Theoretical analysis of a new, efficient microfluidic magnetic bead separator based on magnetic structures on multiple length scales

We present a theoretical analysis of a new design for microfluidic magnetic bead separation. It combines an external array of mm-sized permanent magnets with magnetization directions alternating between up and down with μm-sized soft magnetic structures integrated in the bottom of the separation channel. The concept is studied analytically for simple representative geometries and by numerical simulation of an experimentally realistic system geometry. The array of permanent magnets provides long-range magnetic forces that attract the beads to the channel bottom, while the soft magnetic elements provide strong local retaining forces that prevent captured beads from being torn loose by the fluid drag. The addition of the soft magnetic elements increases the maximum retaining force by two orders of magnitude. The design is scalable and provides an efficient and simple solution to the capture of large amounts of magnetic beads on a microsystem platform.     

A microfluidic flow-converter based on a double-chamber planar micropump

A microfluidic flow-converter that transforms an oscillatory flow into a steady-like flow in a reciprocating-type pumping device is successfully developed in this study. The flow quality at the outlet is found to be significantly improved. The present micro-device is composed of two single-chamber PZT micropumps in parallel arrangement and can be fabricated using simple micro-electro-mechanical-system (MEMS) techniques. Based on the concept of the electronic bridge converter, the flow rectification is supported by four passive planar valves. Two operation modes, in-phase and anti-phase, were used to test the performance of the present device. In addition, the flow characteristics at the outlet were examined by an externally triggered micro-PIV system. The results reveal that the current flow-converter provided both high volume and smoothly continuous flow rates at the outlet when it was in anti-phase mode. Moreover, the volume flow rate was linearly proportional to the excitation frequency within a specific frequency regime. This indicates that the flow-converter was easily operated and controlled. The present microfluidic flow-converter has great potential for integration into future portable micro- or bio-fluidic systems.     

A roadmap for implementing new manufacturing technology based on STEP-NC

Manufacturing is changing. New ideas of control, the maturity of CAM techniques and computer technology have enabled the definition of an advanced machine tool control standard, STEP-NC. STEP-NC is one part of a larger manufacturing picture with links to different manufacturing applications using the STEP suite of standards. STEP-NC is the key to a door behind which there is a rich field of research on manufacturing techniques and opportunities for lean, intelligent and flexible manufacturing. The problem is to pass through that door. Many potential users are waiting for a lead from control developers. Control developers are waiting for market interest. Existing legacy machinery and investment in traditional machining add inertia. Instead of having a clear development path, manufacturing has become something of a Gordian knot waiting to be disentangled. New research projects are addressing these issues as well, but this paper takes a different route in showing how strategic planning can lead to adoption of the new techniques in a phased way, a so-called ‘Roadmap’. The contribution of this paper is the manner in which the overall task of implementation has been subdivided into tasks and phases to achieve the introduction of the new technology.     

A new measurement microphone based on MEMS technology

This paper presents a new type of measurement microphone that is based on MEMS technology. The silicon chip design and fabrication are discussed, as well as the specially developed packaging technology. The microphones are tested on a number of key parameters for measurement microphones: sensitivity, noise level, frequency response, and immunity to disturbing environmental parameters, such as temperature changes, humidity, static pressure variations, and vibration. A sensitivity of 22 mV/Pa (-33 dB re. 1 V/Pa), and a noise level of 23 dB(A) were measured. The noise level is 7 dB lower than state-of-the-art 1/4-inch measurement microphones. A good uniformity on sensitivity and frequency response has been measured. The sensitivity to temperature changes, humidity, static pressure variations and vibrations is fully comparable to the traditional measurement microphones. This paper shows that high-quality measurement microphones can be made using MEMS technology, with a superior noise performance.     

一种新型的基于样本的Web信息检索技术

本文提出了一种新型的基于样本的信息检索方法.首先,通过归纳学习不同站点的样本页面,生成抽取规则;然后,用这些规则把不同站点页面的信息抽取出来,把这些信息整合到一个虚拟的关系数据库中;最后,可以直接检索数据库中的信息.从而,一次可以检索多个站点的信息,大大提高了检索效率.     

A one-step microfluidic approach for controllable preparation of nanoparticle-coated patchy microparticles

In this work, we describe a one-step microfluidic method for fabricating nanoparticle-coated patchy particles. Janus droplets composed of curable phase and non-curable phase were produced via a co-axial microfluidic device first. Nanoparticles were dispersed into the continuous phase or the non-curable phase to realize the surface coating of the curable phase. The curable phase was then polymerized by UV light and nanoparticle-coated patchy particles were obtained. The SEM characterization shows that the particles are monodispersed with nanoparticle selectively distributed on the convex or concave surface. The dispersity, size and shape of the particles could be easily controlled by changing the microfluidic flow parameters. Three different types of nanoparticles were successfully used to synthesize the patchy particles to demonstrate the validity of the method.     

