Impedance Matching Mechanism Research Articles

Metal organic frameworks derived core-shell structured C@TiC nanocomposites with excellent microwave absorption performance

With aim to prepare nano-microwave absorption material with excellent microwave absorption performance, core-shell structured C@TiC nanocomposites with tunable nanostructures and morphologies were successfully synthesized through one-step pyrolysis of the Ti-based MOFs precursors at a low temperature. Effects of various metal/linker ratio, solvent types and Hacac addition on the microstructures and properties of the C@TiC nanocomposites were thoroughly investigated, demonstrating that the TiC core-C shell structure could be effectively tailored. Compared to pure TiC nanoparticles, the C@TiC nanocomposites exhibited significantly improved microwave absorption performance, including the stronger RL peak of -35.64 dB (10.72 GHz) at 2.4 mm thicknesses and the enhanced effective microwave wave absorption width (EAB, RL≤-10 dB) spanning the entire C-band and X-band, which is ascribed to the better impedance matching and richer microwave loss mechanisms. As a result, C@TiC nanocomposites show great potential to be applied as absorbers with strong microwave absorption and wide absorption bandwidth.

Synthesis and high electromagnetic wave absorption performance of carbon-enriched porous SiOC ceramics

The carbon-enriched porous SiOC ceramics with enhanced electromagnetic wave (EMW) absorption properties were synthesized through the hydrothermal method followed by a polymer-derived ceramics (PDCs) process. As the annealing temperature rises from 1200 °C to 1500 ℃, SiC and SiO2 crystals are gradually separated from the porous amorphous SiOC matrix, and the degree of graphitization of free carbon increases. The porous SiOC ceramics annealed at 1400 °C exhibit the presence of SiC, SiO2, turbostratic graphite, and amorphous SiOC phases, which significantly impact the impedance matching and attenuation constant of the material. The minimum reflection loss (RLmin) value of the SiOC ceramics reaches −67.98dB with a matching thickness of 3.19mm and the effective absorption bandwidth (EAB) is 4.45GHz at 1.39mm. The carbon-enriched porous SiOC ceramics with strong absorption capacity and wide absorption bandwidth are primarily owing to appropriate impedance matching and multiple attenuation mechanisms, such as conduction loss, interfacial polarization, and defect-induced polarization, indicating that the SiOC ceramics exhibit significant potential as a high-performance EMW absorbing material.

Cascaded nanocavity-shaped metasurfaces for realizing an intensive radiation absorption in the mid-to-long infrared region based on electromagnetic wavefield resonance response and accumulation

A type of cascaded metal-insulator-metal nanocavity-shaped (CMNM) metasurface has been developed for realizing an intensive radiation absorption in the mid-to-long infrared (IR) region. The radiation absorption characteristics are analyzed according to the impedance matching mechanism. By evaluating the electromagnetic wavefield properties at several wavelength points selected, the spatial resonance morphology of the electric field and magnetic field components excited mainly by the resonance of the free electrons over the surfaces of the metasurface are simulated effectively. The stimulating and redistributing behaviors of the conductive electric-currents, including the surface equivalent eddy-currents surrounding a couple of dielectric films configurated in the cascaded nanocavities, and the net charges distributed over three Ti films, which will induce a resonant accumulation enhancement of the wavefields in the metasurfaces corresponding to the incident IR radiation, are exhibited. An average absorption level of more than 85% in the 3–14µm wavelength region is already achieved. Due to the IR responding and manipulating approaches proposed by us, the CMNM samples also exhibit an insensitivity of the beam incident angle for some typical applications in uncooled infrared imaging and thermal radiation detection.

