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This paper proposes a method of electrochemical micromachining through a metallic mask to reduce the undercutting of micro grooves and improve machining localization. In this method, a metallic mask with through-slit was directly placed on the workpiece instead of using the traditional insulated masks. This decreases the undercutting by reducing the electric field intensity at the edge of micro grooves. In addition, a porous cathode with jet flow mode was employed to allow firm contact of the mask with the workpiece so as to enhance the mass transfer in the machining area. Simulated results show that the metallic mask reduces the current density at the edge of micro groove effectively, and so the undercutting of the profile is evidently reduced. Experimental results indicate that for the same depth, the etch factor (EF) for micro grooves reaches 5.6 by using a metallic mask, and the machining localization is improved significantly. The pulse duty cycle has an important effect on the machining localization and with a pulse duty cycle of 20% a micro groove with better machining localization is obtained. Although a metallic mask improves machining localization of micro grooves, however a low current efficiency is observed with this process as compared to traditional electrochemical micromachining.

Micro-channels have been widely used in variety of devices including bipolar plate, micro-chemical reactor, and micro-heat pipe. Electrochemical machining (ECM) is a promising approach to manufacture such structure on metallic surface. This paper proposed a modified jet-ECM for generating micro-channels. A flexible insulated mask with micro-through-holes was covered on the head surface of a metallic nozzle. During machining, the mask on the modified nozzle was contacted with the workpiece, and the jetting electrolyte in the nozzle was divided into different machining regions by the micro-through-holes in the mask; then, the micro-channels could be generated by moving the workpiece with an effective voltage applied between the nozzle and workpiece. Compared with traditional jet-ECM, the machining region in this method could be confined by the micro-through-hole, which was efficient for generating channel in micro-scale. In addition, multiple micro-channels could be generated by using a mask with a single row of micro-through-holes rather than assembling multiple nozzles. The experimental results showed that the pulse duty cycle has a significant influence on the dimension of micro-channel, while the pulse frequency has slight influence in contrast. In addition, the material removal rate (MRR), effective material removal rate (MRRe), and current efficiency (CE) were investigated with different machining parameters. The results indicated that although MRR was increased with the increasing pulse duty cycle, both MRRe and CE were reduced, leading to a deviation between the theory and experiment. The moving speed of workpiece also has a significant influence on CE. Increasing moving speed was useful for enhancing the CE, from 0.48 to 0.66 with the moving speed increasing from 20 to 80 μm/s. Finally, several kinds of micro-channels such as multiple micro-channels, micro-reactor, and cross micro-channels were well manufactured with this method, demonstrating a flexible and efficient process.

Surface structures with micro-grooves have been reported to be an effective way for improving the performance of metallic components. Through-mask electrochemical micromachining (TMEMM) is a promising process for fabricating micro-grooves. Due to the isotropic nature of metal dissolution, the dissolution of a workpiece occurs both along the width and depth. Overcut is generated inevitably with increasing depth, which makes it difficult to enhance machining localization. In this paper, a method of electrochemical machining using a conductive masked porous cathode and jet electrolyte supply is proposed to generate micro-grooves with high machining localization. In this configuration, the conductive mask is directly attached to the workpiece, thereby replacing the traditional insulated mask. This helps in achieving a reduction in overcut and an improvement in machining localization. Moreover, a metallic nozzle is introduced to supply a jetted electrolyte in the machining region with enhanced mass transfer via a porous cathode. The simulation and experimental results indicate that as compared with an insulated mask, the use of a conductive mask weakens the electric field intensity on both sides of machining region, which is helpful to reduce overcut and enhance machining localization. The effect of electrolyte pressure is investigated for this process configuration, and it has been observed that high electrolyte pressure enhances the mass transfer and improves the machining quality. In addition, as the pulse duty cycle is decreased, the dimensional standard deviation and roughness of the fabricated micro-groove are improved. The results suggest the feasibility and reliability of the proposed method. ispartof: MICROMACHINES vol:11 issue:6 ispartof: location:Switzerland status: published

Commonly, the code noise and multipath error is considered to fully obey the Gaussian distribution. While in the cases with different elevation angles and orbit types, the assumption may be inappropriate. Based on an empirical study, by considering both the elevation angle and the orbit type, a new code noise and multipath distribution model is proposed to describe a more accurate code noise and multipath distribution in this paper. Actual code noise and multipath data from 10 observation stations during two months are researched, and the parameters and elevation angle range of code noise and multipath distribution model are determined. The code noise and multipath distribution model is verified to be more accurate than the model presented in the Global Navigation Satellite System Evolutionary Architecture Study report, according to the analysis on the code noise and multipath overbounding, position error overbounding, and the availability of receiver autonomous integrity monitoring. This model provides more accurate prior information for receiver autonomous integrity monitoring, especially its availability.

