Computer-Aided Design and Test for Digital Microfluidics

This article discusses several aspects of design and test methodology centered on digital microfluidics, including modeling, simulation, synthesis, test, and reconfiguration. The automated design methods for digital electronics and adaption of them to droplet-based microfluidics are explained. The test methodology detects both catastrophic and parametric faults by electrically controlling and tracking the motion of the test stimuli droplets and also facilitates concurrent testing, in which fault testing and biomedical assays run simultaneously on a microfluidic system.     

Solid texture synthesis for heterogeneous translucent materials

We present a method to synthesize solid textures from heterogeneous translucent materials that have a complex pattern and subsurface scattering effect. A solid texture provides consistent texture throughout the volume, so that it can be used to model the texture on an arbitrary geometry. However, solid texture synthesis requires a huge amount of time to generate the volume. Moreover, a synthesized solid texture acquires only the color information from an input exemplar. Therefore, it has been difficult to render the appearance of a translucent object realistically without additional appearance data. In this paper, we introduce a new search method to accelerate synthesizing of solid textures. This method decomposes the candidates in an exemplar into several subgroups and searches for the best similar neighborhood in each decomposed subgroup. We also apply subsurface scattering effects to the shell layer of a synthesized object for realistic rendering of a translucent solid texture. Experimental results show that our rendering method can produce realistic rendering results for various heterogeneous translucent objects. It can also represent cross-sections of an object realistically without reconstructing the texture and surface geometry.     

Polymer Microfabrication for Microarrays, Microreactors and Microfluidics

Polymer microfabrication methods are becoming increasingly important as low-cost alternatives to the silicon or glass-based MEMS technologies. Polymer hot embossing and injection molding are replication methods applicable to microreplication of a diversity of materials and microstructures.

Equipment with high precision control of pressure and temperature for hot embossing of polymer materials is now available commercially. These systems have made possible the replication of chips containing microchannels for capillary electrophoresis (CE) and microfluidics devices, microoptical components and microreactors. Stable and reproducible polymer microstructures have been demonstrated in several types of materials with structural and optical properties meeting other biocompatibility and detection requirements. The process involves few variable parameters and results in high structural accuracy suited for a wide range of microfabrication applications.

After demonstrating equivalent and, in cases, improved performance, the alternative use of plastic as the microdevice material addresses needs for rapid prototyping in product development and provides cost advantages in product commercialization. Thus an increasing number of devices have been reported recently in the literature, fabricated on a variety of polymer substrates and using different fabrication methods such as laser ablation, injection molding, silicone rubber casting or embossing for microfabrication.     

Acoustically Driven Programmable Microfluidics for Biological and Chemical Applications

In summary, we described a novel and unconventional technique to manipulate smallest amounts of liquid on a chip. Using SAW on a piezoelectric substrate, we are able to actuate individual droplets along predetermined trajectories, or induce acoustically driven internal streaming in the fluid. This internal acoustic streaming can efficiently be used to agitate, mix, and stir very small liquid volumes, where the low Reynold's number usually only allows for diffusive mixing. We described several applications of the SAW driven microfluidics, including a nanomixer for microarray applications, a contactless mixer for MTPs, a programmable microfluidic chip for droplet-based assays, and finally a chip performing high resolution microliter PCR. The technique is equally well suited to actuate or agitate small amounts of liquids either in closed volumes or in an open, droplet-based geometry. Each of the approaches has its clear advantages, but also disadvantages. Droplet-based fluidics is certainly well suited to handle smallest amounts of fluids without the risk of cross contamination etc. High temperature processes, however, require additional means like covering the droplet with an oil film. SAW pumping, mixing, and stirring on closed volumes is advantageous over many other pumping schemes as the pumps are easily incorporated into most of the existing microfluidic device or lab-on-a-chip. The combination of the SAW actuated droplet-based fluid handling and SAW driven fluidics in closed volumes opens a wide field of many different applications, a few of which I had the pleasure to present in this article. Many more applications, and many more visualizations of the technology described above can be looked up on Advalytix' website http://www.Advalytix.de.     

Meniscus-Assisted High-Efficiency Magnetic Collection and Separation for EWOD Droplet Microfluidics

This paper describes a technique to increase the efficiency of magnetic concentration on an electrowetting-on-dielectric (EWOD)-based droplet (digital) microfluidic platform operated in air, i.e., on dry surface. Key differences in the force scenario for droplet microfluidics vis-a-vis the conventional continuous microfluidic systems are identified to explain the rationale behind the proposed idea. In particular, the weakness of the magnetic force relative to the bead-substrate adhesion and the liquid-air interfacial tension is highlighted, and a new technique to achieve high-efficiency magnetic collection with the assistance of the interfacial force is proposed. An improvement in collection efficiency (e.g., from ~ 73% to ~ 99%) is observed with the new technique of ldquomeniscus-assisted magnetic bead collectionrdquo. In addition, isolation of the magnetic species from a mixed sample of magnetic and nonmagnetic beads is demonstrated. Comparison with other related reports is also presented.     

