Name: high-speed optical diagnostics of a supersonic ping-pong cannon
Uploaded: 2023-03-24T13:10:00
Description: Watch this Scientific Journal Video about High-Speed Optical Diagnostics of a Supersonic Ping-Pong Cannon at JoVE.com

这项工作得到了NSF本科教育部（奖项#2021157）的支持，作为IUSE：EHR计划的一部分

1. 乒乓球大炮（PPC）的建造和组装
<ol><li>根据 图1组装PPC的所有组件。</li>
	<li>在大炮的侧面插入两个高透明度的亚克力窗口，以便对大炮内部进行光学探测。<ol><li>在大炮出口附近的 PVC 相对两侧的孔中钻两个 1/2。</li>
		<li>使用激光雕刻机准备两个 1/8 英寸厚的亚克力窗口。下载三个补充 svg 文件。 注意：有三个文件标记为“JoVE_AcrylicWindows_Step1_Engrave.svg”<br...

<ol>
	<li>Peterson, R. W., Pulford, B. N., Stein, K. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+ping-pong+cannon:+A+closer+look.">The ping-pong cannon: A closer look.</a> The Physics Teacher. 43 (1), 22-25 (2005).</li><li>Olson, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+shock+waves+in+expansion+tube+accelerators.">The role of shock waves in expansion tube accelerators.</a> American Journal of Physics. 74 (12), 1071-1076 (2006).</li><li>Cockman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+vacuum+bazooka.">Improved vacuum bazooka.</a> The Physics Teacher. 41 (4), 246-247 (2003).</li><li>Ayars, E., Buchholtz, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+the+vacuum+cannon.">Analysis of the vacuum cannon.</a> American Journal of Physics. 72 (7), 961-963 (2004).</li><li>Thuecks, D. J., Demas, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+the+effect+of+air-intake+aperture+size+in+the+ping-pong+ball+cannon.">Modeling the effect of air-intake aperture size in the ping-pong ball cannon.</a> American Journal of Physics. 87 (2), 136-140 (2019).</li><li>Liepmann, H. W., Roshko, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Elements of gas dynamics. , (1957).</li><li>Settles, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Schlieren and shadowgraph techniques. , (2001).</li><li>Geisert, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+single+mirror+schlieren+optical+system.">A single mirror schlieren optical system.</a> American Journal of Physics. 52 (5), 467 (1984).</li><li>French, R. M., Gorrepati, V., Alcorta, E., Jackson, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mechanics+of+a+ping-pong+ball+gun.">The mechanics of a ping-pong ball gun.</a> Experimental Techniques. 32 (1), 24-30 (2008).</li><li>French, M., Zehrung, C., Stratton, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+supersonic+ping-pong+gun.">A supersonic ping-pong gun.</a> arXiv. , (2013).</li><li>French, F., Choudhuri, R., Stratton, J., Zehrung, C., Huston, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+modular+supersonic+ping-pong+gun.">A modular supersonic ping-pong gun.</a> arXiv. , (2018).</li><li>Fredrick, C. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Complementary+studies+on+supersonic+nozzle+flow:+heterodyne+interferometry,+high-speed+video+shadowgraphy,+and+numerical+simulation.">Complementary studies on supersonic nozzle flow: heterodyne interferometry, high-speed video shadowgraphy, and numerical simulation.</a> WIT Transactions on Modelling and Simulation. 59, 223-234 (2015).</li></ol>

我们已经提出了一种构建PPC和SSPPC的方法，以及用于测量球速和表征大炮出口附近冲击传播的光学诊断。标准 PPC 由 2 m 截面 1.5 在附表 80 PVC 管中构成。管道两端各装有法兰、快速连接真空接头和出口附近的亚克力窗口，用于激光诊断。PPC的详细原理图如图 1所示。在射击之前，将乒乓球插入大炮中，并密封末端。出口端通过将胶带直接固定在法兰上来密封。在管道的另一端?...

