Dielectric Attenuation Research Articles

Heterogeneous Junctions of Magnetic Cip and Binary Dielectric Carbon-Based Material Toward High-Efficiency Microwave Attenuation

Heterogeneous Junctions of Magnetic Cip and Binary Dielectric Carbon-Based Material Toward High-Efficiency Microwave Attenuation

Dispersion and Dielectric Attenuation Properties of a Wideband Double-Staggered Grating Waveguide for Subterahertz Sheet-Beam Traveling-Wave Amplifiers

The dispersion and dielectric attenuation characteristics of a double-staggered grating waveguide (DSGW) are two crucial features related to the output characteristics of a sheet-beam traveling-wave amplifier and have been previously studied by using theoretical analysis and simulations. In this work, these two characteristics are both experimentally studied. Two <inline-formula> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula>-band (220&#x2013;325 GHz) DSGW circuit prototypes with and without dielectric attenuators made of the BeO-TiO₂ composite ceramic were machined by using nanocomputer numerical control milling. Experimental studies of the dispersion property were performed successfully where the measurement results were in good agreement with those predicted by simulations, exhibiting a wide passband of 70 GHz (230&#x2013;300 GHz). The measured transmission coefficient has been decreased from &#x2212;5 to &#x2212;55 dB after the introduction of dielectric attenuators, experimentally verifying the feasibility of the adopted methodology. The effects of the variations of dispersion relation and transmission loss on the beam-wave interaction stability were also investigated.

Rational construction of heterogeneous interfaces for bimetallic MOFs-derived/rGO composites towards optimizing the electromagnetic wave absorption

Rational construction of heterogeneous interfaces is an effective strategy to explore high-performance electromagnetic waves (EMWs) absorption materials. Herein, we adopt a facile solvothermal and pyrolysis process to fabricate the multicomponent and multidimensional composites containing the bimetallic FeNi or FeCo@N-doped graphene layer core–shell heterojunctions/N-doped carbon nanorods/reduced graphene oxide (FeNi@NC/NCR/rGO or FeCo@NC/NCR/rGO) derived from NH2-bimetallic (FeNi or FeCo)-metal organic frameworks (MOFs)/GO precursors. The excellent EMWs absorption performances are effectively achieved and regulated via the content of rGO and the filler loading. Compared with the case without rGO, the FeNi@NC/NCR/rGO composite (25 wt% filler loading) displays a strong reflection loss (RL) of −52.61 dB at 14.44 GHz with a thin thickness of 1.65 mm, and effective absorption bandwidth (EAB) is 4.64 GHz. And the FeCo@NC/NCR/rGO composite (20 wt% filler loading) displays a strong RL of −59.42 dB at 17.8 GHz with a thinner thickness of 1.42 mm, and EAB is 5.28 GHz at 1.66 mm. Their excellent absorption properties result from the synergistic effect between the increased dielectric loss (interfacial polarization, dipole polarization and conduction loss), impedance matching and attenuation constant. These results provide a pathway to prepare the multicomponent and multidimensional composites with superior EMWs absorption.

Constructing yolk-shell Co@void@PPy nanocomposites with tunable dielectric properties toward efficient microwave absorption

The cobalt-based absorbing materials with core-shell structure have been widely investigated and developed in the microwave absorption territory, but their shortcomings such as relatively high density and weak dielectric loss limit their practical applications. In this work, taking the modification of microstructure and coating material as the cut-in point, we fabricated the Co@void@polypyrrole (PPy) nanocomposites (NCs) with yolk-shell structure and conductive polymer PPy coating via an integration of hydrogen plasma-metal reaction (HPMR), in-situ SiO2/PPy coating and SiO2-etching approaches. The Co@void@PPy with a PPy layer thickness of 7.6 nm exhibits the optimal microwave absorption performance. The minimum reflection loss (RL) value comes up to −28.4 dB at 1.4 mm, and the corresponding effective absorption bandwidth (EAB, RL≤ −10 dB) is 5.7 GHz. The optimal EAB is 7.2 GHz with a thickness of only 1.6 mm, where the RLmin is −23.4 dB. Such excellent dielectric loss property and attenuation ability is closely related to the PPy coating and the yolk-shell structure, which give rise to abundant interfaces between PPy and Co core and greatly promote multiple scattering and interface polarization. Accordingly, the yolk-shell structured Co@void@PPy NCs can be a competent candidate in the region of high-performance absorbers.

