Materials Science Forum Vols. 505-507

Abstract: A new full-field 3-D micro surface profilometer using digital micromirror device (DMD)-based fringe projection strategy and confocal principle is presented in the article. In viewing the fact that conventional laser confocal measurement method not only easily encounters undesired irregular scattering problems, but also lack scanning efficiency due to its single-point type measurement, the newly developed automatic surface profilometer deploys a DMD chip to project spatially encoded digital fringe patterns with dynamic light intensity, onto the object to obtain excellent measurement performance. A novel digital fringe pattern design with adaptive sinusoidal intensity modulation was developed for active fringe projection, to obtain optimized depth resolution with a micrometer lateral resolution in confocal measurement. Some of semiconductor components have been measured to attest the feasibility of the developed approach. The depth measurement resolution can reach better than 0.1μm and the maximal measured error was verified to be less than less than 0.5 % of the measured step size.

Abstract: Precise and efficient tool setting technique and accurate tool shape monitoring are of essential importance in ultra-precision diamond turning operation. The traditional way of tool setting are typically laborious, inefficient and rely heavily on experience. A big part of the tool setting is done by using a contact probe such as LVDT. The contact tool setting station can normally, depending on the resolution of the probes, place the tool tip to within a 1~10μm positioning accuracy. However, it is running the risk of damage the delicate tool tip and has the ambiguity introduced by contact point of tool and touch probe. The optical/non-contact way of setting the tool do have the advantage of not having to touch the tool, but its resolution is limited by the optical diffraction limit and the resolution of the CCD device used (mm/pixel). A non-contact precision tool setting system is developed and built in this study using edge-detection image processing and sub-pixel dividing techniques in conjunction with CNC controller of the precision turning machine to improve the system presently available. Depending on the sampling distance of the images, the error band gets wider when the sampling step becomes larger. In the case of 0.1μm sampling distance the obtained error band was within ±0.1μm and the results showed that tools of different shapes namely round, half-round and sharp tool could all be positioned to within an error band of ±0.1μm by using the developed tool setting system.

Abstract: DVD player is regarded as a mature and low-cost commercial product for multimedia and computer data storage. Fundamentally the pickup head is a key part of the DVD player and it uses focused laser beam to read the data on the DVD disk tracks whose width is approximately 0.74μm. This research focused on the control aspect applied to a DVD pickup head for the development of an auto-focusing laser probe. Practically, the laser pickup head has the S-curve linearity property with the measuring range of about 7μm [3]. To extend the measurement range, the feedback control of VCM in the focusing direction is needed. This study used Genetic Algorithms (GAs) to search for appropriate PID gains for VCM control. In MATLAB simulation, the GAs tuning scheme could produce the optimised gains within less than 0.02 sec. Moreover, the experimental results demonstrated that the VCM auto-focusing measurement range could be extended to 1350μm.

Abstract: This study performs molecular dynamics (MD) simulations to investigate the tensile behavior of Helical Multi-Shell (HMS) gold nanowires. As their name suggests, these nanowires have a multi-shell helical structure rather than a conventional bulk FCC structure. The mechanical properties and deformation behaviors of the 7-1, 11-4 and 14-7-1 HMS structures are examined under tensile testing at temperatures between 4K and 300 K and a constant strain rate of 0.003% −1 ps . The results reveal that temperature influences the yielding stress, the Young’s modulus, and the deformation behaviors of HMS nanowires. The yielding stress of the 7-1 structure is found to be higher than that of the 11-4 or 14-7-1 structures. Finally, under different temperature conditions, many different close-packed structures are identified in the nanowires before they fracture.

Abstract: This paper proposes a numerical and experimental investigation of mixing behaviors of two liquid samples in microchannels that are shaped into different geometric barriers. The micro-mixers utilized in this study are fabricated on low-cost glass slides using a simple and reliable fabrication process. Samples are driven by a hydrodynamic pump to lead them into the mixing section of the microchannels. The effects of mixing performance of various kinds of barrier shape are discussed in this study. The numerical and experimental results show that a better mixing efficiency can be obtained in the microchannels while using the elliptic-shape barriers in compare with the leaking side-channels. In this study, the simulated and experimental results are in good agreement. The investigation of mixing efficiency in microchannels with different geometric barriers could be crucial for microfluidic systems.

Abstract: For the design of a vibrating micro-beam structure, modal and stability analyses of the structure actuated by electrostatic force is performed in the present study. Static deflection of the micro-beam caused by the electrostatic force is first obtained by solving the nonlinear equilibrium equation and the modal and stability characteristics are calculated at the static equilibrium position. It is found that the amplitude and the frequency of the applied electrostatic voltage influence the stability of the structure significantly. A design specification of a vibrating micro-beam structure can be effectively determined from the modal and the stability analysis results.

Abstract: This paper presents an experimental investigation on the use of high-resolution injection techniques to deliver sample plugs within electrophoresis microchips. Two novel injection microfluidic chips are proposed, which employ conventional cross-shaped and U-shaped injection system combined with an expander to deliver high-quality sample plugs for detection in separation channel. The valving characteristics on microfluidic devices are controlled through appropriate manipulations of the electric potential strengths during the sample injection and separation steps. These novel injection techniques developed in this study has an exciting potential for use in high-quality, high-throughput chemical analysis applications and in many other applications throughout the field of micro-total-analysis systems.

Abstract: The droplet formation process of a novel piezo-actuated micro-injector is studied using a computational approach. In simulations, the theoretical model is based on the time-dependent threedimensional conservation equations of mass and momentum. The surface tension effect at the gasliquid boundary is treated using the continuous surface force (CSF) scheme. The volume-of-fluid (VOF) method in conjunction with the piecewise linear interface construction (PLIC) technique is exploited to describe interfacial movements. The time evolution of the droplet meniscus shape is predicted throughout the formation process and compared with Shield's micro-photographed images for the computer package validation. To explore the feasibility of proposed new micro-injector in practical applications, the droplet deformation characteristics are determined in terms of droplet topology, breakup length and time, and flight velocity for dispensing different liquids such as water, anisol, Pedot, PLED, and blood.