Impedance Matching Behavior Research Articles

Hierarchical-porous acoustic metamaterials: A synergic approach to enhance broadband sound absorption

A novel design for hierarchical-porous acoustic metamaterials (HPAM) is proposed to enhance the functionality of Helmholtz-type resonators and porous materials, achieving continuous and efficient broadband sound absorption. This method can potentially eliminate absorption valley and improve the coupling strength through a synergistic energy dissipation mechanism and hybrid impedance matching behavior. Excellent sound-absorbing capability of the elaborately crafted HPAM was demonstrated analytically, numerically, and experimentally. Specifically, the results revealed an impressive average absorption coefficient of 0.77, with 73 % of the α points exceeding 0.8 across the entire test frequency range. Furthermore, the sound absorption of HPAM can be further optimized to attain ultra-broadband properties by modifying the hierarchical configuration and composite design of the porous materials. The physical mechanism is revealed through the integration of the hierarchical scaling effect and the energy-trapped mode. Numerical simulations revealed the emergence of three distinct absorption peaks at frequencies of 0.76, 1.4, and 3.6 kHz, respectively, and the effective absorption spectrum exceeded 3.4 kHz. Overall, the proposed design highlights the role of hierarchical structures and porous materials in synthesizing superior sound-absorbing properties that fullyelucidate the relationship between structure and performance,and provide an avenue for potential noise-control applications.

Interface Engineering of Titanium Nitride Nanotube Composites for Excellent Microwave Absorption at Elevated Temperature

HighlightsThe boosted heterogeneous interfaces in titanium nitride (TiN) nanotube/polydimethylsiloxane (PDMS) composite contributed to strong polarization loss relaxation ability.The TiN nanotubes/PDMS composite possessed both good impedance matching behavior and strong dielectric loss ability in wide temperature spectrum.The TiN nanotubes/PDMS composite exhibited excellent EMWA performances (effective absorption bandwidth value of 3.23 GHz and minimum reflection loss value of − 44.15 dB) at the varied temperature from 298 to 573 K.

Improved Stable Read Range of the RFID Tag Using Slot Apertures and Capacitive Gaps for Outdoor Localization Applications.

This paper proposes a small-size UHF RFID tag antenna, which was designed to function in the frequency interval of 860-960 MHz, with a large-read range of up to 17 m. In this work, the effects of capacitive slots and gaps on the impedance matching between conventional industrial chips and a designed RFID antenna was investigated. Simulated and measured results provided a clear indication that these two techniques can efficiently improve the return loss parameter and the antenna impedance matching behavior at the UHF band. Three-dimensional electromagnetic (EM) simulations results further proved that a better impedance matching between an industrial chip and a proposed RFID antenna occurs at 870 MHz, where the estimated input antenna impedance was about Za = 16 + j184 (Ω), and the calculated read range reached a value of up to 17 m with a measured return loss value of -14 dB. The proposed RFID antenna can almost maintain the same read range value over a 180 degree angle variations on the horizontal plane owing to its omnidirectional radiation pattern. The fabrication and test stages of the antenna prototype were scheduled to validate the simulated characteristics. Experimental results confirmed the performances of our proposed RFID tag antenna and proved its potential ability for localization applications. EM simulations have been performed using the well-known commercial EM software simulator CST MWS.

Microrod superstructure of graphene nanocages with enhanced microwave absorption performance

The carbon based microwave absorption materials are considered as new generation absorbers owing to their lightweight, thin-thickness and good electronic conductivity. The challenge to develop excellent carbon absorbers is to improve its impedance matching behavior through decreasing its skin effect. In this study, the microrod superstructure of graphene nanocages (MSGN) have been prepared via a combination method of the precipitation, CVD and etching techniques. The MSGN realizes an optimal reflection loss of − 52.45 dB and an effective absorption bandwidth of 14.64 GHz. The unique superstructure might facilitate interfacial polarization loss and improve impedance matching behavior, thus resulting in an enhanced microwave absorption performance. Besides, the Radar Cross Section (RCS) simulation shows that MSGN delivers a reduction value of 13.50 dBm2 at the detective angle of 0°, suggesting that MSGN can be an eligible absorber for actual application.