Enhanced electromagnetic wave absorption performance of Ta₄C₃Tx MXenes with optimized interlayer spacing via hydrofluoric acid etching

Ta4C3Tx MXene, a novel two-dimensional material, shows significant application potential for electromagnetic wave (EMW) absorption because of its unique layered structure and high conductivity. In this study, hydrofluoric acid etching was used to obtain Ta4C3Tx MXenes with varying interlayer spaces by adjusting the etching duration, which enhanced the EMW absorption performance. The impact of interlayer spacing on the EMW absorption performance of Ta4C3Tx MXene was systematically evaluated for the first time. The results show that the sample etched with hydrofluoric acid for 48 h (S2-48 h) exhibited the best EMW absorption performance. For S2-48 h, the optimal reflection loss (RL) value was −33.53 dB at a frequency of 9.74 GHz and a thickness of 1.4 mm. In addition, the widest effective absorption bandwidth was 2.97 GHz (10.73–13.7 GHz), which was achieved at a frequency of 11.72 GHz and a thickness of 1.2 mm. This outstanding performance is mainly attributed to good impedance matching and multiple loss mechanisms induced by the etching process, including conduction loss, dipolar polarization, interfacial polarization, and multiple RLs. Furthermore, this research expands the application potential of two-dimensional MXene materials in EMW absorption.

Optimizing the electromagnetic wave attenuation properties of carbon encapsulated FeCoNiCuMnx high entropy alloy nanoparticles

With the advancement of wireless technology, there is a significant need for magnetic/carbon nanocomposites capable of absorbing electromagnetic waves across a wide frequency spectrum. However, designing these absorbers with uniformly distributed magnetic nanoparticles without agglomeration, to obtain optimal magnetic loss performance remains a significant challenge. In this work, FeCoNiCuMn alloy nanoparticles encapsulated in a graphitic C-shell have been successfully synthesized using metal-organic chemical vapor deposition. The incorporation of magnetic nanoparticles boosts magnetic loss, complementing dielectric loss to optimize electromagnetic waves attenuation, while the core/shell architecture further improves impedance matching. Moreover, adjusting the Mn contents enables the regulation of absorption performance in terms of thickness and working frequency. Thanks to their optimized impedance matching and multiple loss mechanisms, the FeCoNiCuMn0.5/C nanoparticles showcased outstanding attenuation capabilities. This included achieving a reflection loss of −52.30 dB at a thickness of 2.35 mm and an effective absorbing bandwidth covers 5.52 GHz at 2.0 mm. Moreover, the coatings containing FeCoNiCuMn0.5/C nanoparticles contributed to notable reductions in radar cross-section values, with the most significant reduction reaching up to 26.04 dBm2. This study highlights the potential practical application of FeCoNiCuMn nanoparticles encapsulated within a graphitic C-shell as highly efficient electromagnetic wave absorbing materials.

Boosting magnetic loss and impedance matching based on laminated structure for balancing low-/high-frequency broadband microwave absorption

Balancing low-/high-frequency broadband absorption is significantly essential for realizing ultra-wideband microwave absorption but mains challenging. In this work, laminated dielectric@magnetic FePO4/CrPO4@FeSiCr flakes have been created using facile vertical ball milling technique and subsequent phosphate passivation process. The flaky morphology provides the strong magnetic loss ability for boosting a lower-frequency microwave absorption. The dielectric@magnetic structure contributes good impedance matching and sufficient double loss mechanism for ensuring a wideband higher-frequency microwave absorption. The unique laminated structure is benefit for multi-scattering and reflection, which can balance the low-/high-frequency broadband absorption. With 6 h ball milling, FePO4/CrPO4 hybrid layer covers FeSiCr flakes deliver effective absorption bandwidth (EAB) of 1.6 GHz covering 2.4–4.0 GHz (S-band) with 3.2 mm, EAB of 3.52 GHz covering 4.40–7.92 GHz (C-band) with 1.9 mm and EAB of 8.24 GHz covering 9.36–17.6 GHz (X+Ku band) with 1.1 mm. Generally, an easy pathway is provided in this work for developing ultra-wide microwave absorbers that balance low-/high- frequencies.