AN AUTOMATIC EXTRACTION METHOD FOR ANTARCTIC SUBGLACIAL LAKE BASED ON RADIO ECHO SOUNDING DATA

Abstract. Detection of subglacial lakes and interpretation their hydrological connectivity is of great importance to understanding the mass balance of Antarctic ice sheet. Over the past five decades, a large number of Radio Echo Sounding (RES) data has been collected in Antarctica. However, the identification of subglacial lakes based on RES data mainly relies on visual interpretation due to the lack of quantitative indicators for subglacial lakes distinguishing. To solve this problem, an automatic subglacial lakes detection method based on the reflective characteristics of B-scan echogram is proposed in this paper. Firstly, the echo strength of the original radar echogram is corrected for the dielectric attenuation and geometric spreading in the ice. Secondly, the original radar echogram is binarized to preserve the bright subglacial lake region, and the thickness of bright pixels is measured along the direction of A-scan. Thirdly, the thickness, the variance of the thickness in the neighbourhood and the corrected echo strength are used to obtain the response value for the subglacial lake. Finally, a threshold for the response value is determined to detect subglacial lakes. It is found that the proposed method can determine the location of the subglacial lake in Antarctica's Gamburtsev Province (AGAP) region with high accuracy.

Measurement of Electrical Properties of Superconducting YBCO Thin Films in the VHF Range.

A new measurement technique of electrical parameters of superconducting thin films at the Very High Frequency (VHF) range is described, based on resonators with microstrip (MS) structures. The design of an optimal resonator was achieved, based on a thorough theoretical analysis, which is required for derivation of the exact configuration of the MS. A theoretical model is presented, from which an expression for the attenuation of a MS line can be derived. Accordingly, simulations were performed, and an optimal resonator for the VHF range was designed and implemented. Production constraints of YBa2Cu3O7 (YBCO) limited the diameter of the sapphire substrate to 3″. Therefore, a meander configuration was formed to fit the long λ/4 MS line on the wafer. By measuring the complex input reflection coefficients of a λ/4 resonator, we extracted the quality factor, which is mainly affected by the dielectric and conductor attenuations. The experimental results are well fitted by the theoretical model. The dielectric attenuation was calculated using the quasi-static analysis of the MS line. An identical copper resonator was produced and measured to compare the properties of the YBCO resonator in reference to the copper one. A quality factor of ~ was calculated for the YBCO resonator, three orders of magnitude larger than that of the copper resonator. The attenuation per unit length of the YBCO layer was smaller by more than five orders of magnitude than that of the copper.

Architecting functionalized carbon microtube/carrollite nanocomposite demonstrating significant microwave characteristics

Biomass-derived materials have recently received considerable attention as lightweight, low-cost, and green microwave absorbers. On the other hand, sulfide nanostructures due to their narrow band gaps have demonstrated significant microwave characteristics. In this research, carbon microtubes were fabricated using a biowaste and then functionalized by a novel complementary solvothermal and sonochemistry method. The functionalized carbon microtubes (FCMT) were ornamented by CuCo2S4 nanoparticles as a novel spinel sulfide microwave absorber. The prepared structures illustrated narrow energy band gap and deposition of the sulfide structures augmented the polarizability, desirable for dielectric loss and microwave attenuation. Eventually, the architected structures were blended by polyacrylonitrile (PAN) to estimate their microwave absorbing and antibacterial characteristics. The antibacterial properties against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) were scrupulously assessed. Noteworthy, the maximum reflection loss (RL) of the CuCo2S4/PAN with a thickness of 1.75 mm was 61.88 dB at 11.60 GHz, while the architected FCMT/PAN composite gained a broadband efficient bandwidth as wide as 7.91 GHz (RL > 10 dB) and 3.25 GHz (RL > 20 dB) with a thickness of 2.00 mm. More significantly, FCMT/CuCo2S4/PAN demonstrated an efficient bandwidth of 2.04 GHz (RL > 20 dB) with only 1.75 mm in thickness. Interestingly, FCMT/CuCo2S4/PAN and CuCo2S4/PAN composites demonstrated an electromagnetic interference shielding efficiency of more than 90 and 97% at the entire x and ku-band frequencies, respectively.