基于微流体芯片结构的PDMS二次倒模工艺研究

研究了用于制作微流体芯片结构的聚二甲基硅氧烷(PDMS)与PDMS之间的倒模方法。首先,通过使用同一个微流体芯片模具倒出多个相同的PDMS负模结构;接着分别在各负模结构上溅射不同种类、不同厚度的金属,然后再对溅射过金属的负模上浇铸PDMS并固化以进行二次倒模,最后对二次倒模出的PDMS微流体结构表面粘连、结构完整性、尺寸等进行观测,从而通过比较得到倒模溅射所需的最佳金属和溅射金属薄膜的最优厚度。此方法倒出的PDMS微流体结构完整性好,不仅提出了一种全新的用于PDMS倒模的方法,而且解决了PDMS与PDMS之间直接倒模时所遇到的相互粘连和结构撕裂等难题。     

Positioning system for particles in microfluidic structures

Fast continuous flow detection of biomolecules in lab-on-a-chip structures is a challenging task. Combining these molecules with small magnetic particles, the interaction between their stray field and, e.g., magneto-resistive sensors can be used to indirectly prove the biomolecules. To position the particles on top of a sensor array at the bottom of the flow channel, we propose a microfluidic structure of changing channel height combining hydrodynamic and gravitational effects. We present numerical calculations predicting an increase in the capture rate by more than 100% in comparison to a straight channel. We experimentally realize an optical analysis of the specific binding of biotin-functionalized Chemagen beads on a streptavidin-coated surface. To prove the binding is not due to the surface effects, a second uncoated bead species is employed.     

一种基于LTCC技术的新型Marchand巴伦滤波器

设计了基于Marchand巴伦结构的小型化分布参数式巴伦滤波器。该巴伦滤波器基于低温共烧陶瓷(LTCC)技术,充分利用该技术的多层优势,通过LTCC多层布线的实现方式缩小巴伦滤波器的体积。该巴伦滤波器的结构采用了螺旋线宽边耦合带状线结构(SBCS),同时采用独特的螺旋交叉堆叠结构,有效减少了巴伦滤波器的体积。设计的巴伦滤波器采用相对介电常数为9.8的介质材料,其尺寸仅为2.0 mm×1.25 mm×0.95 mm,在1.805 GHz～2.17 GHz范围内回波损耗小于-12 dB,幅度不平衡度小于±1.2 dB,相位不平衡度小于±10°,完全能够满足当今通信设备小型化的需求。     

低成本聚合物微流控芯片加工技术综述

针对传统微流控芯片加工方法成本高昂、耗时长的问题,近年来出现了多种低成本的微流控芯片加工方法,在聚合物、纸等材料上加工、完成了能够满足其应用需求的微流控芯片。对当前各类基于聚合材料的低成本微流控芯片加工技术进行了梳理和总结,并对未来低成本微流控芯片的发展进行了展望。     

基于微流控技术的营养盐原位分析方法的研究

现有国内的营养盐监测手段主要采用岸边在线监测或现场取样+实验室分析,不能实现原位长期监测,因此无法反映较远海域的营养盐参数变化趋势。为此,提出一种可用于原位监测营养盐参数的微缩实验室方法,采用微流控技术+光电检测技术,依据信号锁相放大原理,实时分析水样的吸光度,最终实现营养盐的原位监测。长期的海试数据与实验室数据的比对结果证明了该方法的可行性。本文提出的分析方法的实现对于海洋富养化生态灾害的监测具有非常重要的意义,也对保护海洋生态环境的健康提供技术支撑。     

A new lossless orthogonal simplification method for 3D objects based on bounding structures

This paper presents a new approach to simplify 3D binary images and general orthogonal pseudo-polyhedra (OPP). The method is incremental and produces a level-of-detail sequence of OPP, where any object of this sequence bounds the previous objects and, therefore, is a bounding orthogonal approximation of them. The sequence finishes with the axis-aligned bounding box. OPP are encoded using the Extreme Vertices Model, a complete model that stores a subset of their vertices and performs fast Boolean operations. Simplification is achieved by using a new strategy, which relies on the application of 2D Boolean operations. We also present a technique, based on model continuity, for better shape preservation. Finally, we present a data structure to encode in a progressive and lossless way the generated sequence. Tests with several datasets show that the proposed method produces smaller storage sizes and good quality approximations compared with other methods that also produce bounding objects.     

