scholarly journals Microwave induced in-situ formation of SiC nanowires on SiCNO ceramic aerogels with excellent electromagnetic wave absorption performance

2021 ◽  
Author(s):  
Keke Yuan ◽  
Daoyang Han ◽  
Junfang Liang ◽  
Wanyu Zhao ◽  
Mingliang Li ◽  
...  
Keyword(s):  
Phase Composition ◽  
High Speed ◽  
Impedance Matching ◽  
Interfacial Polarization ◽  
Microwave Treatment ◽  
Treatment Temperature ◽  
Effective Bandwidth ◽  
Composite Aerogels ◽  
Environmental Robustness

AbstractElectromagnetic absorption (EMA) materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles. However, meeting these two requirements is always a great challenge, which excluded the most attractive lightweight candidates, such as carbon-based materials. In this study, SiCnw-reinforced SiCNO (SiCnw/SiCNO) composite aerogels were fabricated through the in-situ growth of SiCnw in polymer-derived SiCNO ceramic aerogels by using catalyst-assisted microwave heating at ultra-low temperature and in short time. The phase composition, microstructure, and EMA property of the SiCnw/SiCNO composite aerogels were systematically investigated. The results indicated that the morphology and phase composition of SiCnw/SiCNO composite aerogels can be regulated easily by varying the microwave treatment temperature. The composite aerogels show excellent EMA property with minimum reflection loss of −23.9 [email protected] GHz, −26.5 [email protected] GHz, and −20.4 [email protected] GHz and the corresponding effective bandwidth of 5.2 GHz, 3.2 GHz, and 4.8 GHz at 2.0 mm thickness for microwave treatment at 600 °C, 800 °C, and 1000 °C, respectively, which is much better than that of SiCN ceramic aerogels. The superior EMA performance is mainly attributed to the improved impedance matching, multi-reflection, multi-interfacial polarization, and micro current caused by migration of hopping electrons.

scholarly journals NiS2@rGO Nanosheet Wrapped with PPy Aerogel: A Sandwich-Like Structured Composite for Excellent Microwave Absorption

Nanomaterials ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 833 ◽  
Author(s):  
Zhi Zhang ◽  
Qi Lv ◽  
Yiwang Chen ◽  
Haitao Yu ◽  
Hui Liu ◽  
...  
Keyword(s):  
Electromagnetic Wave ◽  
In Situ Polymerization ◽  
Impedance Matching ◽  
Interfacial Polarization ◽  
The Novel ◽  
Step Method ◽  
Absorption Bands ◽  
Absorption Performance ◽  
Electromagnetic Pollution

To reduce electromagnetic pollution as well as increase the accuracy of high-precision electronic equipment, more attention has been paid to new electromagnetic wave (EMW) absorbing materials, which have the advantages of strong absorption, wide absorption bands, and a narrow thickness. In this study, a novel ternary type of the NiS2@rGO/polypyrrole (PPy) sandwich-like structured composites was synthesized via a facile two-step method, in which the hydrothermal method was used to prepare NiS2@rGO binary composites and then the in situ polymerization method was used to synthesize the PPy, which acted as the outer layer of the sandwich-like structure. The morphologies and electromagnetic absorption performance of the NiS2@rGO/PPy were measured and investigated. A sample with 6 wt% NiS2@rGO/PPy loading paraffin-composite obtained an outstanding reflection loss (RL) of −58.7 dB at 16.44 GHz under a thickness of 2.03 mm. Simultaneously, the effective electromagnetic wave absorption bandwidth for RL < −10 dB, which covered 7.04 to 18.00 GHz (10.96 GHz), was achieved by changing the thickness of the absorber from 2.0 to 3.5 mm. The results not only suggest that the NiS2@rGO/PPy composite has excellent performance in the field of EMW absorption but also prove that the novel sandwich-like structure can contribute to appropriate impedance matching through multiple relaxation and interfacial polarization processes.

scholarly journals Polypyrrole Chains Decorated on CoS Spheres: A Core-Shell Like Heterostructure for High-Performance Microwave Absorption

