to prepare a sandwich structure shielding material (FePA/LIG composite). 3D porous LIG with excellent conductivity is conducive to promote reflection and multiple reflections of incident electromagnetic waves (EMWs), while the transmitted EMWs will be further absorbed and attenuated via FePA composite due to its high impedance matching and microwave absorption (MA) properties. Near-zero EMWs transmission can be achieved and the average EMI shielding effectiveness (SE) of FePA/LIG composite (with thickness less than 2 mm) over the entire X-band and Ku-band is 50 dB and 63 dB, respectively. The admirable EMI shielding performance and flexibility of FePA/LIG composite endows enormous potential in portable electronic devices.