Functionalized carbon microfibers (biomass-derived) ornamented by Bi2S3 nanoparticles: an investigation on their microwave, magnetic, and optical characteristics

The biomass-derived materials emerged as novel, low-cost, green, and light-weight microwave absorbers. On the other hand, the sulfide nanostructures due to narrow band gap demonstrated significant dielectric features. In this research, the pure carbon microfibers were prepared using Erodium cicutarium harvest and they were functionalized by a sonochemistry method. The treated microfibers were coated by Bi2S3 nanoparticles, obtained by a novel modified solvothermal route. X-ray powder diffraction, Fourier transform infrared, diffuse reflection spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy, and vector network analyzer analyses were applied to characterize the features of the prepared structures. The obtained results manifest that the anchoring nanoparticles onto the functionalized microfibers narrowed band gap to 1.35 eV and reinforced polarizability of the nanocomposite, desirable for dielectric attenuation. In this study, the interfacial interactions were modulated using polyacrylonitrile (PAN) and polyvinylidene fluoride. Interestingly, FCMF blended in PAN demonstrated an eye-catching efficient bandwidth as wide as 8.13 GHz (RL > 10 dB) with only 2.00 mm in thickness, whereas it illustrated an outstanding reflection loss of 81.96 at 11.48 GHz with a thickness of 2.50 mm. More significantly, FCMF/Bi2S3/PAN nanocomposite promoted the efficient bandwidth to 3.07 GHz (RL > 20 dB). Noteworthy, all of the samples illustrated total electromagnetic interference shielding effectiveness (SET) more than 15 dB entire the x and ku-band frequency.

Core-heteroshell FeNi3/NiFe2O4/NiSex via facile one-step selenylation for enhanced electromagnetic performance

A simple and facile method has been provided to develop novel core-heteroshell electromagnetic (EM) wave absorbers via selenylation of FeNi3 nanoparticles. Core-heteroshell composites containing multiple phases including the FeNi3, NiFe2O4 and NiSex can been obtained with increased surface gradient of Se with the growth mechanisms revealed. Not only synergistic effects of magnetic and dielectric attenuation have been introduced, the multiple components also give rise to tunable impedance and enhanced interfacial polarization for improved EM wave absorbing performance. Such effective one-step route may be extendable to achieve core-heteroshell structure with multiple components for applications in other fields including energy, catalysis and sensing.

Double ligand MOF-derived pomegranate-like Ni@C microspheres as high-performance microwave absorber

Metal-organic framework (MOF)-derived functional composites have received extensive attention, especially in microwave absorption (MA) materials. However, the delicate design of the spatial structure, designed components, and heterojunction interfaces of MOF derivatives remains a great challenge in the MA application. Herein, a simple double organic ligand strategy and controllable pyrolysis treatment were used to regulate the Ni-MOF derived pomegranate-like Ni@C Microspheres. Their morphology and crystallization can be accurately controlled by a simple hydrothermal method. After pyrolysis, hierarchical magnetic-carbon Ni@C microspheres were obtained which consists of many nickel-carbon core–shell units within the carbon layer. MOF-derived Ni@C microspheres possessed plentiful interfaces, unique three-dimensional conduction network, and magnetic-dielectric synergy system. The pomegranate-like Ni@C microspheres shown excellent microwave absorption performance of a maximum reflection loss (−46.9 dB at 3.5 mm), which can be attributed to the dielectric attenuation, magnetic loss, and matched impedance. Precision regulation of MOF precursors and MOF derivatives provide a novel platform of magnetic-dielectric Ni@C composites that offers excellent MA applications.

On the Effect of Field Spatial Separation on Slow Wave Propagation

This article introduces a description of the slow wave effect based on the analysis of spatial field separation. Considering an ideal parallel-plate framework, approximate analytical expressions are derived for the slow wave factor (SWF), as well as dielectric attenuation. In particular, it is shown that the SWF can be related to the spatial distribution of both electric and magnetic fields. It is also demonstrated that the dielectric attenuation increases by the same factor as the velocity reduces. The derived principles are applied to a study case consisting of a parallel-plate waveguide partially filled with vertically grown metallic nanowires.

Graphene quantum dots interfacial-decorated hierarchical Ni/PS core/shell nanocapsules for tunable microwave absorption

Graphene quantum dots interfacial-decorated hierarchical Ni/PS core/shell nanocapsules were successfully synthesized by three-step liquid chemical method. The morphologies and electromagnetic properties were carefully studied in order to investigate the dielectric shells modulated tunable microwave absorption in 1–18 GHz (L–Ku), based on the anisotropic nanoflakes assembled magnetic core. With different GQDs/PS ratio in the shells, the dielectric attenuation can be flexibly tuned by the interfacial polarizations deriving from the density modulation of interfacial-decorated polar GQDs in the nonpolar insulative PS matrix. The calculated impedance matching maps, microwave absorption efficiencies (RE), reflection loss (RL) and simulations illustrated the coincident effect with an obvious rise-fall performance in X–Ku band. The tunable RL value in fixed frequency of X band and shifting absorption peaks from Ku to X band were achieved in different absorber thickness with the minimum RL below −42.5 dB and the effective absorption bandwidth (RL < −10 dB) above 2.04 GHz.