Nanomaterials ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 166 ◽  
Author(s):  
Hui Liu ◽  
Guangzhen Cui ◽  
Ling Li ◽  
Zhi Zhang ◽  
Xuliang Lv ◽  
...  
Keyword(s):  
Microwave Absorption ◽  
High Performance ◽  
In Situ Polymerization ◽  
Impedance Matching ◽  
Synthesis Method ◽  
Interfacial Polarization ◽  
Cobalt Sulfide ◽  
Core Shell ◽  
Loss Mechanism

Cobalt sulfide composites have exhibited great potential in terms of microwave absorption, owing to their low price, relatively high capacitance, and excellent electrocatalytic activity. Thus, a novel core-shell like structure comprising cobalt sulfide@polypyrrole (CoS@PPy) composite was synthesized by a facile solvothermal synthesis method and in situ polymerization. When coated by the heterostructure polypyrrole aerogel, CoS@PPy composite exhibited excellent microwave absorption properties with an optimal reflection loss (RL) of −41.8 dB at 6.96 GHz. Furthermore, the absorption bandwidth (RL < −10 dB) of 5.4 GHz could be reached at a coating thickness of 2.05 mm, probably attributing to the synergistic effect of good impedance matching, interfacial polarization, dipole polarization, and conductivity loss. Moreover, this work proposed a loss mechanism mode which probably occurred in the CoS@PPy composites. It was demonstrated that the CoS@PPy composite is a promising material in the field of electromagnetic wave absorption.

scholarly journals Lotus Leaf-Derived Gradient Hierarchical Porous C/MoS2 Morphology Genetic Composites with Wideband and Tunable Electromagnetic Absorption Performance

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Fei Pan ◽  
Zhicheng Liu ◽  
Baiwen Deng ◽  
Yanyan Dong ◽  
Xiaojie Zhu ◽  
...  
Keyword(s):  
Reflection Loss ◽  
Impedance Matching ◽  
Surface States ◽  
Effective Bandwidth ◽  
Material System ◽  
Lotus Leaf ◽  
Electromagnetic Absorption ◽  
Hierarchical Porous ◽  
Absorption Performance

AbstractInspired by the nature, lotus leaf-derived gradient hierarchical porous C/MoS2 morphology genetic composites (GHPCM) were successfully fabricated through an in situ strategy. The biological microstructure of lotus leaf was well preserved after treatment. Different pores with gradient pore sizes ranging from 300 to 5 μm were hierarchically distributed in the composites. In addition, the surface states of lotus leaf resulted in the Janus-like morphologies of MoS2. The GHPCM exhibit excellent electromagnetic wave absorption performance, with the minimum reflection loss of − 50.1 dB at a thickness of 2.4 mm and the maximum effective bandwidth of 6.0 GHz at a thickness of 2.2 mm. The outstanding performance could be attributed to the synergy of conductive loss, polarization loss, and impedance matching. In particularly, we provided a brand-new dielectric sum-quotient model to analyze the electromagnetic performance of the non-magnetic material system. It suggests that the specific sum and quotient of permittivity are the key to keep reflection loss below − 10 dB within a certain frequency range. Furthermore, based on the concept of material genetic engineering, the dielectric constant could be taken into account to seek for suitable materials with designable electromagnetic absorption performance.

scholarly journals NiS2@MoS2 Nanospheres Anchored on Reduced Graphene Oxide: A Novel Ternary Heterostructure with Enhanced Electromagnetic Absorption Property

Nanomaterials ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 292 ◽  
Author(s):  
Zhi Zhang ◽  
Xuliang Lv ◽  
Yiwang Chen ◽  
Pin Zhang ◽  
Mingxu Sui ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Reduced Graphene Oxide ◽  
Impedance Matching ◽  
Interfacial Polarization ◽  
Effective Bandwidth ◽  
Military Equipment ◽  
Electromagnetic Absorption ◽  
Reduced Graphene ◽  
Absorption Performance ◽  
Minimum Reflection Loss

