On-Demand DNA Synthesis on Solid Surface by Four Directional Ejectors on a Chip

This paper presents a synthesis technique for any random deoxyribonucleic acid (DNA) sequences on different substrates such as glass, plastic or silicon by an array of directional droplet ejectors. Any DNA sequence can be synthesized by ejecting droplets of DNA bases by an ultrasonic transducer having lens with air-reflectors (LWARs) that requires no nozzle. The LWAR is capable of ejecting liquid droplets around 80 mum in diameter, and reduces the amount of reagents needed for the synthesis from most of conventional microarray techniques. One major advantage of the nozzleless ejector is that it can eject droplets in any direction, so that a spot can be inked by four ejectors (carrying four DNA bases) without moving the ejector. The directional ejection of the droplets removes the need for aligning the substrate with the ejector, and minimizes the automation and control circuitry. To demonstrate the DNA synthesis capability of the directional droplet ejectors, four LWAR ejectors were used to synthesize a 15-mer 5'-CGCCAAGCAGTTCGT-3' on a substrate surface. This paper describes the concept and scheme of the on-demand DNA synthesis (with MEMS ejector integrated with microfluidic components) along with experimental results of an actual DNA synthesis by four directional droplet ejectors.     

Control of serial microfluidic droplet size gradient by step-wise ramping of flow rates

This paper describes a method to control and detect droplet size gradient by step-wise flow rate ramping of water-in-oil droplets in a microfluidic device. The droplets are generated in a cross channel device with two oil inlets and a water inlet. The droplet images are captured and analyzed in a time sequence in order to quantify the droplet generation frequency. It is demonstrated that by controlling the ramping of the oil flow rates it is possible to manipulate the ramping of droplet sizes. Increasing or decreasing of droplet sizes is achieved for a step-wise triangular ramping profile of the oil flow rate. The dynamic behavior of droplets due to the step-wise flow pulses is investigated. Uniform linear size ramping of water-in-oil droplets from 73 to 83 μm in diameter is generated with an oil flow ramping range from 1 to 11 μL/min in a minimum of five steps while water flow rate is held constant at 2 μL/min.     

Pneumatic dispensing of nano- to picoliter droplets of liquid metal with the StarJet method for rapid prototyping of metal microstructures

This study presents a new, simple and robust, pneumatically actuated method for the generation of liquid metal micro droplets in the nano- to picoliter range. The so-called StarJet dispenser utilizes a star-shaped nozzle geometry that stabilizes liquid plugs in its center by means of capillary forces. Single droplets of the liquid metal can be pneumatically generated by the interaction of the sheathing gas flow in the outer grooves of the nozzle and the liquid metal. For experimental validation, a print head was build consisting of silicon chips with a star-shaped nozzle geometry and a heated actuator (up to 280°C). The silicon chips are fabricated by Deep Reactive Ion Etching (DRIE). Chip designs with different star-shaped geometries were able to generate droplets with diameters in the range of the corresponding nozzle diameters. The StarJet can be operated in two modes: Either continuous droplet dispensing mode or drop on demand (DoD) mode. The continuous droplet generation mode for a nozzle with 183?μm diameter shows tear-off frequencies between 25 and 120?Hz, while droplet diameters remain constant at 210?μm for each pressure level. Metal columns were printed with a thickness of 0.5–1.0?mm and 30?mm height (aspect ratio >30), to demonstrate the directional stability of droplet ejection and its potential as a suitable tool for direct prototyping of the metal microstructures.     

基于机器视觉的BGA连接器焊球检测

文章提出了一种基于机器视觉的BGA器件焊球质量检测方法。该方法在同一视点下,用相同光源分别以两种不同入射方向角照射被测BGA连接器焊球,获得两幅图像,然后得到BGA连接器焊球在x方向的曲面信息,以此计算出被测焊球的主要质量参数。最后给出了BGA连接器焊球检测的主要算法。     

自主移动机器人定位系统中Kalman滤波算法改进*

为了解决常规Kalman滤波算法在移动机器人定位过程中运算量大、精度不高的问题,在分析传统Kalman滤波器缺点的基础上,提出了一种基于UT参数变换的方法对常规Kalman滤波算法进行了改进。改进后的Kalman滤波算法消减了传统Kalman滤波器高阶项无法忽略而带来的误差。实验结果表明,改进型的Kalman滤波算法使机器人的最大位置偏差得到减小,对移动机器人的定位精度有明显改善,误差仿真曲线表明,改进后的定位结果误差波动不明显,使定位系统的稳定性得到了较大提高。     

Global network design for robust operation of microfluidic droplet generators with pressure-driven flow

