基于液滴润湿形态测定接触角的图像处理方法

接触角是表征液体与固体润湿程度的重要度量参数,焊料、焊剂、焊盘及阻焊层的接触角与电子制造焊接工艺密切相关。针对目前基于图像测量接触角的精度还不够高的现状,提出运用Young-Laplace方程的物理原理作为图像处理的方法,基于液滴润湿形态图像处理体积并捕获顶点坐标作为拟合参数,获得良好的接触角测量精度,显著减小了重力、液滴体积和光反射干扰对测量结果的影响。     

A dynamic model for predicting the motion of solder droplets during assembly

The dynamic motion of a solder droplet during assembly is a complex, unsteady, free surface problem involving surface tension and viscous effects. The motion of the droplet is coupled with the motion of the component or chip to be assembled and involves dynamic contact lines. A methodology based on a non-uniform rational b-spline (NURBS) discretization has been developed for the dynamic analysis of the droplet motion. A surface energy based formulation has been developed to incorporate the surface tension effects. The developed methodology leads to an updated Lagrangian scheme with a Galerkin in space and Least square in time formulation. The NURBS representation used for the spatial discretization enables the method to handle problems involving complex droplet geometries. The ability of the NURBS representation to provide both global and local control, along with the least square method used in this methodology, enables us to develop an unconditionally stable time integration scheme which can be optimized to achieve desired accuracy and numerical dissipation efficiently. A sample problem of droplet shape evolution has been solved to demonstrate the path prediction capability of the proposed methodology. In future, the method can be applied to solve various real world dynamic motion problems associated with droplets.     

A Versatile Approach for Direct Patterning of Liquid Metal Using Magnetic Field

Patterning of liquid metal (LM) is usually an integral step toward its practical applications. However, the high surface tension along with surface oxide makes direct patterning of LM very challenging. Existing LM patterning techniques are designed for limited types of planar substrates, which require multiple‐step operation, delicate molds and masks, and expensive equipment. In this work, a simple, versatile, and equipment‐free approach for direct patterning of LM on various substrates using magnetic field is reported. To achieve this, magnetic microparticles are dispersed into LM by stirring. When a moving magnetic field is applied to the LM droplet, the aggregated magnetic microparticles deform the droplet to a continuous line. In addition, this approach is also applicable to supermetallophobic substrates since the applied magnetic field significantly enhances the contact between LM and substrate. Moreover, remote manipulation of the magnetic microparticles allows direct patterning of LM on nonplanar surfaces, even in a narrow and near closed space, which is impossible for the existing techniques. A few applications are also demonstrated using the proposed technique for flexible electronics and wearable sensors.     

基于光纤干涉法的液体表面张力系数测量及温度影响研究

为了提高液体表面张力系数的测量精度,并充分 发挥光纤干涉法的高精度、 非接触等优点,提出了一种利用干涉原理的空心光纤(HOF)液体表面张力系数测量 方法。即利用HOF一端与单模光纤(SMF)相连,另一端与待测液面接触形成Fabry-Perot(F- P)腔 实现液体表面张力系数的测量。毛细效应使得被测液体进入HOF内,不同 的表面张力导致HOF形成的F-P腔腔长发生变化,通过检测F-P腔两个相邻干 涉峰的间距就可以间接得出液体的表面张力系数大小。实验中,分别测定了相同 温度下5种不同液体的表面张力系数和不同温度下蒸馏水的表面张力系数,对测 量的结果进行最小二乘法线性拟合。实验中,温度的改变采用水浴加热法,不同温 度下蒸馏水表面张力系数的测量结果与理论值的最大误差为0.26%。 本文方法结构 简单,容易操作,有较高的灵敏度,可为实际液体表面张力系数测量提供参考。     

Wetting‐Assisted Crack‐ and Wrinkle‐Free Transfer of Wafer‐Scale Graphene onto Arbitrary Substrates over a Wide Range of Surface Energies

The polymer‐supported wet transfer of chemical vapor deposition‐grown graphene provides high‐quality large‐area graphene on a target substrate. The transfer‐induced defects that result from these processes, such as micrometer‐scale folds and cracks, have been regarded as an inevitable problem. Here, the transfer processes are thoroughly examined stage‐by‐stage and it is found that lamination wrinkles, which cause defects in the graphene, are generated as a result of the high contact angles of the trapped transfer medium liquids. Systematic theoretical and experimental studies demonstrate that a liquid droplet with a low surface tension trapped between the polymer/graphene film and the substrate minimizes lamination wrinkles during the transfer process by completely wetting the target substrate, regardless of the surface energy. In connection with these results, a simple and broadly applicable transfer method is developed using an organic liquid with a low surface tension to uniformly transfer high‐quality graphene onto arbitrary substrates, even onto superhydrophobic substrate. The graphene obtained using the proposed organic liquid transfer method displays better electrical and mechanical properties than the graphene transferred by the conventional method using water. This effective and practical transfer method provides an approach to obtaining high‐quality graphene for use in graphene‐based devices.     