For the purposes of strength, military equipment camouflage, and protecting the health of organisms, electromagnetic wave absorbing materials have received a lot of attention and are widely studied. In addition to having a strong absorption intensity and a wide effective absorption bandwidth, materials that are lightweight, thermally stable, and antioxidative are also highly desirable. In this study, we fabricated core–shell structured NiS2@MoS2 nanospheres anchored on reduced graphene oxide (rGO) nanosheets (NiS2@MoS2/rGO) by a simple two-step hydrothermal method. The combination ratio was adjusted to achieve proper impedance matching. The electromagnetic parameters and the absorption performance were investigated in detail. A composite loaded with 30 wt.% of the sample achieved a minimum reflection loss (RL) value of −29.75 dB and the effective bandwidth (RL value of less than −10 dB) ranged from 4.95 GHz to 18.00 GHz (13.05 GHz), with a thickness ranging from 1.5 mm to 4.0 mm. This study proved that the generated significant interfacial polarization and synergetic interaction between components can result in NiS2@MoS2/rGO composites with enhanced electromagnetic absorption performance.

scholarly journals In situ impedance matching in Nb/Nb2O5/PtIr memristive nanojunctions for ultra-fast neuromorphic operation

Nanoscale ◽  
2018 ◽  
Vol 10 (41) ◽  
pp. 19290-19296 ◽  
Author(s):  
Dániel Molnár ◽  
Tímea Nóra Török ◽  
Botond Sánta ◽  
Agnes Gubicza ◽  
András Magyarkuti ◽  
...  
Keyword(s):  
High Speed ◽  
Impedance Matching ◽  
High Bias

We demonstrate Nb2O5 memristive devices with tuneable low-bias resistances and optimized high-bias impedance for high speed neuromorphic operation.

An atomic-resolution microscope study of Al contracts on GaAs

1986 ◽  
Vol 44 ◽  
pp. 726-727
Author(s):  
Z. Liliental-Weber ◽  
C. Nelson ◽  
R. Ludeke ◽  
R. Gronsky ◽  
J. Washburn
Keyword(s):  
High Speed ◽  
Schottky Contacts ◽  
Detailed Knowledge ◽  
The Past ◽  
Semiconductor Interfaces ◽  
Deposited Metal ◽  
Microwave Applications ◽  
Free Interfaces ◽  
Potential Use

The properties of metal/semiconductor interfaces have received considerable attention over the past few years, and the Al/GaAs system is of special interest because of its potential use in high-speed logic integrated optics, and microwave applications. For such materials a detailed knowledge of the geometric and electronic structure of the interface is fundamental to an understanding of the electrical properties of the contact. It is well known that the properties of Schottky contacts are established within a few atomic layers of the deposited metal. Therefore surface contamination can play a significant role. A method for fabricating contamination-free interfaces is absolutely necessary for reproducible properties, and molecularbeam epitaxy (MBE) offers such advantages for in-situ metal deposition under UHV conditions

Effects of Heat Treatment Temperature on Photocatalytic Activity of TiO2/SiO2 Composite Aerogels

2013 ◽  
Vol 27 (10) ◽  
pp. 1079-1083
Author(s):  
Zhao-Hui LIU ◽  
Gen-Liang HOU ◽  
Xun-Jia SU ◽  
Feng GUO ◽  
Zhou XIAO ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Photocatalytic Activity ◽  
Heat Treatment Temperature ◽  
Treatment Temperature ◽  
Composite Aerogels

scholarly journals Spatially Resolved Experimental Modal Analysis on High-Speed Composite Rotors Using a Non-Contact, Non-Rotating Sensor

Sensors ◽  
2021 ◽  
Vol 21 (14) ◽  
pp. 4705
Author(s):  
Julian Lich ◽  
Tino Wollmann ◽  
Angelos Filippatos ◽  
Maik Gude ◽  
Juergen Czarske ◽  
...  
Keyword(s):  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Fiber Reinforced ◽  
Structural Dynamic ◽  
Spatially Resolved ◽  
Glass Fiber Reinforced ◽  
Vibration Responses ◽  
And Performance