This study investigates the influence of both local generator design and global network architecture in improving the stability and operational performance of microfluidic droplet generators. We identify naturally occurring short-term and long-term oscillations that are related to changes in the flow of the two phases. Short-term oscillations are related to the creation of each droplet and are quantified by tracking droplet speed in the network. Long-term oscillations are caused by dynamic feedback associated with the periodic change in the hydrodynamic resistance of the network as droplets enter and exit the system. Our analysis identifies that these long-term oscillations are best quantified by measuring changes in droplet spacing rather than the conventional method of using droplet size. Furthermore, we find that these long-term oscillations have a periodicity that matches the residence time of droplets within the network. In combination with experiments, a simple compact model is developed to study these oscillations and guide the network design of droplet generators. As part of this analysis a set of design rules is developed to help improve overall generator performance using pressure-driven flow.     

Study on stable delivery of charged uniform droplets for freeform fabrication of metal parts

Electrostatic delivery of charged uniform metal droplets is a novel method to deposit metal parts with short process period and low cost. But the delivery process is unstable and delivery accuracy of charged droplets deteriorates because of actions of mutual interactions of closely charged droplets. A droplet generator with droplet charging and deflecting system has been established to find out the way for stably and accurately deflecting droplets. The parameters for generating uniform droplets were first s...     

Electrostatic actuation of microscale liquid-metal droplets

This paper reports sliding of micro liquid-metal droplets by electrostatic actuation for MEMS applications, bi-stable switching in particular. Basic theory concerning droplets on a plane solid surface is exposed followed by experimental study. Being a major parameter in the modeling of sliding droplets, the contact angle has been characterized in the case of mercury on an oxidized silicon wafer. The method used involves both traditional optical microscope and confocal laser imaging. The contact angle is found to be around 137/spl deg/ with an associated standard deviation of 8/spl deg/. The sample preparation is detailed. The droplets deposition method is based on selective condensation of mercury vapor on gold dots acting as preferred nucleation sites. This technique provides control of droplet dimensions and locations and is suitable for batch fabrication. Experimental study of electrostatic actuation coupled with finite-element method (FEM) analysis is described, leading to the determination of the sliding condition parameter, which represents a contact angle hysteresis of about 6/spl deg/. Experimental results also confirm the proportionality between minimum driving force and droplet dimension. Finally, a design optimization methodology is proposed, based on the use of finite-element model simulations.     

Micro cell encapsulation and its hydrogel-beads production using microfluidic device

In this paper, we propose a cell encapsulation and hydrogel-beads production method using droplet formation in a microchannel. The hydrogel-beads produced by the microfluidic device developed here have smaller diameter and narrower distribution in their diameter compared to the conventional method, such as the droplet extrusion and the emulsification. The effects of the flow velocity and microchannel wall were analyzed based on fluid dynamical analysis. The results revealed that the wall effect of the microchannel strongly affected to the diameter of the droplet and the shape of the hydrogel-beads.     

Piezoelectric-actuated drop-on-demand droplet generator control using adaptive wavelet neural network controller

This paper presents the design, fabrication and control of a piezoelectric-type droplet generator which is applicable for on-line dispensing. Adaptive wavelet neural network (AWNN) control is applied to overcome nonlinear hysteresis inherited in the LPM. The adaptive learning rates are derived based on the Lyapunov stability theorem so that the stability of the closed-loop system can be assured. Unlike open-loop dispensing system, the system proposed can potentially generate droplets with high accuracy. Experimental verifications focusing on regulating control are performed firstly to assure the reliability of the proposed control schemes. Real dispensing is then conducted to validate the feasibility of the piezoelectric-actuated drop-on-demand droplet generator. In order to illustrate the effectiveness of the proposed method, experimental results obtained using the AWNN scheme are compared with their counterparts using traditional PID control. The results indicate that the proposed AWNN scheme not only outperforms PID control but also works well in developing the piezoelectric-actuated drop-on-demand dispensing system. The proposed dispensing system provides droplet chains with an averaged mass as small as 31.5 mg while the associated standard deviation is as low as 0.72%.     

Design, Fabrication, and Visual Servo Control of an XY Parallel Micromanipulator With Piezo-Actuation

This paper presents a complete design and development procedure of a new XY micromanipulator for two-dimensional (2-D) micromanipulation applications. The manipulator possesses both a nearly decoupled motion and a simple structure, which is featured with parallel-kinematic architecture, flexure hinge-based joints, and piezoelectric actuation. Based on pseudo-rigid-body (PRB) simplification approach, the mathematical models predicting kinematics, statics, and dynamics of the XY stage have been obtained, which are verified by the finite-element analysis (FEA) and then integrated into dimension optimization via the particle swarm optimization (PSO) method. Moreover, a prototype of the micromanipulator is fabricated and calibrated using a microscope vision system, and visual servo control employing a modified PD controller is implemented for the accuracy improvement. The experiments discover that a workspace size of 260 mum times 260 mum with a 2-D positioning accuracy and repeatability around 0.73 and 1.02 mum, respectively, can be achieved by the micromanipulator.     