Phase Engineering on MoS2 to Realize Dielectric Gene Engineering for Enhancing Microwave Absorbing Performance

AbstractPolarization relaxation loss caused by defects and interfaces has become a fascinating electromagnetic wave (EMW) loss mechanism. However, the logical relationship between impedance matching and various loss mechanisms requires further elucidation to facilitate more comprehensive and in‐depth research. Herein, phase engineering on molybdenum disulfide (MoS2) is proposed as the main controller of permittivity, offering a straightforward and highly effective method for regulating permittivity. Through the main control of phase engineering, a small gradient, monotonic change of the permittivity across a substantial area is achieved, leading to the gradual transition of the material system from strong loss but impedance mismatching to weak loss but EMW transparent phase. Thanks to the fundamental regulation of impedance characteristic and attenuation capacity by the dielectric gene engineering controlled by the phase engineering, combined with the ingenious coordination of sulfur vacancy‐induced polarization and interfacial polarization, t‐60 harvests an effective absorption band of 6.8 GHz and a minimum reflection loss of −59.8 dB. This study effectively expands the dielectric gene pool and improves the research logic for various loss mechanisms, offering valuable insights for the development of advanced EMW absorbing materials.

Construction of ZIF-67 derived multi-interfacial composites embedded in carbonized pomelo peel for enhanced microwave absorption with 8 wt% filler loading

The development of lightweight, environmentally friendly, and cost-effective microwave absorbers with robust absorption capabilities represents a challenging yet imperative undertaking. Herein, we present a methodology wherein derived ZIF-67 (abbreviated as Co/C) embedded in carbonized pomelo peel (CPP) through a combination of pyrolysis and in-situ growth methods, demonstrates effectiveness in microwave absorption. The Density Functional Theory (DFT) provides a comprehensive analysis of the preparation and operating principles underlying the CPP@Co/C absorber. The modification of CPP with Co/C not only facilitates the creation of numerous multiple interfaces but also mitigates impedance mismatching phenomena associated with CPP. It indicates that CPP@Co/C-150 achieves a remarkable 90% wave radiation within the frequency range of 3.52–18 GHz at a mere 8 wt% loading, covering the entire C, X, and Ku bands. Furthermore, CPP@Co/C-100 exhibits a minimum reflection loss (RLmin) value of −42.5 dB at a thickness of 1.82 mm, with an effective absorption bandwidth (EAB) extending to 5.2 GHz at 2.00 mm. This represents a substantial increase of 340% and 209% compared to CPP absorbers, respectively. The exceptional absorption performance is attributed to favorable impedance matching, conductivity loss, polarization loss, and magnetic loss mechanisms. This study introduces novel strategies and benchmarks for the production of low-cost and environmental-friendly microwave absorbers with a straightforward preparation process.

A perspective on impedance matching and resonance absorption mechanism for electromagnetic wave absorbing

Broadband absorption is urgently desirable for microwave stealth or photothermal conversion, but is a significant challenge in thin layer applications. Impedance mismatch and undesired dielectric relaxation are the main obstacles to realizing simultaneous resonant absorption at multiple frequency bands. In this perspective, the key issues in broadband absorption are briefly reviewed, which must be addressed by the community to enable microwave absorption promoting and widening. Then, impedance matching coefficient used to identify microwave absorbing ability is highlighted. Finally, an ideal model of dielectric dispersion for carbon-based materials is proposed to be used to design broadband absorbing materials, after deducing the inner nature of the typical quarter-wave resonance absorption existing in absorbers.

Effect of carbon allotropes and thickness variation on the EMI shielding properties of PANI/NFO@CNTs and PANI/NFO@RGO ternary composite systems.

The innovative design of thin, multiphase flexible composite systems with good mechanical properties, low density and improved EMI shielding properties at low filler content has become a key area of research. In this work, we report the low temperature synthesis of three-dimensional ternary composites (PANI/NFO@CNTs and PANI/NFO@RGO) by oxidative chemical polymerization of aniline in the presence of two different binary composites, viz. NFO@CNTs and NFO@RGO. Enhanced impedance matching is achieved by varying the ratio of the carbon allotropes (CNTs and RGO) to the ferrite component. The synthesis of NFO, PANI/NFO@CNTs and PANI/NFO@RGO is validated by XRD and FTIR spectroscopy. Field emission scanning electron microscopy (FE-SEM) confirmed the synthesis of core-shell structures of PANI/NFO@CNTs and PANI/NFO@RGO, where the binary composites (NFO@CNTs and NFO@RGO) serve as a core onto which a tubular PANI layer was coated. Shielding effectiveness of 22.36 dB (99.41% attenuation) is exhibited by the ternary composite PANI/NFO@CNTs (8 : 1), while for PANI/NFO@RGO (20 : 1) a total shielding effectiveness of 31 dB equivalent to 99.92% attenuation was observed at a thickness of 2 mm. The ternary composite PANI/NFO@RGO (20 : 1) 4 mm showed a maximum SET of 43 dB corresponding to 99.996% attenuation of incident EM waves. The enhanced EMI shielding properties of the synthesized ternary composite systems are accredited to good impedance matching, effective dielectric and magnetic loss mechanisms and good conductivity, which facilitate multiple reflections and scattering of incident radiation.