Fabrication of high-performance electromagnetic wave absorbing SiC composites reinforced by 3D printed carbon-based nanonetwork with Fe3O4 nanoparticles

Here a free-standing and high-performance electromagnetic wave (EMW) absorber is developed by the in-situ growth of SiC into 3D-printed carbon-based scaffolds by chemical vapor deposition (CVD). The porous and interconnected network of graphene nanoplatelets (GNPs)/carbon nanotubes (CNTs) is oriented constructed and Fe-based magnetic nanoparticles are uniformly dispersed. Accompanied by the optimization of SiC to the mechanical properties of composites, the impedance matching behavior and attenuation capacity can be regulated by reducing the electrical conductivity of the carbon-based nanonetwork. Therefore, the as-prepared composites present a minimum reflection loss (RL) value of −48.7 dB, and a 2 mm-thick absorber whose reflection loss is better than −10 dB in 11.5–15.8 GHz is also achieved. Besides, the absorbing properties of the material remained consistent after annealing at 400 °C for 4 h. The controllable fabrication of composites shows appropriately promising potential as absorbers in a high-temperature environment with considerable EMW absorption performance.

Performance Improvement of an Archimedean Spiral Antenna for 2–18 GHz Applications

Low-profile wideband spiral antennas suffer from poor impedance matching and cross polarization at lower frequencies or high variation in gain at higher frequencies. These significant differences, primarily caused by electromagnetic coupling with a conventional conductive backing, and the resulting interference are addressed in this letter by suitably designing the profile of the conductor. The proposed geometry has a maximum height of 0.08 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{m}$</tex-math></inline-formula> at the minimum operating frequency and has wideband circular polarization performance with a good boresight gain response over 2–18 GHz range. After numerical investigations, a prototype antenna is fabricated and characterized. An excellent impedance matching and circular polarization behavior are measured close to 2 GHz while the variation in gain is limited between 5.8 and 8.6 dBic above 10 GHz.

Hybrid carbonaceous materials for radar absorbing poly(vinylidene fluoride) composites with multilayered structures

AbstractPoly(vinylidene fluoride) (PVDF) based composites loaded with 3 wt% of carbon black (CB), graphite (GF), and the hybrid CB/GF (1.5/1.5 wt%) were prepared by melt mixing and tested as microwave absorbing material at X‐band frequencies (8–12 GHz). The materials were processed and pressed at 220°C into plates of 20 × 20 × 0.1 cm3. Dielectric and magnetic properties were evaluated using the wave‐guide accessory to simulate the reflectivity of single‐layered PVDF composites through impedance matching behavior. The best absorbing properties were achieved with the composite loaded with the CB/GF hybrid material, whose maximum of radiation attenuation of −33 dB at 9.3 GHz was predicted with 4 mm thickness. Afterwards, the reflectivity of sandwiched structures (20 × 20 cm2 in size) with one‐layer honeycomb core sandwiched by two plates of PVDF composites was measured. The PVDF/HB‐honeycomb‐PVDF/HB structure reached reflection loss = −12 dB (Ea = 94%) on a broadband frequency. CB/GF hybrid material in PVDF composites has a promising future as a lightweight and cost‐effective microwave absorbing materials for both telecommunication and stealth technology.

Constructing γ-MnO2 hollow spheres with tunable microwave absorption properties

Hollow γ-MnO2 sphere was obtained by annealing the precursor at 400 °C with different holding time. The influences of different holding time on the morphology and crystalline structure of final products have been discussed in detail, and the microwave absorption properties of the as-products were also investigated. The results exhibited that finer crystalline feature of the γ-MnO2 and larger pore size in the hollow γ-MnO2 sphere could be obtained with the extended holding time. The MnO2/paraffin composites (50 wt% loading) present extraordinary microwave absorption performance, and the minimum reflection loss (RL) values is −51.3 dB at 4.9 GHz with the thickness of 3.5 mm. The excellent electromagnetic absorption properties can be ascribed to the hollow structure, perfect impedance matching behavior and the multiple interface polarization effect.