光纤传感器在液体参量测量中的应用

介绍了一种利用锥形光纤探头测量液体参量的新方法,并且对不同探测条件下的灵敏度作出了比较。在标准的纤芯-包层-涂敷层传感光纤的光线泄漏区,液体通过压力管口被喷射到光纤上作为涂敷层。液滴由压力管口自动喷射出来,通过改变气体压力以及液体密度、黏度、表面张力等物理参量,就可以控制液滴的直径、折射率等参量。在光线泄漏区,传感光纤包层模式功率随着液体参量的改变而改变,从而锥形光纤探头探测到的输出功率也随之改变。实验以橄榄油、甘油、松节油为测量对象,解决了油类液体参量测量难度大的问题,测量灵敏度可以达到折射率每变化0.01,功率改变2~4 dB。该方法与以往所做的对沿光纤传播的包层模式功率的损失特性的简单分析对比,测量结果与理论曲线十分相符。     

基于模式分类的喷嘴料液雾滴速度测量研究

测量烟叶加料过程中料液雾滴喷射后的速度变化,为烟叶加料均匀性的评价提供有效数据。实验从喷嘴的轴向面采集喷出的雾滴图像,对采集到的图像进行预处理和图像分割,采用模式分类对分割出的雾滴分类,根据高速相机成像的测量方法计算出每一类雾滴的速度。研究结果表明,由模式分类统计出的数据,其准确率达到95.65%,使用该数据计算出的速度误差为4.6%,两项数据均在规定范围之内。使用高速摄像机获取图像,采用软件计算出雾滴速度,与早期实验方案相比,降低了测量设备价格,实现低成本测量;模式分类的测量方法准确率较高,为后续加料均匀性分析提供可靠的数据,且效率更高,同时为数据测量的智能化打下基础。     

Static charge removal with IPA solution

Due to the an increase in pattern densities and wafer diameters, it is extremely difficult for wet chemical processing to perform complete cleaning, rinsing and drying for highly rugged surface of very fine pattern ULSI devices. IPA Vapor Drying is a widely used drying method in semiconductor manufacturing. As IPA has low surface tension and very high solubility to water, it is suitable for IPA vapor process to perfectly eliminate contamination of the wafer surface. This drying system also has an ability to eliminate static charge and can essentially achieve the high quality of the surface cleanliness. Therefore, the mechanism of static charge removal was studied using a quantitative method for the direct measurement of static charge     

Electric Field and Gradient Microstructure for Cooperative Driving of Directional Motion of Underwater Oil Droplets

Driving a liquid droplet with control of directional motion on a solid surface, by introducing a surface wettability gradient or external stimuli, has attracted considerable research attention. There still remain challenges, however, due to the slow response rate and slow speed of continuous liquid droplet motion on the structured surface. Here, an approach to continuously drive the underwater oil droplet with control of directional motion by the cooperative effects of an electric field and the gradient of a porous polystyrene microstructure is demonstrated. The gradient microstructure induces the liquid droplet to take on an asymmetrical shape, causing unbalanced pressure on both ends to orient the droplet for motion in a particular direction. Meanwhile, the electric field decreases the contact area and the corresponding viscous drag between the droplet and the gradient‐structured surface. Then, the unbalanced pressure pushes the underwater oil droplet to move directionally and continuously at a certain voltage. This work provides a new strategy to control underwater oil droplets and realize unidirectional motion. It is also promising for the design of new smart interface materials for applications such as electrofluidic displays, biological cell and particle manipulation, and other types of microfluidic devices.     

Collective Wetting of a Natural Fibrous System and Its Application in Pump‐Free Droplet Transfer

Novel wetting strategies in plants have inspired numerous notable biomimetic surfaces over the past decade, such as self‐cleaning surfaces mimicking the water repellency of lotus leaves and directional water transport surfaces imitating the slippery surface on carnivorous plants. Here, a new wetting behavior in dandelion seed (genus Taraxacum) is found, characterized by capturing a droplet inside it. The critical conditions required for wetting of the fiber assay in terms of the fibrous geometry and liquid surface tension are identified, and how these factors quantitatively affect the volume of the captured droplet is shown further. More importantly, the reverse process can be triggered by introducing a competitive liquid phase with smaller surface tension to the wetted fiber assay, as it is demonstrated by the release of the captured water droplet in oil. These results enhance the understanding on wetting of fibrous structures and would benefit the design of novel intelligent and responsive devices. This newly identified wetting behavior holds great potential for fine control and micromanipulation of liquid. As a demonstration, it is illustrated that the natural fibrous structure is capable of manipulating a small volume of liquid for droplet‐based multiplexed chemical reaction.     