PPC是一种流行的物理演示，用于显示人们不断暴露于的巨大气压1，2，3，4，5。该演示涉及将乒乓球放置在内径大约等于球直径的管道中。管道两端用胶带密封，并抽真空到小于 2 Torr 的内部压力。管道一端的胶带被刺破，这允许空气进入大炮，并导致球经历大约 5，000 g 的峰值加速度。仅通过大气压力加速的球在行进 300 m 后以大约 m/s 的速度离开大炮 2 m。
虽然PPC通常作为大气压力的简单演示进行操作，但它也是一种表现出复杂可压缩流动物理的装置，这导致了许多开放式学生项目。球的动力学受壁面摩擦、球周围空气泄漏、加速球形成冲击波等次要因素的影响。球的大幅加速度引入了一个大振幅的压缩波，该压缩波沿着球前方的管子传播。这些压缩的传播速度比局部声速快，导致压缩波变陡，最终形成冲击波6。以前的工作已经研究了由于球和管子的胶带出口之间的冲击波的反射以及由此产生的胶带在球出口之前在管子出口处压力的快速积聚2。使用单镜纹影成像技术的高速视频揭示了磁带对反射冲击波的响应以及磁带在PPC7，8 出口处的最终分离（视频1）。因此，PPC既可以作为吸引所有年龄段观众的气压的简单演示，也可以作为展示复杂流体物理的设备，可以在实验室环境中进行详细研究。
使用标准PPC，乒乓球速度受到声速的限制。本文涵盖了PPC的这个基本版本，以及用于将球提升到超音速的改进加农炮。在French等人以前的工作中，超音速乒乓球速度是通过通过会聚发散喷嘴9，10，11的压力驱动流来实现的。这里介绍的SSPPC利用加压（驱动器）管在乒乓球上提供比单独大气压更大的压差。使用薄聚酯隔膜将驱动管与包含球的真空（从动）管分开。该隔膜在足够的表压下破裂（通常为5-70 psi，取决于隔膜厚度），从而将乒乓球加速到1.4马赫的速度。超音速乒乓球产生驻留冲击波，使用高速阴影成像技术7，12（视频2）可以看出。
低功率（II类）氦氖激光器用于对大炮的性能进行光学诊断研究。HeNe激光束分为两条路径，一条路径穿过大炮出口附近的一组亚克力窗口，第二条路径穿过大炮出口。每条路径在光电接收器上终止，信号显示在双通道示波器上。在大炮发射过程中记录的示波器轨迹揭示了有关加速乒乓球速度以及球从大炮出口之前的可压缩流动和冲击波的信息。直径为40毫米的乒乓球在每个光束位置的速度与球阻挡光束的时间直接相关。灵敏的“刀刃”冲击检测设置是通过用一块黑色电工胶带覆盖检测器的一半并将胶带的边缘定位在光束2的中心来实现的。通过这种设置，由可压缩流动诱导的折射梯度指数产生的氦氖激光束的轻微偏转在示波器迹线上清晰可见，如电压尖峰。向大炮出口传播的冲击波和反射的冲击波使光束向相反的方向偏转，因此由正或负电压尖峰识别。
在这里，我们提供了构建和使用优化的PPC和SSPPC的说明，以及光学诊断技术（图1，图2和图3）。光学诊断技术和测量是通过前几年的研究1，2开发的。

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high-speed optical diagnostics of a supersonic ping-pong cannon

传统的乒乓球大炮（PPC）是一种教育设备，仅使用大气压力即可将乒乓球发射到疏散的管道中，达到接近声速的速度。SSPPC是PPC的增强版本，通过以大于大气压的速度加速球来实现超音速。我们提供了构建和使用优化的PPC和SSPPC的说明。
实施光学诊断的目的是研究大炮动力学。通过管道出口附近的两个丙烯酸窗口发送的HeNe激光器端接在光接收器传感器上。微处理器测量光束被乒乓球阻挡的时间，以自动计算球的速度。结果会立即显示在LCD显示屏上。 
光学刀口设置提供了一种高灵敏度的方法来检测冲击波，方法是切断传感器处的一小部分HeNe光束。冲击波引起光束的折射诱导偏转，这在光接收器的电信号中被观察到为小的电压尖峰。 
所介绍的方法具有高度可重复性，并为在实验室环境中进行进一步研究提供了机会。

在这里，我们提供了PPC和SSPPC的构建和使用说明，以及用于冲击表征和速度测量的光学诊断的实施。还提供了具有代表性的实验结果。PPC 和 SSPPC 的完整系统以及必要的附件如图 1 和 图 2 所示。SSPPC是PPC的增强版本，其中管道的驱动加压部分连接到PPC的从动管。用于冲击波的刀口检测和乒乓球速度测量的光学诊断设置如图 3所示。?...