Design of Four Layer Microwave Absorber Based on Polyaniline-Expanded Graphite Composites: Role of Layer Interfaces in Impedance Matching

The present work investigated design simulation of single and multi-layer microwave absorber based on mono-phase (polyaniline) and dual—phase (polyaniline-expanded graphite) dielectric composite material. The work is the extension of author’s earlier work on carbon–based material using the unique behavior of polyaniline and highly conducting Expanded Graphite as fillers. The dual phase composites of polyaniline/Expanded Graphite prepared by in situ polymerization of aniline with different EG concentration of (0.00, 0.15 and 0.25 wt.%) were mixed with Novolac Phenolic Resin (NPR) in (10, 20 and 30 wt.%) to form (PA1-PA3 & PG1-PG3, PG4-PG6). Based on microwave characterization results and employing transmission line model, a theoretical analysis has been qualitatively done on four layer design simulation of absorber to achieve high performance absorption peak and bandwidth and subsequently fabrication of the designed structure for X-band microwave absorption. A calculated reflection loss ∼−80 dB is observed at 10.69 GHz for PG1-PG3-PG5-PA3 four layer designs having overall thickness of 8.6 mm and promising measured reflection loss ∼−63 dB at 10.66 GHz near the central frequency of the experimental frequency range. High performance absorption is interpreted as impedance matching behavior at the layer interface of the multilayer structure.

Hyper-Cross-Linked Polymers-Derived Porous Tubular Carbon Nanofibers@TiO2 toward a Wide-Band and Lightweight Microwave Absorbent at a Low Loading Content.

An enormous challenge exists in the achievement of one-dimensional (1D) dielectric carbon composite high-performance microwave absorbents at a low filling ratio. Porous/core-shell dual microstructures have been considered as the potential candidate for designing remarkable microwave absorbers with strong absorption and wide band. Herein, novel multiple-structured tubular carbon nanofibers@TiO2 (TCNFs@TiO2) hybrids were constructed via the sequential steps of hydrolysis and pyrolysis. The dielectric properties of the as-prepared composites can be tuned by adjusting the relative content of the TiO2 shell and carbonaceous temperature to enhance the impedance matching behavior. Notably, the minimum reflection loss (RLmin) value reaches up to -61.2 dB with an effective absorption bandwidth (EAB) of 3.2 GHz at 3 mm, and the EAB can cover 5.3 GHz with a thickness of merely 2 mm when 1.3 mL of tetrabutyl titanate (TBT) and 700 °C pyrolysis temperature are optimized, respectively. Delightedly, the mixing ratio is only 10 wt %, outperforming that of the most-related composites. The heterogeneous interfaces in TCNFs-TiO2 are beneficial for the interfacial polarization relaxation. Besides, the hybrids are enriched with numerous pores to favor the lightweight absorbers. The desirable design in the microstructure can provide a promising route in wide-band and lightweight microwave absorbents.

Ferrocene decorative phenolic epoxy resin as lightweight thermal-stable dielectric relaxor for electromagnetic wave absorption

Given the severe electromagnetic (EM) energy wasting and radiation interference, it is critically regarded to develop EM absorbing materials. In this work, a new type of lightweight heat-resistant polymer-based dielectric relaxor was manufactured as an efficient electromagnetic absorber by ferrocene (Fc) decorative phenolic epoxy resin (EPN) ferroelectric. A series of resin samples have been obtained as different amount of hydroxyethyl ferrocene (Fc-OH) was taken part in the EPN curing systems with 4,4′-diaminodiphenylmethane (DDM) as curing agent. Finally, the obtained results indicated that the EPN was gradually transformed into a typical relaxor ferroelectric from normal ferroelectric with the increasing amount of Fc decoration. The thermal stability was greatly optimized as the onset temperature of thermal decomposition was increased to 245 °C. It was confirmed that the optimized dielectric properties have strengthened the impedance matching and polarization relaxation behavior, which resulted in excellent EM dissipation. In details, the minimum reflection loss (RLmin) of EPN with 15 wt% Fc decoration reached -30.79 dB with an effective absorption band (fE) of 3.92 GHz at 1.9 mm and the maximum fE was 4.08 GHz at 2.00 mm. It is worth emphasized that the matching thickness was effectively decreased by modification of Fc moieties. Therefore, this research provides an effective path for EM absorption, opening up novel ideas for exploration of lightweight high-performance polymer-based EM absorbers.

