Key Engineering Materials Vols. 364-366

Abstract: The past few years, have witnessed a rapid increase in the application of microfluidic devices to chemical and biological analyses. These devices offer significant advantages over their traditional counterparts, including reduced reagent consumption, a more rapid analysis and a significant improvement in performance. Species mixing is a fundamentally important aspect of these devices since it is this mixing which generates the biochemical reactions necessary for their successful operation. Many microfluidic applications require the mixing of reagents, but efficient mixing in these laminar (i.e., low Reynolds number) systems are typically difficult. Instead of using complex geometries and/or relatively long channels, an electric field is applied to drive flow mixing in microchannels. Generally, the fluid is driven by the application of an external periodic AC electric field. However, the chaotic AC electric filed is never used to drive flow mixing in microchannels. Chaotic behavior is a very interesting nonlinear effect. In some physical systems, chaos is a beneficial feature as it enhances mixing in chemical reactions. This paper presents a numerical investigation of electrokinetically-driven flow mixing in microchannels with chaotic electric field. The simulation results show that the application of a chaotic external field enables a reduction in the mixing channel length and a high degree of mixing efficiency. It is shown that a mixing performance as high as 90% can be achieved by chaotic external electric field.

Abstract: This paper describes an innovative system to produce nanoparticles based on the theory of gas condensation in producing nanoparticles. In a vaccuum environment, the system used the energy produced by high frequency induction to vaporize a pure zinc rod inside the crucible. During the vaporization the chamber was filled with He gas, so the high-temperatured vaporized metal can undergo momentum exchange with He gas and at the same time, induce the vaporized metal to move to the cold trap. Upon reaching the wall of the cold condenser, the vaporized metal instantly condensed, forming nanoparticles. The TEM image shows that their average diameter was 30 nm, and the size was very consistent. In addition, the Zeta potential and average diameter of the ZnO nanofluid was also measured under different pH conditions to determine the stability of the ZnO nanofluid. Moreover, in order to verify the practicability of the fabricated ZnO nanoparticles, the ZnO nanofluid was inspected by UV/Vis absorption spectrum, and the results show that ZnO nanoparticles absorption ability was within a wavelength range from 350nm to 550nm.

Abstract: Wet etching processes have been widely used for producing micro-components for various applications. These processes are simple and easy to implement. The selection of suitable chemical solution which is called etchant is the most important factor in the wet etching processes. It affects etch rate and surface finish quality. Copper and its alloys are important commercial materials in various industries, especially in electronics industry. Their wide applications are due to their excellent electrical and thermal conductivity, ease of fabrication, good strength and fatigue properties. The present study examines the possible etchants for copper and its alloys and reviews studies in detail to find out optimum etchant and its application parameters. The study is also aimed to provide information about safety, health and environmental issues caused by using various etchants in wet etching processes of copper and copper alloys.

Abstract: Lapping plate wear is of great influence on shape precision of workpiece. Investigation on the wear uniformity of uncertain eccentricity plane lapping was carried out in this research. The relative velocity function of the plate to the workpiece is obtained through kinematic analyses in the mode of uncertain eccentricity plane lapping, and material removal rate (MRR) function and wear uniformity function were deduced based on Preston equation. Effects of the ratio and eccentricities on the wear uniformity are discussed in detail through MATLAB simulation. Theoretical analysis and simulation results show that the ratio k1 of workpiece revolution speed to lapping plate is the key to decide whether the lapping plate is lapped uniformly. Theoretically, when k1<0, the greater |k1| is, the better the lapped uniformly of lapping plate can be. The ratio k2 of workpiece rotation speed to lapping plate has great influence on the lapped uniformly when k1 approximate 1, and k2 has little influence on the lapped uniformly when k1<0 or k1>1, Besides, a bit bigger eccentricity e1 is propitious to the lapping uniformly of the lapping plate, and bigger eccentricity e2 are also helpful to lapping uniformly of the lapping plate. And the conclusion could be extended to single-side plane lapping and double-side plane lapping process.