With the rapid implementation of ultra-high-voltage direct current (UHVDC)—voltage beyond 800 kV—transmission in China, engineers are paying increased attention to the electrical environment of the lines, with major focus on electrical phenomena such as ground electric field, ion current density, magnetic field, audible noise, and radio interference. The electric field, which is the superposition of electrostatic fields generated by the surface charge on the conductor and the space charge in the surrounding air, is significantly influenced by space-charge distribution. Electrical environment tests of UHVDC transmission lines show that when large amounts of charged particles are suspended in the air, there is a substantial increase in the ground electric field. In this study, the air filtration method was used to measure the distribution of the space charge under UHVDC transmission lines in order to determine its influence on the ground electric field and to decide the design parameters for UHVDC transmission lines. The measurement error of the air filtration method is small, and the measurement position is not restricted. Further, compared with other methods, the air filtration method is more convenient and suitable for measuring the space charge caused by UHVDC transmission lines.

In this paper, two methods are proposed, namely the unified processing method and the distributed processing method, to process the global navigation satellite system observation data in integrated navigation simulation which uses the strapdown inertial navigation system as the reference system and the multi-global navigation satellite systems as the sub-systems. The unified processing method takes all the global navigation satellite systems as a whole as one sub-system while the distributed processing method takes each global navigation satellite system as one sub-system. The centralized filter and federated filter are utilized respectively to process the global navigation satellite system observation data in the unified processing method and the distributed processing method. The mathematical models of the unified processing method and the distributed processing method are given in detail. Through theoretical derivation and mathematical simulations, the performances of the unified processing method and the distributed processing method are investigated and compared, showing that while they have the same position (velocity) accuracy, the distributed processing method offers better efficiency than the unified processing method especially when the number of global navigation satellite systems is large (>3).

Micro groove, as a typical surface texture, has played an important role in the development of many advanced fields. This paper introduced an electrochemical machining of micro groove using masked porous cathode. A porous metallic plate covered with a mask was prepared as the masked porous cathode. During machining, the masked porous cathode was covered on the workpiece, and the electrolyte could flow into the machining region through the porous structure in the cathode for machining. As the machining unit was closed, the distribution of electrical field was uniform on the machining surface, which could improve the machining accuracy. In addition, the masked porous mask had no damage during machining and could be reused, which improved the machining efficiency. With this method, multiphysics coupling model, including flow field model, electric current model, heat transfer model, reactant transport model, and moving mesh model, was built to investigate their influence on the machining process with different flow modes. The simulation and experiment results indicated that compared with other two flow modes, jet flow mode could provide a high electrolyte velocity in the machining region around the nozzle, and the mass transfer process was enhanced, which was helpful to improve the machining quality. The effect of pulse duty cycle was investigated, and the pulse duty cycle of 20% with the frequency of 2 kHz could further improve the mass transfer process and was preferred to generate micro groove with low standard deviation and roughness. In addition, with the applied voltage rising, the depth of micro groove increased, and increasing the nozzle reciprocating motion number could enhance the mass transfer process during machining, which further improved machining quality. Finally, with the optimized flow mode and machining parameters, a group of ten micro grooves were well generated by using a masked porous cathode with ten micro slits, and the width was about 330 μm with the depth of 45 μm.

The availability of advanced receiver autonomous integrity monitoring for vertical guidance down to altitudes of 200 ft (LPV-200) is discussed using real satellite orbit/ephemeris data collected at eight international global navigation satellite system service stations across China. Analyses were conducted for the availability of multi-constellation advanced receiver autonomous integrity monitoring and multi-fault advanced receiver autonomous integrity monitoring, and the sensitivity of availability in response to changes in error model parameters (i.e. user range accuracy, user range error, Bias-Nom and Bias-Max) was used to compute the vertical protection level. The results demonstrated that advanced receiver autonomous integrity monitoring availability based on multiple constellations met the requirements of LPV-200 despite multiple-fault detections that reduced the availability of the advanced receiver autonomous integrity monitoring algorithm; the advanced receiver autonomous integrity monitoring availability thresholds of the user range error and Bias-Nom used for accuracy were more relevant to geographic information than the user range accuracy and Bias-Max used for integrity at the eight international global navigation satellite system service stations. Finally, the possibility of using the advanced receiver autonomous integrity monitoring algorithm for a Category III navigation standard is discussed using two sets of predicted errors, revealing that the algorithm could be used in 79% of China.