Double-layer absorbers based on hierarchical MXene composites for microwave absorption through optimal combination

Abstract

Magnetic Fe nanoparticle to decorate N dotted C as an exceptionally absorption-dominate electromagnetic shielding material

Conversional electromagnetic shielding material with strong reflection coefficient are becoming insufficient for today's application, since the serious 2nd electromagnetic pollution. Herein, we demonstrate a magnetic carbon based shielding material constructed by magnetic Fe nanoparticles (NPs) and N dotted amorphous carbon nanosphere (~200 nm). The structure, morphology, chemical composition of the samples have been studied in depth. It is observed that the average sizes of Fe NPs is ~8.0 nm and can be loaded well on the surface of N dotted amorphous spheres. The electromagnetic shielding performance has been investigated. Significantly, the as-prepared samples show excellent electromagnetic shielding performance. The maximum shielding effectiveness can up to 30 dB under a thickness of 1.2 mm. More importantly, the reflection coefficient can be reduced to 2.3 dB, presenting excellent absorptiondominate shielding performance. The desirable shielding mechanism with less reflection are attributed to the boosted loss ability and matched impedance matching behavior, which originate from N doping and magnetic component. This work which integrates magnetic component with N dotted amorphous carbon has been demonstrated as a useful strategy for the development of absorption dominate EM shielding material.

Facile Synthesis of Three-Dimensional Porous Co/MnO Composites Derived from Bimetal Oxides for Highly Efficient Electromagnetic Wave Absorption

In this work, we report the synthesis of porous flower-like Co/MnO composite microspheres assembled by plentiful lamellae for microwave absorption applications. Electron microscopy observations indicated that, in the composites, Co nanoparticles with the size of 20–30 nm are uniformly distributed in the MnO matrix. We investigated the electromagnetic (EM) wave absorption properties of the Co/MnO composites with different Co proportions. When the molar ratio between Co and MnO is 2:1, the best electromagnetic wave absorption performance is achieved. Notably, the optimal reflection loss value reaches −64.2 dB at 10.9 GHz corresponding to the thickness of 2.3 mm, and the effective absorption bandwidth (RL < −10 dB) is up to 6.0 GHz with the thickness of 2.1 mm. The prominent absorption performance of the as-prepared Co/MnO composites mainly arises from the superior impedance matching behavior and strong attenuation capacity as a consequence of the synergistic effect between Co and MnO nanoparticles as well a...

Synthesis of popcorn-like α-Fe2O3/3D graphene sponge composites for excellent microwave absorption properties by a facile method

Popcorn-like α-Fe2O3/3D graphene sponge (α-F/3DGS) composites have been successfully fabricated by a novel and facile two-step synthetic route combining template-assisted preparation and co-precipitation method for microwave absorption application. The results show that the popcorn-like α-Fe2O3 nanoparticles with an average diameter about 150–200 nm are uniformly encapsulated into the 3DGS exhibiting a porous microstructure with plenty of wrinkles. The composite displays the optimum microwave absorption properties with the minimum reflection loss (RLmin) of − 55.7 dB and the maximum effective microwave absorption bandwidth up to 4.42 GHz (12.30–16.72 GHz) when the thicknesses are merely 1.4 and 1.7 mm, respectively, exhibiting greatly enhanced microwave absorption properties compared to those of some 2D graphene-based microwave absorbing materials. The excellent microwave absorption properties are attributed to the synergistic effect between dielectric loss and magnetic loss mechanism and improvement for the impedance matching behavior. This study paves a way for designing and fabricating lightweight and high performance microwave absorption materials based on 3D graphene composites.

In-situ growth strategy to fabrication of MWCNTs/Fe3O4 with controllable interface polarization intensity and wide band electromagnetic absorption performance

This research employed an in-situ growth method to fabrication of multi-walled nanotubes (MWCNTs)/Fe3O4 electromagnetic absorber. Such a binary material system is featured with good impedance matching behavior and moderate attenuation ability, thus exhibits excellent electromagnetic absorption properties. The results reveal that MWCNTs/Fe3O4 exhibits distinct polarization relaxation phenomenon which inducted by interface polarization. This intensity of interface polarization is tunable by controlling the contact area of Fe3O4 and MWCNTs. Due to the contribution of interface polarization loss behavior, the MWCNTs/Fe3O4 sample achieves a wide band electromagnetic absorption property which the frequency region with RL < −10 dB can covers 5.7 GHz at 1.5 mm. The method of utilizing interface strategy to boost dielectric loss ability has an efficient way to gain wide band electromagnetic absorber.

