基于数字散斑相关的封装热机械耦合效应测量

利用数字散斑相关方法(DSCM),对COB封装结构在热循环状态下的表面热机械耦合效应进行了测量.利用CCD摄像机采集封装芯片在不同温度场中的散斑图像,对比采集到的图像,获取封装芯片在温度场作用下的面内变形.根据三角法测量技术原理,将离面位移的测量转化为面内位移的测量,从而获得了芯片受热后的翘曲形变和弹性应变分布.将实验测量与有限元模拟以及理论计算的结果进行了对比,3种结果吻合得比较好,表明了实验方法的有效性和可行性.     

数字梯度敏感法在静态断裂力学实验中的应用

为了研究断裂力学问题中裂纹尖端区域的局部变形场和断裂特性,采用数字梯度敏感法对带有中心贯穿裂纹的有机玻璃有限宽板条进行了静态实验研究。实验过程中通过CCD记录裂纹尖端区域不同应力状态下的散斑图,对记录的散斑图进行相关运算,得到了不同应力状态下裂纹尖端周围区域内的光线偏转角,并通过偏转角对Ⅰ型裂纹的应力强度因子进行了提取。结果表明, 通过数字梯度敏感方法计算得到的应力强度因子与理论值吻合相对较好。     

数字梯度敏感法测量PMMA板裂纹尖端的应力强度因子

用数字梯度敏感法(DGS)测量了聚甲基丙烯酸甲酯(PMMA)板的张开型应力强度因子(SIF)。用DGS方法测量了PMMA板裂纹附近应力集中区的应力梯度(或偏转角)。此方法先用数字图像相关法(DIC)测量了透明试件裂纹尖端附近的全场位移,再根据光弹效应获得光线在透明固体应力集中区的全场偏转角,在平面应力条件下,偏转角可以与应力梯度建立联系从而获得应力集中区的应力梯度。由应力梯度场测量了裂纹尖端的应力强度因子。在应力强度因子的求解过程中提出了一种迭代最小二乘拟合应力梯度场的方法,此方法可同时得出应力强度因子与裂纹尖端位置。将实验结果与理论值进行了比较,结果显示数字梯度敏感方法准确地测量了复合型应力强度因子。     

球栅阵列倒装焊封装中的热应变值的测试

利用高温云纹实验方法测试球栅阵列(BGA)封装焊点的热应变,采用硅橡胶试件光栅复制技术,使测试环境温度提高到200℃.通过实时热应变测量,得到各焊点的热应变关系以及封装材料、电路板各部分的热应变分布状况,为研究集成电路封装组件焊点的建模和热疲劳破坏机理提供了可靠的实验依据.     

球栅阵列倒装焊封装中的热应变值的测试

利用高温云纹实验方法测试球栅阵列(BGA)封装焊点的热应变,采用硅橡胶试件光栅复制技术,使测试环境温度提高到200℃.通过实时热应变测量,得到各焊点的热应变关系以及封装材料、电路板各部分的热应变分布状况,为研究集成电路封装组件焊点的建模和热疲劳破坏机理提供了可靠的实验依据.     

基于梯度法的数字散斑图像相关亚像素搜索算法

数字散斑图像相关法是对全场位移和应变进行测量的十分有用的无损检测技术.设计精确的亚像素搜索算法是提高测量精度的关键问题.研究了数字散斑图像相关技术的基本原理,在梯度法的基础上,提出了一种基于梯度法的变步长的亚像素搜索算法并应用到相关搜索中,通过对模拟散斑图的位移分析证明了该算法的可靠性和稳定性,并对刚体平移实验进行了测...     

数字散斑相关法及其在材料强度测试中的应用

数字散斑相关法具有精度高、适用于工程现场等特点,是现代光力学测试技术中重要的方法之一。具体应用时该技术通过采集待测物体的变形前后的两幅散斑图,经过数字图像处理获取待测物由于外界因素(外力,温度等)变化对待测物所产生的位移、应变及应力。本文通过将该方法应用于结构强度测试等工程实例,对其应用进行了详细探讨,从该方法应用中得出数字散斑相关法是测试结构位移和应变的较为便利的手段而且结果以全场方式显示。数字散斑相关技术在学术界和工业界已有广泛应用,预测未来在骨科、口腔等生物医学工程领域的强度测试中具有更大的发展和应用空间。     

基于ESPI的集成电路封装热特性研究

为了快速有效地测试和分析集成电路封装的热特性,本文以激光电子散斑干涉术(ESPI)为测量手段,在分析了集成电路热学结构模型的基础上,建立了离面位移的响应方程。选用大规模的集成电路CPU486为实验对象,并以动态老化的方式实现了实验样品的功率加载,通过电子散斑干涉方法得到了离面位移的响应曲线,并对其处理得到了热阻-热容关系曲线。实验结果与相关文献数据吻合,表明利用电子散斑测量集成电路封装的热特性是可行性的。     