冲击载荷下BGA焊点应有限元模拟

从动力学角度分析了PBGA组件在高加速度冲击载荷下的响应.采用解析法与有限元分析相结合的方式考察了PBGA组件的结构参数和材料特性等因素对焊点应力的影响,并运用参量分析法比较了这些因素对焊点应力的影响程度.分析结果表明:在冲击载荷下,焊点位置对焊点应力的影响最大,应力峰值出现在PBGA器件的最外端焊点上,而焊点高度、BGA模量以及PCB模量对焊点应力影响较小.增大焊点直径或减小焊点模量均可有效减小焊点的应力,选择适当的PCB厚度也可降低焊点的应力.     

Fluid dynamic behavior of dispensing small droplets through a thin liquid film

This paper presents a technology for dispensing droplets through thin liquid layers. The system consists of a free liquid film, which is suspended in a frame and positioned in front of a piezoelectric printhead. A droplet, generated by the printhead, merges with the film, but due to its momentum, passes through and forms a droplet that separates on the other side and continues its flight. The technology allows the dispensing, mixing and ejecting of picolitre liquid samples in a single step. This paper overviews the concept, potential applications, experiments, results and a numerical model. The experimental work includes studying the flight of ink droplets, which ejected from an inkjet print head, fly through a free ink film, suspended in a frame and positioned in front of the printhead. We experimentally observed that the minimum velocity required for the 80 pl droplets to fly through the 75 ± 24 μm thick ink film was of 6.6 m s^?1. We also present a numerical simulation of the passage of liquid droplets through a liquid film. The numerical results for different initial speeds of droplets and their shapes are taken into account. We observed that during the droplet–film interaction, the surface energy is partially converted to kinetic energy, and this, together with the impact time, helps the droplets penetrate the film. The model includes the Navier–Stokes equations with continuum-surface-tension force derived from the phase-field/Cahn–Hilliard equation. This system allows us to simulate the motion of a free surface in the presence of surface tension during merging, mixing and ejection of droplets. The influence of dispensing conditions was studied and it was found that the residual velocity of droplets after their passage through the thin liquid film well matches the measured velocity from the experiment.     

Embedded printing trace planning for aluminum droplets depositing on dissolvable supports with varying section

Droplet-based 3D printing is a promising method to manufacture thin-walled parts with high-quality cavity surfaces of a complex geometry by virtue of dissolvable supports. However, conventional equispaced droplet scanning strategies cannot be used for dissolvable support assisted droplet printing that involves more complex impingement conditions, particularly when the dissolvable supports possess varying sections. This paper investigates the printing strategies for aluminum droplets depositing on dissolvable support that possesses preset dimensions, inclined surfaces and corners. Experimental and numerical results show that: (1) printing orientation on the oblique surfaces of dissolvable supports significantly influences the formation of hole-defects; (2) the printing strategy for corners should be specially adjusted to minimize defects. Moreover, the droplet scanning spacings on the support surfaces with preset shape and dimensions are elaborately regulated according to four different cases. Finally, the fabrication experiments of aluminum horns are performed to further examine the formability of the established droplet scanning strategies. The density of the printed horn is measured to be ~98% using the standard Archimedes method, and the corresponding industrial CT scanning results also verify a porosity-free inner structure. The cavity surfaces of the horn are smooth without obvious defects, and the average surface roughness of the inner surface is ~Ra 4.2 μm (only 0.53% of the droplet diameter). These measurement results indicate that the proposed strategies can effectively eliminate hole-defects that are commonly seen in equispaced printing.     

Transfer of low nanoliter volumes between microplates using focused acoustics—automation considerations

Acoustic droplet ejection (ADE) gently and precisely aliquots nanoliter and picoliter liquid volumes without any physical contact with the solution being transferred. The technology is very automation-friendly, as it is compatible with conventional microplates. Focused energy from an acoustic transducer induces droplet ejection into an inverted standard microplate. The commercial system transfers low-nanoliter volumes of dimethyl sulfoxide–dissolved compound libraries and thereby enables cell-based assays to be performed in 1536-well plates.     

Low‐cost display assembly and interconnect using ink‐jet printing technology

Ink‐jet printing methods may be utilized for efficient micro‐deposition of solder bumps, spacer balls, and adhesive sealant/bond lines, as well as liquid‐crystal and color‐filter droplets, in the manufacture of display panels. Advantages realized by this approach include data‐driven low‐cost high‐speed non‐contact environmentally friendly processing.     