Development of sulfide-doped Graphene/Fe3O4 absorber with wide band electromagnetic absorption performance

Graphene has been confirmed as an ideal lightweight and high-performance electromagnetic (EM) absorber if used to deal with increasingly electromagnetic interference issue. However, the actual EM absorption performance of graphene is not desirable in a thin thickness which is due to poor impedance matching behavior and single conductive loss form. To overcome this difficulty, this research employed S doping and magnetic Fe3O4 nanoparticles loading strategies to boost EM attenuation ability by introduction of various EM loss forms, e.g. dipolar, interface, and magnetic loss ability etc. Besides, the impedance matching ability of SGN/Fe3O4 has significant improved as compared to pure graphene, primarily owing to the sharply decrease of relative complex permittivity (εr) values. The as-prepared S-doped graphene/Fe3O4 (denote as SGN/Fe3O4) absorber shows excellent wideband electromagnetic absorption property at a thin thickness of 2.0 mm which the frequency width with a reflection loss < -10 dB reach 5.3 GHz.

Tuning the Electromagnetic Synergistic Effects for Enhanced Microwave Absorption via Magnetic Nickel Core Encapsulated in Hydrogenated Anatase TiO2 Shell

Owing to tremendous potential applications, hydrogenated TiO2 (H-TiO2) nanomaterial has been considered an important member in the field of microwave absorption. In this paper, a kind of core–shell structured microspheres (MPs) consisting of outer-shell hydrogenated anatase TiO2 (H-A-TiO2) and inner-core magnetic Ni MPs were prepared successfully using a simple method. Experimental results revealed the as-prepared hydrogenated anatase TiO2@Ni (H-A-TiO2@Ni) composite exhibited enhanced microwave absorption property, when compared to pristine anatase TiO2@Ni (A-TiO2@Ni). (1) The minimum reflection loss (RL) of the H-A-TiO2@Ni/wax composite reached −64.2 dB at a thickness of 2 mm, indicating a large absorption efficiency over 99.99%. (2) The H-A-TiO2@Ni showed an effective microwave absorption bandwidth (RL < −20 dB) in a range from 2.2 to 11 GHz. Due to the introduction of core–shell media, coating Ni microspheres with H-A-TiO2 shells not only will be beneficial for impedance matching behavior but also impr...

How to exhibit the efficient electromagnetic wave absorbing performance of RGO aerogels: less might be better

In this work, it was presented that both the electromagnetic dissipation capacity and the impedance matching behavior were associated with the mass fraction of reduced graphene oxide (RGO) aerogels in the composites. Optimized, when the mass fraction of the RGO aerogels in composite is only 2.0 wt.%, the composites exhibit > 90% microwave attenuation at 2–18 GHz. By increasing the filler content, the negative resonances of imaginary permeability mean that magnetic energy is radiated out from the composites. The results are beneficial to designing lightweight and high efficiency microwave absorption materials based on the family of graphene.

The Outside-In Approach To Construct Fe3O4 Nanocrystals/Mesoporous Carbon Hollow Spheres Core–Shell Hybrids toward Microwave Absorption

It is widely accepted that building a core–shell structure is an effective way to modify impedance matching behavior and induce interfacial polarization relaxtion. In this work, we adopted a novel impregnation process and subsequent calcination treatment to construct Fe3O4 nanocrystals/mesoporous carbon hollow spheres (MCHS) core–shell hybrids. From the perspective of microwave absorption, MCHS possess favorable dielectric loss ability and lightweight features. Fe3O4 could produce magnetic loss and regulate impedance matching characteristics. Besides, hollow voids and mesopores facilitate microwave absorption, while multiple interfacial polarization induced between Fe3O4 nanocrystals and MCHS contributes to microwave attenuation. Combining these advantages, a maximum reflection loss value of −60.2 dB at 15.5 GHz and a broad effective bandwidth of 5.7 GHz can be achieved for the as-prepared sample at a thickness of 2.3 mm. Furthermore, the excellent microwave absorption properties with a ultrawide bandwidt...