Strategies for Volumetric Recovery of Large Scale Damage in Polymers

The maximum volume that can be restored after catastrophic damage in a newly developed regenerative polymer system is explored for various mixing, surface wetting, specimen configuration, and microvascular delivery conditions. A two‐stage healing agent is implemented to overcome limitations imposed by surface tension and gravity on liquid retention within a damage volume. The healing agent is formulated as a two‐part system in which the two reagent solutions are delivered to a through‐thickness, cylindrical defect geometry by parallel microvascular channels in thin epoxy sheets. Mixing occurs as the solutions enter the damage region, inducing gelation to initiate an accretive deposition process that enables large damage volume regeneration. The progression of the damage recovery process is tracked using optical and fluorescent imaging, and the mixing efficiency is analyzed. Complete recovery of gaps spanning 11.2 mm in diameter (98 mm²) is achieved under optimal conditions.     

条纹投影轮廓术系统模型与标定综述

条纹投影轮廓术能较好地兼顾系统灵活性与测量精度,是光学三维表面成像与测量的主流技术。利用条纹投影轮廓术进行三维成像,首先需要建立合适的系统模型,然后通过系统标定来确定描述模型的系统参数,最后利用标定的系统模型进行三维重建,获得物体的三维表面形貌。由此可见,系统标定与系统模型密不可分,对三维成像的性能有直接影响。根据相位-三维映射和双目立体视觉两类不同的工作原理,对条纹投影轮廓术的系统模型和系统标定方法进行了综述,并简要总结了评估系统精度的方法和依据。     

基于条纹反射法的平面镜面形测量

为了评价平面镜面形误差,采用基于条纹反射法的面形检测原理、通过平面镜法线偏移实现面形误差评价的方法。将正弦条纹投射至光屏,经被测平面镜反射至相机,通过小孔成像原理和四步相移法获得被测平面镜上一点的法线,并与经最小二乘算法面形重建的该点理论法线比较,获得该点法线偏移,利用法线偏移实现对平面镜的面形评价。对测量方法进行计算机仿真,以证明其正确性;搭建实验测量系统,并对某一款手机屏幕进行测量实验。结果表明,该测量方法的重复性精度优于1mrad,测量重复性高。该研究为玻璃面板等具有高反射特性的平面面形误差提供了参考。     

Measurement of the surface tension of water using microwavebackscatter from gravity-capillary waves

A technique developed for measuring the surface tension of fluid based on the resonant scattering of microwave radiation from gravity-capillary waves on the surface of the fluid is discussed. The method was implemented by generating monochromatic water waves in a tank, illuminating them with microwave radiation, and then tuning the water-wave frequency until Bragg resonance was observed, that is, until the backscattered power was observed to reach its maximum value. At resonance, the wavelength and wave frequency can be calculated from the physical parameters of the system and from the Doppler shift of the scattered radiation. Laboratory experimental results indicate an accuracy on the order of ±1.6 dyn/cm for the surface-tension measurement. This accuracy is in agreement with an error model based on the width of the Bragg resonance line. The technique is, in principle, nonintrusive and thus can be used for observing the properties of surfactants on water surfaces     

Energy minimization-based analysis of electrowetting for microelectronics cooling applications

Electrowetting (EW)-induced droplet motion has been studied over the last decade in view of its promising applications in the field of microfluidics. The objective of the present work is to analyze the physics underlying two specific EW-based applications for microelectronics thermal management. The first of these involves heat absorption by liquid droplets moving on the surface of a chip under EW actuation. Droplet motion between two flat plates under the influence of an electrowetting voltage is analyzed. An energy minimization framework is employed to predict the actuation force on a droplet. This framework, in combination with semi-analytical models for the forces opposing droplet motion, is used to develop a model that predicts transient EW-induced droplet motion. The second application is targeted at hot-spot thermal management and relies on the control of droplet states on artificially structured surfaces through an applied EW voltage. The influence of an electrowetting voltage in determining and altering the state of a static droplet resting on a rough surface is analyzed. An energy minimization-based modeling approach reveals the influence of interfacial energies, surface roughness parameters and electric fields in determining the apparent contact angle of a droplet in the Cassie and Wenzel states under the influence of an EW voltage. The model is used to establish preliminary criteria to design rough surfaces for use in the hot-spot mitigation application. The concept of an electrically tunable thermal resistance switch for hot-spot cooling applications is introduced and analyzed.     