Abstract: In ion beam figuring process, typically, the smaller ion beam diameter has a good ability to “correct” the optical surface error, i.e. the smaller ion beam diameter indicates the higher material removal efficiency ε. The material removal efficiency is defined as the ratio of the volume of desired material removal to that of the real material removal. However the smaller ion beam diameter always results in more processing time, which usually decreases the process reliability. In this paper, the relationship between the material removal efficiency and the ion beam diameter is analyzed. The theoretical result shows that the material removal efficiency is a negative exponential function of the ratio of ion beam diameter to the spatial error wavelength, (i.e. d/λ). And when d/λ= 0.5, the material removal efficiency is 87%, which is acceptable in ion beam figuring process. When d/λ = 1, it rapidly decreases to 58%, which is unacceptable. According to theoretical analysis and simulation results, we recommend that d/λ should be less than 0.5 in order to obtain acceptable material removal efficiency in ion beam figuring process.

Abstract: Remarkable progress had been made in both technology and production of optical elements including aspheric lens. Especially, requirements for machining glass materials have been increasing in terms of limitation on using environment, flexibility of material selection and surface accuracy. In the past, precision optical glass lenses were produced through multiple processes such as grinding and polishing, but mass production of aspheric lenses requiring high accuracy and having complex profile was rather difficult. Against such a background, the high-precision optical GMP process was developed with an eye on mass production of precision optical glass pasts by molding press. This GMP process can produce with precision and good repeatability special form lenses such as for cameras, video cameras, aspheric lenses for laser pickup, f-θ lens for laser printer and prism, and fine glass parts including diffraction grating and V-grooved base. Generally, GMP process can be classified into batch and progressive type. In these types, because progressive type has many merits in that productivity is higher and repair/retouch of mold is easier than batch type, progressive GMP process is mainly used to produce aspheric glass lenses these days. In this paper, as a fundamental study to develop the multi-cavity mold for higher productivity of progressive GMP process used in fabrication of aspheric glass lens, compression tests for K-PBK40, which is the material of aspheric glass lens, were conducted at high temperature. As a result, flow characteristics of K-PBK40 were obtained for aspheric glass lens press simulation.

Abstract: Micro electrical discharge machining (EDM), enhanced with ultrasonic vibration, is explored and assessed as a method for developing microelectrode array, for microelectrode array fabricated by LIGA has shortcomings such as complex technology and high price. Based on the mechanism of micro-EDM, micro-hole array discharges to fabricate microelectrode array by reverse copying. In the process of reverse copying, the thicker rod electrode can not rotate, resulting in electric arc and short-circuit occurring easily, so it is necessary to add ultrasonic vibration on the plane plate electrode, in order to exclude debris as soon as possible and stabilize machining process. In the process of machining, four parameters, such as working voltage, working capacity, ultrasonic amplitude and holes spacing, are important to machining efficiency, each parameter has four typical values. In order to reduce experiment times, a scheme of orthogonal experiment was designed with different parameters combination. With result of experiments, the ratio of mean square deviation to error mean square deviation of each parameter was calculated and significance of each parameter was obtained, and the best parameters combination was asserted through theoretical calculation. Also, experimental study of using microelectrode array to machine micro-hole array by Micro- EDM was made and influence curve of each parameter was drawn. Finally, 5×5 arrays of microelectrode were obtained, the diameter of single electrode is less than about 30.m and heightto- width aspect ratios is more than 8, moreover, these microelectrode arrays have good coaxiality and surface quality.

Abstract: ASPHERO5 is a funded German research project (project prime: Schneider OpticalMachines) with the goal of economic fabrication of high precision aspheres. The research is concentrated on the classical process chain consisting of grinding and polishing. The characterization of the incoming and outgoing surface quality is one issue to characterize the improvements. The variation of the local removal rate related to local curvature is one of the limiting factors of the polishing process. In this paper we report on first results characterizing the surface quality with a PSD (Power Spectral Density) algorithm and analyzing the local removal rates for the polishing step. In our research, two types of aspheres with 30 and 60 mm diameter were polished with a spinning tool process. The final deviation between simulation and experiment was less than 10 percent. That’s the starting point for further investigations within the project.

Abstract: Optical lenses are used in signal lighting to control intensity distributions. Brightness and viewing angle are two essential requirements that have to be considered in manufacturing a traffic signal lamp. This paper discusses design considerations for microstructure optics designed for LED traffic signal light, strategies for obtaining particular intensity distributions, optical functions of the lens and matters concerning the manufacturing process. The mould inserts of the optical surfaces were machined by CNC high-speed milling. Results of surface finish and profile accuracy analyses using the Form Talysurf instrument are presented.