Influence of Nano Particle Size on Attenuation and Dielectric Properties of Plantain Husk Powder Using Microwave Techniques at X-Band Frequency

Ferrite are conventional materials used for microwave absorption, however, they are expensive, constitute health hazard and pollutes the environment. For these reasons, there is need to explore safe and environmental friendly materials that can serve as radiation absorbers and be used in fabricating microwave devices. In the light of the above, this work was geared towards exploring the use of Unripe Plantain Husk (UPH) waste material for microwave absorber applications. The usability was determined by investigating the dielectric properties and attenuation of the UPH powder with respect to particle size and frequency of operation. The nano particle of the UPH was prepared aseptically by washing in water and acetone, sliced, sundried and grinded. The grinded UPH powder was then subjected to high energy milling using a SPEX 8000D shaker for 4 hours, 8 hours, 10 hours and 12 hours. The milled powder was then prepared into pellets by suppressing with hydraulic press and mold which were then used for characterization. Results from investigation and analysis showed that the milled powder was in nano dimension using transmission electron microscope (TEM). The UPH powder sizes were in the range of 63.35 nm, 52.05 nm, 42.86 nm and 21.43 nm for the 4, 8, 10 and 12 hours milling, respectively. The dielectric constants for the as produced, 4, 8, 10 and 12 hours milled powder were 2.96, 4.97, 5.66, 6.97 and 10.36, respectively. The highest magnitude for attenuation was calculated for the 12 hours milled powder with a value of 14.92 dB and the least attenuation was calculated for the as produced powder with a value of 6.72 dB. Based on the results obtained it is concluded that nano particles of UPH powder is good for microwave attenuation and is a potential for fabricating electronic components.

The conductivity, dielectric and electromagnetic attenuation properties of MgZr4P6O24 ceramics at elevated temperature

The work was to develop novel high temperature microwave absorbing material based MgZr4(PO4)6 (MZP) ceramic. The results show that thermal expansion process at higher temperature expand along c-axis while shrink along the a-axis. The conductivity of MZP ceramic was increased by 1000 orders due to the increase in magnesium ion mobility. In addition, the results indicates that the dielectric properties were dependent on temperature at all measured frequencies. The real and imaginary parts of dielectric constant increased from 4.0–5.2 and 0.024 to 0.4, respectively. The reflection loss varied with the change in thickness and the minimum reflection loss value was -26.66 dB at 800℃, suggesting that MZP ceramic was a promising novel high temperature microwave absorbing material.

Study and Research the Tensor of Dielectric Permittivity and Attenuation Transient in the Bended on Spiral Optical Fiber

This paper investigates the assumption of spiralshaped index leads to an optimal result for the optical fiber modes. It also shows how to decrease the effect of optical fibers parameters such as attenuation and dispersion on the quality of transmitted signals, and to improve it into an acceptable form. The dielectric permeability tensor εij related to the curvature and torsion parameters ( χ , υ ) in the coordinates system ( r, φ ) was analyzed. The dependence of εij tensor on the bent on spiral optical fiber parameters was mathematically calculated. Also to study the exchange of power between the waves HEo 11 and HEe 11 .The Transient attenuation dependence on spiral parameters of optical fiber with a length of (one kilometer) as a case study will be studied also.

Facile synthesis of the one-dimensional flower-like yolk-shell Fe3O4@SiO2@NiO nanochains composites for high-performance microwave absorption

One-dimensional (1D) microwave absorbers have attracted wide attention in the field of microwave absorption (MA) because of the significant anisotropy and great dielectric attenuation of 1D architecture. In this work, the novel 1D flower-like yolk-shell Fe3O4@SiO2@NiO (FSN) nanochains have been fabricated through a modified Stöber and a simple hydrothermal method. The unique 1D flower-like yolk-shell architectures have large surfaces, multiple interfaces and void spaces. Benefitting from these advantages, the FSN nanochains showed excellent MA properties. Compared with the sample loaded with 10 wt% 1D flower-like yolk-shell FSN nanochains, the sample loaded with 30 wt% showed strong MA performance with a minimum reflection loss (RL) value of −54.28 dB (12.9 GHz) and an effective absorption bandwidth of 4.0 GHz (11.05–15.05 GHz) at the thickness of 2.54 mm. The 1D flower-like yolk-shell FSN nanochains with strong absorption, broad absorption bandwidth and thin layers, provided a new method for fabricating 1D MA materials and will become the promising candidates in the practical MA fields.