Suspended SU-8 structures for monolithic microfluidic channels

SU-8 photoresist is commonly used in the field of microfabrication as structural material or for molding of microfluidic devices. One major limitation, however, is the difficulty to process partially freestanding SU-8 structures or monolithic closed cavities and channels on-chip. We propose here a simple method for the fabrication of suspended structures, in particular of monolithic SU-8 microchannels. The method is based on the processing of a SU-8 double-layer. Appropriate modification of the optical properties of the upper layer allows for selective crosslinking in the layer sandwich. This process is suitable for versatile layouts comprising open and hollow SU-8 structures on the same chip.     

A perspective on computational structures technology

Computational structures technology (CST), which blends structural modeling with computational methods and is an outgrowth of matrix methods used to analyze the dynamic and static responses of structures, is reviewed. The authors summarize CST's history and status, emphasizing software development, goals, and promising research areas. Example applications of CST from the aerospace field are presented     

构建WebGIS系统的Flash解决方法

通过对Flash SWF文件和ActionScript 3.0编程语言的分析,将其应用于空间地理信息的Web发布,试图设计一种基于Flash的WebGIS解决方案,以改善目前WebGIS数据传输量大,带宽要求高的缺陷,并提高WebGIS的执行效率。通过应用实例开发运行,详细分析了利用Flash开发WebGIS的优越性与可行性,给出了详细的总体设计框架,并分析了其实现的关键技术。研究表明开发基于Flash的WebGIS配置简单方便,客户端也不需要特别的设置,又是直接利用已有的数据文件格式,还兼容原有的信息系统,是一种值得重视和深入开发利用的技术。     

A vapor based microfluidic flow regulator

We introduce a flow regulating technology that uses trapped air bubbles in a hydrophobic microfluidic channel. We present basic designs for flow regulators and flow valves using trapped air. Experiments have successfully demonstrated the capability of this technique for delivering constant and varying flow rate, and for on-off valving. This approach to valving provides a simple, yet effective way to monolithically integrate flow and valve control on polymer Lab-on-Chip devices.     

基于数据融合的陶瓷窑炉温度记录仪的研究

根据陶瓷窑炉的功能和技术指标要求,给出了测温系统的设计方案。设计中采用了基于算术平均值与分批估计的软件数据融合的热电偶线性化处理算法,很好地解决了系统中热电偶测温的不确定性,提高了测量精度,保证了测量数据的可靠性。同时该无纸温度记录仪,具有高测量精度、高可靠性、高稳定性、低成本的特点,通用性强。     

Automated digital microfluidic sample preparation for next-generation DNA sequencing

Next-generation sequencing (NGS) technology is a promising tool for identifying and characterizing unknown pathogens, but its usefulness in time-critical biodefense and public health applications is currently limited by the lack of fast, efficient, and reliable automated DNA sample preparation methods. To address this limitation, we are developing a digital microfluidic (DMF) platform to function as a fluid distribution hub, enabling the integration of multiple subsystem modules into an automated NGS library sample preparation system. A novel capillary interface enables highly repeatable transfer of liquid between the DMF device and the external fluidic modules, allowing both continuous-flow and droplet-based sample manipulations to be performed in one integrated system. Here, we highlight the utility of the DMF hub platform and capillary interface for automating two key operations in the NGS sample preparation workflow. Using an in-line contactless conductivity detector in conjunction with the capillary interface, we demonstrate closed-loop automated fraction collection of target analytes from a continuous-flow sample stream into droplets on the DMF device. Buffer exchange and sample cleanup, the most repeated steps in NGS library preparation, are also demonstrated on the DMF platform using a magnetic bead assay and achieving an average DNA recovery efficiency of 80%±4.8%.     

Rapid and low cost replication of complex microfluidic structures with PDMS double casting technology

In this paper, a new method for fast and precise replication of high-aspect-ratio microfluidic structures is reported. First, SU-8 microfluidic structures on the master mold were replicated into Polydimethylsiloxane (PDMS), which served as an intermediate, negative mold, by a conventional soft lithography process. The PDMS negative mold was then treated by wetting its surface with a diluted aqueous solution of a hydrophilic polymer, hydroxypropylmethylcellulose and rinsed with deionized water. Last, the negative mold was used in yet another PDMS molding process to produce a PDMS replica of the microfluidic structures (the hydrofocusing unit for a micro-cytometer) with the same structures as the master mold. Experimental results showed that microstructures with high-aspect-ratio could be consistently replicated with high fidelity. This technique can not only greatly simplify the design and fabrication of master molds, but also protect the expensive and fragile original master mold. The process does not require sophisticated equipment and is well suited for the replication of precision master structures in bulk quantities at low cost.