Watch this Scientific Journal Video about High-Speed Optical Diagnostics of a Supersonic Ping-Pong Cannon at JoVE.com

High-Speed Optical Diagnostics of a Supersonic Ping-Pong Cannon

我们描述了一种制造超音速乒乓球加农炮（SSPPC）的方法，以及用于测量球速和表征大炮发射过程中传播冲击波的光学诊断技术。

超音速乒乓球炮的高速光学诊断

The traditional ping-pong cannon (PPC) is an educational apparatus that launches a ping-pong ball down an evacuated pipe to nearly sonic speeds using ...

我们提供制造和操作超音速乒乓球炮的说明，以及用于测量球速和检测冲击波的光学诊断技术。光学刀刃设置对激光束的微小横移偏转高度敏感，并提供了一种检测与大炮相关的冲击波的方法。首先，通过将光接收器和激光模块连接到 15 伏限流电源和激光电源来为它们供电。然后，使用 BNC 电缆将光接收器连接到示波器的两个通道。对于光学诊断设置，将激光器垂直于制造的加农炮放置，第一束穿过管道内的亚克力窗口，第二束穿过大炮出口外。将黑色电工胶带放在照片接收器传感器的一半上，创建刀刃冲击检测设置。为避免削波，请调整刀口上的光束位置，使基线电压约为最大值的 50%。接下来，调整示波器上的设置以收集 2000 万个数据点。使用水平刻度旋钮将数据采集速率设置为 500 兆赫兹。转动触发旋钮，在略低于从光接收器获取的设定基线的电压下跳闸。在发射PPC之前，请佩戴耳罩和护目镜。将乒乓球插入大炮的出口，轻轻吹入大炮的末端，直到它击中管道入口附近的真空配件。用两块方形胶带密封大炮的出口法兰和亚克力帽。确保激光束以刀口为中心，扳机正确定位，并且捕获容器牢固。打开真空泵，将管道抽真空到低于两托的绝对压力。一旦达到足够的真空度，使用宽头尖端刺穿入口处的胶带。点火后，关闭真空泵并从出口法兰和亚克力帽上取下任何剩余的胶带。要发射超音速PPC，请关闭连接驱动管和空气压缩机的阀门并填充空气压缩机油箱。吹球，如前所述。密封超音速 PPC 出口法兰后，在两个橡胶垫圈之间插入一个薄的预切聚酯隔膜，并将它们放置在大炮的驱动器和从动部分之间。使用四个凸轮夹连接两个部分。一旦管道中的压力降低，将空气压缩机的压力释放到驱动管中，使压力增加，直到隔膜破裂并且驱动管内的压缩空气充满抽真空的从动管。超音速PPC点火后，关闭空压机和真空泵。从大炮上取下破裂的聚酯隔膜和胶带。在整个大炮发射过程中反射的传播冲击波由电压相对于时间的变化表示。正或负尖峰表示信号中冲击波的方向，并通过球切断光束产生的方形脉冲宽度计算速度。微处理器用于处理来自横跨管道内部的光束的信号，以自动计算和显示大炮出口附近的球速。示波器迹线演示了超音速PPC的双通道发射。上面的迹线表示穿过大炮内部的光束，靠近出口。而下部迹线对应于离开大炮后穿过乒乓球路径的光束。截止信号表示球通过并阻碍了每个光束。压差与马赫数的关系图显示，0.001和0.002英寸厚的隔膜在足够的压差下破裂，将乒乓球加速到超音速。球速始终大于1.3马赫，膜片厚度为0.002英寸。所展示的超音速乒乓球炮和光学诊断将提高大炮的价值，既作为演示设备，又作为后续实验室实验的设备。