Strong and wide microwave absorption of multilayered metastructure enhanced by impedance matching mechanism

The present study proposes a strong and wide microwave absorption of multilayered metastructure (SWMAMM) capable of achieving an ultra-wideband absorption of −20 dB and 60° oblique incidence. SWMAMM primarily consists of metasurface-Ⅰ (MS-Ⅰ), metasurface-Ⅱ (MS-Ⅱ), and a top absorption-enhanced skin, which are separated by three support dielectric slabs. Based on impedance matching theory and the interference model, MS-Ⅰ serves as the core functional layer for wideband absorption; whereas MS-Ⅱ not only provides ultra-wideband impedance matching but also enhances absorptivity, distinguishing it from most designs. To further improve impedance matching, different hole arrays are incorporated into the substrates of MS-Ⅰ, MS-Ⅱ, and the top absorption-enhanced skin by modifying their equivalent reactance. The measurement results demonstrate that the −10 dB and −20 dB reflection bands are separately in the range of 3.97–23.19 GHz and 5.24–21.81 GHz when the oblique incidence angle reaches 5°; the −10 dB reflection band can cover the range of 5.99–25.00 GHz when the oblique incidence angle reaches 60°. Our approach, which involves impedance matching design of MS-Ⅱ and optimizing impedance matching by incorporating different hole arrays into the substrates of the MS-Ⅰ, MS-Ⅱ, and the top absorption-enhanced skin, can be applied to various unit cells and dielectric materials. This approach offers significantly enhanced convenience and efficiency compared to existing designs, thereby facilitating further optimization and development of Electromagnetic absorbers.

Facile manufacturing of core-shell MnO@C microspheres toward enhanced electromagnetic wave attenuation

Exploring highly efficient electromagnetic wave (EMW) absorbing materials with strong absorption and low density is a viable strategy to address the growing issue of electromagnetic pollution. A type of carbon-coated MnO (MnO@C) microspheres with enhanced EMW absorption properties was synthesized via the precipitation method, followed by a facile sol-gel process. The results demonstrate that the carbon source content is critical in determining the thickness of the carbon shell, which in turn has a great impact on impedance matching and attenuation constant. Due to the moderately complex permittivity of MnO@C microspheres, the minimum reflection loss (RLmin) reaches − 43.69 dB at 15.03 GHz with an ultra-thin matching thickness of only 1.53 mm. Additionally, the corresponding effective absorption bandwidth (EAB) is 4.81 GHz. The enhanced performance can mainly be attributed to appropriate impedance matching and multiple attenuation mechanisms, including interfacial polarization, defect-induced polarization, and conduction loss. Therefore, the MnO@C microspheres are considered to be suitable for high-efficiency microwave absorbers.

Inimitable 3D pyrolytic branched hollow architecture with multi-scale conductive network for microwave absorption

To solve the electromagnetic pollution problem, the reasonable structure design and component control of the electromagnetic absorber is prominent. In this work, three-dimensional (3D) pyrolytic branched hollow architecture carbon PBHAC/MoS2 composites were prepared via a hydrothermal and calcination two-step strategy. The narrow-gap nano-size MoS2 acquired after vulcanization and micro-size 3D branched carbon skeleton PBHAC possess intensified conduction losses. Particularly, the presence of potential differences between different phases creates a space charge region at the heterogeneous interface, resulting in strong interfacial polarization. The resulting 3D branched hollow PBHAC/MoS2 composites exhibit optimized impedance matching and multiple loss mechanisms. Finally, the 3D branched hollow carbon PBHAC/MoS2 composites have the best electromagnetic wave (EMW) absorption performance. The minimum reflection loss (RLmin) is –57.8 dB at 1.93 mm and the maximum effective absorption bandwidth (EABmax) is 6.08 GHz at 2 mm, which indicates the excellent EMW absorption performance of the composites. Accordingly, this composite is expected to be a microwave absorber with the characteristics of “thin, light, wide, and strong”.

