Micromachines2015, 6(8), 984-992; doi:10.3390/mi6080984 - published 24 July 2015 Show/Hide Abstract
Abstract: This paper reports the design, micromachining and characterization of an array of electromagnetic energy harvesters (EHs) with multiple frequency peaks. The authors present the combination of three multi-modal spring-mass structures so as to realize at least nine resonant peaks within a single microelectromechanical systems (MEMS) chip. It is assembled with permanent magnet to show an electromagnetic-based energy harvesting capability. This is the first demonstration of multi-frequency MEMS EH existing with more than three resonant peaks within a limited frequency range of 189 to 662 Hz. It provides a more effective approach to harvest energy from the vibration sources of multiple frequency peaks.
Micromachines2015, 6(8), 969-983; doi:10.3390/mi6080969 - published 23 July 2015 Show/Hide Abstract
Abstract: The aim of this paper is to fabricate micro-gears via laser shock punching with Spitlight 2000 Nd-YAG Laser, and to discuss effects of process parameters namely laser energy, soft punch properties and blank-holder on the quality of micro-gears deeply. Results show that dimensional accuracy is the best shocked at 1690 mJ. Tensile fracture instead of shear fracture is the main fracture mode under low laser energy. The soft punch might cause damage to punching quality when too high energy is employed. Appropriate thickness and hardness of soft punch is necessary. Silica gel with 200 µm in thickness is beneficial to not only homogenize energy but also propagate the shock wave. Polyurethane films need more energy than silica gel with the same thickness. In addition, blank-holders with different weight levels are used. A heavier blank-holder is more beneficial to improve the cutting quality. Furthermore, the simulation is conducted to reveal typical stages and the different deformation behavior under high and low pulse energy. The simulation results show that the fracture mode changes under lower energy.
Micromachines2015, 6(7), 953-968; doi:10.3390/mi6070953 - published 22 July 2015 Show/Hide Abstract
Abstract: This study presents experiments and computational simulations of single-layer passive micromixer designs. The proposed designs consist of chains of interlocking semicircles and omega-shaped mixing modules. The performance of the new designs is compared with the concentric spiral channel configuration. The micromixers are intended to be integrated into a lab on chip (LOC) micro-system that operates under continuous flow conditions. The purpose behind the multi-curvature in these designs is the introduction of Dean vortices in addition to molecular diffusion in order to enhance the mixing performance. The micromixers were fabricated in PDMS (Polydimethylsiloxane) and bonded to a glass substrate. A three-dimensional computational model of micromixers was carried out using Fluent ANSYS. In experiments, the mixing of a 1 g/L fluorescein isothiocyanate diluted in distilled water was observed and photographed using a charge-coupled device (CCD) microscopic camera. The obtained images were processed to determine the mixing intensity at different Reynolds numbers. The standard deviation (σ) of the fluorescence indicates the mixing completeness, which was calculated along the width of the channel at various locations downstream from the channel inlet. The value of σ = 0.5 indicates unmixed streams and 0 is for complete mixing. It is found that the two new designs have a standard deviation of nearly 0.05. Additionally, complete mixing was observed at the channel outlet as demonstrated by the fluorescence images and the numerical results. However, the location of complete mixing at different positions depends on the Reynolds number, which varies between 0.01 and 50. Good agreement was found between the experiment and the numerical results. A correlation to predict the length scale where complete mixing can be achieved is given in terms of the radius of curvature, the mixing module, and the Reynolds number.
Micromachines2015, 6(7), 926-952; doi:10.3390/mi6070926 - published 16 July 2015 Show/Hide Abstract
Abstract: Numerous solutions/methods to solve the existing problems of pedestrian navigation/localization have been proposed in the last decade by both industrial and academic researchers. However, to date there are still major challenges for a single pedestrian navigation system (PNS) to operate continuously, robustly, and seamlessly in all indoor and outdoor environments. In this paper, a novel method for pedestrian navigation approach to fuse the information from two separate PNSs is proposed. When both systems are used at the same time by a specific user, a nonlinear inequality constraint between the two systems’ navigation estimates always exists. Through exploring this constraint information, a novel filtering technique named Kalman filter with state constraint is used to diminish the positioning errors of both systems. The proposed method was tested by fusing the navigation information from two different PNSs, one is the foot-mounted inertial navigation system (INS) mechanization-based system, the other PNS is a navigation device that is mounted on the user’s upper body, and adopting the pedestrian dead reckoning (PDR) mechanization for navigation update. Monte Carlo simulations and real field experiments show that the proposed method for the integration of multiple PNSs could improve each PNS’ navigation performance.
Micromachines2015, 6(7), 915-925; doi:10.3390/mi6070915 - published 13 July 2015 Show/Hide Abstract
Abstract: A microfluidic droplet mixer is developed for rapid detection of Hg(II) ions. Reagent concentration and droplets can be precisely controlled by adjusting the flow rates of different fluid phases. By selecting suitable flow rates of the oil phase, probe phase and sample phase, probe droplets and sample droplets can be matched and merged in pairs and subsequently well-mixed in the poly (dimethylsiloxane) (PDMS) channels. The fluorescence enhancement probe (Rhodamine B mixed with gold nanoparticles) encapsulated in droplets can react with Hg(II) ions. The Hg(II) ion concentration in the sample droplets is adjusted from about 0 to 1000 nM through fluid regulation to simulate possible various contaminative water samples. The intensity of the emission fluorescence is sensitive to Hg(II) ions (increases as the Hg(II) ion concentration increases). Through the analysis of the acquired fluorescence images, the concentration of Hg(II) ions can be precisely detected. With the advantages of less time, cost consumption and easier manipulations, this device would have a great potential in micro-scale sample assays and real-time chemical reaction studies.
Micromachines2015, 6(7), 902-914; doi:10.3390/mi6070902 - published 10 July 2015 Show/Hide Abstract
Abstract: In this work, a mathematical model was developed to relate the mechanochemical characterizations of molecular motors with the macroscopic manifestation of muscle contraction. Non-equilibrium statistical mechanics were used to study the collective behavior of myosin molecular motors in terms of the complex conformation change and multiple chemical states in one working cycle. The stochastic evolution of molecular motor probability density distribution during the contraction of sarcomere was characterized by the Fokker-Planck Equation. Quick muscle contraction was demonstrated by the collective dynamic behavior of myosin motors, the muscle contraction force, and the muscle contraction velocity-force relation. Our results are validated against published experiments, as well as the predictions from the Hill’s model. The quantitative relation between myosin molecular motors and muscle contraction provides a novel way to unravel the mechanism of force generation.