Modeling and characterization of an industrial inkjet head for micro-patterning on printed circuit boards

A conceptual design using computational fluid dynamics (CFD) and micro-electro-mechanical systems (MEMS) fabrication has been performed to develop an industrial inkjet head for micro-patterning on printed circuit boards. The printhead has been fabricated with silicon and silicon on insulator (SOI) wafers by MEMS process and silicon to silicon bonding method. The measured displacement waveform from a piezoelectric actuator by laser doppler vibrometer (LDV) was used as input data for the three-dimensional flow solver to simulate the droplet formation. The mechanism of droplet ejection from piezoelectric-type inkjet heads was investigated by simulating two-phase flows of the air and metal inks. As a preliminary approach, liquid metal jetting phenomena are identified by simulating droplet ejection and droplet formation in a consequent manner. Parametric studies are followed by the design optimization process to deduce key factors to inkjet head performance: nozzle geometry, droplet size, ejecting speed, pulse amplitude, and ink viscosity. The present design tool, based on a two-phase flow solver and experimental measurements, has shown its promising applicability to various concept designs of industrial inkjet system for micro-patterning on electronic chips and boards.     

Nanoliter compound-droplet generation with composition variation

A new method for generation of nanoliter-volume, two-phase (compound) droplets with the ability to vary composition (i.e., encapsulant thickness) is presented. Thermocapillary-driven levitation of water droplets, a capability with potential for the improvement of lab-on-a-chip (LOC) processes, requires encapsulation by a secondary, less-volatile fluid that will also avoid the adverse effects of water-surface contamination on the driving surface motion. Key components of the closed system include the droplet generator actuated by a piezoelectric diaphragm, a pressure-control device, and a specialized nozzle for delivery of the encapsulating liquid. Experimental investigations demonstrate how system pressure variations allow composition changes, and voltage waveform input parameters regulate ejection dynamics, necessary for droplet capturing during the levitation process.     

Generation of uniform-size droplets by multistep hydrodynamic droplet division in microfluidic circuits

A microfluidic system is presented to generate multiple daughter droplets from a mother droplet, by the multistep hydrodynamic division of the mother droplet at multiple branch points in a microchannel. A microchannel network designed based on the resistive circuit model enables us to control the distribution ratio of the flow rate, which dominates the division ratios of the mother droplets. We successfully generated up to 15 daughter droplets from a mother droplet with a variation in diameter of less than 2%. In addition, we examined factors affecting the division ratio, including the average fluid velocity, interfacial tension, fluid viscosity, and the distribution ratio of volumetric flow rates at a branch point. Additionally, we actively controlled the volume of the mother droplets and examined its influence on the size of the daughter droplets, demonstrating that the size of the daughter droplets was not significantly influenced by the volume of the mother droplet when the distribution ratio was properly controlled. The presented system for controlling droplet division would be available as an innovative means for preparing monodisperse emulsions from polydisperse emulsions, as well as a technique for making a microfluidic dispenser for digital microfluidics to analyze the droplet compositions.     

High throughput micro droplet generator array controlled by two-dimensional dynamic virtual walls

A chamber-free two-dimensional-array micro droplet generator has been realized by precise time-delayed control of micro bubble arrays as virtual chamber walls. Droplets can be ejected out by the bubbles around the ejection site in specific configuration of excitation, thus replacing physical chamber walls for pressure preservation. The micro droplet generator array was fabricated by heater lithography and direct nozzle formation on a laminated SU-8 dry film without any solid chamber wall among heaters. The nozzle density of this compact droplet generator can be five to ten times higher than that of commercial inkjet printheads in one-dimensional formats. The volume and initial speed of the generated droplets was 3.6–5.7 pL and 14–15 m/s, respectively, meeting the standard of commercial printheads. The micro droplet generator is free of satellite droplets due to the precise meniscus control. The analyzed data shows the meniscus undergoes a “push–pull–push” progress which effectively cuts the liquid column short. The refilling time of the innovative micro droplet generator was estimated to be 0.296 μs from the simplified chamber model, and it was one-tenth of the commercial printheads. In addition, the frequency response was estimated to be higher than 20 kHz by observing the meniscus fluctuation condition. Finally, a 3 × 5 heater array was used to generate two droplets simultaneously, which shows that the crosstalk problem can be eliminated by precise time-delayed control. An interlacing operation was also proposed to address the large array control algorithm. To summarize, a 330-dpi monolithic micro droplet generator prototype has been proposed for high speed and large 2D format printing.