数字散斑联合变换相关法测量微小位移的研究

提出一种利用联合变换相关法对位移前后的散斑图像实现数字相关运算,通过相关峰的距离与散斑图所携带的位移信息之间的关系,测量物体的面内位移量。通过对全场的位移计算,得出对散斑图像先做限幅预处理后,再进行边缘提取,有效减弱了影响相关峰的不利因素,提高了相关点的精确性。对同一组散斑图进行匹配滤波相关运算和联合变换相关运算,把得到的全场位移矢量图进行比较,得出两者测量的结果是一致的。     

数字散斑时间序列相关三维面形测量中提高精度的方法

本文提出一种基于数字散斑时间序列相关三维面形测量法中提高测量精度的方法－多相关峰优化法。在数字散斑时间序列相关测量法中,当物体表面存在复杂细微结构时,被物体调制的散斑图中局部区域的散斑子图像会出现明显变形和局部阴影,这时相关曲线会出现多相关峰。由于相关值很低,这些相关峰对应高度都有可能是测量点的高度值。本文用特殊的算法对这些相关峰对应高度值进行辨别,找出最适合的高度值作为测量值,对测量结果进行优化。实验证明该方法对改善因局部区域的散斑子图像的变形和局部阴影影响而导致的测量误差具有非常显著的效果,使得数字散斑时间序列相关三维面形测量法能够用来测量复杂三维物体面形。     

非刚体图像配准的变形场拓扑约束研究

利用正则化方法约束非线性变形场是非刚体图像配准领域的一个重要研究方向。为得到具有拓扑保持能力的非线性变形场,本文在分析粘流体配准和扩散模型配准算法的实现原理基础上,提出一种基于弹簧约束的变形场拓扑保持方法。该方法在可变形图像上附加不规则网格,通过保持网格结点间的连接关系不变达到控制图像变形的目的。将本文算法应用在不同人脑磁共振图像配准和脑内核结构分割中,结果表明,本文方法具有保持变形场拓扑不变的能力,且能够给出更为准确的分割结果。      

Template Deformation‐Tailored ZnO Nanorod/Nanowire Arrays: Full Growth Control and Optimization of Field‐Emission

Here, a facile and effective route toward full control of vertical ZnO nanorod (NR)/nanowire (NW) arrays in centimeter‐scale areas and considerable improvement of field‐emission (FE) performance is reported. Controlled deformation of colloidal crystal monolayer templates is introduced by heating near glass‐transition temperature. The NR/NW density, uniformity, and tapering were all adjusted through selection of template size and deformation, and electrolyte composition. In line with the adjustments, the field‐emission performance of the arrays is significantly improved. A low turn‐on electric field of 1.8 V µm^?1, a field‐enhancement factor of up to 5 750, and an emitting current density of up to 2.5 mA cm^?2 were obtained. These improved parameters would benefit their potential application in cold‐cathode‐based electronics.     

用三带和全带模型蒙特卡罗方法模拟纤锌矿相GaN体材料输运特性结果的比较

报道了分别用三带和全带模型蒙特卡罗方法模拟纤锌矿相GaN体材料输运特性的结果,并对基于两种模型的模拟结果进行了比较.在低场区,基于两种模型获得的输运特性基本相同,但在高场区却表现出明显的差别.这是因为在高场区,电子平均能量较高,多数电子处于能带图中的高能态位置,电子能量与波矢量的关系表现出明显的非椭圆特性.由于三带模型假定了能量与波矢量简单关系,故算得的平均能量,高于由全带蒙特卡罗模拟算得的能量.从而导致其它特性的差别.全带模型包含了基于能带理论算得的能带结构的所有特性,故模拟结果更加精确.     

用三带和全带模型蒙特卡罗方法模拟纤锌矿相GaN体材料输运特性结果的比较

报道了分别用三带和全带模型蒙特卡罗方法模拟纤锌矿相GaN体材料输运特性的结果,并对基于两种模型的模拟结果进行了比较.在低场区,基于两种模型获得的输运特性基本相同,但在高场区却表现出明显的差别.这是因为在高场区,电子平均能量较高,多数电子处于能带图中的高能态位置,电子能量与波矢量的关系表现出明显的非椭圆特性.由于三带模型假定了能量与波矢量简单关系,故算得的平均能量,高于由全带蒙特卡罗模拟算得的能量.从而导致其它特性的差别.全带模型包含了基于能带理论算得的能带结构的所有特性,故模拟结果更加精确.     

Analysis of 3-D myocardial motion in tagged MR images using nonrigid image registration

Tagged magnetic resonance imaging (MRI) is unique in its ability to noninvasively image the motion and deformation of the heart in vivo, but one of the fundamental reasons limiting its use in the clinical environment is the absence of automated tools to derive clinically useful information from tagged MR images. In this paper, we present a novel and fully automated technique based on nonrigid image registration using multilevel free-form deformations (MFFDs) for the analysis of myocardial motion using tagged MRI. The novel aspect of our technique is its integrated nature for tag localization and deformation field reconstruction using image registration and voxel based similarity measures. To extract the motion field within the myocardium during systole we register a sequence of images taken during systole to a set of reference images taken at end-diastole, maximizing the normalized mutual information between the images. We use both short-axis and long-axis images of the heart to estimate the full four-dimensional motion field within the myocardium. We also present validation results from data acquired from twelve volunteers.     