改进的微粒群优化算法在过程综合中的应用

针对过程综合中的混合整数非线性规划(Mixed Integer Non-Linear Programming,MINLP)问题,利用改进的微粒群优化(Particle Swarm Optimization,PSO)算法对其进行求解。在基本的PSO算法的基础上,通过利用罚函数和引入sigmoid函数把PSO算法应用到MINLP问题的求解中,利用两个测试函数和一个过程综合的实例对其进行了测试并与其它算法所得的结果进行了比较,结果表明,PSO算法在使用的普遍性、求解的准确性方面都优于一般的算法,是一种有效的求解MINLP问题的方法。     

An extended particle swarm optimization algorithm for pattern synthesis of conformal phased arrays

In this article, an extended particle swarm optimization (EPSO) algorithm is proposed for designing conformal phased arrays. On the basis of traditional particle swarm optimization (PSO), novel velocity updating mechanism, new exceeding boundary control operator, and global best perturbation are introduced in EPSO to overcome the drawbacks of PSO. To validate the efficiency of the proposed algorithm, both the classical test functions and the scenarios concerning a 1 × 9‐element cylindrical conformal phased array and a 3 × 9(27)‐element cylindrical conformal array with flat‐top shaped‐beam pattern are presented. Simulation results show that the proposed method is superior to genetic algorithm (GA) and PSO when applied to both the classical test functions and the practical problems of conformal antenna array synthesis. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Microparticle Concentration and Separation by Traveling-Wave Dielectrophoresis (twDEP) for Digital Microfluidics

This paper describes highly efficient in-droplet particle concentration and separation where particles are concentrated and separated into droplets by traveling-wave dielectrophoresis (DEP) and subsequent electrowetting-on-dielectric droplet splitting. A successful concentration for 5-mum aldehyde sulfate (AS) latex particles was experimentally achieved using microfabricated devices, showing that 98% of the total particles were concentrated into a split daughter droplet. In addition, in-droplet particle separation was successfully achieved using the following two different cases of particle mixtures: case 1) a mixture of 5-mum AS latex beads and 8-mum glass beads; and case 2) a mixture of ground pine (GP) spores and 8-mum glass beads. In case 1), 97% of the total AS beads were separated into one split droplet and 77% of the total glass beads into the other split droplet. In case 2), over 92% of the GP spores were separated into a split daughter droplet, whereas 86% of the glass beads were separated into the other split daughter droplet. In all these concentration and separation experiments, the applied frequency and the conductivity medium are key parameters influencing the concentration and separation performance, which have been optimally determined by measuring the DEP and electrorotation spectra of the used particles prior to the concentration and separation experiments. This integrated in-droplet separation and concentration method may provide an additional functionality to digital microfluidics.     

Marginalized particle filter for spacecraft attitude estimation from vector measurements

An algorithm based on the marginalized particle filters （MPF） is given in details in this paper to solve the spacecraft attitude estimation problem： attitude and gyro bias estimation using the biased gyro and vector observations. In this algorithm, by marginalizing out the state appearing linearly in the spacecraft model, the Kalman filter is associated with each particle in order to reduce the size of the state space and computational burden. The distribution of attitude vector is approximated by a set of particles and estimated using particle filter, while the estimation of gyro bias is obtained for each one of the attitude particles by applying the Kalman filter. The efficiency of this modified MPF estimator is verified through numerical simulation of a fully actuated rigid body. For comparison, unscented Kalman filter （UKF） is also used to gauge the performance of MPE The results presented in this paper clearly derfionstrate that the MPF is superior to UKF in coping with the nonlinear model.     

Effect of relative particle size on large particle detachment from a microchannel

The detachment of a single rigid sphere in a cylindrical PDMS microchannel has been investigated for systems where the particle occupies greater than 50% of the channel cross-sectional area. The fluid velocity required to detach a particle adhering to a microchannel wall is a function of many variables; however, only the effect of particle size is considered in this paper. Experiments were performed for Reynolds numbers less than 0.1, and the ratio of particle diameter, d _p, to channel dimension, D, was varied from 0.50 to 0.95 in a 230 μm channel. A nonionic surfactant (Tween 80) was used to minimize the effect of adhesive forces other than van der Waals forces. In addition, a simple force-balance model based on particle lift, buoyancy, drag, gravitational forces, and adhesion due to van der Waals forces has been developed to predict the velocity required for particle detachment. The predicted and experimentally measured velocities agree relatively well within the limit of experimental error. The detachment velocity was qualitatively found to increase with decreasing d _p /D.     

Application of artificial neural network for prediction of particle size in pharmaceutical cocrystallization using mechanochemical synthesis

Neural Computing and Applications - Milling by mechanical means is vital unit operation in pharmaceutical processing which can be used for controlling particle size reduction. This approach can be...     