The evolution of the various structures required for hearing in Latimeria and tetrapods

Sarcopterygians evolved around 415Ma and have developed a unique set of features, including the basilar papilla and the cochlear aqueduct of the inner ear. We provide an overview that shows the morphological integration of the various parts needed for hearing, e.g., basilar papilla, tectorial membrane, cochlear aqueduct, lungs, and tympanic membranes. The lagena of the inner ear evolved from a common macula of the saccule several times. It is near this lagena where the basilar papilla forms in Latimeria and tetrapods. The basilar papilla is lost in lungfish, certain caecilians and salamanders, but is transformed into the cochlea of mammals. Hearing in bony fish and tetrapods involves particle motion to improve sound pressure reception within the ear but also works without air. Lungs evolved after the chondrichthyans diverged and are present in sarcopterygians and actinopterygians. Lungs open to the outside in tetraposomorph sarcopterygians but are transformed from a lung into a swim bladder in ray-finned fishes. Elasmobranchs, polypterids, and many fossil fishes have open spiracles. In Latimeria, most frogs, and all amniotes, a tympanic membrane covering the spiracle evolved independently. The tympanic membrane is displaced by pressure changes and enabled tetrapods to perceive airborne sound pressure waves. The hyomandibular bone is associated with the spiracle/tympanic membrane in actinopterygians and piscine sarcopterygians. In tetrapods, it transforms into the stapes that connects the oval window of the inner ear with the tympanic membrane and allows hearing at higher frequencies by providing an impedance matching and amplification mechanism. The three characters-basilar papilla, cochlear aqueduct, and tympanic membrane-are fluid related elements in sarcopterygians, which interact with a set of unique features in Latimeria. Finally, we explore the possible interaction between the unique intracranial joint, basicranial muscle, and an enlarged notochord that allows fluid flow to the foramen magnum and the cochlear aqueduct which houses a comparatively small brain.

Excellent microwave absorption of void@carbon@TiO2 cubes by a template sol method

The ingenious design of heterogeneous structures is an effective strategy for developing advanced microwave absorption materials. In this study, high-efficiency void@carbon@TiO2 (void@C@TiO2) cubes were synthesized by a template sol method. Compared with void@carbon (void@C) and void@TiO2 cubes, the void@C@TiO2 cubes/paraffin composites of 2.1 µm edge length show excellent microwave absorption performances (MAPs). When the thickness is 2.1 mm, the minimum reflection loss (RL) of – 69.8 dB is superior to – 31.5 dB of void@C cubes at 4.1 mm and – 3.1 dB of void@TiO2 cubes at 3.7 mm. The effective absorption frequency covers 11.8 GHz (6.2–18.0 GHz, RL below – 10 dB) by matching the coating thickness with 1.7–5.0 mm. The enhanced MAPs originated from the synergistic processes of good impedance matching (|Zin/Z0|) and various microwave dissipation mechanisms, including electrical conduction, interfacial charge accumulation, and defect dipolar polarization. The void@C@TiO2 cubes are a lightweight, easy, environment-friendly, and extendible strategy for microwave absorption applications.

