Characterization of polypropylene/magnesium oxide/vapor-grown carbon fiber composites prepared by melt compounding

In this paper, we discussed the characteristics and properties of polypropylene (PP)/magnesium oxide (MgO) composites prepared by melt compounding. In addition, we also discussed the effect of adding vapor-grown carbon fiber (VGCF) to PP/MgO composite on the properties of the composites. The thermal conductivity of PP/MgO increased with MgO content. In the region of MgO content of more than 30 vol%, the thermal conductivity of PP/MgO with MgO-10 (particle size of 10 μm) is the largest by comparison of other PP/MgO with different MgO sizes. The thermal conductivity of PP/MgO became increased by adding VGCF in PP/MgO. According to the estimation of thermal conductivity using Bruggeman’s equation, no synergistic effect was observed by adding VGCF into the PP/MgO composite. The surface resistance of PP/MgO significantly decreased by adding VGCF at a content of more than 3 vol%. At VGCF content of 1 vol%, the surface resistance of the composite became large, and the value was more than 109 Ω/sq. In addition, the Non-Newtonian property of PP/MgO composite melt was enhanced by the addition of VGCF into the composite.

Evaluation of the nonlinear surface resistance of REBCO coated conductors for their use in the FCC-hh beam screen

To assess the feasibility of using high-temperature superconductors for the beam screens of future circular colliders, we have undertaken a study of the power dependence of the microwave surface resistance in state-of-the-art REBCO coated conductors at about 8GHz and 50K. We have employed a dielectric resonator to produce radio-frequency electromagnetic fields on the surface of the coated conductors having amplitudes similar to those generated by proton bunches circulating in the vacuum chamber of the proposed hadron-hadron Future Circular Collider at CERN. We show that surface resistances in REBCO coated conductors without artificial pinning centers are more affected by a radio-frequency magnetic field than those containing nano-inclusions. Despite that, at 8GHz, 50K, and 9T, most REBCO coated conductors studied outperform copper in terms of surface resistance, with the best sample having a 2.3mΩ surface resistance while being subject to an RF field 2.5 times stronger than that in the FCC-hh. We also extrapolate the measured data to 16T and 1GHz, the actual FCC-hh dipole magnetic field, and mid beam frequency spectrum, demonstrating the possibility of lowering the surface resistance of the vacuum chamber by up to two orders of magnitude compared to copper. Further, we discuss the correlation between the time structure of the electromagnetic fields provided by vector network analyzers compared to the proton bunches' time structure in the collider and present the effect of low alternating magnetic fields on vortex displacement and the possibility of demagnetization of superconducting samples.

The Spread of Corrosion of the Deposited Material Using the Cold Spray Method

A layer of copper was applied to the base aluminum material using the cold spray method (cold kinetic deposition). The samples were exposed to corrosion in a salt chamber for 100, 200 and 300 hours. The change in the size of the internal and surface resistance of the samples was monitored. The corrosion results were also examined using an electron microscope.

Effect of humidity and contaminants on dry band formation in Outdoor Distribution Current Transformer 20 kV

This study reports the effect of humidity and pollutants on the formation of dry band phenomena on the insulation surface of an outdoor 20 kV distribution current transformer. From the results of measurements at high humidity 95% and high conductivity 36 mS/cm at a working voltage of 2-20kV test there is a change in the curve of increasing the value of the leakage current which is very volatile. Wet layer of impurity will cause a drastic decrease in surface resistance resulting in a large increase in leakage current. At a high conductivity of 36 mS/cm, the results of the measurement of surface resistance at low humidity of 55% worth 30.2 giga ohms decreased to 2.1 giga ohms at high humidity of 95%. While the value of the leakage current curve is very fluctuating from the value of 206 - 678 A at high conductivity with heavy pollutants. This information confirms the hypothesis that the boundary region of the two air-solid dielectrics of the epoxy resin causes surface discharge problems in dry band formation due to an increase in the non-uniform local electric field in the impurity layer adhering to the surface of the distribution current transformer. Keywords : leakage current, dry band, surface discharge, contaminants

Comparison of Experimental Towing Test and CFD Analysis of a Bare Hull Model on the Surface

In designing submarines, hull form selection, resistance, and powering are key aspects. The bare hull form of a submarine can be considered according to five parameters. Surface resistance is important should it be necessary to operate at relatively high Froude Numbers. Due to the complex nature of the flow around the hull, model experiments are still the most reliable approach to determining surface resistance. CFD simulations enable surface condition analysis using FINEMarine. The towing mechanism must be taken into account and so this was designed to fix the pitch motion and measure the hydrodynamic forces. This paper outlines the towing method, comparing the model test and the CFD results, as well as providing a comparison of wave formation from the towing test and the CFD results. The results show that resistance increased significantly above a model speed of 1.4 m/s. Furthermore, above this speed, as the resistance of the model rose, the downforce gradually decreased.

Influence of elastic 3D printed polymers on the mechanical properties and tribology of textile fabrics

Combining textile fabrics with 3D printing has been investigated intensively during the last years. Mostly, research concentrated on the adhesion between both partners of the composite or on the new freedom of design, enabled by combining these techniques. Here, we present examinations of the influence of elastic 3D printed patterns on the elongation and wearing out of elastic textile fabrics as well as on the tribological properties of the textile surface, comparing pure and imprinted textile fabrics. Therefore, thermoplastic polyurethane (TPU) was 3D printed in different patterns on diverse textile fabrics. Our study shows that for a sufficient adhesion, reached by small enough nozzle-fabric distance, elastic 3D printed patterns can indeed improve the surface resistance against wear.

Reduction of scattering cross section of path antennas

This report considers the possibility of reducing the scattering cross section of patch antennas when using emitters of various shapes and when using structures with non-zero surface resistance. The report presents the results of the influence of the choice of the shape of a emitter on the SCS in the region of resonant scattering frequencies. The scattering indicatrices of various emitters for the resonant scattering frequency are analyzed. Comparative analysis results of the decrease estimation for the SCS of the square path when using various forms of regions with impedance surface are presented.

Advantages of graphene technologies in the design of antenna systems for the Internet of Things in the decimeter range of cellular operators (LTE, GSM, 5G)

The characteristics and resistance to external influences of flexible graphene antennas are considered. In particular, the analysis of the influence of single and cyclic bends at different cycle times is carried out. Resistance to water of such antennas is analysed. The results of characteristics comparison of the literature data with the results obtained by the authors are presented. The design of a flexible graphene eco-friendly two-layer antenna on a paper substrate operating in the LTE frequency range has been proposed. The technology discussed in this report will help fill the gap in the literature in eco-friendly double-sided graphene printing technologies. The literature review shows that the development of graphene inks for printing on flexible substrates has made a breakthrough in the development of flexible electronics due to their unique advantages. The influence of edge effects on the change in the graphene surface resistance at the edges of the manufactured sample is estimated.