Rapid radiative platinisation for dye‐sensitised solar cell counter electrodes

The successful transition of dye‐sensitised solar cell (DSC) manufacture from laboratory to factory requires new thinking in terms of lowering cost and removing time consuming manufacturing process. Platinisation of the fluorine doped tin oxide (FTO) glass counter electrode is essential for the operation of a conventional DSC and is usually carried out by thermal decomposition of chloroplatinic acid at 385 °C for 30 min. Here, near infrared radiation is used to directly heat the FTO layer resulting in full platinisation in 12.5 s. These platinised electrodes behave identically to those produced via conventional static thermal treatment in assembled DSC devices. Copyright © 2013 John Wiley & Sons, Ltd.     

Contact-Driven Snapping in Thermally Actuated Metamaterials for Fully Reversible Functionality

Mechanical instability is often harnessed in mechanical metamaterials to generate a diverse range of functionalities, and can be triggered by either a mechanical or a field stimulus, such as temperature. Existing field-responsive metamaterials with snap-through instability, however, need to rely on a mechanical input to realize functional reversibility, a limitation depriving them of the capacity to operate solely via the applied field. This work demonstrates reversible snap-through instability in a bi-material framework that is exclusively driven by environmental temperature. The need for mechanical intervention is bypassed by leveraging the thermally induced contact and mismatched thermal expansion of the constituent materials. A combination of experiments, theory and simulations, unveils the physics underpinning the thermally driven snapping undergoing four successive regimes of deformation: noncontact, full contact, partial contact, and release. The advantages of the concept are showcased in two applications. The first is the development of thermal switches with ternary operation (OFF-ON-OFF) and logic functions, going beyond the capabilities of current binary switches. The second is reversible temporal morphing in deployable structures programmed to snap sequentially in multiple locked configurations at predefined values of temperature, opening the door to applications across sectors, such as deployable antennas, soft robots, and self-reconfigurable medical devices.     

Predicting mask distortion, clogging and pattern transfer for stencil lithography

One of the ultimate tasks for stencil lithography is the ability to fabricate arrays of structures with controlled dimensions on the nanometer scale precisely positioned on a suitable surface. The race to shrink feature sizes requires the limits of conventional lithography to be extended to high-throughput, low cost, reliable and well-controlled processes of which stencilling is a promising candidate for nanoscale applications. Identifying, predicting and overcoming issues accompanying nanostencil lithography is critical to the successful and timely development of this technique for a wide range of potential applications. This paper addresses phenomena associated with stencil nanopatterning and presents the results of modelling and simulation studies for predicting the deleterious effects of mask distortion and clogging during pattern transfer. It is shown that degrading effects of stress-induced deformation of stencils can be dealt with via optimal design of corrugation structures which in turn reduce stencil deformation and significantly improves pattern definition. Modelling results are validated by comparison to experiment. The corrugation structures can be used to define practical design rules for fabrication of stable large area (“full scale”) purpose-designed stencil membranes. The accurate modelling of the clogging phenomenon combined with gradually evolving stencil deformation, also presented in the paper, can be used for prediction of pattern distortion, to calculate maximum thickness of a deposited layer and/or for prediction of the stencil lifetime.     

A small-baseline approach for investigating deformations on full-resolution differential SAR interferograms

This paper presents a differential synthetic aperture radar (SAR) interferometry (DIFSAR) approach for investigating deformation phenomena on full-resolution DIFSAR interferograms. In particular, our algorithm extends the capability of the small-baseline subset (SBAS) technique that relies on small-baseline DIFSAR interferograms only and is mainly focused on investigating large-scale deformations with spatial resolutions of about 100/spl times/100 m. The proposed technique is implemented by using two different sets of data generated at low (multilook data) and full (single-look data) spatial resolution, respectively. The former is used to identify and estimate, via the conventional SBAS technique, large spatial scale deformation patterns, topographic errors in the available digital elevation model, and possible atmospheric phase artifacts; the latter allows us to detect, on the full-resolution residual phase components, structures highly coherent over time (buildings, rocks, lava, structures, etc.), as well as their height and displacements. In particular, the estimation of the temporal evolution of these local deformations is easily implemented by applying the singular value decomposition technique. The proposed algorithm has been tested with data acquired by the European Remote Sensing satellites relative to the Campania area (Italy) and validated by using geodetic measurements.     

Surface alignment of an elastic body using a multiresolution wavelet representation

An algorithm for nonlinear registration of an elastic body is developed. Surfaces (outlines) of known anatomic structures are used to align all other (internal) points. The deformation field is represented with a multiresolution wavelet expansion and is modeled by the partial differential equations of linear elasticity. A hierarchical approach that reduces algorithm complexity is adopted. The performance of the algorithm is evaluated by two-dimensional alignment of sections from mouse brains located in the olfactory bulbs. The registration algorithm was guided by manually delineated contours of a subset of brain structures and validated based on another subset of brain structures. The wavelet alignment algorithm produced a twofold to fivefold improvement in accuracy over an affine (linear) alignment algorithm.