high-speed-optical-diagnostics-of-a-supersonic-ping-pong-cannon

Research

Education

JoVE Core

JoVE Journal

Mechanical Engineering

Engineering

Unit 1

Kinematics of a Particle

SCIENTISTS IN ACTION

Construction and Testing of Coin Cells of Lithium Ion Batteries

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime. Lithium ion batteries have also been considered to be used in electric and hybrid vehicles1 or even electrical grid stabilization systems2. All these applications simulate a dramatic increase in the research and development of battery materials3-7, including new materials3,8, doping9, nanostructuring10-13, coatings or surface modifications14-17 and novel binders18. Consequently, an increasing number of physicists, chemists and materials scientists have recently ventured into this area. Coin cells are widely used in research laboratories to test new battery materials; even for the research and development that target large-scale and high-power applications, small coin cells are often used to test the capacities and rate capabilities of new materials in the initial stage. 
 In 2010, we started a National Science Foundation (NSF) sponsored research project to investigate the surface adsorption and disordering in battery materials (grant no. DMR-1006515). In the initial stage of this project, we have struggled to learn the techniques of assembling and testing coin cells, which cannot be achieved without numerous help of other researchers in other universities (through frequent calls, email exchanges and two site visits). Thus, we feel that it is beneficial to document, by both text and video, a protocol of assembling and testing a coin cell, which will help other new researchers in this field. This effort represents the "Broader Impact" activities of our NSF project, and it will also help to educate and inspire students.
In this video article, we document a protocol to assemble a CR2032 coin cell with a LiCoO2 working electrode, a Li counter electrode, and (the mostly commonly used) polyvinylidene fluoride (PVDF) binder. To ensure new learners to readily repeat the protocol, we keep the protocol as specific and explicit as we can. However, it is important to note that in specific research and development work, many parameters adopted here can be varied. First, one can make coin cells of different sizes and test the working electrode against a counter electrode other than Li. Second, the amounts of C black and binder added into the working electrodes are often varied to suit the particular purpose of research; for example, large amounts of C black or even inert powder were added to the working electrode to test the "intrinsic" performance of cathode materials14. Third, better binders (other than PVDF) have also developed and used18. Finally, other types of electrolytes (instead of LiPF6) can also be used; in fact, certain high-voltage electrode materials will require the uses of special electrolytes7.

A protocol to construct and test coin cells of lithium ion batteries is described. The specific procedures of making a working electrode, preparing a counter electrode, assembling a cell inside a glovebox and testing the cell are presented.

钮扣电池锂离子电池的建设和测试

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime.  Lithium ion ...

科研

工程学

Fabricating Metamaterials Using the Fiber Drawing Method

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves 2. This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks 3, negative refractive index materials 4, and lenses that resolve objects below the diffraction limit 5. However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano- and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size 6-7. Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response 8. We combine the stack-and-draw technique used to produce microstructured polymer optical fiber 9 with the Taylor-wire process 10, using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 &deg;C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro- and nano- scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

Metamaterials at terahertz frequencies offer unique opportunities, but are challenging to fabricate in bulk. We adapt the fabrication procedure for microstructured polymer optical fibers to inexpensively fabricate metamaterials potentially on an industrial scale. We produce polymethylmethacrylate fibers containing ~10 &mu;m diameter indium wires separated by ~100 &mu;m, which exhibit a terahertz plasmonic response.

制造超材料使用光纤拉丝法

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe ...