Due to their lightweight properties, fiber-reinforced composites are well suited for large and fast rotating structures, such as fan blades in turbomachines. To investigate rotor safety and performance, in situ measurements of the structural dynamic behaviour must be performed during rotating conditions. An approach to measuring spatially resolved vibration responses of a rotating structure with a non-contact, non-rotating sensor is investigated here. The resulting spectra can be assigned to specific locations on the structure and have similar properties to the spectra measured with co-rotating sensors, such as strain gauges. The sampling frequency is increased by performing consecutive measurements with a constant excitation function and varying time delays. The method allows for a paradigm shift to unambiguous identification of natural frequencies and mode shapes with arbitrary rotor shapes and excitation functions without the need for co-rotating sensors. Deflection measurements on a glass fiber-reinforced polymer disk were performed with a diffraction grating-based sensor system at 40 measurement points with an uncertainty below 15 μrad and a commercial triangulation sensor at 200 measurement points at surface speeds up to 300 m/s. A rotation-induced increase of two natural frequencies was measured, and their mode shapes were derived at the corresponding rotational speeds. A strain gauge was used for validation.

Enhanced Grain Refinement of W18Cr4V High‐Speed Steel using in situ TiN‐Nb‐Cr@Graphene/Fe Nanocomposite Inoculant

2021 ◽  
Author(s):  
Lina Bai ◽  
Chunxiang Cui ◽  
Jianjun Zhang ◽  
Lichen Zhao ◽  
Guixing Zheng ◽  
...  
Keyword(s):  
Grain Refinement ◽  
High Speed ◽  
High Speed Steel

scholarly journals Influence of Hydrogeochemistry on Tunnel Drainage in Evaporitic Formations: El Regajal Tunnel Case Study (Aranjuez, Spain)

2021 ◽  
Vol 13 (3) ◽  
pp. 1505
Author(s):  
Ignacio Menéndez Pidal ◽  
Jose Antonio Mancebo Piqueras ◽  
Eugenio Sanz Pérez ◽  
Clemente Sáenz Sanz
Keyword(s):  
High Speed ◽  
Civil Engineering ◽  
Saturation Index ◽  
The Subject ◽  
Under Construction ◽  
Underground Flow ◽  
Very High ◽  
Over Time

Many of the large number of underground works constructed or under construction in recent years are in unfavorable terrains facing unusual situations and construction conditions. This is the case of the subject under study in this paper: a tunnel excavated in evaporitic rocks that experienced significant karstification problems very quickly over time. As a result of this situation, the causes that may underlie this rapid karstification are investigated and a novel methodology is presented in civil engineering where the use of saturation indices for the different mineral specimens present has been crucial. The drainage of the rock massif of El Regajal (Madrid-Toledo, Spain, in the Madrid-Valencia high-speed train line) was studied and permitted the in-situ study of the hydrogeochemical evolution of water flow in the Miocene evaporitic materials of the Tajo Basin as a full-scale testing laboratory, that are conforms as a whole, a single aquifer. The work provides a novel methodology based on the calculation of activities through the hydrogeochemical study of water samples in different piezometers, estimating the saturation index of different saline materials and the dissolution capacity of the brine, which is surprisingly very high despite the high electrical conductivity. The circulating brine appears unsaturated with respect to thenardite, mirabilite, epsomite, glauberite, and halite. The alteration of the underground flow and the consequent renewal of the water of the aquifer by the infiltration water of rain and irrigation is the cause of the hydrogeochemical imbalance and the modification of the characteristics of the massif. These modifications include very important loss of material by dissolution, altering the resistance of the terrain and the increase of the porosity. Simultaneously, different expansive and recrystallization processes that decrease the porosity of the massif were identified in the present work. The hydrogeochemical study allows the evolution of these phenomena to be followed over time, and this, in turn, may facilitate the implementation of preventive works in civil engineering.

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