Ultrathin MoS2 Nanosheets Encapsulated in Hollow Carbon Spheres: A Case of a Dielectric Absorber with Optimized Impedance for Efficient Microwave Absorption.

A dielectric loss-type electromagnetic wave (EMW) absorber, especially over a broad frequency range, is important yet challenging. As the most typical dielectric attenuation absorber, carbon-based nanostructures were highly pursued and studied. However, their poor impedance-matching issues still exist. Here, to further optimize dielectric properties and enhance reflection loss, ultrathin MoS2 nanosheets encapsulated in hollow carbon spheres (MoS2@HCS) were prepared via a facile template method. The diameter and shell thickness of the as-prepared HCSs were ∼250 and ∼20 nm. The encapsulated MoS2 nanosheets presented high dispersity and crystallinity. Compared to a pure HCS or MoS2 absorber, MoS2@HCS exhibited an optimized impedance characteristic, which can be attributed to the synergistic effects between HCSs (ensuring rapid electron transmission and compensating the low conductivity of MoS2) and MoS2 nanosheets (exposing sufficient numbers of active sites for polarizations and multi-reflection). Consequently, the MoS2@HCS was endowed with -65 dB EMW attenuation ability under 2 mm and the effective attenuation bandwidth under -20 dB was ∼3.3 GHz over the K-band under 1.2 mm and ∼3.4 GHz over the Ka-band under merely 0.7 mm. These results suggested that the MoS2@HCS is a promising dielectric absorber for practical applications. Meanwhile, this work introduces a facile and versatile strategy, which could in principle be extended to other transition metal sulfide@HCS for designing novel EMW absorbers.

Bimetal oxide-derived flower-like heterogeneous Co/MnO@C composites with synergistic magnetic–dielectric attenuation for electromagnetic wave absorption

Flower-like heterogeneous Co/MnO@C composites were facilely synthesized for highly efficient electromagnetic wave absorption. The effect of Co contents on the electromagnetic performance and the absorption mechanism was thoroughly investigated.

Evaluation of the dielectric rod attenuation using the modified parallel strips that provide a relatively reasonable field environment

A thin film is often coated on the dielectric rods used in traveling wave tubes to provide microwave attenuation. The quality of the thin film will affect the performance of the traveling wave tube. To evaluate the quality of the thin-film by measuring the attenuation performance of the dielectric rod, modified parallel strips with a sample hole are designed to provide a relatively reasonable field working environment for the attenuation evaluation. After analyzing the field distribution of the parallel strips, a sample hole is designed on the side of parallel strips, which is tangent with the outer edge of the strip. An arcuate taper is introduced into the parallel strips to reduce the impedance mismatching. Finally, two unqualified and qualified dielectric rods are measured using the modified parallel strips at frequencies 12 GHz and 18 GHz. The measured results indicate that it is feasible to evaluate whether the thin-film coated on the dielectric rod is qualified or not.

MOFs-derived multi-chamber carbon microspheres with enhanced microwave absorption

Microstructure is playing a more and more important role in upgrading the performance of microwave absorption materials (MAMs) nowadays. Herein, we demonstrate the successful synthesis of multi-chamber carbon microspheres (MCCMs) with abundant interior cavities. The reflection loss (RL) characteristics of MCCMs and the effect of microstructure on electromagnetic properties have been discussed thoroughly. It is found that compared with the solid carbon microspheres, MCCMs possess reinforced dielectric loss and attenuation ability towards incident electromagnetic waves, and in contrast to hollow carbon microspheres, the unique multi-chamber architecture endows MCCMs with better impedance matching characteristic. More importantly, it is proved that the consolidated multiple reflection effect originated from multi-chamber microstructure can contribute to reinforced attenuation ability and optimized impedance matching characteristic simultaneously. In consequence, MCCMs exhibit enhanced microwave absorption properties, including the minimum RL intensity of −28.5 dB at 10.2 GHz with the thickness of 2.0 mm and the widest effective absorption bandwidth of 5.7 GHz with the thickness of 1.8 mm. It is believed that these results will provide some practical significance for high-performance MAMs based on carbon-related materials with profitable microstructure.