Optical Trapping of Nanoparticles

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping and manipulating small biological particles. Ashkin and co-workers first demonstrated optical tweezers using a single focused beam1. The single beam trap can be described accurately using the perturbative gradient force formulation in the case of small Rayleigh regime particles1. In the perturbative regime, the optical power required for trapping a particle scales as the inverse fourth power of the particle size. High optical powers can damage dielectric particles and cause heating. For instance, trapped latex spheres of 109 nm in diameter were destroyed by a 15 mW beam in 25 sec1, which has serious implications for biological matter2,3.
A self-induced back-action (SIBA) optical trapping was proposed to trap 50 nm polystyrene spheres in the non-perturbative regime4. In a non-perturbative regime, even a small particle with little permittivity contrast to the background can influence significantly the ambient electromagnetic field and induce a large optical force. As a particle enters an illuminated aperture, light transmission increases dramatically because of dielectric loading. If the particle attempts to leave the aperture, decreased transmission causes a change in momentum outwards from the hole and, by Newton's Third Law, results in a force on the particle inwards into the hole, trapping the particle. The light transmission can be monitored; hence, the trap can become a sensor. The SIBA trapping technique can be further improved by using a double-nanohole structure.
The double-nanohole structure has been shown to give a strong local field enhancement5,6. Between the two sharp tips of the double-nanohole, a small particle can cause a large change in optical transmission, thereby inducing a large optical force. As a result, smaller nanoparticles can be trapped, such as 12 nm silicate spheres7 and 3.4 nm hydrodynamic radius bovine serum albumin proteins8. In this work, the experimental configuration used for nanoparticle trapping is outlined. First, we detail the assembly of the trapping setup which is based on a Thorlabs Optical Tweezer Kit. Next, we explain the nanofabrication procedure of the double-nanohole in a metal film, the fabrication of the microfluidic chamber and the sample preparation. Finally, we detail the data acquisition procedure and provide typical results for trapping 20 nm polystyrene nanospheres.

The following setup approach details low power optical trapping of dielectric nanoparticles using a double-nanohole in metal film.

纳米粒子的光学捕获

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping ...

High-resolution, High-speed, Three-dimensional Video Imaging with Digital Fringe Projection Techniques

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces.&#160;Like the human eyes and brain, DFP uses triangulation between matching points in two views of the same scene at different angles to compute depth.&#160;However, unlike a stereo-based method, DFP uses a digital video projector to replace one of the cameras1. The projector rapidly projects a known sinusoidal pattern onto the subject, and the surface of the subject distorts these patterns in the camera&#8217;s field of view. Three distorted patterns (fringe images) from the camera can be used to compute the depth using triangulation.
Unlike other 3D measurement methods, DFP techniques lead to systems that tend to be faster, lower in equipment cost, more flexible, and easier to develop.&#160;DFP systems can also achieve the same measurement resolution as the camera.&#160;For this reason, DFP and other digital structured light techniques have recently been the focus of intense research (as summarized in1-5). Taking advantage of DFP, the graphics processing unit, and optimized algorithms, we have developed a system capable of 30&#160;Hz 3D video data acquisition, reconstruction, and display for over 300,000 measurement points per frame6,7.&#160;Binary defocusing DFP methods can achieve even greater speeds8.
Diverse applications can benefit from DFP techniques. Our collaborators have used our systems for facial function analysis9, facial animation10, cardiac mechanics studies11, and fluid surface measurements, but many other potential applications exist.&#160;This video will teach the fundamentals of DFP techniques and illustrate the design and operation of a binary defocusing DFP system.

This video describes the fundamentals of digital fringe projection techniques, which provide dense 3D measurements of dynamically changing surfaces.&#160;It also demonstrates the design and operation of a high-speed binary defocusing system based on these techniques.

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces.&#160;Like the human eyes and brain, DFP uses ...

Construction of a High Resolution Microscope with Conventional and Holographic Optical Trapping Capabilities

High resolution microscope systems with optical traps allow for precise manipulation of various refractive objects, such as dielectric beads 1 or cellular organelles 2,3, as well as for high spatial and temporal resolution readout of their position relative to the center of the trap. The system described herein has one such "traditional" trap operating at 980 nm. It additionally provides a second optical trapping system that uses a commercially available holographic package to simultaneously create and manipulate complex trapping patterns in the field of view of the microscope 4,5 at a wavelength of 1,064 nm. The combination of the two systems allows for the manipulation of multiple refractive objects at the same time while simultaneously conducting high speed and high resolution measurements of motion and force production at nanometer and piconewton scale.

The system described herein employs a traditional optical trap as well as an independent holographic optical trapping line, capable of creating and manipulating multiple traps. This allows for the creation of complex geometric arrangements of refractive particles while also permitting simultaneous high-speed, high-resolution measurements of the activity of biological enzymes.

