Design of Window Grille Shape-Based Multiband Antenna for Mobile Terminals

Combined with the classic Chinese window grille structure, this paper proposes and designs a multiband microstrip antenna that can be used in wireless mobile terminal equipment. The antenna radiator adopts a rectangular bending structure with four loops, which increases the effective current path of the antenna radiator in a limited space, so that the overall antenna is miniaturized. The branch structure of the four-ring phase set increases the current path of the antenna, making the antenna multiband. The electromagnetic simulation software HFSS was used for antenna modeling and parameter optimization, and the influence of the feed structure, feed mode, and ground plate shape on the antenna was compared and analyzed. The test results show that the antenna can cover four bands, 0.85–1.1 GHz, 1.2–1.8 GHz, 2.40–2.7 GHz, and 5.05–6.3 GHz, and produce 6 main frequency points, 0.9 GHz, 1.3 GHz, 1.6 GHz, 2.55 GHz, 5.3 GHz, and 6.05 GHz. The antenna can cover various navigation systems, Bluetooth, WLAN, ISM frequency band, and 5G (5.725–5.825 GHz).

Selective Capture of Magnetic Wires to Particles in High Gradient Magnetic Separation

High gradient magnetic separation (HGMS) achieves effective separation to fine weakly magnetic minerals using numerous small magnetic wires in matrix, and its separation performance is inherently dependent on the capture characteristics of the wires. In this work, the selective capture of magnetic wire to particles in high gradient magnetic field was theoretically described and simulated using COMSOL Multiphysics. It was found that the capture trajectories of a small amount of particles under the ideal condition was significantly different from those of a large amount of particles under the actual condition, and non-magnetic particles would be much more easily entrained into magnetic deposits captured onto the wire surface under the actual condition than those under the ideal condition. These theoretical and simulated results were basically validated with the experimental magnetic capture to an ilmenite ore, and the wires in slow feed mode have achieved much higher capture selectivity than those in the fast feed mode. For instance, at the magnetic induction of 0.8 T, the TiO2 grade of magnetic deposits captured by 3 mm diameter wire in the slow feed model reached 36.78%, which is higher than 28.32% in the fast feed model. The selective capture difference between the fast and slow feed models increased with increase in the magnetic induction and with decrease in the pulsating frequency. This investigation contributes to improve HGMS performance in concentrating fine weakly magnetic ores.

Experimental Study and Numerical Simulation of the Intermittent Feed High-Speed Grinding of TC4 Titanium Alloy

This paper proposes intermittent feed high-speed grinding, which shows considerable advantages in terms of reducing grinding temperature, relieving grinding wheel blockage and improving workpiece surface integrity. In this grinding, the continuous feed mode of the workpiece is changed into the normal feed + fast retreat reciprocating feed mode by a fast linear feed worktable. By reasonably setting the normal feed distance of single grinding, the action time of the grinding wheel and workpiece is reduced, so that the grinding heat transfer process does not reach a stable state, reducing the grinding temperature during single grinding. Besides this, the surface temperature is cooled to nearly room temperature and the grinding wheel is flushed by the timely retreating of the grinding wheel to allow the grinding fluid to enter the grinding zone fully, which greatly reduces the phenomenon of heat accumulation and grinding wheel loading. An intermittent feed high-speed grinding experiment on Ti-6Al-4V (TC4) titanium alloy was systematically carried out, and the influence of the grinding parameters on grinding force and grinding temperature was deeply analyzed. The instantaneous grinding temperature field and thermal stress field of TC4 titanium alloy in intermittent feed high-speed grinding were constructed with the finite element method. The surface morphology of the grinding wheel and TC4 titanium alloy specimens after intermittent feed grinding were analyzed and were compared with those after traditional continuous grinding. It was found that the curves of the grinding force and temperature varied with time in the process of machining, consisting of many “pulse” peaks. Under the same grinding parameters, the magnitude of the grinding force is the same as that of continuous grinding. In a certain range, the grinding temperature is greatly affected by the single feed distance and the interval time. The numerical simulation results are in good agreement with the experimental results, and the error is controlled within 12%. Compared with traditional high-speed grinding, under the same process parameters, the grinding temperature is greatly reduced, the surface integrity of the workpiece is better, and the clogging of the grinding wheel is greatly reduced.

Assessing the Feasibility of Micro-Plasma Technology for Additive Manufacturing

In this research, a micro-plasma system was investigated for its capability in additive manufacturing (AM). Micro-plasma AM system has the advantage of lower cost and higher deposition rate over laser based AM systems, and generates leaner and cleaner weld deposit than other arc based AM systems. However, the micro-plasma system is complex and involves a large number of process variables. In this study, the feasibility of using a micro-plasma system for additive manufacturing was assessed based on surface features, mechanical properties and microstructure. In addition, two arc and wire feed modes were examined to understand the effects of these two variables. Each was used to produce IN 718 superalloy samples for macro- and microstructure evaluation, hardness, wear, and tensile tests along both long and transverse directions. Preliminary results showed that crack free samples, measured up to 100 mm × 40 mm, can be generated without measurable distortion. Some surface discoloration was observed, ranging from light straw to a purple tint. After heat treatment, the hardness of the samples varies from 403 to 440 HV, with the transverse surface showing slightly lower hardness values. Pin-on-disk wear test yielded consistent wear volume for three sets of the samples produced using different process parameters; however, samples produced with no modifications to the current and wire feed mode showed marginally higher wear rate. Microstructural analysis with SEM and EDS revealed presence of small pinholes, measured from submicron up to 22 μm in diameter, and no indication of any cracks or boundary layers between passes. SEM analysis revealed the presence of high contrast Nb/Mo rich carbides along with γ″-Ni3Nb in the γ matrix. Finally, tensile test was carried out to understand the anisotropic behavior; the results showed that transverse direction had lower tensile strength and ductility. Samples produced with pulsed current and wire feed mode had lower yield/tensile strength but higher ductility than that without current and wire feed mode modification.