A novel dual-band miniaturized frequency selective surface adopting fractal elements is proposed. The proposed structure is composed of interconnected four SZ curves of second generation. Such a design is to provide two pass-bands with stable performance, the first band resonates at S-band with a center frequency of 3.02 GHz and the second band is at C-band centered at 7.22 GHz. In addition, the compact structure employing the space filling curve can further reduce the size of the FSS. The dual-band FSS achieves better miniaturization compared with other single layer FSS in previous literature, the dimension of the unit cell is only 0.072λ × 0.072λ, where λ represents the free space wavelength at first resonant frequency. Furthermore, the proposed FSS exhibits great resonance stability for different polarizations and incidence angles. Both the simulation and measurement verify the stable performance of the FSS.
Science and technology management studies are the frontiers subject between science and technology studies(science studies,technology studies) and management science.Rising of science and technology management studies was dating from the research of science and technology management in 1980s.By keywords frequency statistics of journal articles and fundamental content generalization of representative works,this paper makes a multi-angle analysis of the research object of science and technology management studies;it hackles many research topics clue.Science and technology management studies have become a disciplinary group which includes numerous sub-disciplinary.It has still made an obvious differentiation trend currently.Some research topics will be possible develop to the new sub-disciplinary based on the enough accumulation of achievements.
An equivalent circuit model-based method for synthesizing wideband band-stop frequency selective surface (FSS) has been proposed in this letter. Compared with previous works, the proposed method solves the problem of acquiring FSS structural parameters from the desired frequency response. In the proposed method, equivalent circuit parameters are first derived from the desired frequency response via the transmission line model, and then FSS structural parameters are determined from the equivalent circuit parameters with curve fitting technique. For verification, a dual-layer band-stop FSS composed of square-loop arrays separated by dielectric substrate has been designed, fabricated, and measured. Simulation results show that the designed FSS can provide a stop band operating at 13.5 GHz with a fractional bandwidth of 88.9%. Good agreements between the simulated and the measured results can be observed.
Pedestrians are the most vulnerable road users. Some studies have verified that the visibility difference between pedestrians and drivers can lead to pedestrian–vehicle crashes at night when pedestrians cross the road. This paper considered the influences of the ratio of driver and pedestrian visibility, the vehicle original speed, the pavement friction coefficient and the vehicle mass on crashes when the pedestrians go through the road during night, and analysed the vehicle movement process and the collision speed and crash severity under different conditions. Besides, the special conditions considering driver characteristics, roadway features and vehicle features were analysed, respectively. From the results, it is observed that the collision speed and crash severity is higher when the ratio of driver and pedestrian visibility is smaller, the original speed is higher and pavement friction coefficient is higher. Moreover, from the results, the least distance between vehicles is also obtained. This study will make some contribution to the traffic safety improvement.
Nickel-based superalloys are indispensable in aerospace engines due to their exceptional high-temperature strength, oxidation resistance, and corrosion resistance, making them critical for joining processes such as inertia friction welding (IFW), which is favored for its efficiency and superior joint quality. In this study, IFW was used to join FGH101 powder superalloy with IN718 deformed superalloy, resulting in significant plastic deformation that formed symmetrical ear-shaped flash on the IN718 side and minor upsetting on the FGH101 side, with a wavy interface due to heat dissipation. Microhardness analysis revealed higher hardness at the weld interface, followed by a sharp decline near the Heat Affected Zone (HAZ) on the IN718 side due to phase re-dissolution, while FGH101 showed quicker recovery. Post-weld aging treatments enhanced hardness and strength through γ′ and δ phase precipitation in FGH101 and γ″ phases in IN718. Room temperature tensile tests demonstrated impressive strength with failures occurring plastically within the IN718 base metal, whereas elevated temperatures shifted failure locations to the weld zone without necking. Fatigue tests exhibited varied lifespans, with fractures initiating either at stress concentrators or within the FGH101 base metal far from the weld center. Scanning electron microscope (SEM) analysis confirmed mixed-mode fracture patterns, underscoring the importance of microstructure on joint performance and suggesting that optimizing IFW parameters can lead to superior weld quality in aerospace components, thus providing valuable insights for future research and industrial applications.
Surface defect detection plays a crucial role in the quality management of precision industrial products and holds significant research value. Defect detection in industrial environments still needs to address two main challenges: first, the proportion of product defects on the surface is too small to capture, presenting a typical small target detection problem; second, some products have complex surfaces with numerous defects, making it difficult to monitor each defect individually. Aiming to address the aforementioned issues, this paper proposes a solution for surface defect detection based on image processing. It successfully detects 11 types of defects on object surfaces and applies this method in industrial settings. First, a lighting platform was built, and defect pictures were collected using industrial cameras and integrated into picture datasets. Secondly, the dataset is preprocessed using image processing to identify four types of defects, and then further processed through image enhancement. The graph is then sent to the deep learning network for training, and the model parameters are adjusted based on the defect state to achieve a convergent model. The experimental results demonstrate that the proposed method can accurately identify 11 types of defects on the product surface with a precision of 98.5%, satisfying the requirements of industrial settings.
Because of high conductivity, acceptable cost and good screen-printing process performance, silver pastes have been extensively used for making flexible electronics. However, there are few reported articles focusing on high heat resistance solidified silver pastes and their rheological properties. In this paper, a fluorinated polyamic acids (FPAA) is synthesized by polymerization of the 4,4′-(hexafluoroisopropylidene) diphthalic anhydride and 3,4′-diaminodiphenylether as monomers in the diethylene glycol monobutyl. The nano silver pastes are prepared by mixing the obtained FPAA resin with nano silver powder. The agglomerated particles caused by nano silver powder are divided and the dispersion of nano silver pastes are improved by three-roll grinding process with low roll gaps. The obtained nano silver pastes possess excellent thermal resistance with 5% weight loss temperature higher than 500 °C. The volume resistivity of cured nano silver paste achieves 4.52 × 10−7 Ω·m, when the silver content is 83% and the curing temperature is 300 °C. Additionally, the nano silver pastes have high thixotropic performance, which contributes to fabricate the fine pattern with high resolution. Finally, the conductive pattern with high resolution is prepared by printing silver nano pastes onto PI (Kapton-H) film. The excellent comprehensive properties, including good electrical conductivity, outstanding heat resistance and high thixotropy, make it a potential application in flexible electronics manufacturing, especially in high-temperature fields.
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