高分辨率显微镜与常规和全息光学捕获能力建设

High resolution microscope systems with optical traps allow for precise manipulation of various refractive objects, such as dielectric beads 1 or cellular ...

High-speed Particle Image Velocimetry Near Surfaces

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The complex nature of these flows may be studied using particle image velocimetry (PIV), a laser-based imaging technique for optically accessible flows. Though many forms of PIV exist that extend the technique beyond the original planar two-component velocity measurement capabilities, the basic PIV system consists of a light source (laser), a camera, tracer particles, and analysis algorithms. The imaging and recording parameters, the light source, and the algorithms are adjusted to optimize the recording for the flow of interest and obtain valid velocity data. 
Common PIV investigations measure two-component velocities in a plane at a few frames per second. However, recent developments in instrumentation have facilitated high-frame rate (&gt; 1 kHz) measurements capable of resolving transient flows with high temporal resolution. Therefore, high-frame rate measurements have enabled investigations on the evolution of the structure and dynamics of highly transient flows. These investigations play a critical role in understanding the fundamental physics of complex flows.
A detailed description for performing high-resolution, high-speed planar PIV to study a transient flow near the surface of a flat plate is presented here. Details for adjusting the parameter constraints such as image and recording properties, the laser sheet properties, and processing algorithms to adapt PIV for any flow of interest are included.

A procedure for studying transient flows near boundaries using high-resolution, high-speed particle image velocimetry (PIV) is described here. PIV is a non-intrusive measurement technique applicable to any optically accessible flow by optimizing several parameter constraints such as the image and recording properties, the laser sheet properties, and analysis algorithms.

表面附近的高速粒子图像测速

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The ...

Visualization of High Speed Liquid Jet Impaction on a Moving Surface

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.

Two experimental devices for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device and a spinning disk device. The apparatuses are used to determine optimal approaches to the application of liquid friction modifier (LFM) onto rail tracks for top-of-rail friction control.

高速喷液嵌塞对移动表面的可视化

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds ...

Fabrication and Operation of a Nano-Optical Conveyor Belt

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological and physical sciences over the past few decades. The progress made in this field invites further study of even smaller systems and at a larger scale, with tools that could be distributed more easily and made more widely available. Unfortunately, the fundamental laws of diffraction limit the minimum size of the focal spot of a laser beam, which makes particles smaller than a half-wavelength in diameter hard to trap and generally prevents an operator from discriminating between particles which are closer together than one half-wavelength. This precludes the optical manipulation of many closely-spaced nanoparticles and&#160;limits the&#160;resolution of optical-mechanical systems. Furthermore, manipulation using focused beams requires beam-forming or steering optics, which can be very bulky and expensive. To address these limitations in the system scalability of conventional optical trapping our lab has devised an alternative technique which utilizes near-field optics to move particles across a chip. Instead of focusing laser beams in the far-field, the optical near field of plasmonic resonators produces the necessary local optical intensity enhancement to overcome the restrictions of diffraction and manipulate particles at higher resolution. Closely-spaced resonators produce strong optical traps which can be addressed to mediate the hand-off of particles from one to the next in a conveyor-belt-like fashion. Here, we describe how to design and produce a conveyor belt using a gold surface patterned with plasmonic C-shaped resonators and how to operate it with polarized laser light to achieve super-resolution nanoparticle manipulation and transport. The nano-optical conveyor belt chip can be produced using lithography techniques and easily packaged and distributed.

The scalability and resolution of conventional optical manipulation techniques are limited by diffraction. We circumvent the diffraction limit and describe a method of optically transporting nanoparticles across a chip using a gold surface patterned with a path of closely spaced C-shaped plasmonic resonators.

一个纳米光输送带的制作和操作

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological ...

Writing Bragg Gratings in Multicore Fibers

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers.

We describe a technique for inscribing identical fiber Bragg gratings into each core of a multicore fiber. This is achieved by introducing an additional surface into the optical path to mitigate lensing by the curved surface of the fiber cladding.

写布拉格光栅在多核纤维

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

紧凑的镜头少数字全息显微镜的MEMS检测与表征

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...