A time domain fluorescence tomography system for small animal imaging

We describe the application of a time domain diffuse fluorescence tomography system for whole body small animal imaging. The key features of the system are the use of point excitation in free space using ultrashort laser pulses and noncontact detection using a gated, intensified charge-coupled device (CCD) camera. Mouse shaped epoxy phantoms, with embedded fluorescent inclusions, were used to verify the performance of a recently developed asymptotic lifetime-based tomography algorithm. The asymptotic algorithm is based on a multiexponential analysis of the decay portion of the data. The multiexponential model is shown to enable the use of a global analysis approach for a robust recovery of the lifetime components present within the imaging medium. The surface boundaries of the imaging volume were acquired using a photogrammetric camera integrated with the imaging system, and implemented in a Monte-Carlo model of photon propagation in tissue. The tomography results show that the asymptotic approach is able to separate axially located fluorescent inclusions centered at depths of 4 and 10 mm from the surface of the mouse phantom. The fluorescent inclusions had distinct lifetimes of 0.5 and 0.95 ns. The inclusions were nearly overlapping along the measurement axis and shown to be not resolvable using continuous wave (CW) methods. These results suggest the practical feasibility and advantages of a time domain approach for whole body small animal fluorescence molecular imaging, particularly with the use of lifetime as a contrast mechanism.      

基于声波驱动的高速变焦液体透镜振动特性分析

高速变焦液体透镜在快速移动物体的目标捕捉方面具有重要的应用.高频声波激励方法在理论上能够实现毛细腔边沿(靠表面张力)约束液滴的高速往复运动,但是相关工艺试验研究是目前该技术成熟应用的关键.文章在对毛细腔贯通液滴共振理论分析的基础上,基于3D打印技术开发了一种采用双源声波激励毛细腔贯通液滴进行振动的实验装置.在分析能量损失的基础上,采用激光多普勒测振仪分析了相关工艺参数对毛细腔贯通液滴振动频率和振幅的影响,总结了相关规律,为实现高速变焦液体透镜技术的应用奠定了基础.     

面向机器视觉测量的液体透镜调焦系统标定方法

高性能光学成像器件是机器视觉测量的重要基础,液体透镜作为一种结构紧凑的快速电控调焦器件,在机器视觉测量领域中具有明确的应用前景。针对液体透镜调焦器件在视觉测量中性能易受环境干扰、系统内参难以准确标定的问题开展研究。首先,构建了基于Optotune液体透镜器件的机器视觉测量系统,分析了液体透镜器件电控调焦工作机理,提出了调焦系统的电流-焦距数学模型,研究了影响液体透镜调焦系统参数的温度、重力因素作用机理,分别提出了温度-焦距、重力-主点位置影响量传递与补偿数学模型;然后,将上述各系统模型与针孔相机成像模型相结合,提出了液体透镜调焦系统的函数化内参表达式,设计了求取表达式全部系数的标定装置与标定流程,并进行了系统内参标定实验,验证了文中内参标定方法的可行性;最后,利用标定所得的内参对边长30 mm的棋盘格靶标进行了测量实验,通过尺寸测量精度反映内参标定精度。实验结果表明,文中方法能够得到比现有插值法更准确的内参标定结果,其中图像角点空间映射位置误差均值为0.10 mm,棋盘格边长测量结果最大相对误差为0.68%,两项误差比插值法所得内参的测量结果分别减小了27.2%和54.4%。     

基于圆盘积分的体积光学测量系统设计

在不规则物体的体积测量中,用量杯进行人工测量是常用的一种方法。以不规则四棱锥的体积测量为例,结合激光学原理和CCD传感器成像技术,提出一种快速的自动测量方法。该方法利用TMS320F28335高速数字信号处理芯片作为主控电路,采用激光三角法和微积分中的圆盘法,实现不规则四棱锥的体积测量。该方法综合考虑了CCD 传感器动态成像时云点坐标的自动采集误差,并通过补全和最小二乘法来提高自动检测的精度和稳定性。实验结果表明,该系统的相对测量精度达到94%以上。     

脉冲Nd:YAG激光诱导水滴等离子体的实验研究

为了研究激光诱导液滴等离子体特性,基于脉冲激光与液滴的同步作用,采用直接成像法和阴影法研究了液滴等离子体羽辉膨胀特性及激光作用液滴的运动情况。首先采用增强型电荷耦合器件直接成像法,研究了水滴等离子体的羽辉随时间的演化;其次利用阴影法研究激光作用水滴的阴影图像的演化,观察到激光作用水滴产生的冲击波及液滴团簇的变化,分析计算了冲击波膨胀距离随时间的变化和膨胀速度。结果表明,激光诱导水滴等离子体的膨胀形状近似为椭圆,其中沿激光入射方向的一侧辐射强度较高;100ns内等离子体的膨胀变化近似为线性膨胀,100ns后膨胀趋于稳定;冲击波膨胀半径随时间线性增长,冲击波的膨胀速率约为90m/s。此研究结果可为激光诱导液滴实验提供一定的参考依据。