Integration of Microfluidics With a Love Wave Sensor for the Fabrication of a Multisample Analytical Microdevice

A novel approach for multisensing has been developed based on the integration of a parallel-channel microfluidic module with a surface acoustic wave (SAW) sensor chip. The microfluidic module was used to compartmentalize the surface of a single SAW sensor into $N$ equal subareas in order to deliver and detect multiple samples on the sensor. The design concerns and fabrication procedure using soft lithography of polydimethylsiloxane are described. Successful demonstration of a four-channel module is reported, along with a sensitivity evaluation and comparison with a standard flow cell used so far. Very promising results were revealed during the tests concerning the system's operation with liquid samples. The reliability and reproducibility of the results in all four subareas render the proposed setup very suitable for biological testing and screening of various biomolecules in an array format.$ hfill$[2008-0031]      

Adaptive particle allocation for multifocal visual attention based on particle filtering

When confronting floods of visual inputs, it is usually impossible for computers to examine all possible interpretations based on given visual data. Despite these computational difficulties, humans robustly perform accurate visual processing. One of the most important keys in human visual processing is attention control. In this article, we first suggest that the particle filter (PF) is a major candidate for a model of multifocal visual attention. PF is a method which approximates intractable integrations in incremental Bayesian computation by means of stochastic sampling. One of the major drawbacks of PFs is a trade-off between computational costs and tracking performance; a large number of particles are required for accurate and robust estimations of state variables, which is time-consuming. This study proposes a computational model for multifocal visual attention which deals with the cost-performance trade-off with a restricted computing resource (the number of particles). Simulation experiments of tracking two targets with only tens of particles demonstrate the feasibility of the model. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Consistency checks for particle filters

An "inconsistent" particle filter produces - in a statistical sense - larger estimation errors than predicted by the model on which the filter is based. Two test variables are introduced that allow the detection of inconsistent behavior. The statistical properties of the variables are analyzed. Experiments confirm their suitability for inconsistency detection.     

Deriving a particle system from continuum mechanics for the animation of deformable objects

Mass-spring and particle systems have been widely employed in computer graphics to model deformable objects because they allow fast numerical solutions. In this work, we establish a link between these discrete models and classical mathematical elasticity. It turns out that discrete systems can be derived from a continuum model by a finite difference formulation and approximate classical continuum models unless the deformations are large. In this work, we present the derivation of a particle system from a continuum model, compare it to the models of classical elasticity theory, and assess its accuracy. In this way, we gain insight into the way discrete systems work and we are able to specify the correct scaling when the discretization is changed. Physical material parameters that describe materials in continuum mechanics are also used in the derived particle system.     

Geometric particle swarm optimization for robust visual ego-motion estimation via particle filtering

Conventional particle filtering-based visual ego-motion estimation or visual odometry often suffers from large local linearization errors in the case of abrupt camera motion. The main contribution of this paper is to present a novel particle filtering-based visual ego-motion estimation algorithm that is especially robust to the abrupt camera motion. The robustness to the abrupt camera motion is achieved by multi-layered importance sampling via particle swarm optimization (PSO), which iteratively moves particles to higher likelihood region without local linearization of the measurement equation. Furthermore, we make the proposed visual ego-motion estimation algorithm in real-time by reformulating the conventional vector space PSO algorithm in consideration of the geometry of the special Euclidean group SE(3), which is a Lie group representing the space of 3-D camera poses. The performance of our proposed algorithm is experimentally evaluated and compared with the local linearization and unscented particle filter-based visual ego-motion estimation algorithms on both simulated and real data sets.     

A parameter selection strategy for particle swarm optimization based on particle positions

In this study, we found that engineering experience can be used to determine the parameters of an optimization algorithm. We came to this conclusion by analyzing the dynamic characteristics of PSO through a large number of experiments. We constructed a relationship between the dynamic process of particle swarm optimization and the transition process of a control system. A novel parameter strategy for PSO was proven in this paper using the overshoot and the peak time of a transition process. This strategy not only provides a series of flexible parameters for PSO but it also provides a new way to analyze particle trajectories that incorporates engineering practices. In order to validate the new strategy, we compared it with published results from three previous reports, which are consistent or approximately consistent with our new strategy, using a suite of well-known benchmark optimization functions. The experimental results show that the proposed strategy is effective and easy to implement. Moreover, the new strategy was applied to equally spaced linear array synthesis examples and compared with other optimization methods. Experimental results show that it performed well in pattern synthesis.     

Data parallel sorting for particle simulation

Sorting on a parallel architecture is a communications intensive event which can incur a high penalty in applications where it is required. In the case of particle simulation, only integer sorting is necessary, and sequential implementations easily attain the minimum performance bound of O(N) for N particles. Parallel implementations, however, have to cope with the parallel sorting problem which, in addition to incurring a heavy communications cost, can make the minimum performance bound difficult to attain. This paper demonstrates how the sorting problem in a particle simulation can be reduced to a merging problem, and describes an efficient data parallel algorithm to solve this merging problem in a particle simulation. The new algorithm is shown to be optimal under conditions usual for particle simulation, and its fieldwise implementation on the Connection Machine is analysed in detail. The new algorithm is about four times faster than a fieldwise implementation of radix sort on the Connection Machine.