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In this paper, a patch array antenna with wideband circular polarization and high gain is proposed by utilizing a hybrid metasurface (MS). A corner-cut slotted patch antenna was chosen as the source due to the possible generation of CP mode. The hybrid MS (HMS), consisting of a receiver MS (RMS) arranged in a 2 × 2 array of squared patches and a linear-to-circular polarization conversion (LCPC) MS surrounding it was then utilized as the superstrate driven by the source. The LCPC MS cell is a squared-corner-cut patch with a 45° oblique slot etched, which has the capability for wideband LCPC. The LCPC unit cell possesses wideband PC capabilities, as demonstrated by the surface current analysis and S-parameter simulations conducted using a Floquet–port setup. The LP EM wave radiated by the source antenna was initially received by the RMS, then converted to a CP wave as it passed through the LCPC MS, and ultimately propagated into space. To further enhance the LCPC properties, an improved HMS (IHMS) was then proposed with four cells cut at the corners, based on the original HMS design. To verify this design, both CMA and E-field were utilized to analyze the three MSs, indicating that the IHMS possessed a wideband LCPC capability compared to the other two MSs. The proposed antenna was then arranged in a 2 × 2 array with sequential rotation to further enhance its properties. As demonstrated by the measurements, the array antenna achieved an S11 bandwidth of 60.5%, a 3 dB AR bandwidth of 2.85 GHz, and a peak gain of 15.1 dBic, all while maintaining a low profile of only 0.09λ0. [ABSTRACT FROM AUTHOR]

The mechanism of coating interface bulge on the TGO growth behavior was studied by analyzing the rule of TGO growth and the interface stress at the top coat/bond coat interface. The results show that the growth rate of TGO in the convex region of the top coat/bond coat interface is higher than that in the other regions. According to the stress analysis of ANSYS, the interface stress increases (from 185 MPa to 406 MPa) with the increase of roughness (from 10 μm to 20 μm). Additionally, the interfacial stress also increases (from 142 MPa to 574 MPa) with the thickness of TGO layer increasing (from 1.6 μm to 9.3 μm). What’s more, during high temperature oxidation, the convex region of the top coat/bond coat interface is mainly characterized by tensile stress and the depressed region is compressive stress.The tensile stress can promote the rapid growth of TGO layer, while the compressive stress exhibits the inhibition on the growth rate of TGO. In summary, reducing the roughness of bond coat can reduce the interface stress and slow the growth rate of TGO, which ensures the effective bonding strength of the coating. Thus, the stability of the TBCs at high temperature can be improved.

In this study, a series of nano-Al2O3 reinforced polyimide (PI) composites were fabricated using the hot compression method. A silane coupling agent was used to modify the surface of nano-Al2O3 powder to enhance the PI/Al2O3 interface compatibility. The effects of Al2O3 contents on the microstructures, thermal behavior and mechanical properties of PI/Al2O3 composites were investigated. The results suggested that chemical reactions occurred during in situ modification. The nano-Al2O3 was cross-linked to the PI matrix, which reduced the mobility of PI chains and improved the elastic modulus of the composites. When the Al2O3 content was 30 wt.%, the compressive strength of composites reached the maximum value of 313 MPa and increased by 26.5% than that of the PI matrix. [ABSTRACT FROM AUTHOR]

Ni-graphite abradable seal coatings were deposited by conventional atmospheric plasma spraying system (APS) and high efficiency supersonic atmospheric plasma spraying system (SAPS) respectively. The influence of the size of lubrication phase on mechanical properties, corrosion resistance and erosion resistance of the Ni-graphite coatings was investigated. The results indicate that the graphite phase in the SAPS coating has a smaller size than the APS coating. The bonding strength (21.0 ± 1.4) MPa and surface hardness (92 ± 1) HR15Y of SAPS coating are 29.6 % and 23.5 % higher than those of APS coating respectively. The relative erosion rates of APS coating at 30° and 90° angle of attack are 7 % and 13% higher than those of SAPS coating respectively, indicating that SAPS coating has a better erosion resistance than APS coating. Both APS coating and SAPS coating exhibit an obvious electrochemical corrosion in acetic acid environment at 250 ℃．However, the corrosion resistance of SAPS coating is better than that of APS coating.

Fe3Al powders with different order degrees were fabricated by a high-energy ball milling process and ordering transformation process. The order degree of the Fe3Al powders with plate structures can be tuned by the calcination temperature. It is found that the order degree of the obtained Fe3Al powders affects the magnetic properties. When the sample is calcined at 500 °C, the obtained Fe3Al contains the most DO3 superlattice structure with an order degree of 40.2%, thus exhibiting the best magnetic properties. Moreover, the best impedance matching ratio and attenuation constant are also achieved, leading to the best electromagnetic wave absorption performance. When the thickness is 1.35 mm, the effective absorption bandwidth with RL ≤ − 10 dB is as wide as 7.2 GHz. [ABSTRACT FROM AUTHOR]

B4C@CNT nanowires were synthesized on the carbon fiber fabric (CFs) surface to form CFs-B4C-CNT hybrid materials via thermal growth method for improving the microwave absorption performance. The microwave absorption property of the CFs-B4C-CNT hybrid materials were studied in the frequency range of 8.2–12.4 GHz. The results exhibited that B4C@CNT nanowires were decorated on CFs surface successfully. The minimum reflection loss (RLmin) value of 2 wt% CFs-B4C-CNT hybrid material was − 19.7 dB at 8.2 GHz with a layer thickness of 2.9 mm. And the maximum effective absorption bandwidth (RL < − 10 dB) was obtained over the frequency range of 8.4–12.1 GHz with a layer thickness of 2.5 mm. Furthermore, the microwave absorption mechanism of the CFs-B4C-CNT hybrid materials were discussed. This work demonstrated that CFs-B4C-CNT hybrid materials possessed high potential as microwave absorbers with good microwave absorption performance, which provided a new idea for the development of nano-hybrid materials to improve electromagnetic microwave absorption performance. [ABSTRACT FROM AUTHOR]

CoSe2 nanostructure was regarded as an excellent electrocatalyst for hydrogen evolution reaction by water splitting owing to its particular electronic configuration. Herein, Ni atoms doped in CoSe2 nanowire arrays was fabricated on carbon fiber paper substrate by two-step hydrothermal routes and subsequent heat treatment. Both common transient analysis, steady-state analysis, and TOF and EIS measurements confirmed that Ni doping effect could significantly enhance the HER performance of CoSe2 in 0.5 M H2SO4 electrolyte. Density functional theory calculation showed that Ni doping effect in CoSe2 lattice can decrease the electronic density of Se p-orbital around the Fermi level. The ΔGH* in Se site of Ni-doped CoSe2 was decreased to 0.196 eV from 0.356 eV (pure CoSe2) because the empty orbital of Se sites could strengthen the adsorption of H atoms. Finally, Ni doping effect provides an effective method for improved HER activity of CoSe2 electrocatalyst. [ABSTRACT FROM AUTHOR]