Optimized impedance matching and enhanced attenuation by heteroatoms doping of yolk-shell CoFe2O4@HCN as highly efficient microwave absorbers

Microwave absorbing (MA) materials with yolk-shell structures have been extensively studied in impedance matching. However, the impedance matching achieved by the complementary effect of the core and the shell does not determine the reflection of the microwaves upon the occurrence at the first incidence. The interaction between the outer layer of materials and the electromagnetic waves significantly impacts the MA properties of materials. In this study, the impedance matching improvement method of the shell structure was further explored by preparing CoFe2O4@HCN (honeycomb carbon with N-doping) through the hydrothermal method followed by hydrolysis, polymerization, etching, and annealing. The resulting structure with heteroatoms doping provided the novel CoFe2O4@HCN with excellent impedance matching and multiple loss mechanisms contributing to MA process. The absorber with a filler loading of 40% exhibited an RLmin of −68.03 dB with a matching thickness of 2.5 mm. The efficient absorbing bandwidth reached 5.92 GHz (a change from 11.92 to 17.84 GHz) at 1.99 mm thickness. Interestingly, these findings look promising for future synthesis and application of yolk-shell structure microwave absorbers.

Bifunctional SiC/Si 3N 4 aerogel for highly efficient electromagnetic wave absorption and thermal insulation

SiC ceramics are attractive electromagnetic (EM) absorption materials for the application in harsh environment because of their low density, good dielectric tunable performance, and chemical stability. However, the performance of current SiC-based materials to absorb EM wave is generally unsatisfactory due to poor impedance matching. Herein, we report ultralight SiC/Si₃N₄ composite aerogels (~15 mg·cm⁻³) consisting of numerous interweaving SiC nanowires and Si₃N₄ nanoribbons. Aerogels were prepared via siloxane pyrolysis and chemical vapor reaction through the template method. The optimal aerogel exhibits excellent EM wave absorption properties with a strong reflection loss (RL, −48.6 dB) and a wide effective absorption band (EAB, 7.4 GHz) at a thickness of 2 mm, attributed to good impedance matching and multi attenuation mechanisms of waves within the unique network structure. In addition, the aerogel exhibits high thermal stability in air until 1000 ℃ and excellent thermal insulation performance (0.030 W·m⁻¹·K⁻¹). These superior performances make the SiC/Si₃N₄ composite aerogel promising to become a new generation of absorption material served under extreme conditions.

Absorption-dominated electromagnetic interference shielding composite foam based on porous and bi-conductive network structures

A porous Ni@MF/CNT/TSM/PDMS composite foam with a bi-conductive network structure was fabricated, which possesses absorption-dominated and excellent EMI shielding properties due to the impedance matching and diversiform dissipation mechanisms.

A double-stage impedance matching mechanism with quasi-arbitrary materials

In wave propagation between two media, a perfect impedance matching eliminates reflection and enables 100% energy transmission. Traditional matching mechanisms, with either single or multiple matching stages, require a specific impedance and dimension of each material, which is impossible to satisfy in many cases due to material unavailability or fabrication constraints. Consequently, many current systems are imperfectly matched with compromised performance. Here we show a universal impedance matching mechanism that realizes ∼100% energy transmission by double stages of quasi-arbitrary materials. The impedance of either matching material ranges from almost zero to almost infinity, as long as the impedance pair satisfies one of the four criteria. We validate the proposed mechanism with acoustic waves based on finite element modeling and experimental characterization. This work relaxes the requirement of matching materials and enables the universal matching of multiple waves with quasi-arbitrary materials.

Progress of metal organic frameworks-based composites in electromagnetic wave absorption

Eelectromagnetic pollution has become an increasingly prominent problem and electromagnetic wave absorbing materials have received widespread attention. Metal organic frameworks (MOFs) derived materials work as wave absorbing materials having the advantages of simple synthesis process, low production cost, high specific surface area and porosity, good thermal stability, and also have excellent impedance matching and various attenuation mechanisms, which have been widely studied in the field of electromagnetic wave absorption. In here, the classification and preparation methods of MOFs are summarized, their wave absorption mechanisms are analyzed. It also details the current research progress and analyses their advantages and disadvantages from the perspectives of monometallic MOF, multi-metallic MOF and wave absorbing materials derived from MOF compounded with other materials (including carbon materials, MXene and conductive polymers). This article aims to illustrate the application of MOFs and their derived composites in the research of electromagnetic wave absorption, and hopes to offer a reference for the further research based on these promising materials.